Geothermal systems of the Corwin Springs-Gardiner area, Montana : possible structural and lithologic
controls
by Eric Mitchell Struhsacker
A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE
in Earth Sciences
Montana State University
© Copyright by Eric Mitchell Struhsacker (1976)
Abstract:
This study is an attempt to determine by means of geologic observations the structural and lithologic
controls on the circulation of geothermal waters in the La Duke and Bear Creek thermal spring
systems. Hot spring activity has persisted in the Corwin Springs-Gardiner, Montana area since the
Pleistocene. Presently the only active hot springs, La Duke and Bear Creek, emerge at opposite ends of
a two square mile Pleistocene travertine deposit.
The hot springs and travertine lie along the northwest trending Gardiner fault, a Laramide high-angle
reverse imbricate fault zone, which bounds the Beartooth crystalline rock uplift on the southwest.
The post-Laramade Reese Creek and Mammoth faults are graben-forming normal faults that extend
from the Yellowstone Park upland, northward into the hanging wall of the Gardiner fault. The local
thermal features lie on or between the intersections of these faults with the Gardiner fault zone.
More than 10,000 feet of Paleozoic and Mesozoic sedimentary rock are preserved within the graben in
the footwall of the Gardiner fault. From a structural high within Yellowstone Park, the sedimentary
units dip gently into the Gardiner fault zone, where they are dragged up and locally overturned to form
an asymmetrical syncline striking northwest. These structural relationships suggest that meteoric
waters flow down permeable sedimentary units within the graben from the Yellowstone upland to great
depth under the Gardiner fault zone, thereby forming a common reservoir for the hot spring systems.
The cavernous Mississippian Madison Limestone, lying near a depth of 10,000 feet under the Gardiner
fault zone, may be the principal aquifer and produces the high Ca content of the active hot springs.
Waters are heated at depth by conduction from rocks whose temperatures depend on the geothermal
gradient. They then ascend through fractures to the surfaced A normal thermal gradient for western
Montana causes base temperatures near 100° C at this depth. However, the proximity of a shallow
magma body beneath the Yellowstone Plateau to the south may accentuate the normal regional thermal
gradient and produce higher base temperatures in the reservoirs. STATEMENT OF PERMISSION TO COPY
In p re s e n tin g t h i s th e s is in p a r t i a l
f u l f i l l m e n t o f the
requirem ents f o r ah advanced degree a t Montana S ta te U n i v e r s i t y , I
agree t h a t th e L i b r a r y s h a ll make i t
f r e e l y a v a i l a b l e f o r in s p e c tio n .
I f u r t h e r agree t h a t perm ission f o r e x te n s iv e copying o f t h i s th e s is
f o r s c h o l a r l y purposes may be granted by my m ajor p r o f e s s o r , o r , in
his absence, by the D i r e c t o r o f L i b r a r i e s .
I t is understood t h a t any
copying o r p u b l i c a t i o n o f t h i s th e s is f o r f i n a n c i a l
be allo w e d w ith o u t my w r i t t e n p erm ission.
S ig n a tu re
Date
V ).
^
M l b ________ ^__
gain s h a ll
not
GEOTHERMAL SYSTEMS OF THE CORWIN SPRINGS-GARDINER
AREA, MONTANA: POSSIBLE STRUCTURAL
AND LITHOLOGIC CONTROLS
by
ERIC MITCHELL STRUHSACKER
A th e s is subm itted in p a r t i a l f u l f i l l m e n t
o f th e requirem ents f o r th e degree
of
MASTER OF SCIENCE
in
E arth Sciences
Approved
C h a irp e rs o n , Graduate Committee
Head, I „
Graduate DeSn
MONTANA STATE UNIVERSITY
Bozeman, Montana
June, 1976
iii
ACKNOWLEDGMENTS
The a u th o r extends his g r a t i t u d e to his a d v i s o r . D r. Robert A.
Chadwick, f o r his h e l p f u l a d vic e and re v ie w of t h i s m a n u sc rip t.
Dr. John Montagne and Dr. Donald L. Smith have been p a r t i c u l a r l y h e lp fu l
i n le n d in g a s s is ta n c e w it h g e o lo g ic i n t e r p r e t a t i o n s and th e s is fo r m a t.
Funding f o r the f i e l d
and l a b o r a t o r y work making t h i s paper
p o s s ib le was provided by th e U.S. G eo lo g ic a l Survey under the Extramural
Geothermal Research Program, Grant No. 14 - 0 8 - 0 0 0 1 -G -238 t o Montana S t a t e
U n iv e rs ity .
Dr. Robert Leonard o f th e USGS Water Resources D i v is i o n
o f f i c e in H e le n a , Montana, c o o rd in a te d the p r o j e c t and provided h e lp ­
f u l a d v ic e in the f i e l d concerning h y d r o lo g ic problems.
The a u th o r a ls o .w is h e s to thank th e many landowners in the
Corwin S p rin g s -C in n a b a r Basin a r e a , as w e ll as Y ellow stone N a tio n a l
P a rk , f o r access to those a r e a s .
is a ls o much a p p r e c ia te d .
The h o s p i t a l i t y o f those people
Thanks i s a ls o extended to Dr. Hunter Ware o f
th e Anaconda Company f o r th e use o f d r i l l
holes f o r h eat flo w measure­
ments.
Most o f a l l
th e au th o r would l i k e to thank h is w i f e , Debra,
f o r her i n v a l u a b l e h e lp w ith the f i e l d work and w ith th e p r e p a r a tio n
o f t h i s m a n u s c rip t.
TABLE OF CONTENTS
Page
LIST OF FIGURES
.................................................................................................
.
vi
LIST OF PLATES..................................... .... ................................................................ v i i
Chapter
1.
INTRODUCTION................................
REGIONAL SETTING ...............................................................................
5
OBJECTIVES AND PROCEDURE .............................................................
6
PREVIOUS. INVESTIGATIONS
2.
I
;
.. . . .
. . . . . . . .
.
GEOLOGIC SETTING ....................................................................................
LOCAL STRATIGRAPHY .....................................
9
9
CENOZOIC STRUCTURES AND FAULTS ...........................
The G a l l a t i n A n t i c l i n e ................................................... ....
7
11
.
11
The G a rd in e r F a u l t ......................................................................
13
The G a l l a t i n H o r s t ......................................................................
19
• The Mammoth F a u l t ................................
21
The S epulcher Graben . .........................................
CENOZOIC VOLCANISM..................................... ........................... ....
Eocene Volcapism . . . . . .
.......................
Q uaternary Volcanism . . . . . . . . . . . . . . .
REGIONAL S E I S M I C I T Y ..............................................
21
.
22
22
24
26
■V
Chapter
3.
Page
CONTROLS ON THERMAL WATER CIRCULATION
.................................
28
LOCAL GEOLOGIC SETTING ................................. i ...........................
28
DISCHARGE PATTERNS............................................................
35
.
.
.
FAULT CONTROL OF RECHARGE..................................................
JOINT CONTROL.OF RECHARGE
. . . . . . .
36
.............................
LITHOLOGIC CONTROL OF RECHARGE................................... .
4.
SOURCES OF H E A T .........................................................
GEOTHERMAL GRADIENT HEAT SOURCE
5.
6.
41
49 ■
..........................................
49
SHALLOW MAGMATIC HEAT SOURCE ...................................................
51
POTENTIAL THERMAL ACTIVITY AT
DEPTH IN ADJACENT A R E A S .............................................................
58
SUGGESTED FUTURE S T U D Y .................................................................
.
62
RESERVOIR TEMPERATURES ............................ ......................................
62
AQUIFER ROCK TYPE
63
...................
CHARACTER OF STRUCTURE AND LITHOLOGY AT DEPTH
. . .
SEISMICITY OF THE CORWIN SPRINGS-GARDINER AREA ,.
CONCEALED THERMAL WATER S O U R C E S ....................... ....
7.
.
36
SUMMARY AND CONCLUSIONS
64
. .■
. .
65
.
65.
. .............................................................
67
APPENDIXES.................................... ................................. ....
71
APPENDIX A ...............................................................................................................
72
APPENDIX B ................... ' ..........................................................................................
75
REFERENCES C I T E D ........................................................................................ ....
88.
vi
' LIST OF FIGURES
Fig u re
.
Page
1.
Index Map
2.
G e n e ra liz e d Bedrock GeologyG ard in e r Region
....................................................................................
10
M a jo r F a u l t Zones and S t r u c t u r a l
F e a t u r e s -G a r d in e r Region ..........................
12
3.
4.
5.
................................................... .........................................
D i s t r i b u t i o n o f Eocene I n t r u s i v e s and
E x tru s iv e s Near Corwin S p r in g s , Montana
Bedrock Geology o f th e Corwin
S p r in g s - G a r d in e r Area
. . .
............................
.....................................
2
23
31
6.
Histogram J o i n t O r i e n t a t i o n s in Precambrian
G r a n i t i c Gneiss Along th e G a rd in e r F a u lt
Zone, Near La Duke Hot S pring " . ....................... ...................... 38
7.
Sketch o f S o lu tio n Features in
the M ission Canyon Formation ........................................................
43
G eologic Cross S e c tio n Along
S epulcher G r a b e n .....................................................................
46
8.
9.
C o m p ila tio n o f Geophysical Anomalies in
th e Y ello w sto n e N a tio n a l Park A r e a ...............................................52
10.
S e i s m i c i t y and Seismic A tt e n u a tio n Compared
to Q uaternary F a u l t and V o lc a n ic S tru c tu re s
in Y ellow stone N a tio n a l P a r k ..............................................................54
11.
Sketch Map o f th e Cinnabar Basin Area:
Major
F a u lts and Madison Group Exposures ..........................................
59
vi'i
LIST OF PLATES
P la te
Page
1.
T r a v e r t i n e D eposit a t Bear Creek Spring .................................
3
2.
T r a v e r t i n e D e p o s it a t La Duke Hot Spring
4 .
3.
T r a v e r t i n e Deposits and P lio c e n e B a s a lt
Flows a t G a r d i n e r ................................................................. ....
14
4.
La Duke Hot S pring Area Seen From E l e c t r i c Peak . . . .
.15
5.
Trace o f the G a rd in e r F a u l t on the
Northern Flank o f Cinnabar Mountain . . ............................ 16
6.
F a u l t B re cc ia in G r a n i t i c Gneiss o f
th e G a rd in e r F a u l t Zone . . . . ,.............................................. .
17
7.
G a rd in e r F a u l t Zone B re c c ia ............................................................
18
8.
View to th e North o f La Duke Hot Spring and
C l i f f y S i l i c i f i e d Limestone B re c c ia Outcrop ...................
29
P a r t l y S i l i c i f i e d Limestone Showing P oss ible
C r in o id Stem Remnants from La Duke Hot S pring . . . .
32
M is sio n Canyon Limestone Exposed Near
D e v ils S l i d e on Cinnabar Mountain . . .
............................
44
9.
10.
■.........................
11.
Photomicrograph
o f B i o t i t e D a c ite ..............................................
78
12.
Photomicrograph
o f H o r n b l e n d e - B i o t i t e D a c ite
. . . . .
81
13.
Photomicrograph
o f H o r n b le n d e r B io t it e A n desite
. . . .
83
. 14.
A n d e s ite Dike C on tain in g C la s ts o f Precambrian
G r a n i t i c Gneiss and B i o t i t e
D a c ite
...................................
86
ABSTRACT
This study is an a tte m p t to d e term ine by means o f geolo g ic
o b s e rv a tio n s th e s t r u c t u r a l and l i t h o l o g i c c o n tr o ls on th e c i r c u l a t i o n
o f geothermal w aters in th e La Duke and Bear Creek thermal spring
systems.
Hot s p rin g a c t i v i t y has p e r s is t e d in th e Corwin S p rin g sG a r d in e r , Montana area s in c e th e P le is to c e n e .
P r e s e n tly th e only
a c t i v e hot s p r in g s , La Duke and Bear C reek, emerge a t o p p o s ite ends •
o f a two square m ile P le is to c e n e t r a v e r t i n e d e p o s it .
The hot s prin gs and t r a v e r t i n e l i e along th e northw est tr e n d in g
G a rd in e r f a u l t , a Laramide h ig h -a n g le r e v e rs e -4 m h ri catie f a u l t zone, .
which bounds the B e a rtooth c r y s t a l l i n e rock u p l i f t on th e southwest.
The p o s t - Laramide Reese Creek and Mammoth f a u l t s a re graben-form ing
normal f a u l t s t h a t extend from th e Y ellow stone Park uplandj, northward
i n t o th e hanging w a ll o f th e G a rd in e r f a u l t .
The lo c a l thermal f e a tu r e s
l i e on o r between th e i n t e r s e c t i o n s o f these f a u l t s w it h th e G ardine r
f a u l t zone.
„
More than 1 0 ,0 0 0 f e e t o f P a le o z o ic and Mesozoic sedim entary
rock a re p re served w i t h i n th e graben i n th e f o o t w a l l o f th e G ardine r
f a u l t . . From a s t r u c t u r a l high w i t h i n Y ellow stone P ark , th e sedim entary
u n it s d ip g e n t l y i n t o th e G a rd in e r f a u l t zone, where th e y a re dragged
up and l o c a l l y o v e rtu rn e d to form an asymmetrical s y n c lin e s t r i k i n g
n o rthw est.
These s t r u c t u r a l r e l a t i o n s h i p s suggest t h a t m e te o ric waters
flo w down permeable sedim entary u n it s w i t h i n the graben from the
Y ellow stone upland to g r e a t depth under th e G ard in e r f a u l t zone,
th e re b y form ing a common r e s e r v o i r f o r th e hot s p rin g systems.
The
cavernous M i s s is s ip p ia n Madison Lim estone, l y i n g near a depth o f 1 0,000
f e e t under th e G a rd in e r f a u l t zone, may be th e p r i n c i p a l a q u i f e r and
produces th e high Ca c o n te n t o f th e a c t i v e hot s p r in g s .
Waters a re heated a t depth by conduction from rocks whose
tem peratures depend on th e geothermal g r a d i e n t .
They then ascend through
f r a c t u r e s to th e s u r fa c e :
A normal thermal g r a d i e n t f o r w estern Montana
causes base tem peratures near IOO0 C a t t h i s depth.
However, the p r o x i ­
m ity o f a shallo w magma body beneath th e Y ellow stone P la te a u to the
south may a c c e n tu a te th e normal r e g io n a l thermal g r a d i e n t and produce
h ig h e r base tem peratures in the r e s e r v o i r s .
Chapter I
INTRODUCTION
Geothermal phenomena have been i n t e r m i t t e n t l y a c t i v e in the
Corwin S p r in g s -G a r d in e r area o f southwestern Montana from th e e a r l y
P le is to c e n e to th e p r e s e n t.
Thermal sp rin g s have produced e x te n s iv e
t r a v e r t i n e d e p o s its up to 60 f e e t in th ic kn es s t h a t extend f o r fo u r
m ile s from th e v i c i n i t y o f L i t t l e T r a i l
C reek, n o rthw est o f G a r d in e r ,
to Bear C reek, e a s t o f G a rd in e r ( F ig u re I ) .
Whereas most o f the
t r a v e r t i n e was d e p o s ited b e fo r e th e l a s t P in e d a le g l a c i a t i o n , minor
thermal s p rin g a c t i v i t y continues on t h i s
warm s p rin g ( P l a t e I )
e t a l , 1 9 6 9 ).
of tra v e rtin e .
tre n d a t th e Bear Creek
and a t La Duke Hot S pring ( P l a t e 2)
(F r a s e r
Both s prin gs a re p r e s e n t l y d e p o s itin g moderate amounts
Base r e s e r v o i r tem peratu res f o r La Duke Hot Spring
a re thought to range from 81° C in th e summer to 130° C i n the w i n t e r
(Chadwick, personal communication, 1 9 7 6 ).
These therm al f e a t u r e s l i e w i t h i n th e northw est tre n d in g
G a rd in e r f a u l t zone on th e north s id e o f th e Y ellow stone R iv e r v a l l e y .
They a ls o l i e
on th e n o rth e rn edge o f th e Y ellow stone geothermal f i e l d .
Most hot s p rin g s w i t h i n th e Y ellow stone f i e l d a c t i v e l y d e p o s it s i l i ­
ceous s i n t e r , and have base tem peratures in excess o f 2 50 ° C ( F o u r n i e r ,
White and T r u e s d e lI ,
1 9 7 5 ).
These hot s p rin g systems a r e thought to
d e r iv e t h e i r h eat from a molten or p a r t i a l Ty c r y s t a l l i z e d r h y o l i t i c
2
Corwin Springs
. La Duke Hot Spring
Trail Ck.
Gardiner
Bear Creek W arm Spring
M am m oth
Hot Spring
YELLO W STO NE
N orris
Geyser
Basin
N A T IO N A L
PARK
Th erm al Areas
Area Mapped
FIGURE
M IL E S
I - INDEX MAP
3
PLATE I .
View to the north
and Bear Creek o f
warm s p rin g l y i n g
sedim entary rocks.
f a u l t zone in th e
a t th e j u n c t i o n o f the Y ellow stone R iv e r
the t r a v e r t i n e d e p o s it a t Bear Creek
on upturned P a le o zo ic and Mesozoic
P lio c e n e b a s a lts cover th e G ardiner
immediate background.
4
PLATE 2.
View west from the t r a v e r t i n e d e p o s it a t La Duke Hot Spring
w ith upturned P a le o zo ic and Mesozoic sedim entary rocks a t
D e v ils S l i d e on Cinnabar Mountain in th e background.
5
magma body l y i n g a t a depth o f f i v e km beneath th e Y ellow stone
v o lc a n ic p la te a u (Eaton e t a l , 1 9 7 5 ).
Regional S e t t i n g
The Corwin S p r in g s -G a r d in e r area occupies a t r a n s i t i o n a l
p o s i t i o n between th e M iddle Rocky Mountain and th e N orthern Rocky
Mountain p h y sio g ra p h ic provinces
( Tho rn b u ry , 1 9 6 5 ).
T h e .Beartooth
b lo c k , an u p l i f t e d mass o f Precambrian c r y s t a l l i n e rock bounded on
th e southwest by th e G a rd in e r r e v e r s e f a u l t , borders th e thermal
area on the n o rth and e a s t .
block s t r u c t u r e , l i e s
G a rd in e r system.
The southern G a l l a t i n Range, a ho rs t
to th e west and south o f the Corwin S prings-
A n d e s ite and d a c i t i c f l o w s , mudflows, and v o lc a n ic
b re c c ia s o f th e Eocene A b s a r o k a - G a lla t in v o lc a n ic f i e l d cover
e x t e n s iv e areas o f both u p l i f t e d b lo c k s , and a re remnants o f a
more e x t e n s iv e cover (Chadwick, 1 9 7 0 ).
The Y ellow stone R iv e r v a l l e y ,
o f pro b a b le e a r l y Eocene a ge, was exhumed from beneath th e v o lc a n ic
cover and now s ep a ra te s th e two u p l i f t e d blocks.
The r e g io n a l
te rra in
is v ery mountainous, d i s p la y in g as much as 5,0 0 0 f e e t o f r e l i e f above
th e f l o o r o f th e Y ellow stone R iv e r v a l l e y , which has an a l t i t u d e o f
5 ,0 0 0 f e e t or more i n th e Corwin S p r in g s -G a r d in e r a r e a .
G la c ie r s
have moved down the Y ellow stone R iv e r v a l l e y from sources w i t h i n
th e Y ellow stone N a tio n a l
Park area on a t l e a s t one occasion during
the P le is to c e n e ( Montagne, personal communication, 1 9 7 6 ).
[
A veneer
'
'
___________________________________________________________________________________ .
'
■
■
'
.
/
I
.
6
o f g la c ia l
till
and ou.twash a llu v iu m remains on th e v a l l e y f l o o r and
w a lls .
O b je c tiv e s and P r o c e d u re .
This study is an a tte m p t, based on g e o lo g ic o b s e rv a tio n s o n l y ,
t o determ ine th e c i r c u l a t o r y p a t t e r n s , recharge mechanisms, and heat
source o f th e Corwin S p r in g s -G a r d in e r geothermal systems.
These
systems a r e o f p a r t i c u l a r i n t e r e s t in t h a t although they l i e
i n close
p r o x im it y to the magmatic h e a t - d r i v e n Y ellow stone systems, they bear
c lo se g e n e t ic resemblance to many o f th e thermal s p rin g systems
throughout w estern Montana.
The q u a n t i t y o f h e at and g e o th e r m a l.
f l u i d s t h a t th e Corwin S p r in g s -G a r d in e r system m ight d e r iv e from the
Y ellow stone f i e l d
is in q u e s tio n h e r e , as is th e p r e s e n t i n t e n s i t y
and volume o f th e thermal c i r c u l a t o r y system a t depth.
The s t r u c t u r a l and l i t h o l o g i c c o n tr o ls o f th e Corwin S p rin g s G ard in e r geothermal fe a t u r e s were i n v e s t i g a t e d during th e summer o f
1975 by means o f d e t a i l e d mapping in. th e La Duke Hot S pring area
( F ig u r e I ,
page 2 ) , and reconnaissance o f th e northw est c o rn e r o f
Y ello w sto n e N a tio n a l
P ark , Cinnabar M ountain, and th e G a rd in e r f a u l t
zone w ith th e guidance o f publishe d g e o lo g ic r e p o r t s .
D e t a ile d g e o lo g ic
data were recorded on 1 :2 0 ,2 0 0 s c a le b la c k and w h ite a e r i a l
Examination o f r e g io n a l
tr e n d s .
photos.
ERTS photos a llo w e d exten s io n o f known f a u l t
Previous I n v e s t i g a t i o n s
No work has been p ublishe d e x c l u s i v e l y concerning the c o n tr o ls
and o r i g i n s o f th e thermal fe a t u r e s along th e G a rd in e r f a u l t .
Waring (1 9 6 5 ) l i s t s
However,
d is c h a rg e tem peratures f o r th e hot s p r in g s , and
B a l s t e r and G r o f f (1 9 7 2 ) b r i e f l y d e s c r ib e p o s s ib le h eat sources f o r
ho t sp rin g s in th e upper Y ellow stone R iv e r v a l l e y .
The American
A s s o c ia tio n o f Petroleum G eo lo g is ts (1 9 7 3 ) and the Montana Bureau o f
Mines and Geology ( B a l s t e r , 1974) have published geothermal g r a d ie n t
maps based on o i l
Montana.
and gas w e ll data from th e e a s te rn p o r t io n o f
U n f o r t u n a t e l y , coverage does not in c lu d e th e Corwin S p rin g s -
G a rd in e r a r e a .
F ra s e r e t a I
( 1 9 6 9 ) , in t h e i r r e p o r t on th e geology
o f th e G a rd in e r a r e a , b r i e f l y d e s c rib e and map the e x t e n t o f t r a v e r t i n e
d e p o s its no rth o f G a r d in e r , and note th e e x is te n c e o f therm al springs
a t Bear Creek and a t La Duke.
Numerous p a p ers , however, have been
p ublishe d on th e geothermal f i e l d s w i t h i n Y ellow stone N a tio n a l Park.
F o u rn ie r and T r u e s d e ll
( 1 9 7 0 ) ; F o u r n ie r , W h ite , and T r u e s d e ll
W h ite , F o u r n i e r , M u f f l e r , and T ru e s d e ll
(1 9 75 );
( 1 9 7 5 ) ; and T r u e s d e ll and
F o u rn ie r (U .S . G e o lo g ic a l S urvey, O p e n - f i l e r e p o r t ) d e s c r ib e the
p h y sic a l and chemical p r o p e r t ie s o f th e geothermal systems w i t h i n the
Park.
Much o f t h e i r work i s based on data obtained by re se a rch d r i l l i n g
in s e le c t e d therm al a r e a s .
Chadwick and Kaczmarek (1 9 7 5 ) discuss
s e v e ra l models f o r hot springs in a d ja c e n t areas o f w estern Montana.
8
LI. S. G eo logical. Survey s tu d ie s by F ra se r e t a I
Ruppel
(1 969) and
(1 9 7 2 ) p ro v id e in fo r m a tio n on th e s t r a t i g r a p h i c s e c tio n and
s t r u c t u r e near G a rd in e r and the n o rthw est c o rn e r o f Y ellow stone
N a tio n a l
e t al
Park.
Papers by Wilson ( 1 9 3 4 a , b ) , Spencer ( 1 9 5 9 ) , Foose
( 1 9 6 1 ) , and Brown (1 9 6 1 ) a ls o c o n t r i b u t e to these s u b je c ts .
Iddings ( 1 8 9 9 ) , Chadwick ( 1 9 7 0 ) , P rostka and Smedes ( 1 9 7 2 ) , and Shaver
(1 9 74 ) d e s c rib e th e d i s t r i b u t i o n and c h a r a c te r o f T e r t i a r y e r u p t iv e
c e n te rs and e x t r u s i v e s .
C h r is tia n s e n and Blank (1 9 7 2 ) discuss the
phases o f Q uaternary r h y o l i t i c volcanism t h a t produced the thermal,
f e a t u r e s o c c u rrin g w i t h i n th e Park tod a y .
Hamilton (1 9 6 0 ) and Love
(1 9 61 ) d i s t i n g u i s h t e c t o n i c f e a t u r e s a c t i v e i n th e Q uaternary in the
Y ellow stone Park-Hebgen Lake a r e a .
Smith e t a I
(1 9 74 ) and Eaton e t a I
(1 9 75 ) p r e s e n t models o f the subsu rface geology o f Y ello w sto n e N a tio n a l
Park and v i c i n i t y based on g r a v i t y , s e is m ic , and aerom agnetic d a ta .
Chapter 2
GEOLOGIC SETTING
Local S t r a t i g r a p h y
More than 1 0 ,0 0 0 f e e t o f m arine and t e r r e s t r i a l
P a le o zo ic and
Mesozoic sedim entary rocks accumulated on th e Precambrian c r y s t a l l i n e
basement b e fo re the beginning o f T e r t i a r y tim e .
About 3 ,0 0 0 f e e t o f
P a le o z o ic m arine sedim entary rocks a re exposed in the southern G a l l a t i n
Range ( Ruppel, 1 9 7 2 ).
The l i t h o l o g y in c lu d e s lim e s to n e , d o lo m ite , and
v o l U m e t r i c a l l y l e s s e r amounts o f c l a s t i c ro c k.
sented except th e S i l u r i a n .
A ll
systems a re r e p r e ­
P a le o z o ic rocks crop out a t Cinnabar
Mountain and a t Bear C reek, though f a u l t i n g removed fo rm a tio n s o ld e r
than O rd o v ic ia n a t Cinnabar Mountain and o l d e r than M is s is s ip p ia n
a t Bear Creek ( F i g u r e 2; P l a t e . I , page 3; and P l a t e 2 , page 4 ) .
More than 8 ,0 0 0 f e e t o f Mesozoic rocks o v e r l i e th e P ale o zo ic
sequence ( F ig u r e 2 ) .
Outcrops o f T r i a s s i c and J u ra s s ic rocks a t
Cinnabar Mountain d i s p la y about 1 ,0 0 0 f e e t o f marine sandstones,
s i l t s t o n e s , and lim e s to n e s .
More than 5 ,0 0 0 f e e t o f m arine and non­
m arine c l a s t i c rocks were de pos ited from Late J u ra s s ic to Late
Cretaceous tim e (F r a s e r e t a l , 1 9 6 9 ).
Exposures o f these rocks on
Cinnabar Mountain in c lu d e t h i c k sequences o f sandstones, s h a le s , and
mudstones.
A l i s t o f th e fo rm a tio n s and rock d e s c r ip t io n s is included
in Appendix A, page 72.
10
0
1
IO
_____ I___
J
M IL E S
Cenozoic rocks
____________________
u
N orm al
D
Fault
CE
Mesozoic
rocks
Reverse
Paleozoic rocks
C ontact
Precam brian
A nticline
—*—
—b~
Inclined
Overturned
S trik e
FIGURE 2
and
rocks
dip of beds
©
Horizontal
Fault
Syncline
A l----------------------- | a '
Line of cross section
GENERALIZED BEDROCK GEOLOGY - GARDINER REGION
(modified from Wilson(1934), Frazer (1 969 ) and Ruppel(l972)
11
Cenozoic S tr u c tu r e s and F a u lts
The G a l l a t i n a n t i c l i n e .
The upper reaches o f th e Y ellow stone
R iv e r d ra in a g e have been s u b jec te d to in te n s e te c to n ism and volcanism
from th e Late Cretaceous to th e p r e s e n t.
Eastward re g r e s s io n o f a .
Cretaceous seaway, in response to a r i s i n g landmass to th e w e s t,
s ig n a le d the beginning o f th e Laramide p e rio d o f d e fo rm a tio n and
u p lift.
A moderate compressional f o r c e from the. southwest produced
.
re g io n a l f o l d i n g along n o r t h w e s t-tr e n d in g a x e s , fo llo w e d by d i f ­
fe re n tia l
u p l i f t o f c r y s t a l l i n e blocks along n o r th w e s t-tr e n d in g o f
high a ngle r e v e rs e f a u l t s and t h r u s t f a u l t s .
Laramide f a u l t s may
have fo llo w e d northw est and n o r t h - n o r t h e a s t - t r e n d in g Precambrian
f a u l t s o r s t r u c t u r a l weaknesses in th e c r y s t a l l i n e basement (F r a s e r
e t a l , 1 9 6 9 ).
Compressional d e fo rm a tio n p e r s is te d i n t o th e e a r l y
Eocene and r a is e d th e sedim entary s e c tio n in the n o rthw est p a r t o f
p re s e n t day Y ello w sto n e N a tio n a l Park i n t o th e g e n t l e n o rth w e s t­
tr e n d in g G a l l a t i n a n t i c l i n e
( Ruppel, 1 9 7 2 ) ,
( F ig u r e 2 ) .
Opposing h ig h -
a ngle r e v e r s e f a u l t s on th e no rth and south limbs o f t h i s a n t i c l i n e
depressed th e c r e s t o f th e a n t i c l i n e between them.
The n o r th e a s t -
d ip p in g G a rd in e r r e v e r s e f a u l t , passing through G a r d in e r , Montana,
forms the southern boundary o f th e B e a rto o th u p l i f t to th e no rth o f
th e a n t i c l i n e , whereas the G ra y lin g Creek f a u l t forms th e north e rn
boundary o f an u p l i f t o f Precambrian c r y s t a l l i n e rock to th e south
o f th e a n t i c l i n e ,
in the v i c i n i t y o f Mount Holmes ( F i g u r e 3 ) .
12
B eartoo th
Block
Cinnabar Mt.-
A Sheep Mt.
G ardiner
Sepulcher
Graben
Mt.
Holmes
G allatin
H o rst
MILES
Norm al
Faults
FIGURE 3
u
______________ _
D
R everse
F au lts
MAJOR FAULT ZONES AND STRUCTURAL
FEATURES
-
(modified from
GARDINER
REGION
Frazer (1 9 6 9 ), Ruppel(1972)
13
The G ard in e r f a u l t .
The G a rd in e r f a u l t is a s t e e p l y n o r th e a s t­
d ip p in g i m b r ic a te r e v e rs e f a u l t zone, along which is preserved n e a r ly
1 0,0 00 f e e t o f P a le o z o ic and Mesozoic sedim entary rocks in i t s
b lo c k .
The f a u l t zone ranges from .2 5 to one. m ile w ide.
fo o t w a ll
I t emerges
from beneath T e r t i a r y v o lc a n ic cover s o u th e as t o f the Grand Loop Road
in Y ellow stone N a tio n a l P a rk , and extends northw est along.Rescue Creek
towards G a r d in e r , Montana ( P l a t e 3 ) .
The f a u l t zone passes along th e
base o f Sheep Mountain j u s t n o rth o f G a rd in e r but is b u rie d beneath
b a s a l t flow s o f probable e a r l y P le is to c e n e age..
re-emerges a t L i t t l e T r a i l
The f a u l t zone
Creek, to be p r o g r e s s iv e ly o f f s e t to the
n o r th e a s t around th e n o rth e rn fla n k s o f Cinnabar Mountain by younger
n o r t h - t r e n d in g normal f a u l t s
( F ig u r e 3 , P l a t e 4 , and P l a t e 5 ) .
A
n o rthw est tr e n d in g zone o f v e ry coarse a u t o c l a s t i c fragments in
Precambrian g r a n i t i c gneiss marks th e l o c a t i o n o f p a r t o f th e G ardiner
f a u l t zone 0 .2 5 m ile s u p h i l l and to th e n o r th e a s t o f La Duke Hot Spring
( P l a t e 6 and P l a t e 7 ) .
The f a u l t zone juxtaposes c r y s t a l l i n e Pre-
cambrian rock o f the B e a rtooth u p l i f t , a g a in s t rock u n it s ranging in
age from O rd o v ic ian to Cretaceous a t d i f f e r e n t l o c a l i t i e s
exposure.
along i t s
The sedim entary u n its a re dragged up and a r e l o c a l l y o v er­
turned along th e f a u l t zone as exposed a t Cinnabar Mountain and a t
Mount E v e rts .
14
P l a t e 3.
View toward the e a s t from E l e c t r i c Peak o f t r a v e r t i n e
d e p o s its (T ) and P lio c e n e b a s a l t flows (B) a t G a rd in e r.
The G a rd in e r f a u l t zone passes beneath these d e p o s its
s t a r t i n g a t th e mouth o f Bear Creek (B C ). A branch o f the
Mammoth f a u l t (M) d e fin e s th e base o f the n o rthw est fl a n k
o f Mount E verts and e n te rs th e G ard in e r f a u l t zone near
(B C ).
15
PLATE 4.
View toward the no rth from E l e c t r i c Peak o f th e La Duke Hot
Spring a re a .
The Reese Creek f a u l t (R) e n te rs the Beartooth
block a t La Duke Hot Spring ( L ) . The G a rd in e r f a u l t zone (G)
passes through La Duke Hot Spring along the n o rth e a s te rn
w a ll o f the Y ellow stone R iv e r V a l l e y .
O f f s e t b a s a lts (B)
i n d i c a t e Q uaternary a c t i v i t y on the G a rd in e r f a u l t zone.
16
PLATE 5.
Trace o f th e G a rd in e r f a u l t on th e n o rth e rn f l a n k o f Cinnabar
Mountain lo o k in g to the n o rthw est from a p o in t .5 m iles
s outhe as t o f Corwin S p rin g s .
(Te = Eocene i n t r u s i v e , pK =
pre -C re ta ce o u s sedim entary ro c k s , PC = Precambrian rock)
17
PLATE 6.
F a u l t b re c c ia in g r a n i t i c gneiss o f the G a rd in e r f a u l t zone
.2 5 m iles n o r th e a s t o f La Duke Hot S p rin g .
Contact o f
und is tu rb e d g r a n i t i c gneiss w ith b re c c ia zone in d ic a te d by
arrow .
Zone s t r i k e s a p p ro x im a te ly N50W and dips 50°NE.
(n o te c i r c l e around man f o r s c a le )
18
PLATE 7.
G a rd in e r f a u l t zone b r e c c ia (b x a ) showing bou ld e r s ize d
c l a s t s o f g r a n i t e .25 m ile s n o r th e a s t o f La Duke Hot
S p rin g .
Cinnabar Mountain l i e s in the background to the
no rth w e s t.
19
The G a l l a t i n h o r s t ,
As u p l i f t o f the B eartooth block and the .
Precambrian b lo c k south o f th e G r a y lin g Creek f a u l t proceeded, a h o r s t
block com prising th e p re s e n t s o u t h e r n . G a l l a t i n Range rose on a n o r th n o r th e a s t tr e n d between th e East G a l l a t i n and West G a l l a t i n normal
fa u lts
( F ig u r e 3 , page 1 2 ) .
These f a u l t s a re t r a c e a b l e from the
southern end o f th e G a l l a t i n Range northward i n t o th e B eartooth b lo c k ,
where they cause ap p are n t l a t e r a l
o ffse ts
in th e t r a c e o f th e G ard in e r
f a u l t on th e s o u th e a s t and northw est sides o f Cinnabar Mountain.
Maximum displacem ents o f 4 ,0 0 0 to 5 ,0 0 0 f e e t have been observed on the
East G a l l a t i n f a u l t ( I d d i n g s , 1904; W ils o n , 1934a; F ra s e r e t a l ,
1969;
R uppel, 1 9 7 2 ) , whereas a p p ro x im a te ly 2 ,5 0 0 f e e t o f displacem ent
have been noted on th e West G a l l a t i n f a u l t
( Ruppel, 1 9 7 2 ).
D is p la c e ­
ment decreases d r a s t i c a l l y as th e f a u l t s s c is s o r closed i n t o the
B e a rtooth b lo c k .
These f a u l t s probably formed as th e block u p l i f t
commenced d u rin g Laramide compression and have been i n t e r m i t t e n t l y
a c t i v e i n t o th e P le is to c e n e (Love, 1961; Ruppel, 1 9 7 2 ).
The G a l l a t i n h o r s t block may be a product o f r e s is t a n c e to
Laramide compressional d e fo rm a tio n which grew on a n o r th -s o u th axis
between th e G a rd in e r f a u l t and th e G r a y lin g Creek f a u l t .
s ills
and l a c c o l i t h s
Paleocene
in tr u d e d along th e P ale o zo ic and Mesozoic rocks
p robably c a u s e d .th e s e c tio n to behave r i g i d l y in response to compression
(S h a ve r, 1 9 7 4 ).
Compressional s tr e s s e s were r e l i e v e d by c r e a t i o n of',
th e normal f a u l t s t h a t now d e f in e th e G a l l a t i n h o r s t.
Precambrian
20
gneiss in th e hanging w a ll
..
:
block o f th e G ard in e r f a u l t r e s t s a g a in s t
O rdovician Bighorn Dolom ite in th e f o o t w a l l
end o f Cinnabar M ountain.
block a t th e no rth e rn
The same Precambrian gneiss r e s t s a g a in s t
Cretaceous Telegraph Creek Sandstone a t L i t t l e T r a i l
C reek, th r e e
m iles s o u th e as t o f Cinnabar Mountain ( F ig u r e 2 , page 1 0 ) .
Reverse
o f f s e t a p p a r e n tly progressed f u r t h e r a t t h i s lo c a t i o n than a t Cinnabar
Mountain w it h the r e s u l t t h a t th e G a rd in e r f a u l t is o f f s e t as i t
approaches Cinnabar Mountain a p p ro x im a te ly 0 . 5 m iles to th e n o r th e a s t
by the Reese Creek e x te n s io n o f th e East. G a l l a t i n f a u l t ( F ig u r e 3 ,
Page 12, and P l a t e 4 , page 1 5 ) .
A f t e r passing over th e n o rth f l a n k
o f Cinnabar M ountain, th e G a rd in e r f a u l t is o f f s e t 0 .2 5 m ile s back
to the southwest by the Mo! Heron Creek e x te n s io n o f th e West G a l l a t i n
fa u lt.
This a p p a re n t l a t e r a l
displa c em e n t r e s u l t s from the v e r t i c a l
displa c em e n t o f th e no rth e a stw a rd d ip p in g G a rd in e r f a u l t zone.
Fig u re 5 , page 3 1 , d e p ic ts t h i s f r a c t u r e p a t t e r n in g r e a t e r d e t a i l .
The G a l l a t i n h o r s t is s i m i l a r to th e compression r e s i s t a n t
block u p l i f t e d along th e r e v e rs e B e a rto o th f a u l t on th e n o r th e a s t
f r o n t o f th e B eartooth b lock near Red.Lodge.
This b lo c k is bordered
by two t e a r f a u l t s having up to 1 0 ,0 0 0 f e e t o f l a t e r a l
( Foose e t a l , 1 9 6 1 ).
displacem ent
The Reese Creek and Mo! Heron Creek f a u l t s
correspond to th e t e a r f a u l t s a t Red Lodge but show much le s s l a t e r a l
d is p la c em e n t.
S h a llo w e r dips and g r e a t e r im b r i c a t i o n along the
21
re v e rs e B e a rtooth f a u l t p e r m itte d g r e a t e r l a t e r a l d isplacem ent o f the
r e v e rs e f a u l t zone a t Red Lodge than a t Cinnabar Mountain.
The Mammoth f a u l t .
The Mammoth f a u l t and r e l a t e d f r a c t u r e s a re
w e s t e r l y d ip p in g normal f a u l t s w it h up to 4 ,0 0 0 f e e t o f displacem ent
( F r a s e r e t a l , 1969; Ruppel, 1 9 7 2 ).
They extend from the v i c i n i t y
o f N o r r is Geyser Basin northward i n t o th e G ard in e r f a u l t zone between
Bear Creek and G a rd in e r ( P l a t e 3 , page 1 4 ) .
The G a rd in e r f a u l t zone,
where exposed, is sheared by th e Mammoth f a u l t .
.
The Mammoth f a u l t ,
l i k e th e East and West G a l l a t i n f a u l t s , appears to s c is s o r closed
r a p i d l y as i t e n te rs th e B e a rtooth b lo c k .
The upturned P a le o zo ic and
Mesozoic u n its a t th e j u n c t u r e o f th e Mammoth and G a rd in e r f a u l t s a re
g r e a t l y d i s t u r b e d , p r e v e n tin g a c c u r a te measurement o f displacem ent
along the Mammoth f a u l t .
The Sepulcher g ra b en .
Downward displacem ent o f th e c r u s t a l
b lock between th e Mammoth and East G a l l a t i n f a u l t s has preserved n e a r ly
5 ,0 0 0 f e e t o f Eocene v o lc a n ic s on top o f th e p r e - T e r t i a r y s e c tio n .
s t r u c t u r e is known as th e Sepulcher Mountain graben.
This
The graben
e f f e c t i v e l y tr u n c a te s th e a x is o f th e G a l l a t i n a n t i c l i n e between
Roaring Mountain and Mount Holmes and plunges a t a g r a d u a l l y steepening
a ngle northward under th e G ard in e r f a u l t .
A segment o f th e G a l l a t i n
a n t i c l i n e is pro b a b ly preserved in th e S epulcher graben, although the
n o r th e rn lim b i s most l i k e l y oversteepened by the g r e a t e r displacem ent
22
o f the graben i n i t s
n o rth e rn e x t e n t r e l a t i v e to d ip angles observed
on the G a l l a t i n h o r s t.
Cenozoic Volcanism
Eocene v o lc a n is m .
Widespread d a c i t i c and a n d e s i t i c volcanism
accompanied th e l a s t stage o f displa c em e n t along the G a rd in e r f a u l t
zone d u rin g Eocene tim e , . A l l o f the G a rd in e r re g io n was covered by
t h i c k sequences o f b re c c ia s and flow s t h a t were p a r t o f th e AbsarokaG a l l a t i n v o lc a n ic f i e l d
(Chadwick, 1 9 7 0 ).
M ajor c e n te rs o f e r u p tio n
i n th e G a rd in e r a rea in c lu d e E l e c t r i c Peak, Bunsen Peak, and s ev e ral
sources to th e n o r th e a s t on th e B e a rto o th b lock ( F r a s e r e t a l ,
1 9 6 9 ).
E l e c t r i c Peak was the p rim ary source f o r th e v o lc a n ic s preserved in
the S epu lcher graben.
The G a rd in e r f a u l t zone a ls o served as a minor c o n d u it f o r
Eocene la v a s .
Numerous d a c i t i c and a n d e s i t i c dikes occupy p o s itio n s
w i t h i n th e f a u l t zone and p a r a l l e l
These dik es a re w e ll
to th e f a u l t plane ( F ig u r e 4 ) .
exposed near La Duke Hot Spring and on the north
f l a n k o f Cinnabar Mountain where they p ro v id e the most r e l i a b l e means
o f i d e n t i f y i n g th e t r a c e o f th e G a rd in e r f a u l t .
The dikes g e n e r a lly
p e n e t r a t e Precambrian g r a n i t i c gneiss and f a u l t b re c c ia s o f th e hanging
w a ll b lo c k .
However, a few dikes on Cinnabar Mountain i n t r u d e lim e ­
stone o f th e f o o t w a l I b lo c k clo se t o th e f a u l t t r a c e .
These dikes .
a re tru n c a te d and o f f s e t along th e G a rd in e r f a u l t zone by the Reese
23
A n d e s ite B r e c c i a
Andesite
Extrusive
Intrusive
Dacite E x t r u s iv e
D a c i t e In tr u s iv e
Sepulcher Form ation
(Rhyodacite
flow - c o r r e l a t i o n
u n c e r t a in )
■ ■ ■
R ev erse
——
a:
ash
eee*
F a u lt
Ui
N o rm a l
1D
F a u lt
C o n ta c t
0
I
J
MILES
AGURE 4. DISTRIBUTION OF EOCENE
IN T R U S lV E S
AND EXTRUSIVES NEAR CORWIN SPRINGS, M O N TA NA
(modified fro m W ilson, 1 9 3 4 a ,
F raser, 1969,
and
U.S. Geological Survey Mop I - 7 1 1, 1 9 7 2 )
24
Creek and Mo! Heron normal f a u l t s .
Several small
and d a c i t e b r e c c ia c u t th e hanging w a ll
f a u l t zone between L i t t l e T r a i l
in tru s io n s ' o f d a c ite
block w i t h i n one m i l e o f the
Creek and Corwin S p rin g s.
The G ard in e r
f a u l t zone probably c o n t r o l l e d th e a sc e n t o f these magmas as w e l l .
Most d isplacem ent along th e G a rd in e r f a u l t zone appears to have been
accomplished b e fo re th e Eocene i n t r u s i v e s were emplaced, as in d ic a te d
by the l a c k o f m ajor r e v e r s e d isplacem ent w i t h i n those i n t r u s i v e s .
However, th e G a rd in e r f a u l t may be re s p o n s ib le f o r some minor b r e c c ia ' t i o n and gouge w i t h i n th e dikes on Cinnabar Mountain, i n d i c a t i n g
some a c t i v i t y along th e f a u l t zone a t th e tim e o f i n t r u s i o n .
rocks a r e d e s c rib e d in g r e a t e r d e t a i l
Q u a ternary v o lc a n is m .
These
in Appendix B, page 75.
F o llo w in g t h i s e a r l y v o lc a n ic e pisode,
volcanism subsided i n th e G a rd in e r area u n t i l
P lio c e n e or
P le is to c e n e tim e when a s e r ie s o f b a s a lts flowed down th e Yellowstone
R iv e r v a l l e y from probable sources w i t h i n Y ellow stone P ark.
At l e a s t
f i v e flow s make up the b a s a l t bench e xtending north o f G a rd in e r from
Deckard F l a t s near Bear Creek to L i t t l e
T ra il
Creek.
Another remnant
outcrop l i e s on an o ld e r o s io n a l s u r fa c e above La Duke Hot S pring.
The age and source o f t h i s sequence o f b a s a lts is u n c e r t a in since
e ro s io n has destroyed any l i n k s w i t h p o s s ib le sources upstream.
Source conduits w i t h i n th e G a rd in e r f a u l t zone no rth o f G ard in e r
were suggested by Wilson (1 934a) but evidence is not c o n c lu s iv e .
25
The b a s a lts resemble those o f th e J u n c tio n B utte B a s a lt Group in t h e i r
b l a c k , a p h a n it ic appearance and p o s i t i o n on top o f a l a t e T e r t i a r y
e ro s io n a l s u r fa c e c u t i n t o u n c o n s o lid a te d sediments and p r e - Eocene
rocks.
The absence o f ash flo w t u f f c l a s t s o f th e Y ellow stone Group
in th e uncons o lid a te d sediments beneath the b a s a lts suggests t h a t the
G a rd in e r b a s a lts were e r u p te d , as were th e J unction B u tte B a s a lt s ,
p r i o r to the i n i t i a l
ou tb re a k o f r h y o l i t i c
P la te a u ( F r a s e r e t a l , 1 9 6 9 ).
lavas on the Y ellow stone
C h r is tia n s e n and Blank (1 9 72 ) have
i d e n t i f i e d vents o f the J u n c tio n B u t t e . B a s a l t Group a t th e e a s t end
o f Mount E v e r ts .
Flows from these vents could have had access to
the G a rd in e r area by means o f e i t h e r th e Y ellow stone R iv e r o r the
G a rd in e r R iv e r d ra in a g e .
S everal P lio c e n e b a s a l t flow s have been
dated by Bush (1 9 6 7 ) a t Hepburn's Mesa 15 m iles down th e Y ellow stone
R iv e r from G a r d in e r .
No c o r r e l a t i o n between the G a rd in e r and Hepburn's
Mesa b a s a lt s has been e s t a b l i s h e d .
Three c ycles o f r h y o l i t i c
t u f f e r u p tio n and c a ld e r a c o lla p s e
began on th e Y ellow stone P la te a u in th e E a r ly P le is to c e n e .
P e r io d ic
e x t r u s io n o f r h y o l i t e f l o w s , domes, and b a s a l t flow s accompanied the
voluminous t u f f e r u p t io n s .
The o l d e s t flow s have been dated a t less
than 2 . 4 m i l l i o n y e a rs b id (C h r i s t i a n s e n and B la n k, 1 9 7 2 ).
The
youngest flow s were extruded as r e c e n t l y as 7 0,0 00 y ea rs ago
(C h r i s t i a n s e n and B la nk, 1 9 7 2 ).
The Sepulcher graben was the s i t e
o f e x t r u s io n o f s e v e ra l young flow s and domes.
These e x t r u s i v e
26
c en ters were p e r ip h e r a l
to th e main c a l d e r a .
No v o lc a n ic s were
erupted in th e Corwin S p r in g s -G a r d in e r area during t h i s p e r io d ,
a lthough th e Y ellow stone R iv e r v a l l e y was deeply b u rie d under r h y o l i t e
t u f f a t l e a s t once as evidenced by remnants o f r h y o l i t e ash flows on
Mount E v e r t s , in th e Bear Creek d ra in a g e no rth o f G a r d in e r , and in
Tom M iner basin no rth w e s t o f Corwin S p rin g s .
Caldera c o lla p s e occurred
on th r e e occasions c e n te re d around th e Y ellow stone Lake area as ra p id
removal o f magma du rin g the t u f f e r u p tio n s l e f t the r o o f o f the magma
chamber unsupported.
Regional S e i s m i c i t y
The g e o lo g ic re c o rd o f th e G a rd in e r area suggests t h a t the
area has been s e i s m i c a l I y a c t i v e s in c e th e l a t e Cretaceous.
mechanical n a tu r e o f t h i s a c t i v i t y has changed w ith tim e .
The
Laramide
compressional s tr e s s subsided by M id d le Eocene tim e as in d ic a t e d by
the la c k o f s i g n i f i c a n t r e v e rs e displa c em e n t in th e Eocene v o lc a n ic s .
A te n s io n a l
s tr e s s regime re p la c e d Laramide compression causing e x te n ­
s iv e normal f a u l t i n g
in th e upper Y ellow stone r e g io n .
Tensional
s tr e s s e s became most in te n s e d u rin g th e P lio c e n e and have continued
i n t o th e Holocene ( R uppel, 1 9 7 2 ).
A f t e r i n i t i a l l y d e ve lo p in g during
th e Laramide, a group o f n o r th -s o u th tr e n d in g normal f a u l t s acquired
most o f t h e i r displa c em e n t d u rin g t h i s
l a t e s t , d e fo rm a tio n a l phase.
These in c lu d e th e East and West G a l l a t i n f a u l t s and th e Mammoth f a u l t .
'
. .
.27,
Normal displa c em e n t a ls o occurred d u rin g th e Holocene along the G ardine r
and G r a y lin g Creek f a u l t s
( F r a s e r e t a l , 1 9 6 9 ).
Such displacem ent may
be observed along th e G a rd in e r f a u l t a t L i t t l e T r a i l
Creek and south­
e a s t o f Mount E v e rts .
The G a rd in e r area l i e s w i t h i n th e In te rm o u n ta in Seismic B e l t ,
a m ajor zone o f Holocene s e i s m i c i t y e xtending from southern Utah to
northw est Montana (Sm ith e t a l , 1 9 7 4 ).
The Y ellow stone c a ld e r a com­
p r is e s the e a s te r n end o f a secondary seism ic zone t h a t extends w est­
ward through th e Hebgen Lake area i n t o c e n t r a l
Idaho.
F a u l t plane
s o lu tio n s by Smith and Sbar (1 9 7 4 ) and Trim bel and Smith (1 9 73 ) suggest
t h a t n o r th -s o u th e x te n s io n p r e s e n t l y p r e v a i l s along t h i s secondary
s eism ic zone whereas e a s t- w e s t e x te n s io n p r e v a i l s along th e r e s t o f
th e In te rm o u n ta in Seismic B e l t to th e no rth and south.
Holocene scarps
along th e normal Deep Creek f a u l t to th e north o f Gardiner, in the
P aradise V a l l e y and along the Teton f a u l t in Jackson Hole to the south
pro v id e c l e a r evidence f o r modern s eism ic a c t i v i t y .
Resurgent magmatic
a c t i v i t y beneath th e Y ello w sto n e c a ld e r a superimposes r a d i a l compres­
s iv e fo rc e s upon th e more general te n s io n a l regime in th e v i c i n i t y
o f th e c a ld e r a (Sm ith e t a l , 1 9 7 4 ).
d i r e c t i o n is in d i c a t e d .
C ru s ta l s h o rte n in g in a r a d ia l
Chapter 3
CONTROLS ON THERMAL WATER CIRCULATION
Control on th e flo w o f thermal w a te r in th e Corwin S p rin g s G a rd in e r thermal systems is e x e rte d by j o i n t s ,
rock u n i t s .
f a u l t s , and permeable
A g e o lo g ic model d e s c r ib in g r e c h a rg e , c i r c u l a t i o n , and
dis cha rge o f these thermal systems, and the r e l a t i v e importance o f
these c o n t r o l l i n g s t r u c t u r e s w i l l
be developed here.
This model
is
an a tte m p t to e x p l a i n th e g e o lo g ic s e t t i n g and p h y s ic a l c h a r a c t e r i s t i c s
o f th e hot s p r in g s .
A b r i e f d e s c r i p t i o n o f the geology o f La Duke
Hot S pring and Bear Creek thermal s prin gs and th e G a rd in e r t r a v e r t i n e
d e p o s its w i l l
th e r e g io n a l
help p la c e the c i r c u l a t i o n model w i t h i n th e c o n te x t o f
g e o lo g ic p i c t u r e developed in Chapter I .
Local Geologic S e t t i n g
The Corwin S p r in g s -G a r d in e r thermal f e a tu r e s a re a lig n e d w i t h i n
th e n o r th w e s t-tr e n d in g G a rd in e r r e v e r s e f a u l t zone.
La Duke Hot
Springs l i e s a t th e i n t e r s e c t i o n o f th e G ard in e r f a u l t and the Reese
Creek f a u l t as i n d i c a t e d in F ig u re 5 , page 31.
Hot w a te r flows from
two m ajor sources and from two small seeps in r e c e n t c o llu v iu m and
fra c tu re d , s i l i c i f i e d
lim es to n e bedrock.
One m ajor source is a c t i v e l y
d e p o s itin g t r a v e r t i n e on th e banks o f th e Yellow stone R iv e r and flows
a t an e s tim a te d 100 gpm from a cement-encased r e s e r v o i r covered by
U. S. Highway 89 ( T a y l o r , 1 9 7 5 ).
The o th e r source is a nonflowing
I
■
■ H K
PLATE 8.
■
aZ ' - : ^ : ! ^ - ^ - .
View to the n o rth o f La Duke Hot Spring and c l i f f y
s i l i c i f i e d lim es to n e b r e c c ia o u tc ro p .
(Qt = Q uaternary
t r a v e r t i n e , bxa = f a u l t b r e c c ia )
30
cement-encased pool l y i n g to the e a s t o f the highway..
The two seeps
d r a in i n t o the borrow p i t about 30 yards to the south on th e e a s t
s id e o f th e highway.
La Duke Hot S pring was th e source o f hot w ater
f o r th e r e s o r t com m unity.at Corwin Springs in the l a t e 1 8 0 0 's .
These s prin gs l i e
a t the base o f a prominent c l i f f composed
o f a coarse a n g u la r f a u l t b re c c ia
( F ig u r e 5 ) .
Most o f the bre c c ia
is a h i g h l y s i l i c i f l e d , dark g r a y , sugary t e x tu r e d ro c k.
However,
t e x tu r e s v i s i b l e in th e rock on th e upper p a r t o f th e outcrop suggest
t h a t d a c i t e makes up a p o r t io n o f t h i s b r e c c ia .
These d a c i t e fragments
may come from a d a c i t e d ik e which cuts th e g r a n i t i c gneiss o f the
B e a rtooth b lo c k im m ed ia te ly u p h i l l
from th e b re c c ia o u tc ro p .
The
low er p a r t o f the b re c c ia outcrop is ah a l t e r e d lim e s to n e which may
be p a r t o f th e Madison Group as suggested by i t s
l i g h t gray c o lo r and
m ic r o s c o p i c a l l y v i s i b l e ghosts o f c r i n o i d stem cross s e c tio n s
(D.
L. S m ith , personal communication, 1 9 7 6 ).
( P l a t e 9)
This i n t e r p r e t a t i o n
is u n c e r ta in but is supported by th e l o c a t i o n o f t h i s outcrop a p p r o x i­
m a te ly on th e s t r i k e p r o j e c t i o n o f th e upturned Madison Group a t
Cinnabar Mountain across th e Y ellow stone R iv e r v a l l e y to th e n orthw est.
The s t r u c t u r a l
o r i e n t a t i o n o f the lim e s to n e outcrop a t La Duke Hot
S pring i s not measurable due to poor exposure.
The lim e s to n e outcrop
may r e p r e s e n t th e e a s te rn margin o f th e G a l l a t i n h o r s t.
However,
th e margin a t t h i s p o in t must be s i g n i f i c a n t l y downdropped, r e l a t i v e
to the h o r s t a t Cinnabar M ountain, by normal d isplacem ent along the
31
T
^
/
n
M cV
(.
x /< ^ C ^ w m V v
^ S sS V
FIGURE 5.
GARDINER
z";
/:
L
Te
^Springs
w^Xxoi
1969,
Pv
/:
/:
BEDROCK GEOLOGY OF THE CORWIN SRRINGSAREA (modified from Wilson, 1934, Fraser,
Ruppel,
1972,
and
Struhsacker, 1976)
Quaternary
sediments
Q u a te rn ary
y/D !
tra v e rtin e
up
Pliocene
V
I/ — X O
yv
:X #
/V
X.
1 1
Xl1QDuk s'
.Spring
_
&
basalt
M IL E S
Eocene
volcanice
re
Cretaceous
P r e - Cretaceous
lx \
X 89 x
T
sedimentary
Precambrian
rocks
sedimentary
gneiss
and
rocks
schist
>
•i:
R ev erse
fa u lt
N orm al
fa u lt
C o ntact
S sV f '
V
p ^ e rtic a l
( ,^ y //\S trik e
XJ
V .
IvV z -
ird in e r
I
P.?/
.
/
k I
\
M am m o th
F a u lt
sar G r e e t
Spring
Overturned
and
dip o f
Inclined
beds
PLATE
9
PARTLY
STEM
S IL IC IF IE D
R EM N A N TS
LIM ESTO N E
FROM
SHOWING
LA DUKE
POSSIBLE
CRINOID
HOTSPRINGS. (CROSSED
NICOLS)
numerous elements o f the Reese C re e k -E a s t G a l l a t i n f a u l t .
These
elements p e n e t r a t e th e G a rd in e r f a u l t zone between L i t t l e T r a i l
and Cinnabar Mountain.
The v e r t i c a l
u n its dragged up in th e f o o t w a l l
Creek
o r i e n t a t i o n o f th e sedimentary
block o f the G a rd in e r f a u l t zone
f r u s t r a t e s any attem pts to determ ine th e amount o f v e r t i c a l d i s p la c e ­
ment t h a t has occurred along the Reese Creek f a u l t zone in th e v i c i n i t y
o f La Duke Hot S p rin g .
The Reese Creek f a u l t and a s s o c ia te d f r a c t u r e s
appear to c o n tin u e northward i n t o the B e a rto o th block as much as one
m ile beyond th e G a rd in e r f a u l t zone as i n d i c a t e d by bedrock f r a c t u r i n g
and top o g ra p h ic T in e ars v i s i b l e on th e ground and on a e r i a l
( F ig u r e 3 , page 1 2 ) .
photos
The f r a c t u r e s s c is s o r shut as they c u t in to
the B eartooth b lo c k.
The Bear Creek thermal s p r in g l i e s
near the i n t e r s e c t i o n o f
the G a rd in e r f a u l t and a branch o f th e Mammoth f a u l t ( F r a s e r e t a l ,
1969)
( F ig u r e 5 ) .
The s p rin g p r e s e n t ly flow s a t les s than one gpm
but has d e p o s ited a .3 square m ile t r a v e r t i n e mound d u rin g the
P le is to c e n e and Holocene.
The t r a v e r t i n e r e s ts on top o f an upturned
sequence o f P a le o z o ic and Mesozoic sedim entary ro c ks .
Reverse f a u l t i n g
has placed Precambrian s c h i s t a g a in s t th e Madison Limestone.
Normal
f a u l t i n g along the Mammoth f a u l t zone has s e v e r e ly sheared th e s e d i­
mentary rocks in the v i c i n i t y o f Bear Creek s p r in g .
N o r th -n o r th e a s t
tre n d in g elements o f th e Mammoth f a u l t zone appear to te r m in a t e w i t h i n
th e G a rd in e r f a u l t zone though Q uaternary cover may obscure
34
c o n tin u a tio n s o f these f r a c t u r e s to the north ( F r a s e r e t a l , 1 9 6 9 ) .
Bear Creek s p rin g issues from the upthrown fo o t w a ll
b lock o f the Mammoth
f a u l t which, in c lu d e s the u p l i f t e d a re a o f Mount E verts to the e a s t o f
the Mammoth f a u l t .
The G a rd in e r t r a v e r t i n e d e p o s its d is c o n tin u o u s ly cap the
P lio c e n e - P l e i s t o c e n e b a s a l t bench im m ediately no rth o f G ard in e r
(F ig u r e 5 ) .
The b a s a l t bench, composed o f f i v e fl o w s , covers upturned
Mesozoic sediments preserved as th e f o o t w a l l block o f th e G ardine r f a u l t
zone w i t h i n the Sepulcher graben.
The t r a v e r t i n e d e p o s its l o c a l l y
a t t a i n th ic kn es s es o f g r e a t e r than 60 f e e t .
as determ ined by reconnaissance f i e l d
The g r e a t e s t th ic k n e s s e s ,
checks, occur in th e v i c i n i t y o f
p o s s ib le i n t e r s e c t i o n s o f elements o f th e Mammoth f a u l t zone w ith the
G a rd in e r f a u l t as mapped by Ruppel
(1 9 7 2 ) . , One such i n t e r s e c t i o n
may occur near th e t r a v e r t i n e q u a r r ie s s l i g h t l y northw est o f G a rd in e r,
th e s i t e o f th e t h i c k e s t t r a v e r t i n e a cc um ula tion.
The t r a v e r t i n e a ls o
covers and is c u t by numerous slump f r a c t u r e s t h a t break th e b a s a lt
bench p a r a l l e l
to th e tre n d o f the G a rd in e r f a u l t zone.
These f r a c t u r e s
a re products o f a r e a c t i v a t i o n a t depth o f the G a rd in e r r e v e rs e f a u l t
zone i n . a normal sense during P le is to c e n e and Holocene tim e (F r a s e r
e t a l , 1 9 6 9 ).
The m a j o r i t y o f th e f r a c t u r e s are probably products
o f slumping o f the b a s a lts on top o f upturned incompetent Cretaceous
sedim entary rocks in response to th e renewed t e c t o n i c a c t i v i t y .
They
most l i k e l y do not p e n e t r a t e more d eeply than the base o f the b a s a l t
35
flo w s .
However, F ra s e r e t a I
(1 9 6 9 ) in d i c a t e s t h a t s e v e ra l f r a c t u r e s
may extend c o n tin u o u s ly i n t o th e G a rd in e r f a u l t zone below th e b a s a l t .
Discharge P a tte rn s
La Duke and Bear Creek thermal s prin gs both dis ch a rg e from
f r a c t u r e s a t th e i n t e r s e c t i o n s o f the G a rd in e r f a u l t zone w it h the
Reese Creek and Mammoth f a u l t s r e s p e c t i v e l y .
Recent s eism ic a c t i v i t y
in th e area m a in ta in s these h ig h ly f r a c t u r e d zones as open c o n d u i t s . .
The G a rd in e r t r a v e r t i n e d e p o s i t s 'a r e products o f s i m i l a r l y lo c a te d
P le is to c e n e s p r in g s .
The hot w a te r probably r i s e s from a heat source
a t c o n s id e r a b le depth i n th e G a rd in e r f a u l t , zone.
Both La Duke and.
Bear Creek springs, appear to have p o in t sources as i n d i c a t e d by the
c lo s e spacing o f th e s prin gs and, in p a r t i c u l a r , th e cone shape o f
the Bear Creek t r a v e r t i n e d e p o s it .
The G a rd in e r t r a v e r t i n e d e p o s its d is p la y s y m m e tr ic a lly round
mounds and s e v e ra l n o rthw est tr e n d in g l i n e a r de pos its t h a t suggest
c o n tr o l o f d is c h a rg e by th e young slump f r a c t u r e s c u t t i n g the b a s a l t
bench w i t h i n th e G a rd in e r f a u l t zone.
One o r two o f these l i n e a r
d e p o s its resemble th e e le p h a n t back rid g e s developing p r e s e n t ly a t
Mammoth Hot Springs where thermal w a t e r flow s outward from a f r a c t u r e
to both sides along i t s
e n t ir e le n g th .
The e le p h a n t back rid g e s a t
G a rd in e r a re about .2 5 m ile s in le n g th and 20 f e e t h ig h .
The lo c a tio n s
o f many o f the s p rin g s and t h e i r r e l a t i v e s t r a t i g r a p h i c p o s itio n s a re
36
obscured by the slump f r a c t u r e s d e sc rib e d p r e v io u s ly and by g l a c i a l
sco u rin g .
F a u l t Control o f Recharge
F a u l t zones may a id th e re ch a rg e process where th e y p rovide
permeable f r a c t u r e s t h a t c o n tin u e to g r e a t depth.
Where seism ic
a c t i v i t y has s u s ta in e d open f r a c t u r e s , groundwater may p e n e tr a te
th e o th e rw is e impermeable sedim entary rocks i n th e Sepulcher graben.
F ra s e r e t al
(1 9 69 ) and Ruppel
(19.72) have suggested t h a t the G a r d in e r ,
Mammoth, and East G a l l a t i n - R e e s e Creek f a u l t s have been r e c e n t l y
a c t i v e , as evidenced by th e d is p la c em e n t o f P le is to c e n e d e p o s its along
those f a u l t s .
Many f r a c t u r e s r e l a t e d to these f a u l t zones cross the
Y ellow stone R iv e r v a l l e y p r e s e n tin g abundant o p p o r t u n it ie s f o r w ater
from t h a t d ra in a g e to p e r c o la t e i n t o t h e bedrock.
g ra in ed r i v e r a llu v iu m and g l a c i a l
to these f r a c t u r e s .
till
However, f i n e ­
may impede access o f w ater
The p e r m e a b i l i t y o f th e f r a c t u r e s may be low s in c e
w ea the ring products and hydrothermal m i n e r a l s , de pos ited by c i r c u l a t i n g
hydrothermal f l u i d s ,
tend to seal f r a c t u r e s r a p i d l y in th e absence,
o f repeated movement along th e f r a c t u r e s .
J o i n t Control o f Recharge
Abundant bedrock j o i n t s w i t h v a ry in g o r i e n t a t i o n s p rovide an
im p o rta n t means o f re ch a rg e f o r th e Corwin S p r in g s -G a r d in e r thermal
c i r c u l a t o r y systems ( F ig u r e 6 ) .
The f r a c t u r e d Precambrian g r a n i t i c
37
gneiss and s c h is ts o f the B e a rtooth b lo c k probably c o n ta in g r e a t e r
f r a c t u r e p e r m e a b i l it y than most o f th e Eocene v o lc a n ic s and
Phanerozoic sedim entary rocks in th e a r e a .
The s u p e r p o s itio n o f.
Laramide f r a c t u r i n g on Precambrian f r a c t u r e p a tte r n s in th e gneiss
and s c h i s t is a p o s s ib le e x p la n a tio n f o r t h e i r g r e a t e r f r a c t u r e
p e r m e a b i l it y .
Prominent j o i n t trends o f l i k e l y Precambrian o r i g i n , as
measured by Spencer (1 9 59 ) on th e e a s te rn p a r t o f th e Beartooth
b lo c k , and by Ruppel
(1 9 7 2 ) in th e G a l l a t i n Range and on th e southwest
p a r t o f th e B eartooth b lo c k , a r e :
N . 65°W.
O ther j o i n t s
and N . 8 5 ° E . , to E.-W.
N .1 5 ° W ., N .4 5 °W ., N . 4 5 ° E . , and
tr e n d N . 5 5 - 6 0 ° E . , N .1 5 o- 2 0 ° E . , N . - S .
Most f r a c t u r e s a r e almost v e r t i c a l
to N . 5 ° E . ,
except near
th e o v e r t h r u s t margins o f the B e a rtooth block where s h a llo w ly dipping
j o i n t s have developed in response to in te n s e Laramide compressional.
s tr e s s e s (S p e n ce r, 1 9 5 9 ).
J o i n t o r i e n t a t i o n s noted by th e author
between La Duke Hot S pring and Cinnabar Basin in th e hanging w a ll
block o f th e G a rd in e r f a u l t suggest t h a t Laramide compression and
subsequent te n s io n a l
s tr e s s strengthened th e N.60°W. and the
N .5 o-30°E.. tre n d s in th e v i c i n i t y o f th e i n t e r s e c t i o n s o f the G ardine r
f a u l t zone w i t h th e tr a n s v e r s e normal f a u l t s
(F ig u r e 6 ) .
The Precambrian rocks appear to c o n ta in r e l a t i v e l y fewer
m i n e r a l i z e d f r a c t u r e s o r f r a c t u r e s rendered impermeable by the depo-r. .
s i t i o n o f c la y e y w e a th e rin g products than do the Phanerozoic rocks.
Number
West
FIGURE 6
East
HISTOGRAM OF JOINT ORIENTATIONS IN PRECAMBRIAN GRANITIC
GNEISS ALONG THE GARDINER FAULT ZONE NEAR LA DUKE HOTSPRING
( Based on 6 7 measurements )
The incom p eten t, s ha ley n a tu r e and th e g r e a t th ic kn es s o f th e c la y r i c h Mesozoic rocks has i n h i b i t e d th e development and. p r e s e r v a t io n o f
permeable f r a c t u r e s .
The e a s i l y weathered Eocene v o lc a n ic b reccias
may s u f f e r s i m i l a r l i m i t a t i o n s to th e development o f f r a c t u r e
p e rm e a b ility .
Clays and i r o n oxides t h a t develop d u rin g w eathering
o f the v o lc a n ic s may e f f e c t i v e l y clog f r a c t u r e s .
The abundance o f
u n m in e ra liz e d f r a c t u r e s i n the g r a n i t i c gneiss is evidence t h a t t h i s
rock may p o t e n t i a l l y be an a q u i f e r .
-
The probable high p e r m e a b i l it y o f the f r a c t u r e d Precambrian
c r y s t a l l i n e rocks suggests t h a t groundwater may p e r c o l a t e to c o n s id e r­
a b le depths through j o i n t s
fa u lt.
The g r e a t a r e a l
in th e hanging w a ll b lock o f th e G ardiner
exposure o f Precambrian rock on th e fla n k s o f
Sheep Mountain between Bear Creek and Cinnabar Mountain and the
c o n s id e r a b le r e l i e f o f th e l o c a l d rain ages could encourage s i g n i f i c a n t
recharge o f th e thermal systems.
The low er f r a c t u r e p e r m e a b i l it y o f
Mesozoic rocks preserved in th e Sepulcher graben to the south o f the
G a rd in e r f a u l t would.impede p e r c o l a t i o n o f groundwater to any g r e a t
depth.
Descending cold groundwater i n th e hanging w a ll
b l o c k . o f the
G a rd in e r f a u l t zone must e n te r th e f a u l t zone a t some p o i n t during
i t s downward flo w (F ig u r e 8 , page 4 6 ) .
i f the flo w o f hot w a te r r i s i n g
in th e G a rd in e r f a u l t zone i s s u f f i c i e n t l y s tr o n g , th e d e n s it y d i f ­
fe re n c e between th e cold and hot w a te r may fo r c e th e h e a v ie r cold
w a te r to g r e a t e r depths w ith o u t a p p r e c ia b le m ixing o f th e w aters as
- "7
40
shown f o r th e Steamboat S p r in g s , Nevada area (W h ite , 1 9 6 8 ).
The cold
w a te r p robably remains w i t h i n the j o i n t s
block
du rin g i t s descent.
w ill
o f the hanging w a ll
As th e descending.- w a te r warms s u f f i c i e n t l y , , i t
e n t e r th e permeable f r a c t u r e s o f the. f a u l t zone.
Pressure from thermal expansion o f the r i s i n g hot w a te r may •
c o n t r i b u t e a m ajor d r i v i n g fo r c e to the h y d r a u lic head p r o p e l l i n g the
c i r c u l a t i n g system.
For example, i n th e case o f Steamboat S p rin g s ,
Nevada, White (1 9 6 8 ) suggests t h a t thermal
expansion o f w a te r a t
170° C c o n t r ib u t e s a fo r c e e q u i v a l e n t to a head o f 900 f e e t o f cold
w a te r in a system t h a t c i r c u l a t e s
to a depth o f 1 0 ,0 0 0 f e e t .
Though
tem peratures o f w aters in the Corwin S p r in g s -G a r d in e r thermal systems
noted in th e in t r o d u c t i o n a re most l i k e l y not as high as those a t
Steamboat S p r in g s , therm al expansion should c o n t r i b u t e to th e d r i v i n g
f o r c e o f th e .s y s te m .
I f upward flo w o f w a te r is weak, as is suggested
by th e p re s e n t flo w r a te s a t th e s u r f a c e , d i l u t i o n o f th e r i s i n g hot
w a te r in th e f a u l t zone by th e cold w a te r from the hanging w a ll
is l i k e l y .
block
S i l i c a geothermometer values a re probably low er than a c tu a l
r e s e r v o i r tem peratures as a r e s u l t o f t h i s d i l u t i o n .
The expansive
t r a v e r t i n e t e r r a c e s a t G a rd in e r i n d i c a t e t h a t flo w o f w a te r i n the
thermal system was more voluminous d u rin g th e P le is to c e n e .
decreased flo w volume may stem from th e f i l l i n g
The
o f f r a c t u r e s in the
G a rd in e r f a u l t zone w it h cal c i t e from th e c a l c i u m - r i c h thermal w a te rs .
41
Recharge may a ls o have decreased as the c lim a t e became d r i e r in the
Holocene.
L i t h o l o g i c Control o f Recharge
Porous rock u n its may s i g n i f i c a n t l y c o n tro l recharge o f the
Corwin S p r in g s -G a r d in e r thermal system.
Precambrian c r y s t a l l i n e r o c k s ,
v o l c a n i c s , and sedim entary rocks may a l l
possess minor i n t e r g r a n u l a r
p o r o s it y t h a t w i l l
p e r m it slow p e r c o l a t i o n o f groundwater.
a sedim entary u n i t d i s p la y in g vuggy o r cavernous p o r o s i t y ,
However,
in a d d i t i o n
to i n t e r g r a n u l a r p o r o s i t y , may b e s t t r a n s p o r t the volumes o f w ater
necessary to supply th e hot s prin gs t h a t produced th e P le is to c e n e
to Recent G ard in e r t r a v e r t i n e d e p o s it s .
The voluminous t r a v e r t i n e
d e p o s its north o f G a rd in e r and th e p re s e n t high calcium c o n te n t o f
s p rin g e f f l u e n t a t La Duke and Bear Creek springs suggest t h a t the
w a te r spent c o n s id e r a b le tim e in c o n ta c t w ith lim es to n e during c i r c u ­
l a t i o n a t depth (Chadwick, personal communication, 1 9 7 5 ).
The Madison
Limestone is th e most l i k e l y o f th e P a le o z o ic and Mesozoic u n its to
s a t i s f y the requirem ents o f a l im e y , cavernous a q u i f e r f o r the recharge
o f thermal w a te rs .
The Madison Limestone c o n s is ts g e n e r a l l y o f l i g h t g r a y , massive
lim es to n e and d o lo m it ic lim e s to n e .
The M ission Canyon Limestone o f
the Madison Group, as d e p ic te d in F ig u re 7 and P l a t e '10, d is p la y s
abundant a n c ie n t and r e c e n t c a v i t i e s and s in kholes in i t s
upper 300
42
f e e t , wherever i t
is exposed in southern Montana and northw estern
Wyoming (A n d ric h u k , 1 9 5 5 ).
R e t i c u l a t e networks o f j o i n t s
enlarged
by th e same s o l u t i o n processes a r e a ls o common (Sando, 1 9 7 4 ).
s o l u t i o n c a v i t i e s a r e thought to be r e l i c t s
topography t h a t developed during s u b a e r ia l
The
o f a widespread k a r s t ■
exposure o f th e Mission
Canyon Limestone during Late M i s s is s ip p ia n to E a r ly Pennsylvanian
tim e ( Roberts,,-,19 6 6 ).
Red calcareous s i l t s tones and sandstones o f
the Pennsylvanian Amsden Formation f i l l
most o f the s o l u t i o n c a v i t i e s .
The M ission Canyon a ls o c o n ta in s two la y e r s o f c arbonate b r e c c ia which,
a re pro b a b le products o f c o lla p s e a f t e r s o l u t i o n o f e v a p o r i t e beds
(R o b e r ts , 1 9 6 6 ).
Laramide u p l i f t exposed th e lim estones and e v a p o r ites
to renewed s o l u t i o n processes.
Such s o l u t i o n a c t i v i t y is probably
a c t i v e a t p re s e n t.
The M ission Canyon dips northward from th e c r e s t o f the
G a l l a t i n a n t i c l i n e o b ta in in g th e p roper s t r u c t u r a l o r i e n t a t i o n to
guide cold groundwater to g r e a t depths w i t h i n the G a l l a t i n f a u l t
zone ( F ig u r e 8 ) .
The exposure o f th e L a n d s lid e Creek Formation a t
G a rd in e r r e q u ir e s a minimum depth o f 1 0 ,0 0 0 f e e t f o r th e Mission Canyon
a q u i f e r in t h a t area s in c e t h i s exposed Late Cretaceous u n i t is
separated from the M ission Canyon by 1 0 ,0 0 0 f e e t o f s e c t i o n .
Over­
steepening o f th e n o rth e rn lim b o f the G a l l a t i n a n t i c l i n e or
s u p e r p o s itio n o f i m b r ic a t e t h r u s t blocks in the G a rd in e r f a u l t zone
could p la c e the. M ission Canyon a t a y e t g r e a t e r depth.
Normal f a u l t i n g
L im e s to n e
FIGURE
CANYON
7.
SKETCH
OF
S O L U T IO N
F O R M A T IO N(m odifled from
FE A T U R E S
IN
R u p p el, 1 9 7 2 , and
THE
M IS S IO N
Sando, 19 74)
44
PLATE 10.
A p o r t i o n o f the M ission Canyon Limestone exposed near
D e v ils S l i d e on Cinnabar Mountain showing cavernous n a tu re
o f th e fo r m a tio n .
45
along the East G a l l a t i n and Mammoth f a u l t zones dropped the c r e s t o f
th e G a l l a t i n a n t i c l i n e a t l e a s t 2 ,0 0 0 f e e t w i t h i n th e Sepulcher
graben ( Ruppel, 1 9 7 2 ).
Exposures o f th e Madison Limestone near the
c r e s t o f th e a n t i c l i n e on th e highlands to t h e . e a s t and west o f the.
graben suggest t h a t th e lim es to n e may have been exposed a t a T e r t i a r y
e ro s io n s u r fa c e t h a t is now covered by n e a r l y 1,0 0 0 f e e t o f Q uaternary
v o lc a n ic s and sediments o f th e Y ellow stone Group ( F i g u r e . 2 , page 1 0 ) .
Water from th e s lu g g is h d ra in a g e system o f the G ard in e r R iv e r
p robably f i n d s access to the Madison by means o f f r a c t u r e s and i n t e r ­
flo w c o n ta c ts w i t h i n th e v o lc a n ic s .
The w a te r then fo llo w s the p e r ­
meable zones in th e lim e s to n e t o depths near 1 0,0 00 f e e t w i t h i n the
G a rd in e r f a u l t zone.
Here th e w a te r is heated a t t h i s depth by
processes to be discussed in th e n e x t c h a p te r .
The lim es to n e has been
dragged up and f r a c t u r e d by r e v e r s e f a u l t i n g p r o v id in g access f o r the
heated w a te r to th e G a rd in e r f a u l t zone.
The f a u l t zone a cts as the
c o n d u it fe e d in g hot sp rin g s a t th e s u r fa c e .
In accordance w i t h th e c i r c u l a t i o n model de sc ribe d h e re ,
the t r a v e r t i n e d e p o s its o f th e G ard in e r-C o rw in Springs thermal systems
a re probably products o f th e s o l u t i o n o f lim es to n e by th e c o ld ,
COg-rich groundwater d u rin g i t s descent from th e s u r f a c e .
In c re a s in g
l i t h o s t a t i c and h y d r o s t a t ic pressures could s u s ta in th e high CO2
p a rtia l
pre ss u re and calcium c o n c e n tr a tio n o f the descending w ater
even as i t i s heated a t depth.
These pressures a re r e le a s e d and
Beartooth block
C re s t o f G a lla tin
a n tic lin e
Sepulcher M t .
Quaternary volcanics
and
meteoric
w ater .
J o in t
Y e llo w s to n e
s e d im en ts
Recharge
R iv e r
5000
T e r tia r y
la c c o lith
Mesozoic
Sedim entary
R ocks
Madison
Limestone
Paleozoic
/
S edim entary
Rocks
-5 OOO-
Precambrian
Gneiss and Schist
M IL E S
FIGURE
8.
RECHARGE
2
fo r
G E O L O G IC
PATTERN
location o f
lin e
CROSS
FOR
S E C T IO N
CORW IN
A —A#)
ALOhfG
SPR IN G S
SEPULCHER
GARDINER
\
GRABEN
THERM AL
n
HEAT
SHOWING
AREAS (r e fe r
PO S SIB LE
to
F ig u re
47
COg is d r iv e n o f f as th e ascending w a te r approaches th e s u r fa c e .
D e p o s itio n o f t r a v e r t i n e r e s u l t s .
Heavy t r a v e r t i n e d e p o s itio n may
choke th e conduits le a d in g to th e s u r fa c e and account f o r the reduced,
s u r fa c e a c t i v i t y o f th e thermal system a t p r e s e n t.
The t h i c k
t r a v e r t i n e d e p o s its d i r e c t l y no rth o f G a rd in e r l i e on th e trends o f
two p o s s ib le branches o f th e Mammoth f a u l t zone, which may have served
to l o c a l i z e flo w a t t h i s
•
l o c a l i t y i n th e G ard in e r f a u l t zone.
■
•
•
■
The
•’
p r e s e n t absence o f sp rin g s in t h i s area suggests t h a t f r a c t u r e conduits
fe e d in g th e form er sp rin g s a re now t e c t o n i c a l l y i n a c t i v e and are
s e a le d .
However, c ontinued t e c t o n i c a c t i v i t y along the Reese Creek
f a u l t and th e easternm ost branch o f th e Mammoth f a u l t may s u s ta in the
p e r m e a b i l it y o f those f a u l t zones and th e flo w o f hot w a te r a t La Duke
and Bear Creek s p r in g s .
Future seis m ic events could open p r e s e n tly
sealed f r a c t u r e s and in c re a s e d is c h a rg e r a t e s .
The recharge mechanisms discussed in t h i s s e c tio n probably
work s im u lta n e o u s ly to s u s t a in t h i s
thermal system.
through th e Mission Canyon a q u i f e r may be e s s e n tia l
However, recharge
to produce the
c a l c i u m - r i c h s p rin g e f f l u e n t and high d is c h a rg e necessary to have formed
th e e x t e n s iv e t r a v e r t i n e de pos its a t th e s u r fa c e .
The Mammoth Hot S p r in g s , in c o n t r a s t to the Corwin S p rin g s I •
'
"
G a rd in e r thermal system, may o b ta in most o f t h e i r hot w a te r from a
northward flo w w i t h i n th e Mammoth f a u l t zone o f w a te r from the N o rris
Geyser Basin ( T r u e s d e ll and F o u r n ie r * O p e n - f i l e r e p o r t ) .
A swarm
48
o f P le is to c e n e normal f a u l t s a t Mammoth Hot Springs cause downward
displa c em e n t to the e a s t and a llo w s most o f t h i s hot w a te r to escape
i n t o the G a rd in e r R iv e r d ra in a g e ( F ig u r e I ,
page 1 2 ) .
page 2 , and Fig u re 3,
C h a p te r 4
SOURCES OF HEAT
A model f o r th e source o f th e h e a t d r i v i n g the thermal system
in th e Corwin S p r in g s - G a r d in e r a rea may be b u i l t from an understanding
o f th e s t r u c t u r a l
r e l a t i o n s h i p s c o n t r o l l i n g recharge and c i r c u l a t i o n o f
w a t e r in th e system.
Y ellow stone N a tio n a l
model.
Geophysical d a t a , c o l l e c t e d from s tu d ie s in
Park and n e ig h b o rin g a r e a s , f u r t h e r d e f i n e the
S u rfa ce tem peratures and s p r in g c hem is try p r o v id e evidence
f o r the i n t e n s i t y o f th e h e a t source.
The g e o lo g ic s e t t i n g o f the
Corwin S p r in g s - G a r d in e r thermal system o f f e r s two p o t e n t i a l sources
o f h e a t.
P o s s ib le deep c i r c u l a t i o n o f groundwater could expose the
w a te r to bedrock warmed by the l o c a l normal geothermal
g ra d ie n t.
A l t e r n a t i v e l y , th e p r o x im it y o f t ^ i s thermal system, to th e r h y o l i t i c
magma body, thought to l i e . a t s h a llo w depth beneath th e Y ellow stone
c a l d e r a , may s u b j e c t groundwater to the h ig h e r h eat flo w a s s o c ia te d
w ith th e magma body.
Geophysical data suggest t h a t a s a t e l l i t e
body o f magma may l i e
beneath G a rd in e r p r o v id in g an i n te n s e source
o f lo c a l
h e a t (Eaton e t a l , 1 9 7 5 ).
The f o l l o w i n g d is c u s s io n w i l l
c o n s id e r th e m e r it s o f these h e a t source concepts.
'
Geothermal G r a d ie n t Heat Source
The g e o lo g ic s e t t i n g and p h y s ic a l c h a r a c t e r i s t i c s o f the
Corwin S p r in g s -G a r d in e r thermal f e a t u r e s bear strong resemblance
5Q
to those o f o t h e r hot s prin gs in w estern Montana.
Kaczmarek (1 974)
de sc ribe s a d i s t i n c t i v e group o f ho t springs in w estern Montana
t h a t a l l . show base r e s e r v o i r tem peratu res between IOO0 C and 120° C.
He m a in ta in s on th e basis o f c o n s is t e n t base tem peratures and the
usual l o c a t i o n o f th e sp rin g s on deep f r a c t u r e zones or s te e p ly
i n c l i n e d permeable rock u n its t h a t th e s p rin g w aters a l l
c i r c u l a t e to
depths o f about 1 0 ,0 0 0 f e e t where th e y a c q u ir e heat from warm country
rock by conduction.
A normal geothermal g r a d ie n t o f 10 C / ! 00 f t . ,
e s tim a te d by Chadwick and Kaczmarek (1 9 7 5 ) f o r w estern Montana,
should im p a r t a base l e v e l
te m p e ratu re o f 107° C to w aters c i r c u l a t i n g
to 1 0 ,0 0 0 f e e t and, t h e r e f o r e , account f o r the base tem peratures
observed a t La Duke Hot S p rin g .
The c i r c u l a t i o n model f o r th e Corwin S p r in g s -G a r d in e r thermal
system, developed in th e preceding c h a p t e r , describes th e tr a n s p o r t
o f m e te o ric w a te r to depths as g r e a t as 1 0,000 f e e t below the s u r fa c e .
Based on a normal geothermal g r a d i e n t , a t t h i s depth w a t e r should
a c q u ir e tem peratures near 100° C.
Unpublished base tem peratures f o r
La Duke Hot S p r in g , as determ ined by R. A. Chadwick (personal com­
m u n ic a tio n , 1976) using the s i l i c a geothermometer method (F o u r n ie r
and T r u e s d e l l , 1970) a r e :
D issolved S i l i c a
(ppm)
3 0 .8
June, 1973
F e b ru a ry , 1975
.
■
8 6 .8
.
Estim ated Base
Temperature ( 0 C)
81
131
•
51
These tem peratures p ro v id e reasonable s u p p o rtin g evidence f o r h e atin g
by deep c i r c u l a t i o n in a re g io n o f near normal geothermal g r a d i e n t
c o n s id e rin g the e x p e c ta b le seasonal v a r i a t i o n s in d i l u t i o n o f the
s p rin g w aters as w e ll as p o s s ib le e r r o r s i n sampling and s i l i c a
d e te r m in a tio n .
Shallow Magmatic Heat Source
The p r o x im it y o f th e r h y o l i t i c magma body beneath th e Y ello w ­
stone c a l d e r a , some 25 m iles south o f G a r d in e r , Montana, r a is e s the
p o s s i b i l i t y o f a s h a llo w magmatic h e a t source f o r th e Corwin S p rin g s G a rd in e r therm al system.
The magma body is thought to l i e between f i v e
and te n k ilo m e te r s beneath th e s u r fa c e (Sm ith e t a l , '1 9 7 4 ).
The
occurrence o f s e v e ra l young r h y o l i t i c v e n t s , along w it h geophysical
d a t a , suggests t h a t a s a t e l l i t e magma body o r perhaps a prong o f
magma may l i e
beneath th e S epulcher graben as f a r n o rth as G ardine r
(Eaton e t a l , 1 9 7 5 ).
R h y o lit e domes as young as 7 0 ,0 0 0 y ea rs i n t r u d e
th e S epu lcher graben between N o r r is Geyser Basin and Mammoth Hot
Springs ( F i g u r e 9 ) .
Eaton e t a l
(1 9 7 5 ) p re s e n t a. complete Bouguer g r a v i t y map
t h a t d e p ic ts a l a r g e g r a v i t y low bounded by th e closed -2 1 0 mgal
contour ( F i g u r e 9 ) .
This contour surrounds th e Y ellow stone c a ld e ra
and o u t l i n e s a r e l a t i v e l y narrow low g r a v i t y c o r r i d o r extending
n o rth to Corwin Springs from N o r r is Geyser Basin on th e rim o f the
52
IOO
I
M IL E S
Residuol
(-3 0 0
o e ro m o g n e tic
to
-IO d
a n o m a ly
o e ro m o g n e tic
(< - 250
FIGURE 9,
gravity fiontour(-2ldmgal)
gam mas)
Yellowstone
O
Residual
Bouger
COMPILATION
rim
■X
a n o m a ly
gam m as)
c a ld e ra
Q u a te rn ary
rh y o lite
vent
OF GEOPHYSICAL ANOMALIES IN THE
YELLOWSTONE PARK AREA(modifled from
Eaton et o l.,
1975)
53
c a ld e ra .
The g r a v i t y low i s thought to be a composite r e p r e s e n ta ­
t i o n o f th e Y ellow stone r h y o l i t e magma and i t s c r y s t a l l i z e d p o r t i o n ,
foundered c r y s t a l l i n e and sedim entary m a t e r i a l s , and h y d ro th e rm a lI y
a l t e r e d zones a s s o c ia te d w it h geothermal systems.
=
The g r a v i t y f i e l d
produced by these m a t e r i a l s stands in c o n t r a s t to th e g r a v i t y highs
produced by a d ja c e n t c r y s t a l l i n e basement r o c k s .
Changes in the b e h a v io r o f seis m ic waves passing through
th e low g r a v i t y area s i m i l a r l y o u t l i n e th e c a ld e r a and proposed
magma body a t depth.
The e a s t- w e s t zone o f high seis m ic a c t i v i t y
passing through Hebgen Lake ends a b r u p t l y a t the w est edge o f the
g r a v i t y low n e ar th e East G a l l a t i n f a u l t (Eaton e t a l , 1975)
( F ig u r e 1 0 ) .
Seismic a c t i v i t y
i s g e n e r a l l y les s in te n s e throughout
th e c a ld e r a and N o r r is -C o r w in Springs c o r r i d o r .
Maximum fo c a l depth
in the c a ld e r a i s f i v e km in c o n t r a s t to g r e a t e r fo c a l
o u ts id e th e c a l d e r a .
depths
P-waves a r e a tte n u a te d as they pa ss.through
the c a l d e r a , whereas S-waves a re commonly absent o r p o o r ly d e fin e d .
N e g a tiv e r e s id u a l aerom agnetic anomalies a ls o h i g h l i g h t the
Y ello w sto n e c a ld e r a and th e N o r r is -C o r w in Springs c o r r i d o r (Eaton
e t a l , 1975)
( F ig u r e 9 ) .
The e x t e n s iv e volumes o f h y d ro th e rm a lI y
a l t e r e d rock w i t h i n these areas a r e i n t e r p r e t e d as p a r t l y re s p o n s ib le
f o r t h i s m agnetic anomaly.
A l a r g e body o f magma o r a c r y s t a l l i n e
p i uton beneath the c a ld e r a could a ls o account f o r th e .b r o a d magnetic
54
Wyoming
Iammoth
X
Hebgen
- X x rx Lake
Norris
44° 30-
Yellowstone
Lake
M IL E S
Hebgen Lake Seismic Zone
3
&
0 O 0 O0
O
° 00 0° O
FIGURE IO
Yellowstone Caldera
Rim
Norm al Faults
Corwin Springs - Norris
Corridor
Active During
Quaternary
Zone of Attenuation of P -waves
( S - waves generally a b s e n t)
SEISMICITY AND SEISMIC ATTENUATION COMPARED TO
QUATERNARY
FAULT AND VOLCANIC STRUCTURES
YELLOWSTONE NATIONAL PARK
(modified
from
Eaton et a l, 1975 )
IN
low.
Surrounding, areas...underlain by c r y s t a l l i n e basement and v ent
f a c ie s o f the Eocene v o lc a n ic s d i s p la y h ig h e r magnetic i n t e n s i t y .
Although th e d a ta summarized here a r e c o n s is t e n t w ith the
e x is te n c e o f magma a t depth beneath the Y ellow stone c a ld e r a and the
N o r r is -C o r w in Springs c o r r i d o r , they a r e not c o n c lu s iv e .
The g e o lo g ic
form, and e r u p t i v e h is to r y , o f th e Y ellow stone c a ld e r a lend s o l i d support
to th e geophysical models t h a t d e p i c t a sh allo w magma body w i t h i n
its
c o n fin e s .
la rly a t its
However, the N o r r is -C o r w in Springs c o r r i d o r , p a r t i c u ­
n o rth e rn end, does no t o f f e r such c onvinc ing g e o lo g ic
evidence in support o f th e geophysical d a ta .
Q uaternary v o lc a n ic
v e n t and c o lla p s e f e a tu r e s a re l a c k in g north o f Mammoth.
The high
i n t e n s i t y o f geothermal a c t i v i t y a s s o c ia te d w ith the magmatic heat,
source w i t h i n th e c a ld e r a does not appear in the Corwin S p rin g s G a rd in e r thermal system.
e s tim a te d base l e v e l
The p ro d u c tio n o f t r a v e r t i n e and the lower
tem peratures observed in th e Corwin S p rin g s -
G a rd in e r area a re c h a r a c t e r i s t i c o f les s vigorous geothermal systems,
p o s s ib ly heated by remnant h e a t emanating from r e c e n t l y c r y s t a l l i z e d
i n t r u s i v e s o r by conduction o f h e a t to deeply c i r c u l a t i n g w a te r .fr o m
ho t cou n try rock (Chadwick and Kaczmar e k , 1 9 7 5 ).
A l t e r n a t i v e e x p la n a tio n s may be a p p lie d to th e geophysical
anomalies observed in th e N o r r is -C d r w ih Springs c o r r i d o r .
The
s h a llo w g r a v i t y low in t h i s area may be due to the d e n s it y c o n tr a s t
between Cretaceous sedim entary rocks and c r y s t a l l i n e basement rocks
56
in nearby u p l i f t e d blocks preserved w i t h i n th e S epulcher graben
(Eaton e t a l , 1 9 7 5 ).
Bonini
(1 9 72 ) l i s t s
assumed average d e n s it ie s
o f 2 .4 0 g /c c f o r Cretaceous sedim entary rocks and 2 .6 7 g /c c f o r
c r y s t a l l i n e Precambrian rocks.
A l o c a l n e g a tiv e c lo s u r e around
G a rd in e r may be caused by th e th ic k e n e d s e c tio n o f sedim entary rock
a t t h a t l o c a l i t y which is due in p a r t to o v e r tu r n in g o f th e s e c tio n
by r e v e r s e f a u l t i n g .
The same exaggerated thic kn es s o f sedim entary
rocks may produce th e r e s id u a l m agnetic low recorded f o r t h a t area
due to th e l a c k o f i r o n - r i c h m in e ra ls in those ro c ks .
An i n s u f f i ­
c i e n t l y long p e rio d o f study may e x p l a i n th e observed absence o f
seis m ic a c t i v i t y in t h i s narrow b e l t .
by Ruppel
S u rfic ia l
evidence produced
(1 9 7 2 ) i n d i c a t e s t h a t f a u l t s have been a c t i v e w i t h i n the
S epulcher graben d u rin g P le is to c e n e and Holocene tim e .
The la c k o f
seism ic d a ta prevents the c o n s t r u c t io n o f a v i a b l e model f o r the
bedrock s t r u c t u r e in th e N o r r is -C o r w in Springs c o r r i d o r .
The preceding arguments weaken th e case f o r a sh allo w
magmatic h e a t source in th e immediate v i c i n i t y o f G a r d in e r .
Deep
c i r c u l a t i o n o f groundwater is pro b a b ly th e prim ary means o f h e atin g
th e w aters fe e d in g th e Corwin S p r in g s -G a r d in e r thermal system.
However, th e w i n t e r s i l i c a
geothermometer re ad in g o f 131° C f o r
La Duke Hot Spring suggests t h a t th e Y ellow stone magma body may be
c lo s e enough to enhance th e r e g io n a l
Corwin S p r in g s - G a r d in e r a r e a .
geothermal g r a d i e n t in the
Hot w a t e r c i r c u l a t i n g northward from
57
th e Y ello w sto n e c a ld e ra along the Mammoth and E ast G a l l a t i n f a u lt s
may a ls o in c re a s e th e lo c a l geotherm al g r a d ie n t.
'
B u t, th e f a u l t
zones must be perm eable enough to tr a n s p o r t q u ic k ly la r g e q u a n titie s
o f w a te r to th e Corwin S p rin g s -G a rd in e r system b e fo re th e w a te r
cools s i g n i f i c a n t l y .
C hapter 5
POTENTIAL THERMAL ACTIVITY AT
DEPTH IN ADJACENT AREAS
The c o n tin u a tio n o f th e G a rd in e r f a u l t zone to th e n orthw est
o f C innabar Mountain may p e rm it th e e x te n s io n o f th e Corwin S p rin g s G a rd in e r therm al system in t h a t d ir e c t i o n .
F a u lt p a tte rn s northw est
o f C innabar Mountain suggest t h a t d is p la c em e n t along the G ard in e r
f a u l t and a s s o c ia te d tra n s v e rs e n o r th -tr e n d in g normal f a u l t s forms
a graben s im ila r to th e S ep u lch er graben.
A m o d ific a tio n o f th e model
proposed h e re in f o r th e c i r c u l a t i o n o f w a te r in th e Corwin S p rin g s G a rd in e r th erm al system may a ls o d e s c rib e p o s s ib le geotherm al
a c t i v i t y a t depth n ear C innabar Basin and Mol Heron Creek (F ig u re 1 1 ).
However, th e e x te n t and th e v e ry e x is te n c e o f such therm al a c t i v i t y
is u n c e rta in due to th e la c k o f s u r f i c i a l m a n ife s ta tio n s o f re c e n t
geotherm al a c t i v i t y .
A t h ic k cover o f Eocene e x tru s iv e s probably
obscures any n e a r-s u rfa c e therm al phenomena.
The m ajor s t r u c t u r a l elem ents com prising th e model f o r
th erm al w a te r c i r c u l a t i o n in th e Corwin S p rin g s -G a rd in e r a rea a ls o
appear on th e w est s id e o f th e southern G a lla t in ran g e.
The G a lla t in
a n t i c l i n e extends northw estw ard from th e G a lla t in h o rs t to the Madison
Range ( R uppel, 1 9 7 2 ).
Normal d is p la c e m e n t along th e West G a lla t in
f a u l t has depressed th e c r e s t o f th e a n t i c l i n e a t l e a s t 2 ,5 0 0 f e e t
to th e w est o f th e h o rs t ( R uppel, 1972)
■Hiv
•'t
(F ig u re 1 1 ).
The Madison
59
___________________ ____
R everse
g
Fault
FIGURE II. SKETCH MAP OF THE CINNABAR BASIN AREA « MAJOR
FAULTS AND MADISON GROUP EXPOSURES (modified from Fraser,
1 9 6 9 , Ruppel, 1972 , and U.S. Geological Survey Map I -711 ,1 9 7 2 )
60
Group crops o u t along both s id es o f th e G a l l a t i n R iv e r upstream from .
its
c o n flu e n c e w ith Specimen Creek (F ig u re 1 1 ).
This u n it dips
g e n e r a lly to th e n o rth e a s t down th e n o rth e rn lim b o f th e a n t i c l i n e .
S ev e ral sm all d iv e r s e ly o rie n te d fo ld s d is tu r b th e g eneral d ip P f
th e Madison.
These beds a re p ro b a b ly dragged up in to an asym m etrical
s y n c lin e as th e y e n te r th e n o rth w est e x te n s io n o f th e G a rd in e r f a u l t
zone beneath Cinnabar Basin alth o u g h th e re is no s u r f i c i a l
fo r th is .
evidence
A swarm o f n o rth w e s t tre n d in g d a c ite d ik es and fr a c tu r e s
which c u t Precam brian g r a n i t i c gneiss i d e n t i f y a p o rtio n o f th e f a u l t
zone as i t d is ap p e a rs beneath Eocene v o lc a n ic s on th e n o rth w e s t w a ll
o f th e Cinnabar Creek gorge.
The G a rd in e r f a u l t p ro b a b ly passes
under th e n o rth e rn m argin o f C innabar B asin and reappears to the
n o rth w e s t as th e Spanish Peaks f a u l t ( R uppel, 1 9 7 2 ).
Creek f a u l t and numerous n e a rly v e r t i c a l
The Mo! Heron
n o rth e a s t tre n d in g fr a c tu r e s
c u t th e Eocene v o lc a n ic cover and c o n tro l th e graben s tr u c tu r e to
th e n o rth w est o f C innabar Mountain (F ig u r e 1 1 ).
A pparent l e f t -
l a t e r a l d is p la c em e n t o f th e d ik e swarm by th e Mol Heron Creek f a u l t
p ro v id es evidence f o r th e o f f s e t o f th e G a rd in e r f a u l t zone and th e
e x is te n c e o f a graben s tr u c tu r e beneath C innabar B asin .
As d e sc rib e d in th e Corwin S p rin g s -G a rd in e r m odel, w a te r
could flo w to c o n s id e ra b le depth through j o i n t s
in th e Precam brian
hariging w a ll b lo c k o f th e G a rd in e r f a u l t though th e v o lc a n ic s c o ve rin g
61
much o f t h is s tr u c tu r e may impede downward flo w .
W ater may a ls o
flo w down th e M is sio n Cartyon a q u if e r from th e G a lla t in R iv e r d ra in ag e
in t o th e G a rd in e r f a u l t zone beneath C innabar B asin.
S ev e ra l s t r u c t u r a l fe a tu re s could o b s tru c t t h is flo w p a tte r n .
The sm all fo ld s on th e n o rth e rn lim b o f th e G a l l a t i n a n t i c l i n e may
tr a p w a te r w ith in th e M is sio n Canyon r e l a t i v e l y high on th e a n t i c l i n e .
S ev e ral e a s t-w e s t tre n d in g normal f a u l t s
in th e v i c i n i t y o f Specimen .
Creek could o f f s e t th e c o n fin e d M issio n Canyon a q u ife r and s im i l a r ly
tr a p descending w a te r.
V e r t ic a l d is p la c em e n t is le s s along th e Mo!
Heron, f a u l t than t h a t along th e Reese Creek f a u l t s u g g e stin g th a t
th e depth o f th e M ission Canyon is n o t as g re a t as t h a t in the
S ep u lch er graben.
Even i f
flo w w it h in th e M ission Canyon is unimpeded,
th e depth a t ta in e d by th e w a te r beneath C innabar Basin may be s i g n i f i ­
c a n tly le s s than t h a t a tta in e d by w a te r in th e Corwin S p rin g s -G a rd in e r
system.
Seism ic a c t i v i t y along th e G a rd in e r f a u l t zone in th e Cinnabar ,
B asin a re a is weak (E aton e t a l , 1975; Smith e t a l , 1 9 7 4 ).
S u r fic ia l
evid en ce f o r re c e n t f a u l t i n g , contemporaneous w ith t h a t a t L i t t l e
T r a il
C reek, is la c k in g .
These fa c ts suggest t h a t th e G a rd in e r f a u l t
and th e tra n s v e rs e normal f a u l t s
and im perm eable.
in C innabar Basin may be sealed
The s ea le d c o n d itio n o f th e f a u l t s e x p la in s the
absence o f therm al s p rin g s a t th e s u rfa c e in C innabar B a s in .
C hapter 6
*
■ I
.
■
SUGGESTED FUTURE STUDY
A more c o m p le te ,u n d e rs ta n d in g o f th e Corwin S p rin g s -G a rd in e r
therm al system would r e q u ir e f u r t h e r e xam in atio n o f bedrock geology
and th erm al fe a tu re s by means o f geophysical and geochemical te c h ­
n iq u e s.
S ev e ra l suggestions f o r c l a r i f y i n g o r s tre n g th e n in g the
th erm al w a te r c ir c u l a t i o n model deduced from mapping d a ta a re
p resen ted h e re.
R e s e rv o ir Tem peratures
Chemical geothermometers should be a p p lie d to e f f l u e n t
samples from La Duke Hot S pring and Bear Creek warm s p rin g to d e te r ­
mine t h e i r base tem p eratu res a t d e p th .
s ilic a
A m ixing model using the
geotherm om eter method as d e s c rib e d by F o u rn ie r and T ru e s d e ll
(1 9 7 4 ) should be used because d i l u t i o n o f these therm al w aters by
c o ld groundw ater from th e Y ello w sto n e R iv e r v a lle y is h ig h ly l i k e l y .
J o in ts d e s c rib e d in th e re ch a rg e model developed f o r th e Corwin
S p rin g s -G a rd in e r therm al system may a llo w descending c o ld w a te r to
mix a t g r e a t depths w ith r i s i n g therm al w a te r in th e G a rd in e r f a u l t
zone.
Cold w a te r in near s u rfa c e a llu v iu m and c o llu v iu m may a lso
d i l u t e th erm al w a te r a t s h allo w d e p th s .
The degree o f d i l u t i o n v a rie s
w ith th e seasonal le v e l o f r u n o ff in th e Y ello w sto n e R iv e r d ra in a g e .
R unoff is n o rm a lly h ig h e s t d u rin g June and J u ly and decreases du rin g
63
th e r e s t o f th e y e a r to i t s
lo w es t le v e l in February and March.
Samples taken d u rin g th e w in te r months should y i e l d th e h ig h e s t
te m p e ratu re s as in d ic a te d by th e p r e lim in a r y s e t o f samples (Chadwick,
personal com m unication, 1976) r e fe r r e d to in C hapter 4.
A q u ife r Rock Type
D is so lv e d catio n s, and anions in th e hot s p rin g e f f l u e n t
may q u a l i t a t i v e l y v e r i f y th e r o le o f th e M issio n Canyon Limestone
as a re c h a rg in g a q u if e r f o r th e Corwin S p rin g s -G a rd in e r therm al
system .
The high d is s o lv e d c alciu m c o n te n t o f th e w a te r suggests
a lim e s to n e a q u i f e r , b u t th e c alciu m cannot be tra c e d d i r e c t l y to
th e M issio n Canyon Lim estone by known geochemical methods.
However,
.
high v alu e s f o r SO^z and Na+ a re quoted by T a y lo r (1 9 7 5 , unpublished
r e p o r t) from F o u rn ie r ( w r i t t e n com m u n icatio n ).
These d a t a .in d ic a t e
t h a t s o lu tio n o f e v a p o r ite beds in th e M ission Canyon may be o c c u rrin g
a t p re s e n t (D . L. S m ith , personal com m unication, 1 9 7 6 ).
S o lu tio n
b r e c c ia s , which a re p ro b a b ly form ing due to th e removal o f e v a p o rite
m in e r a ls , c o n ta in zones o f high p o r o s ity .
The Na+ and SO^z values
c it e d above a re based on an u n c e rta in number o f samples and should
be v e r i f i e d by a d d itio n a l sam pling.
W hether these v alu e s a re anoma­
lous should be a s c e rta in e d by comparison w ith values from s p rin g
w aters o r ig in a t in g in nearby c r y s t a l l i n e basement ro c k s .
Since
n a tu ra l co ld s p rin g s a re scarce in th e v i c i n i t y o f La Duke Hot
64
S p rin g , w a te r w e lls should be co n sid ered f o r sam pling.
in s e c tio n 5 , I . . 9 S . , R. S E . ,
S p rin g , and in s e c tio n 1 4, I .
R esidents
im m ed ia te ly south o f La Duke Hot
9 S . , R. S E . ,
s o u th e a s t o f L a .Duke
Hot S p rin g , may have w e l l s . t h a t ta p w a te r d ra in in g from th e Precamb r ia n t e r r a i n o f Sheep M ountain.
C h a ra c te r o f S tr u c tu r e and
L ith o lo g y a t Depth
The g r a v it y survey o f Y ello w sto n e N a tio n a l Park and v i c i n i t y
r e f e r r e d to in C hapter 4 lo c a te s a g r a v it y low in th e Corwin Springs
G a rd in e r a re a .
The g r a v it y d a ta suggest t h a t th e Y ello w sto n e R iv e r
v a lle y in t h is a rea may be u n d e rla in by a g re a t th ic k n e s s o f s e d i­
m entary ro c k s , a h y d ro th e rm a lly a lt e r e d zone, o r a magma, body..
A
d e t a ile d g r a v it y survey o f th e v a lle y between Corwin S prings and .
Bear Creek may h e lp d e te rm in e th e n a tu re o f the bedrock and f a u l t
zones w it h in th e v a lle y and improve E a to n 's su b su rface model f o r
n o rth w e s tern Y ello w sto n e Park.
A d e t a ile d knowledge o f th e v e r t i c a l and l a t e r a l e x te n t o f
th e G a rd in e r t r a v e r t i n e d e p o s its would a s s is t in th e i d e n t i f i c a t i o n
o f fr a c tu r e s fo rm e rly c o n t r o llin g th e o u tflo w o f therm al w a te r.
A c tiv e seis m ic tech n iq u es could r e a d ily d is tin g u is h th e base o f the
t r a v e r t i n e ly in g on th e P lio c e n e -P le is to c e n e b a s a lt and produce data
s u ita b le f o r making an isopach map o f th e t r a v e r t i n e d e p o s it.
The
isopach map and o u tc ro p .o b s e rv a tio n s could p ro v id e e vid en ce f o r th e
65
m ig ra tio n o f s p rin g s w ith tim e due to te c to n ic a c t i v i t y o r s e a lin g
o f c o n d u its .
S e is m ic ity o f th e Corwin
S p rin g s -G a rd in e r Area
P assive s eis m ic m o n ito rin g o f th e Corwin S p rin g s -G a rd in e r
a rea is necessary to d e term in e th e s e is m ic ity o f th e f a u l t zones
c o n t r o llin g th e lo c a l
therm al system .
The p e r m e a b ility o f th e f a u l t
zones is dependent upon th e freq u en cy and i n t e n s it y o f movements
along th e f a u l t zones.
R e c u rre n t te c to n ic movement is probably
needed to p re v e n t s e a lin g o f th e therm al w a te r c o n d u its by th e
d e p o s itio n o f t r a v e r t i n e from th e c a lc iu m -r ic h therm al w a te r.
Low
s e is m ic ity in th e a re a may be re s p o n s ib le f o r th e p re s e n t i n a c t i v i t y
o f th e s p rin g s t h a t b u i l t th e G a rd in e r t r a v e r t i n e t e r r a c e s .
M ic ro ­
e arth q u ake a c t i v i t y should be m onitored s in c e such s e is m ic ity is
g e n e r a lly a s s o c ia te d w ith vig orous therm al systems (Comb and M u f f le r ,
1 9 7 3 ).
M icroseism s p ro b a b ly r e s u l t from c o n tin u a l movements along
f a u l t s w it h in th e therm al system.
Concealed Thermal W ater Sources
C o n s id e ra b le therm al w a te r may escape in to th e Y ello w sto n e
1
R iv e r d ra in a g e from sources hidden beneath s u rfa c e m a te ria l in the
v i c i n i t y o f th e a c t iv e s p rin g s and elsew here along th e G a rd in e r f a u l t
zone.
E l e c t r i c a l and e le c tro m a g n e tic tech n iq u es t h a t measure th e
66
e l e c t r i c a l r e s i s t i v i t y o f m a te ria ls a t depth could be ,used to a tte m p t .
to d e term in e th e tr u e e x te n t o f th e h o t s p rin g system from th e s u rfa c e
‘
. r
1
to depths as g r e a t as two m ile s (Combs and M u f f l e r , 1 9 7 3 ).
Rock
bodies t h a t a re s a tu ra te d w ith therm al waiter should show d i s t i n c t i v e l y
low e l e c t r i c a l
r e s is ta n c e .
These methods could be used to produce
th r e e d im ensional models o f th e th e r m a lly a c t iv e zones.
Numerous
tra v e rs e s across th e G a rd in e r f a u l t zone between B a s s e tt Creek and
L i t t l e T r a il
Creek would h e lp d e fin e th e r e a l e x te n t o f h e a r-s u rfa c e
o u tflo w p a tte rn s o f th e La Duke Hot S p rin g therm al a re a .
An assessment o f p re s e n t therm al, a c t i v i t y and th e energy
p ro d u c tio n p o te n tia l o f th e therm al system would b e n e f it most from
th e recommended g eo ch em ical, p a ss iv e s e is m ic , and e l e c t r i c a l o r
e le c tro m a g n e tic r e s i s t i v i t y te c h n iq u e s .
These techniques could help
lo c a te and d e fin e th e m argins o f a c t iv e hydrotherm al zones a t depth.
C h a p te r 7
SUMMARY AND CONCLUSIONS
The Corwin S p rin g s -G a rd in e r geotherm al system , in c lu d in g
I
La Duke Hot S p rin g and Bear Creek warm s p r in g , resem bles many o f
th e geotherm al systems s c a tte re d th ro u g h o u t w estern Montana in i t s
s im i l a r g e o lo g ic s e t t in g and ty p e o f h e a t source.
la tin g
The w a te r c ir c u ­
in t h i s d i s t i n c t group o f geotherm al systems is
thoug ht to
d e r iv e h e a t by descending to g r e a t depths along f r a c t u r e zones or
perm eable ro ck u n its where i t reaches therm al e q u ilib r iu m w ith the
co u n try rock t h a t is warmed by th e lo c a l therm al g r a d ie n t .
These
geotherm al system s, in c lu d in g the Corwin S p rin g s -G a rd in e r system ,
a re to be d is tin g u is h e d from the Y ello w sto n e system t h a t o b ta in s h e at
from a s h a llo w ly emplaced magma body.
Chadwick and Kaczmarek (1 9 7 5 ) c la s s i f y Montana therm al systems
in fo u r d i s t i n c t types a cco rd in g to t h e i r p a r t i c u l a r rech a rg e mecha­
nisms.
These types in c lu d e :
(2 ) hot. s p rin g s in v a lle y f i l l
( I ) warm s p rin g s in c a rb o n a te ro c k ,
o v e r ly in g fr a c tu r e d o r porous bedrock,
(3 ) h o t s p rin g s in f r a c t u r e d , c r y s t a l l i n e bedrock, and (4 ) hot
s p rin g s fe d from d eep i c o n fin e d a q u if e r s .
A com bination o f th e l a t t e r
two types o f therm al systems p ro b a b ly d e s c rib e s re c h a rg e and c ir c u l a ­
tio n in La Duke and Bear Creek warm s p rin g s .
The therm al w aters s u s ta in in g La Duke and Bear Creek sprin gs
r i s e alo n g th e n o rth w e s t-tre n d in g G a rd in e r f a u l t zone and emerge from
..68
fr a c tu r e s where th e n o r th -tr e n d in g Reese Creek and Mammoth normal f a u lt s
in t e r s e c t th e G a rd in e r f a u l t .
Ascending therm al w a te r i s ,
in p a r t , re p la c e d a t depth by groundw ater t h a t p e rc o la te s downward
‘
through j o i n t s
■
.
V
«
in th e Precam brian g r a n i t i c gneiss o f th e G ard in e r
f a u l t hanging w a ll b lo c k .
The groundw ater is heated a t depth by
co n d u ctio n from th e c o u n try rock and is d is p la c e d upward in t o open
fr a c tu r e s in th e G a rd in e r f a u l t zone by th e denser c o ld w a te r
descending from above.
Perhaps an even g r e a t e r supply o f m e te o ric w a te r flo w s down
a cavernous a q u ife r w ith in a L a te M is s is s ip p ia n p a le o k a rs t zone o f.
th e M issio n Canyon Lim estone.
The M is sio n Canyon a q u if e r dips g e n tly
to th e n o rth under the. s te e p ly n o rth -d ip p in g G a rd in e r f a u l t zone from
th e c r e s t o f th e n o rth w e s t-tre n d in g G a l l a t i n a n t i c l i n e w ith in
Y ello w sto n e N a tio n a l
P ark.
The a q u if e r p ro b a b ly a t t a in s a depth o f
1 0 ,0 0 0 f e e t w ith in th e S epu lcher graben where i t
f a u l t zone.
in te r c e p ts th e G a rd in e r
W ater heated a t t h is depth then ascends th e f a u l t zone.
Base te m p e ratu re s f o r La Duke Hot S p rin g , as determ ined by
th e s i l i c a
geotherm om eter m ethod, range from 8 1 ° C in th e summer, to
130° C in th e w in t e r .
I f th e lo c a l therm al g ra d ie n t approxim ates
th e re g io n a l average o f I
C/100 f e e t f o r w estern M ontana, i t may
supply s u f f i c i e n t h e a t to produce base tem peratu res n e a r 100° C in
w a te r t h a t c ir c u la t e s to a depth o f 1 0 ,0 0 0 f e e t . . High summer w a te r
le v e ls
in th e Y ello w sto n e R iv e r d ra in a g e p ro b ab ly cause c o n s id e ra b le
d i l u t i o n o f th e therm al w aters and low er th e c a lc u la te d base tem pera­
tu r e s .
T h e r e fo r e , th e w in te r base te m p e ratu re values, a re probably
more r e l i a b l e .
However, th e w in te r base tem peratu res o f 1 3 1 ° .C
exceeds th e v a lu e expected from th e re g io n a l average therm al g ra d ie n t
which is
10 C / ! 00 f e e t .
a d d itio n a l source.
Thus, h e a t is p ro b a b ly o b ta in e d from an
The p ro x im ity o f th e Y ello w sto n e magma body
about 25 m ile s to th e south o f G a rd in e r may cause an anomalous
s te e p e n in g o f th e therm al g ra d ie n t le a d in g to th e observed w in te r
base te m p e ra tu re v a lu e .
The base te m p e ra tu re in d ic a te s a therm al
g r a d ie n t o f I .2 5 °C /1 0 0 f e e t .
,.H o t s p rin g a c t i v i t y
in th e Corwin S p rin g s -G a rd in e r system
appears, to be. d e c lin in g from t h a t i n t e n s it y o f flo w which produced
th e G a rd in e r t r a v e r t i n e te r r a c e s .
I n a c t i v i t y o f th e G a rd in e r f a u l t
in re c e n t c e n tu rie s and th e s e a lin g o f f r a c t u r e c o n d u its by the
d e p o s itio n o f t r a v e r t i n e a re th e p ro b a b le causes f o r t h is d e c lin e .
A d ecrease in th e supply o f w a te r re c h a rg in g th e system may a ls o have
developed as th e c lim a te became d r i e r a t th e c lo s e o f th e P le is to c e n e ,
w ith r e s u lt in g decreased d is c h a rg e .
The Corwin S p rin g s -G a rd in e r therm al system does n o t o f f e r
much p ro m ise.as an e l e c t r i c a l
power source using c u r r e n t te c h n o lo g y.
Base tem p eratu res in d ic a t e t h a t th e therm al system cannot gen erate
s u f f i c i e n t steam to d r iv e tu rb in e s o f th e type used to produce
e le c tr ic it y
in geotherm al p la n ts now o p e ra tin g .
These power p la n ts
70
r e q u ir e r e s e r v o ir tem p eratu res in excess o f 150° C f o r e f f i c i e n t
power p ro d u c tio n (W h ite , 1 9 7 3 ).
T e c h n o lo g ic a l advances may a llo w
u t i l i z a t i o n o f therm al w aters ra n g in g in te m p e ratu re from 100° C
to 150° C f o r e l e c t r i c power g e n e ra tio n (Chadwick and Kaczmarek,.
1 9 7 5 ).
However, th e therm al w aters may be most e f f e c t i v e l y used to
h e a t b u ild in g s o r greenhouses in th e Corwin S p rin g s -G a rd in e r v i c i n i t y .
S h allo w d r i l l i n g may re v e a l a d d itio n a l h o t w a te r sources along th e
G a rd in e r f a u l t zone.
.
APPENDIXES
APPENDIX A
GENERALIZED STRATIGRAPHIC SECTION:
GARDINER REGION
The fo llo w in g s e c tio n is g e n e ra liz e d from s e c tio n s measured by W ilson
(1 9 3 4 b ), F ra s e r e t a l (1 9 6 9 ), and Ruppel (1 9 7 2 ) a t C innabar M ountain,
Mount E v e r ts , and th e sou th ern G a l l a t i n Range.
CRETACEOUS
L a n d s lid e Creek Form ation: about 2 ,0 0 0 f e e t t h i c k , g ra y , p o o rly
s o rte d sandstone and conglom erate made up p r i n c ip a l l y o f
a n d e s itic fra g m e n ts .
E ve rts F o rm ation: about 1 ,2 0 0 f e e t t h i c k , f in e - g r a in e d , tu ffa c e o u s
s a l t and pepper sandstone w ith , in te rb e d d e d gray s h a le .
E agle Sandstone:
about 800 f e e t t h i c k , m assive, c a lc a re o u s , s a l t
and pepper sandstone w ith t h in in te rb e d d e d s h ale and c o a l.
T e leg rap h Creek F o rm ation: about 300 f e e t t h i c k , l i g h t - g r a y , f i n e ­
g ra in e d c alc are o u s sandstone and in te rb e d d e d gray s h a le .
Cody S h a le :
about 1 ,2 0 0 f e e t t h i c k , d a rk -g ra y s h a le , b e n to n ite
beds, and t h in b ro w n ish -g ray d i r t y sandstone beds.
F r o n tie r Sandstone: 4 0 -6 0 f e e t t h i c k , g ra y-b ro w n , w e l l - s o r t e d , s a l t
and pepper sandstone.
Mowry S h a le :
3 0 0 -3 2 0 f e e t t h i c k , h a rd , b la c k sandy s h a le , in terb ed d ed
san d sto n e, and b e n to n ite .
Therm opolis S h a le :
3 9 0 -5 0 0 f e e t t h i c k , d a rk -g ra y f i s s i l e
in te rb e d d e d sandstone and s il t s t o n e .
s h ale and
Kootenai Form ation ( C lo y e rly e q u iv a le n t ) :
250-400 f e e t t h i c k ,
c o a rs e , c h e rt-p e b b le conglom erate and massive s a l t and pepper
che.rty sandston e, g ra y , f i s s i l e s h a le , and T ig h t-g r a y lim e s to n e .
73
JURASSIC
M orrison Form ation:
2 0 0 -3 2 0 f e e t t h i c k , g r a y is h -r e d , d a rk -g ra y , a n d .
g ra y is h -g re e n p a r t l y calc are o u s s h a le , mudstone, s i l t s t o n e , and
sandstone.
E l l i s Group:
S w if t Form ation:
1 5-60 f e e t t h i c k , brown to gray c alcareo u s
sandstone and lim e s to n e .
Rierdon Form ation: 4 0 -6 0 f e e t t h i c k , o o l i t i c lim e s to n e , red
s i l t s t o n e , mudstone, and s h a le .
Sawtooth F o rm ation:
140 f e e t t h i c k , lim e s to n e , red to gray
s i l t s t o n e , mudstone * and s h a le . .
TRIASSIC
Thaynes F o rm ation:
'■
1 5 -2 0 f e e t t h i c k , g ra y , calc are o u s sandstone.
Woodside F o rm a tio n . ( Chugwater e q u i v a l e n t ) :
s i l t s t o n e , s h a le , and sandstone.
Dinwoody F orm ation:
lim e s to n e .
7 5 -1 0 0 f e e t t h i c k , red
0 -8 0 f e e t t h i c k , w h it e , porous, t h i n l y bedded
PERMIAN
Shedhorn Sandstone (P h o s p h o ria ):
c h e rty sandstone.
1 1 5 -1 6 0 f e e t t h ic k p h o s p h a tic ,
PENNSYLVANIAN
Quadrant Sandstone:
130-300 f e e t t h i c k , l i g h t brown o r th o q u a r tz ite
w ith some d o lo m ite .
Amsden Fo rm ation:
2 0 -1 6 0 f e e t t h i c k , red c alcareo u s o r d o lo m itic
s i l t s t o n e , s h a le , o r sandstone.
M IS S IS S IP P I
Madison Group:
M is sio n Canyon Lim estone: 800 f e e t t h i c k , massive f o s s ilif e r o u s
lim e s to n e w ith .d o lo m ite and d o lo m ite b re c c ia zones.
LodgepoTe Lim estone:
480 f e e t t h i c k , th in ly -b e d d e d , f o s s i l i f e r o u s ,
c h e rty lim e s to n e .
74
DEVONIAN
Three Forks Form ation:.
lim e s to n e .
J e ffe rs o n F o rm ation:
and d o lo m ite .
8 0 -1 2 0 f e e t t h i c k , in te rb e d d e d s h a le and
120-240 f e e t t h i c k , brown, f e t i d
lim es to n e
ORDOVICIAN
Bighorn D o lo m ite :
8 0 -1 3 0 f e e t t h i c k , m assive d o lo m ite and lim e s to n e .
CAMBRIAN
Snowy Range Form ation:
110-300 f e e t t h i c k , in te rb e d d e d s h a le ,
sandstone and lim e s to n e .
P ilg r im Lim estone:
Park S h a le :
lim e s to n e .
9 0-12 0 f e e t t h i c k , g ra y is h -g re e n s h a le .
Meagher Lim estone:
Wolsey S h a le :
160-300 f e e t t h i c k , d o !omit i c
T40-400 f e e t t h i c k , t h i n l y bedded lim e s to n e .
8 0 -2 0 0 f e e t t h i c k , g re e n is h -g ra y sandy s h a le .
F la th e a d Sandstone:
4 0 -1 6 0 f e e t t h i c k , q u a r t z i t i c sandstone.
PRECAMBRI AN
G r a n it ic g n e is s , s c h is t , a m p h ib o lite .
APPENDIX B
DESCRIPTION.OF EOCENE DACI TES AND ANDESITES .
D is t r ib u t io n
Exposures o f Eocene d a c i t i c and a n d e s itic e x tru s iv e s and
in tr u s iv e s a re common in th e v i c i n i t y o f th e Corwin S p rin g s -G a rd in e r
h o t s p rin g system s.
These rocks a re im p o rta n t to th e in t e r p r e t a t io n
o f Laramide s tr u c tu r e and chronology t h a t a f f e c t th e occurrence o f
th e lo c a l therm al f e a tu r e s . .
.
T h ic k p ile s o f d a c i t i c and a n d e s itic flo w s and b re c c ia s are
p reserved in th e S epu lcher g ra b en , on th e B e a rto o th b lo c k , and in
th e C innabar Basin a re a .
The S ep u lc h e r v o lc a n ic s p ro b a b ly erupted
from th e E l e c t r i c Peak s to c k ( Id d in g s , 1 8 9 1 ), whereas th e Cinnabar
Basin u n its may have e ru p te d from any o f a number o f vents s c a tte re d
alo ng th e G a lla t in
Range, th e B e a rto o th blocks and th e Y ellow stone
R iv e r v a lle y northw ard from E l e c t r i c Peak.
These v o lc a n ic s occupy
a p o r tio n o f th e w es te rn b e l t o f e r u p tiv e c e n te rs known as the
A b s a r o k a -G a lla tin V o lc a n ic p ro v in c e , which extends from th e Southern
end o f th e Absaroka Range in Wyoming, to th e n o rth e rn end o f the
G a lla t in Range in Montana (C hadw ick, 1 9 7 0 ).
A number o f d ik e s and sm all stocks ly in g w i t h i n - t h e G ard in e r
f a u l t zone may be in c lu d e d in th e group o f vents p o s tu la te d f o r the
A b s a fo k a -G a lla tin v o lc a n ic ;p ro v in c e , though t h e i r c o n tr ib u tio n to
76
th e e x tr u s iv e p i l e
is p ro b a b ly m inor (F ra s e r e t a l , 1 9 6 9 ).
These
in tr u s io n s presum ably shared a common magma source w ith th e m ajor
c e n te rs o f e ru p tio n in th e a r e a , b u t s e l e c t i v e l y fo llo w e d th e G a rd in e r
f a u l t zone d u rin g th e l a t t e r p a r t o f t h e i r a scen t to th e s u rfa c e .
The d ik es range from s e v e ra l inches to 200 f e e t w id e .
They a re b e st
exposed as a swarm s t r i k i n g n o rth w e s te rly w ith a steep n o rth e a s t d ip
between L i t t l e
T r a i l Creek and C innabar Creek.
This swarm o f dikes
may extend n o rth w est toward th e Spanish Peaks e x te n s io n o f the G a rd in e r
f a u l t , under th e Eocene e x tr u s iv e c o ver o f th e n o rth e rn G a lla t in
Range.
The d ik e swarm p ro b a b ly in t e r s e c t s th e tre n d o f th e Western
Absaroka B e lt (C hadw ick, 1970) o f Eocene v o lc a n ic c e n te rs in the
v i c i n i t y o f Tom M in er B a s in .
The W estern Absaroka B e lt extends south
o f th e G a rd in e r f a u l t zone through E l e c t r i c Peak and Mount Washburn
in Y ello w sto n e N a tio n a l P ark .
The d ik es tre n d to th e s o u th e a s t under
th e P lio c e n e -P l e i stocene b a s a lts c o v e rin g th e G a rd in e r f a u l t zone
n o rth o f G a rd in e r (F ig u re 4 , page 2 3 ) , and reap p ear a t Bear Creek
where th e G a rd in e r f a u l t is exposed.
S ev e ral sm all d a c i t i c stocks have in tru d e d th e hanging w a ll
o f th e G a rd in e r f a u l t between L i t t l e
T r a il
The in tr u s io n s seem to be r e s t r i c t e d
to w ith in one m ile o f th e f a u l t
zone.
Creek and C innabar Creek.
The Tom M in e r and Cinnabar in tr u s iv e s
i d e n t i f i e d by Shaver (1 9 7 4 )
may in tr u d e th e hanging w a ll o f th e covered n o rth w est e x te n s io n o f th e
77
G a rd in e r f a u l t in a s im ila r fa s h io n .
Remnant patches o f d a c it ic
flo w s , flo w b r e c c ia s , and v o lc a n ic sedim ents l i e
on slopes to the
n o rth e a s t o f th e G a rd in e r f a u l t zone above Corwin S p rin g s .
These
exposures may b e , in p a r t , th e e x t r u s iv e products o f th e aforem entioned
v e n ts .
P etrography
Those Eocene i n t r u s iv e rocks w hich e x p lo ite d th e G ard in e r
f a u l t zone may be. c a te g o riz e d in t o th re e d i s t i n c t groups according
to t h e i r m in e ra lo g y .
These groups in c lu d e a b i o t i t e d a c it e , a
h o rn b le n d e -b io t i t e d a c i t e , and a h o rn b le n d e -b io t i t e a n d e s ite .
The
grouping's p resen ted here a re based on average m in e ra l percentages
observed in hand sample and in t h in s e c tio n . . The v a r ia t io n s in
m in era lo g y re p re s e n t g ra d a tio n s o f a fundam ental magma.
c h illin g
tio n s .
In a d d itio n ,
n ear d ik e m argins may produce f i n e g ra in e d t e x t u r a l v a r ia ­
These rock types a re d is tin g u is h e d as fo llo w s .
B i o t i t e D a c ite
B i o t i t e d a c ite outcrops in d ik es along th e G a rd in e r f a u l t
zone on th e n o rth e rn sh o u ld er o f C innabar Mountain w est o f Corwin
S prings and a ls o as a plug on th e w est fa c in g slopes o f Sheep Mountain
above Corwin S prings and La Duke Hot S p rin g (F ig u re 4 , page 2 3 ).
This d a c ite c o n ta in s phenocrysts o f c a lc ic andesine and o lig b c la s e ,
b i o t i t e , q u a r ts , and m a g n e tite o r p y r it e
( P la t e 1 1 );
The p la g io c la s e
78
I
I
IM M
PLATE 11.
Photom icrograph o f b i o t i t e d a c ite from d ik e .2 5 m iles
e a s t o f La Duke Hot S p rin g ; q u a rtz ( Q ) , p la g io c la s e ( P ) ,
b i o t i t e (B ) (n ic o ls u n c ro ss e d ).
79
forms 0 .5 to 3 mm euhedral and broken g r a in s , some o f which show
; o s c illa t o r y .a n d p a tc h y ,z o n in g .
A few zoned phenocrysts a re a lt e r e d
to s e r i c i t e and c a l c i t e . ;
The b i o t i t e g ra in s a re f r e s h , euhedral
fla k e s
Q u artz forms rounded and embayed phenocrysts <
I to 2 mm a c ro s s .
up to 2 mm a c ro s s .
Small anhedral aggregates up to 0 .5 mm across
appear in th e groundmass.
q u ite s c a rc e .
Phenocrysts o f hornblende occur b u t are
Small euhedral to subhedral m a g n e tite and p y r it e g ra in s
a re s c a tte r e d th ro u g h o u t th e groundmass. . H em atite and o th e r iro n
oxides form rim s on some b i o t i t e p h e n o c rys ts .
The groundmass is
g e n e r a lly a p i l o t a x i t i c m ix tu re o f K-f e ld s p a r , q u a r t z , p la g io c la s e
m i c r o l i t e s , g la ss and o re .
groundmasses.
A few specimens e x h i b i t a p l i t i c
te x tu re d
This d a c ite outcrops in an a u to b re c c ia te d form w ith
d a c ite fra g m e n ts , as d e s c rib e d above, r e s t in g in a h e m a titic glass
m a tr ix .
Both th e d a c ite and th e a u to b re c c ia c o n ta in random c la s ts
o f Precam brian g r a n i t i c gneiss and s e r i c i t i c
H o rn b le n d e -B io t i t e
s c h is t.
D a c ite
The h o r n b le n d e - b io tite d a c ite appears in one d ik e on th e
n o rth fla n k o f C innabar M o u n tain , and in a sm all s to c k one m ile n o rth
o f Corwin Springs on w est fa c in g slo pes o f S heep.M ountain.
a ls o com prises th e flo w s and t u f f s which l i e s
unconform ably above,
b i o t i t e d a c ite in tr u s iv e s n o rth e a s t o f Corwin Springs
page 2 3 ).
This d a c ite
(F ig u re 4 ,
The h o rh b le n d e -b io t i t e d a c ite includes, phenocrysts o f
80
c a lc ic p la g io c la s e , b i o t i t e , h o rn b le n d e, q u a r t z , and m a g n e tite
( P la t e 1 2 ).
The p la g io c la s e forms 0 .5 to 5 mm euhedral g ra in s and
fragm ents showing p e rv a s iv e o s c i l l a t o r y and patchy zo n in g .
tw in n in g is . a ls o common.
sen" c i t e and c al C it e ..
2 mm a cro s s .
P e r ic lin e
The phenocrysts a re in p a r t a lt e r e d to
B i o t i t e g ra in s a re -fresh euhedral fla k e s I to
H ornblende.form s b ro k en , corroded p h e n o c ry s ts , and a
few fre s h euhderal g r a in s .
a lt e r e d to b i o t i t e .
Some hornblende phenocrysts a re p a r t ly
Opaque rim s appear on some p h e n o c rys ts .
Many
o f th e phenocrysts a re c o m p le te ly a lt e r e d to h e m a tite and c a l c i t e .
Q u artz forms, s u b h e d ra l, rounded o r embayed phenocrysts up to I mm
a c ro s s , as w e ll as sm all aggregates o f anhedral g ra in s w it h in the
groUndm ass.. Q u artz i i
scarce in some specimens.
Small euhedral
m a g n e tite g ra in s a re d is se m in ated th ro u g h o u t.th e groundmass.
The
groundmass is g e n e r a lly a p i l o t a x i t i c m ix tu re o f K -fe ld s p a r , q u a r tz ,
p la g io c la s e m ic r o !i t e s , . g la s s , and o re .
A few c la s ts o f g r a n it ic
gneiss and b i o t i t e d a c ite appear along w ith fragm ents o f h ornblendeb i o t i t e d a c it e .
A u to b re c c ia tio n is riot as w e ll developed as in the
b i o t i t e d a c ite ..
Hand samples o f h o r n b le n d e -b io tite d a c ite d is p la y phenocrysts
o f p la g io c la s e , b i o t i t e , and hornblende in a gray groundmass.
q u a rtz phenocrysts a re r a r e .
V is ib le
Casts o f hornblende phenocrysts are
q u ite abundant on w eathered s u rfa c e s .
Green and orange d is c o lo r a tio n
■o f th e plug n o rth o f Corwin S prings suggests fu m a ro lic o r hydrotherm al
81
.
I__ _______ I
IMM
PLATE 12.
Photom icrograph o f hornblende b i o t i t e d a c ite from d ik e
.5 m ile s w est o f Corwin Springs on C innabar M ountain;
Q u artz ( Q ) , p la g io c la s e ( P ) , hornblende (H) a lt e r i n g to
b i o t i t e , b i o t i t e (B ) (n ic o ls u n c ro s s e d ).
82
a c tiv ity .
Green m o n tm o r illo n ite , c h l o r i t e , and iro n oxides may produce
these c o lo rs .
H o r n b le n d e -B io tite A n d e s ite
The h o rn b le n d e -b io t i t e a n d e s ite occupies s c a tte re d dikes
and sm all s tr in g e r s w ith in th e G a rd in e r f a u l t zone and i t s
w a ll.
Some flo w m a te ria l s im ila r to t h is
hanging
in t r u s iv e l i e s on th e w est
fa c in g slopes o f Sheep M o u n tain , u p h ill from Corwin S prings (F ig u re 4 ,
page 2 3 ) .
However, th e source o f t h is rock may be one o f th e more
p r o l i f i c a n d e s itic vents d e s c rib e d by F ra s e r e t a I
B e a rto o th b lo c k to th e e a s t.
(1 9 6 9 ) on the
The h o rn b le n d e -b io t i t e a n d e s ite c o n ta in s
phenocrysts o f la b r a d o r it e p la g io c la s e , h o rn b le n d e, b i o t i t e , a u g ite ,
and m a g n e tite ( P la t e 1 3 ) .
A few sm all q u a rtz g ra in s a re a ls o v i s i b l e .
P la g io c la s e ranges from andesine to la b r a d o r it e in composi ton and
forms 0 .5 to 2 mm euhedral phenocrysts t h a t e x h ib it some o s c i l l a t o r y
zo n in g .
Overgrowths o f sen" c i t e and c al c i t e a re common.
Hornblende
forms fre s h euhedral la th s I to 2 mm across as w e ll as s c a tte re d
c r y s ta l a g g re g a te s .
Hornblende la th s may be corroded o r a lt e r e d
to iro n oxides o r c al c i t e .
B i o t i t e g ra in s a re fre s h and e u h e d ra l.
A few corroded phenocrysts o f a u g ite a re a ls o p re s e n t.
The groundmass
is g e n e r a lly a p i l o t a x i t i c mass o f p la g io c la s e m i c r o l i t e s , anhedral
m a fic m in e r a ls , and o r e , along w ith some K -fe ld s p a r and q u a rtz .
The
83
I
I
IMM
PLATE 13.
Photom icrograph o f h o r n b le n d e -b io tite a n d e s ite showing
s u b tra c h y tic te x tu r e from d ik e .5 m iles n o rth o f La Duke
Hot S p rin g ; p la g io c la s e ( P ) , b i o t i t e ( B ) , hornblende (H)
(n ic o ls c ro s s e d ).
84
a n d e s ite d ik e exposed w est o f th e Corwin Springs b rid g e co n tain s
c la s ts o f g r a n i t i c gneiss and b io .t it e d a c it'e .
Hand samples o f h o rn b le n d e -b io t i t e a n d e s ite c o n s is t o f fre s h
phenocrysts o f p la g io c la s e ., h o rn b le n d e , and b i o t i t e
groUndmass.
in a dark gray
The c h i l l e d m argins o f th e d ik es a re e x c e e d in g ly .fin e ­
g ra in e d and c o n ta in no phen o crysts.
. P e tro lo g y and Chronology
P e tro g ra p h ica I l y v th e th re e d e sc rib e d in tr u s iv e s a re q u ite
s im i l a r s u ggesting t h a t th e y a re comagmatic.
a re products o f normal d i f f e r e n t i a t i o n
The th re e in tr u s iv e s
o f a c a lc - a I k a l i n e magma.
^
Each o f th ese rock types c o n ta in s p la g io c la s e , h o rn b le n d e , b i o t i t e ,
q u a r tz , and m a g n e tite o r p y r it e p h e n o c ry s ts .
o f these phenocrysts d i f f e r s
in a l l
However, th e p ro p o rtio n ,
th r e e cases.
r e f l e c t th e degree o f magmatic d i f f e r e n t i a t i o n
These d iffe re n c e s
t h a t o ccurred as each
in t r u s iv e ascended to th e upper c r u s t o r s u rfa c e from i t s
source in th e upper m a n tle o r lo w er c r u s t .
and p r e v a le n c e .o f b i o t i t e
probable
The abundance o f q u a rtz
in th e b i o t i t e d a c it e , suggest t h a t d i f ­
f e r e n t i a t io n progressed f u r t h e r than in th e o th e r rock, ty p e s .
Bowen
(1 9 2 8 ) d e s c rib e s q u a rtz and b i o t i t e as l a t e stage d i f f e r e n t i a t e s
c o o lin g b a s a lt ic magmds.
Hornblende has a h ig h e r c r y s t a l l i z a t i o n
te m p e ra tu re and commonly appears a t an in te rm e d ia te s ta g e in the
d i f f e r e n t i a t i o n process.
Thus, th e h o rn b le n d e -b io t i t e d a c ite
/
in
85
re p re s e n ts an in te rm e d ia te stage in th e d i f f e r e n t i a t i o n process. .
The remnant a u g ite . in th e h o rn b le n d e - b iq t ite a n d e s ite suggests th a t
,
c r y s t a l ] i z a t i b n was Completed a t a y e t h ig h e r te m p e ra tu re when
d i f f e r e n t i a t i o n was le s s advanced,
in tr u s iv e S was p ro b a b ly r ic h
th e magma t h a t produced these!
in w a te r as a r e s u l t o f d i f f e r e n t i a t i o n
as w e ll as c r u s ta l c o n ta m in a tio n o f th e magma d u rin g i t s
a s c e n t. . The
high w a te r c o n te n t in flu e n c e d d i f f e r e n t i a t i o n by lo w e rin g th e c r y s t a l ­
liz a t io n
te m p e ra tu re o f a l l components in th e magma.
Cross c u ttin g r e la tio n s h ip s and re c o g n iz a b le x e n o lith s p ro ­
v id e evid ence f o r the. o rd e r o f emplacement o f th e d e s c rib e d in t r u s iv e s .
These r e la tio n s h ip s a re b e s t observed on th e n o rth fla n k o f C innabar .
Mountain about 0 .5 m iles , w est o f Corwin S p rin g s , where a d ik e o f .
hornbl e n d e -b i o t i t e da c i t e cuts b i o t i t e d a c ite d ik e s .
A few .hornblende-,
b i o t i t e a n d e s ite d ik es up to 20 f e e t in th ic k n e s s c u t both d a c ite s
( P la t e 1 4 ).
The s u p e rp o s itio n o f h o rn b le n d e -b io t i t e d a c ite flow s on
b i o t i t e d a c ite in tr u s iv e s 0 .2 5 m ile s n o rth e a s t o f Corwin Springs
f u r t h e r s u p p o rt th ese age r e la t io n s h ip s .
th e l a t e s t in tr u s iv e s a t a ! I l o c a l i t i e s
A n d e s ite d ik es a re c le a r l y ,
examined.
C o r r e la tio n o f In tr u s iv e s
The m in e ra lo g ie s and te x tu r e s o f th e Corwin S prings d a c ite
d ik es resem ble those o f th e C innabar-M ol Heron and L i t t l e
T r a i l Creek
d a c i t e . i n t r u s iv e s described- by Shaver (1 9 7 4 ) and' suggest t h a t these .
86
PLATE 14.
A n d e s ite d ik e c o n ta in in g c la s ts o f Precam brian g r a n it ic
gneiss (G) and b i o t i t e d a c ite (D ) about .5 m ile s west
o f Corwin S p rin g s .
87
in tr u s iv e s a re th e same age.
o f th e s e in tr u s iv e s d i f f e r .
However, th e s t r a t ig r a p h ic p o s itio n s
The. C innabar-M ol Heron d a c ite s appear to
c u t th e a n d e s ite b re c c ia s f i l l i n g
Cinnabar. Basin (S h a v e r, 1 9 7 4 ), whereas
th e Corwin S prings d a c ite d ik es a re p ro b ab ly covered unconform ably
by th e b r e c c ia s .
These b re c c ia s have been t e n t a t i v e l y i d e n t i f i e d
by Chadwick (p e rs o n al com m unication, 1975) a 5 th e Golmeyer Creek
V o lcam 'cs which l i e
d i r e c t l y on th e Corwin Springs d a c ite s and
beneath th e younger H y a lite .P e a k V o lcam 'c s.
Chadwick (1 9 6 9 ) suggests
t h a t th e Golmeyer Creek V o lc a n ic s a re about 53 m i l li o n y e a rs o ld .
T h is a g e , a cco rd in g to P ro stka and Smedes (1 9 7 2 ), dates th e Golmeyer
Creek V o lc a n ic s as E a rly Eocene, and th e r e fo r e dates th e Corwin S prings
d a c ite d ik es as E a rly Eocene o r o ld e r .
S ince th e G a rd in e r f a u l t does
not s i g n i f i c a n t l y f r a c t u r e th e Corwin S prings d a c ite d ik e s , the l a t e s t
p o s s ib le tim e f o r m ajor re v e rs e d is p la c em e n t along th e G a rd in e r f a u l t ,
zone is th e E a rly Eocene.
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