faultzoneinthe
history
ofPaiarito
Structural
rift,NewMexico
Basin,RioGrande
Espanola
Houston,
TX
Institute,
MA,andLunarandPlanetary
Amherst,
of Massachusetts,
University
ofGeology
andGeography,
byMatthew p. Gotombek,Department
Introduction
The central section of the Rio Grande rift
consists of three distinct, north-trending en
echelon basins that step to the right. These
three basins are from south to north: the
Albuquerque-Belen, Espafiola, and San Luis
Basins. Individual basins are approximately
60 km wide, fault bounded, and asymmetric,
with valley-fill sediments tilted oppositely in
each successive basin (Kelley, 1979). Sediments within the Espafiola Basin are tilted to
the west.
The border faults of the Espafiola Basin are
poorly exposed.Moreover, the easternedgeof
the Espaflola Basin is not marked by a single
major fault (fig. l) but is defined by the both
depositional and faulted contact of the basin
fill (Santa Fe Group) with the Precambrian
rocks of the Sangre de Cristo uplift. The western margin of the Espaflola Basin is marked
by a seriesof northeast-trending, down-to-theeast faults. However, part of this fault zone is
covered by young volcanics, indicating inactivity in the past few m.y.
Manley (1979) defined the central intrarift
Velarde graben within the Espaflola Basin.
Stratigraphic relations indicate that the
Velarde graben began forming in early Pliocenetime; detectableseismicity (Jiracek, 1974)
and crustal subsidence (Reilinger and York,
1979) indicate that it is still active. Manley
(1979) mapped the eastern border of the
Velarde graben as a zone of prominent yet partially obscured north-trending, west-side-
down faults that cut the SantaFe Group at
least20 km to the west of the easternmargin
of the EspafiolaBasin. The westernedgeof
the Velardegrabenis definedby the Pajarito
fault zone which exhibits predominantly
In the Jemez
displacements.
down-to-the-east
Mountains,this fault zonecutsa l.l-m.y.-old
ash-flow tuff (Doell and others, 1968),producing a prominent fault scarp (Golombek'
1981).The objectivesof this study are to define the kinematics,timing, and tectonicsof
the Pajarito fault zone by meansof detailed
mappingand structuralanalysis,therebyproviding new insight into the evolution of this
portion of the Rio Granderift. Completediscussionof theseresultsis reportedin Golombek(1982).
StratigraPhY
Volcanic rocks of the Jemez Mountains
havebeencombinedinto threegroups(Bailey
and others, 1969; Smith and others, 1970;
Griggs, 1964):the oldest Keres Group (age
datesof 9.1-8.5m.y.; Dalrympleand others,
1967) found as highlands in the southern
PolvaJemezMountains,the intermediate-age
deraGroup (agedatesof 7.4'3.7 m.y.; Dalrymple and others, 1967)found as highlands
in the northern Jemez Mountains, and the
youngestTewa Group (age datesof 1.4-0.4
m.y.; Doell and others, 1968)erupted from
centralcalderasin the JemezMountainsand
found within and flanking them as broad,
gently dipping plateaus(fig. 2). Beneaththe
volcanicrocksare the formationsof the Santa
Fe Group (Galushaand Blick, l97l), a predominantly Miocene, fossiliferous,sedimenduringrifting.
that accumulated
tary sequence
The SantaFe Group restsunconformablyon
the GalisteoFormation, which was deposited
in prerift Eocenebasins(Stearns,1943).
General characteristics
EXPLANATION
Quoternory lo Miocene
volconic rocks of
Jemez Mounloins
ouolernory to Pliocene
tholeiitic ond olkoli
olivine bosolts
T--l
I I
Lower Tertlory, Mesozoic,
o n d P o l e o z o i cr o c k s
r:'i]
f-'r'l
Ll
Precombrion rocks
U
-a.-
|
|
L-J
Pliocene lo Eocene
sedimentory rocks within
the Espofrolo Bosin
.v
\._
Conlocl
Foult ( bor ond boll
on
downlhrown side)
River
FIGURE l-GexeneuzED cEoI-ocrcrvrlpor EspeNoleBnsrx,Rro GnnNoERtFr,NEw MExtco (from Manley, 1979,with modifications).
The Pajarito fault zoneextendsin a northnortheastdirectionalongthe eastflank of the
JemezMountains(fig. l). Markedchangesoccur in both the stratigraphicsectionsof volcanicrocksand the characterof the fault zone
along strike. These structural and stratigraphic changespermit subdivision of the
fault zone into segments(fig. 2). Thesesegmentsare,from north to south:
1) SeNra Clann sncvnNr-single large
fault scarp100-200m high; fault cuts
intermediate-agePolvadera Group
rocks and derivedvolcaniclasticsediments;
2) Gul,:E MoUNTAIN srclranNr-complex
zone of small faults with displacementsdown both to the eastand west;
fault zone disrupts intermediate-age
PolvaderaGrouP rocks and derived
sediments;
volcaniclastic
New Mexico Ceology
August1982
(Manley, 1979),suggesting
the entireVelarde
grabenfloor rampsup.
Because
acrossthe Pajatotal displacement
rito fault zone has been from 200 to 600 m
during its entire history (5 m.y. ago-present;
(indicated
Manley, 1979),centraldepressions
by gravity minima; Cordell, 1979)filled with
wereprob2-2.5 km of low-densitysediments
ably formedby old faultsthat becameinactive
by middleMioceneand are not presentlyvisiDisplacements
ble on the surface.The relativecontributionof
Where the fault zone cuts the l.l-m.y.-old
prerift and synrift sedimentsto this gravity
BandelierTuff it has produceda prominent minima is unknown. However,in at leastone
placealongthe Pajarito fault zone(St. Peter's
50-100-m-highfault scarp(Golombek,l98l).
Correlationof ash-flowbedsacrossthe fault dome), prerift sedimentaryrocks probably
indicatethat in most placesthe scarpheightis contributesignificantlyto the anomaly(Golequal to the stratigraphicdisplacement.Dis- ombek,1982).
placementsof rock units older than the BanControlson thelocationand trendof the
delier Tuff were estimatedusing standard
Pajaritofault zone
techniques
that utilizeknowledgeof the stratigraphy.Theseestimatesof the total displaceAbrupt facies changes between older volment acrossthe fault during its 5-m.y. history canics and volcaniclastic sediments of the
arebetween200-600m. Ratesof displacement Jemez Mountains appear to have controlled
for the time periods0-5, 0-1.1, and l.l-5
the local position, trend, and character of the
m.y. ago rangefrom .020to .136mm/year. Pajarito fault zone. Erosion during the active
The lack of significant east-side-down
dis- life of a volcanic dome would result in the depplacementsin the Guaje Mountain segment osition of volcaniclastic sedimentsin an apron
(fig. 2) implies that the west side of the around the dome. Thus, the periphery of a
Velardegrabenlocallyrampsup. An east-side- volcanic dome would be characterized by indown fault is present(fig. l) along the east terfingering of volcanics and volcaniclastic
side of the Velarde graben at this latitude sediments. If the periphery of a dome re3) Palenrro PLATEAUsEclreNr-prominent 100-m fault scarp in youngest
Bandelier Tuff which underliesthe
gently eastward-sloping
Pajarito Plateau:and
4) Sr. PernR's DoME secvnNr-wedgeshaped zone of two faults; Keres
Group rocks on upfaultedside adjacentto 30-100-mfault scarp.
n
tl
B o n d e l i eT
r u ff ( 1 . 4 - l . tm . y . )
N
P o l v o d e r oG r o u p( 7 . 4 - 3 7 m . y . )
V o l c o n i c l o s t i cs e d i m e n t s
(7.4-2.8n.y.1
KeresG r o u p( 9 .t - 8 . 5m . y . )
E-JJ
S o n l o Fe Group
Con?oct
(-/
Foult (bor ond boll
o n d o w n l h r o w ns i d e )
Pojorifo
P lo f e o u
se9ment
N
O
6km
St. Peler's dome
segment
FICURE 2-SecvnHrs
August1982
New Mexico Geology
Extensional Tectonics
Mesoscopicfracture data were collectedat
30 stations,most of which are in the Tshirege
Member of the BandelierTuff. Slickensides
faults in the TshiregeMember
on mesoscopic
are typically well developedwith very smooth
and polishedsurfaces.Displacements
wereinvariably pure dip-slip and normal, indicating
extensionapproximatelyperpendicularto the
strikeof the fault. Fig. 3 illustratesthe traceof
the Pajarito fault zone, the extensiondirections for each station in the BandelierTuff,
and compositeplots for each domain (area
with similarly striking mesoscopicfaults and
derivedextensiondirections).Every domain
S o n l o has an extensiondirection oriented approximatelyperpendicular
to the local trend of the
Cloro
s e g m e n t fault zone. Theseextensiondirectionscould
result from reorientationof the regionaleastwestextensionby the Pajarito fault zoneto a
direction perpendicularto the fault zone in
eachsegment.
In addition. most domains have extension
Guoje
directionsorientedapproximatelyparallel to
Mounloin
subparallelto the local trendof the fault zone.
segmenl
Theseextensiondirectionscould be because
of
stressreleaseparallelto the intermediatestress
directionwhich will be locally parallel to the
fault if the direction of maximum extension
has beenreorientedso as to be approximately
perpendicularto the fault zone. This implies
that both the intermediateand minimumstress
directionsweretensional.
n
m
I'F
mainedin about the sameplaceduring its active life, then the stratigraphicrecord at the
peripherywould showan abrupt changefrom
mostly igneousrocks to mostly volcaniclastic
sedimentsin a direction radially away from
the volcaniccenter.This rapid facieschange
betweenKeresand PolvaderaGroup volcanics
and volcaniclasticsedimentsappearsto have
controlledthe positionand trend of the Pajarito fault zone. The fault zone bows and/or
stepseastwardwheretwo largevolcaniccomplexesare presentin the St. Peter'sdome and
Guaje Mountain segments,but the zone is
found further west in betweenand at either
end of the volcaniccomplexes.One complex
in the Guaje Mountain segmentwas sufficientlymassiveto interferewith the development of the Velarde graben, causing the
grabento ramp up.
or PnleRrro FAULTzoNE.
Tectonic and geologic history of Espafiola Basin
in Pajarito fault zone area
In the area of the Pajarito fault zone, the
early developmentof the Rio Granderift was
marked by the depositionof SantaFe Group
sediments(early Miocene) directly on flatlying, prerift GalisteoFormation and did not
involvepervasivefaulting or tilting. Localized
faulting createdcentraldepressions,
indicated
by gravity minima, in the EspaflolaBasin.
Sedimentation concomitant with faulting
allowedaccumulationof thick deposits(2-2.5
km) of SantaFe Group within the centraldepressions(fie. 4a). Faulting endedby middle
Miocene,when filling of the EspafiolaBasin
was completedin the study area (approximately l0 m.y. ago); these faults are not
presentlyvisibleon the surface.
n =l o 3
a) Eenlv MrocENn rrve. Fault depicted allowed accumulation of 2-2.5 km of low-density sedimentary
fill (Santa Fe Group) in central subbasin within
Espafrola Basin.
n =4 3
b) 8-9 u.v. aco. Faults of central subbasin have become inactive. west tilting, due to movement on
faults defining western margin of Espaflola Basin,
has occurred after eruption of Keres Group volcanics in St. Peter's dome area.
+
o^"
oo
. J :
n=39
.-)_
)A'
/\
n =4 0
FIGURE 3-KINeulrlcs
or Prunntro reulT zoNE.Dotted line is trace of major faults of Pajarito fault zone;
solid lines indicate extension directions for all stations in Bandelier Tuff. Composite fracture-domain plots
on lower hemisphere equal area projection; n : number of faults for indicated stations. Because faults at
many stations cluster into two distinct setsindicating two extension directions, faults have been coded into
two sets:solid dots are poles to faults that cluster into setsthat strike north to east, open circlesare poles to
faults that cluster into sets that strike north to west. Domains are, from north to south: Santa Clara segment and northern Guaje Mountain segment, southern Guaje Mountain segment, Pajarito Plateau segment, and St. Peter's dome segment. Extension directions perpendicular to local trend of fault zone aie
due to reorientation of regional east-westextension by Pajarito fault zone. Extension directions parallel
(northern Guaje Mountain segment) and parallel to subparallel (Pajarito Plateau and St. Peter's dome
segments)to local trend of fault zone are thus parallel to intermediate stressdirection if reorientation occurs as suggestedabove, thus implying that both minimum and intermediate stress directions are tensional.
North-northeast-extensiondirections in southern Guaje Mountain segmentdo not fit proposed pattern.
Volcanism was underway by l0 m.y. ago,
about when the western margin border faults
became active. West tilting of sediments and
old volcanics (Keres Group) occurred from 8.5
to 7.5 m.y. ago. BecauseSantaFe Group sediments on the upthrown side of the Pajarito
fault zone are tilted to the west at the same (or
larger) angle than Santa Fe Group sediments
on the downthrown (east) side, faults responsible for the west tilting must be located to the
west, probably along the western border of the
Espaflola Basin (fig. 4b). With eruption of the
Polvadera Group, volcanic activity shifted
northward. Volcaniclastic sediments were
shed off the volcanic constructs in the north
and south (fig. 4c).
The Pajarito fault zone and Velarde graben
subbasin formed about 5 m.y. ago. Volcanism
in the north slowed by 3 m.y. ago and shifted
to the center of the Jemez Mountains. culminating with the eruptions of the Bandelier
Tuff 1.4 and l.l m.y. ago. The last volcanic
activity occurred about 0.4 m.y. ago, but
faulting along the Pajarito fault zone has continued to the present, offsetting the Bandelier
Tuff as much as 100 m in the past l.l m.y.
(fig. ad).
(continued on p. 48)
c) Jusr nnron ro 5 v.y. lco. Volcanism has shifted to
north depositing Polvadera Group. QTvc are eroded
volcaniclastic sediments from Keres and Polvadera
Grouos.
d) PnnsnNr. Paj".ito fuult ron" formed about 5 m.y.
ago with movement continuing to present displacing
Bandelier Tuff. Canyons eroded through Pajarito
Plateau.
FICURE 4-Evor-urroNlRy
BLocK DTAGRAMoF
Plllnlto
FAULTzoNE annl. Symbols for geologic
units: Qb-Bandelier Tuff, QTvc-volcaniclastic
sediments, Tp-Polvadera
Group, Tk-Keres
Group, Tsf-Santa Fe Group (synrift deposits),
(prerift
Tg-Galisteo
Formation
deposits),
pattern-pre-Galisteo rocks.
New Mexico Geology
August1982
Palarito fault zone
leaflocality
LateCretaceous
(continuedfrom
(continuedfromp.45)
p. 41)
References
Bailey,R. A., Smith,R. L., and Ross,C. S., 1969,Stratigraphic nomenclatureof volcanic rocks in the Jemez
Mountains, New Mexico: U.S. GeologicalSurvey, Bull.
1274-P,p.l-19
Cordell, L., 1979,Gravimetric expressionof graben faulting in Santa Fe country and the EspafrolaBasin, New
Mexico: New Mexico Geological Society, Guidebook
30th field conference,p. 59-64
Dalrymple,G. B., Cox, A., Doell, R. R., and Gromme,C.
S., 1967, Pliocene geornagneticpolarity epochs:Earth
and PlanetaryScienceLetters,v.2, p. 163-173
Doell, R. R., Dalrymple,G. 8., Smith, R. L., and Bailey,
R. A., 1968, Paleomagnetism,potassium-argonages,
and geology of rhyolites and associatedrocks of the
Valles caldera, New Mexico: Geological Society of
America, Mem. | 16,p. 2l | -248
Galusha,T., and Blick, J. C., 1971,Stratigraphyof the
SantaFe Group, New Mexico: AmericanMuseumof Natural History,Bull., v. lrM, art. l, 128p.
Golombek,M. P., 1981,Geometryand rate of extension
across the Pajarito fault zone, Espaiola Basin, Rio
Crande rift, northern New Mexico: Geology, v. 9, p.
2t-24
-,
1982,Geology,structure,and tectonicsof the Pajarito fault zone in the EspafiolaBasin of the Rio Grande
rift, New Mexico: GeologicalSocietyof America, Bull.,
ln revlew
Griggs, R. L., 1964,Geology and ground water resources
of the Los Alamos area, New Mexico: U.S. Geological
Survey,Water-supplyPaper 1753,107p.
Jiracek,G. R., 1974,Geophysicalstudiesin the Jemez
Mountains region, New Mexico: New Mexico Geological
Society,Guidebook25th field conference,p. 137-144
Kelley, V. C., 1979, Tectonics, middle Rio Grande rift,
New Mexico, tr Rio Granderift-tectonics and magmatism, R. E. Riecker,ed.: Washington,D.C., American
GeophysicalUnion, p. 57-70
Manley, K., l9?9, Stratigraphyand structureof the Espaflola Basin, Rio Granderift, New Mexico, in Rio Grande
rift-tectonics and magmatism, R. E. Riecker, ed.:
Washington, D.C., American Geophysical Union, p.
7l - 8 5
Reilinger,R. 8., and York, J. 8., 1979,Relativecrustal
subsidencefrom levelingdata in a seismicallyactivepart
of the Rio Grande rift, New Mexico: Geology, v. 7, p.
t39-143
Smith, R. L., Bailey,R. A., and Ross,C. S., 1970,Geologic map of the JemezMountains,New Mexico:U.S.
GeologicalSurvey,Misc. Inv. Map I-571
Stearns,C. 8., 1943, The Galisteo Formation of northcentralNew Mexico:Journalof Ceology,v. 51, p. 301319
E
APPENDIX
Unia
No.
A (continued)
Totsl ahickness-16.t4m (55.9ft)
Unil
No.
Description
0 1 0 White sandstone,medium-grained;
with larg€ plant fragments up to 5
cm'1;well indurated and forms characteristic popcorn surface texture
upon weathering;somehoodoo (columnsor pinnacles)development
009 White sandstone, fine-grained;
about 5q0 plant debris concentrated
in laminae. Undulating bedding
finely developed; well indurated
with frne laminationsand mud oartrngs
008 Dark gray-greenmudstonewith 1520olo plant debris up to 3.5 cm'1;
coarsensupward
oo7 Gray-green mudstone with about
590 plant fragments and stems;
gradesupward into 008
006 Sandstone,white, medium-grained;
with large fragmentsof plants up to
5 cm'; about loqo plant content
005 Mudstone, gray-green; with
approximately l09o carbonaceous
debris;coarsensupwardsinto 006
0(X Carbonaceousmudstone,dark-gray;
up to 40qoplant debrisis up to 2 cm'
poorly sorted;coarsensupwards;becomesmuch lesscarbonaceous
laterally (about l09o)
003 Olive sandstone, medium-grained;
with some iron staining along bedding planes;5-1090plant debris
002 Gray siltstone;590plant debris;iron
stainingin fractures
001 White sandstone;fine-grainedlenses
of sand rich in carbonizedplant debris and silt lacking plant debris;
lensessubparallelto bedding; fines
upward into 002; much lateral variation in plant debriscontent(5-20q0)
Thickness
(ctn, inches\
89
60
30
28
t1
z5
IO
6l
24
28
tt7
lI
47
l8
30
T2
APPENDIX B-MsesunEp secrroN
Unil
No.
Descriplion
Concretion, dark-brown; siderite
with veins of barite; rare, poorly
preserved leaf impressions extend
l a t e r a l l yl . 8 m ( 5 . 9 f t )
Thickness
(cm, tnches\
35.6
14.2
I)escripaion
Thickness
(cm, inches)
Siltstone, gray-green; scattered
subrounded plant fragments; wellsorted,averaging5 mm (.2 inches)in
l5.2
diameter
C Mudstone, gray-green; a few
scattered stem fragments; poorly
3.8
sortedup to 3 x 5 cm (1.2x 2 inches)
D Mudstone, gray-gre€n; occasional
horizons with leaves 3 cm (1,2
inches)in length and also horizons
of poorly sorted stemsup to 1,3 x 2
22.8
cm (.5 x .8 inches)
Mudstone, gray-green; many
jumbled leaves,many of which overlap; leavessubcomplete2-5 cm (.8-2
inches)in length,small fragmentsup
to 5 mm (.2 inches)in length; poorly
sorted stem fragments l-5 cm (.4-2
inches)in lengthand up to .75cm (.3
inches) wide; slickensidesup to 39
cm (16 inches)in length, leaveson
laminaeaveraging.3 cm (.12 inches)
17.8
apart
Mudstone, gray-green; scattered
leavesfew in number: (a), lens of a) 7.6
few scatteredcompleteleavesgrades
laterally into stems and poorly
sortedsmall plant fragments,but no
leaves;stems 5-10 cm (2-4 inches)
long and up to I cm (.4 inches)wide,
fragmentsare subrounded2-.25 mm
(.08-.01 inches) in diameteri O) b) 5.0
sameas lateral, stem-richportion of
(a), sharp contact with plant-rich
portion of (a)
G Lateral from (a) and (b) siltstone,
yellow-green;few broken plant fragments(no leaves);lens-shapedcross
section7 x 60 x 15 cm (2,8 x 24 x 6
inches)
7.0
Mudstone, gray-green; full of
overlapping complete leaves that
cover 10090of surface on laminae
about every .5 cm (.2 inches);intervening layers produce complete
7,7
leavesnot overlapping
Mudstone, gray-green;large stems
5-10 cm (2-4 inches)long and I cm
(.4 inchcs) wide, also rnany small
stempieces,subroundedfrom 3 to 8
mm (.12to .32inches)in diameter
15.2
J Grades down with less stem to
subrounded fragments less than 2
mrn (.08 inches)in diameter to un45.9
fossiliferousgray-greenmudstone
6.1
t.5
9.1
a,
3.0
2.0
2.8
3,1
3.1
IE.4
o
il0. Bol[ 0rBanilrnon
U.SPOSTAGI
PAIII
NEW
SOCORRO,
PERMII
NO9