Lithotectonic Maps of the
Northern Rocky Mountains —
Archean to Cenozoic
Continental Margins
Art Bookstrom
John Wallis
Mike Zientek
U.S. Department of the Interior
U.S. Geological Survey
Reference list available on request
to abookstrom@usgs.gov
Lithotectonic
Map, Northern
Rocky Mtns
Kalispell
Spokane
Bozeman
Boise
• 44 geologic maps,
1:100k to 1:250k
• Zientek et al.
(2005) spatial
database USGS
OF-2005-1235
• Lithotectonic unit —
rocks formed in a
shared tectonic
setting during a
shared time interval
• A series of timeslice lithotectonic
maps follows
PO >2.6-1.5
S
Medicine Hat
K
3.3-2.6
Selway
2.4-1.6
lue Mtns
.3-0.15
B
Basementmap underlay
S/W
BZ
WY
3.5-2.7
Frm
Grouse Cr. < 2.5
>2.5
WY
• MT(Sims et al. ‘04)
ID (Sims et al. ‘05)
• Terranes & ages
(Ga) from Foster et
al. ‘06
• Wyoming, Medicine
Hat, and Grouse
Cr. Blocks (W)
• Selway and
Farmington
terranes (X)
• Pend Oreille
terrane (W-Y)
• Blue Mtns (P-J)
NW part of Wyoming craton —
1 of ~35 known Archean cont. nucleii
46N
25 km
44N
112W
Archean (W)
- metased. rocks
(~3.5-3.4)
- felsic metavolc.
gneiss (~3.5-3.3)
– orthoamphibolite
(~3.2)
– Tn-Trnd-Gd
(3.0-2.8), Gd (~2.8)
• Wsic – Stillwater
complex (2.7 Ma,
plume- or rift-related
– granite (~2.6?)
Crust ~50 km thick, with mafic lower crust, upper
meta- sedimentary & volcanic strata, TT and G
plutons, & the Stillwater layered intrusion
Paleoprot (X)
convergence
Subduction
zone
30 km
ID
Big Sky orogen was active during
assembly of supercont. Nuna (Columbia).
X crust (1.9-1.7 Ga)
between Wmh and
Wwy blocks
(~1.8 Ga) implies
subduction to NW?
(Vogl et al., ‘04)
ages
metam. reset from
W to X (~ 1.6)
(1.9-1.6 Ga) active
as seaway closed
• X island arc thrust
over Wyo blk @1.6
(Harms et al. ‘04)
Ydt
Mesoproterozoic
Belt-Purcell basin
• Rift Stage — Y1 Yim
Y2 Y3
~15 km in 20 m.y.
~1.47-1.45 Ga
• Sag stage —Y4 Yvm
Y5
• ~5 km in 200 m.y.,
(1.45-1.25 Ga)
Lemhi sub-basin
• Rift to sag — Y4L Yg
Ygb ~15 km in 50
m.y., (1.45 to ~ 1.37
Ga)
40 km
~1.15
West half of rifted Belt basin may be in Siberia. Detrital
zircons (1.6-1.5 Ga) in Y1-Y3 may be from Australia (Sears ‘07).
0 km
DeerTrail
basin
0 km
2.2 km
Lemhi
subbasin
12 km
Ma
1070 Ma
1270 Ma
1390 Ma
1454 Ma
Belt
basin
Sedimentaccumulation
curve for the
Belt basin
(from Sears,
2007), and
also for the
Lemhi subbasin and
the Deer
Trail basin
(added here)
Belt-Sediment Source Areas (Ross and Villeneuve ‘03)
Belt detrital zircon populations match ages of rocks
in N.American sources to the east and south, but
also require a western non-N. American source.
N.America-Siberia-Australia at ~1.5 Ga (Sears ’07)
This reconstruction
puts the Belt basin
adjacent to the
Udzha trough in the
Siberian craton,
which is adjacent to
the NE Australian
craton (to the SE).
These 3 cratons
are part of Nuna (a
supercontinent
from ~ 1.5-1.0 Ga).
Reconstruction constrained by possible sources for
detrital zircons), correlation of orogenic belts, and
apparent polar wander paths, showing nearly
coincident poles at ~1.5 Ga.
Laurentia, Australia & Antarctica
in Rodinia, 1.6-0.6 Ga
(Karlstrom et al. 1999)
The N. America-Siberia-Australia model
may be better for Nuna and the Belt
basin (~1.5-1.3 Ga), but the LaurentiaAustralia model may be better for
Rodinia and the Windermere rift.
Supercontinent Cycle
(after Bradley, 2011)
Data
gap
Ages of northern Rocky Mtn orogens and rifts
generally fit the global supercontinent cycle.
Neoproterozoic to Triassic
inner
miogeocline
outer
miogeocline
• ZOr – Windermere upper
crustal rift
• ZOi – within-plate intrusions
• Sr(i) ~ 0.706 - rifted
continental basement
• COk - Kootenay miogeo.
• ODce - Covada eugeo.
• Dm – Milligen basin (blk sh)
• DMc – Copper basin (delta
w/ basal Antler-arc cgl)
• Mc – Carbonate banks
• PPNw – Wood R. delta
• Pp – Phosphoria
epicontinental basin
• TRc – Continental redbeds
Rifted continental margin is overlain by a miogeoclinal
wedge that thickens toward the paleo-Pacific Ocean.
Permian to Jurassic
accreted island arcs
next
suture
50km
• PJq – Quesnellia islandarc
• PJb – Blue Mountains
island-arc complex
• Westward subduction
beneath oceanic island
arcs stopped during
collisional accretion, and
• Eastward subduction
began outboard from
and beneath the
augmented continental
margin.
Blue Mtns accreted
island-arc terranes
• Baker (PTRb)
• Wallowa-SevenDevils
(PTRw)
• Martin Bidge ls (TRls)
Olds Ferry (Trof)
• Riggins Gp. (PJr)
• Igneous intrusions
(Pji)
• Jizee (Jiz)
• Metam & Ig rx (Jkmi) rx
• West-Idaho suture zone
(
~135-74 Ma
25 km
Blue Mtns island-arcs probably formed in a tectonic
setting similar that of the Philippine islands.
TRJi
Cretaceous
retro-arc
foreland basin(rfb) continental arc
fold-thrust
belt(KT)
accreted
terranes
foldpbb
thrust
belt(K)
50 km
• TRJi ~205-162 Ma
• Kai – Alk int ≤ 115
• Kgk – Kaniksu
~107-67
• Kga - Atlanta~90-67
rfb • Kgb - Boulder
~79-66
• KTgb – Bitterroot
~66-54
• KTai - Back-arc hi-K
ig rx (≤ 75)
Plate convergence, collisional accretion and NE
subduction drove crustal thickening, arc-to-backarc
magmatism, NE thrusting, and foreland subsidence.
Eocene
eoTmc
–
metamorphic core
complexes
• eoTv – Eocene
volcanics (early
andesite & later
rhyodacite)
• eoTi – Eocene
intrusions
(monzodiorite and
monzogranite
porphyries)
50 km • eoTb – extensional
eoTmc
fault-bounded basins
Bimodal magmatism and extensional tectonism and
may have occurred in response to slab-window
over-ride, less convergence & steeper subduction.
Neogene features
•
•
•
CRB - Columbia R. basalt
(17-6 Ma)
JD – Joseph dike swarm
CNR – Central Nevada
rift & basalt (17-14)
CRB
JD
- Snake River Plain,
basalt, seds (< 3)
CNR
Plume-related volcanism, doming & collapse. Uplift of
overthick crust, widely distributed extensional faulting.