1. Lithotectonic Maps of the Northern Rocky Mountains —Archean to Cenozoic Continental Margins
Art Bookstrom
John Wallis
Mike Zientek
Reference list available on request to

2. Map, Northern Rocky Mtns
Lithotectonic
Map, Northern Rocky Mtns
44 geologic maps, 1:100k to 1:250k
Zientek et al. (2005) spatial database USGS OF
Lithotectonic unit — rocks formed in a shared tectonic setting during a shared time interval
A series of time-slice lithotectonic maps follows
Kalispell
Spokane
Bozeman
Boise

3. Basement- map underlay
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)
Medicine Hat
PO > K S
Great Falls
tectonic zone
Selway BZ WY
Blue Mtns
S/W WY B
Frm
< 2.5
Grouse Cr.
>2.5

4. Archean (W) Wms Wsic Wfg Wttg Wa Wg NW part of Wyoming craton —
1 of ~35 known Archean cont. nucleii
Archean (W)
Wms - metased. rocks (~ )
Wfg - felsic metavolc. gneiss (~ )
Wa – orthoamphibolite (~3.2)
46N
Wms
Wsic
Wfg
Wttg
Intrusions
Wttg – Tn-Trnd-Gd ( ), Gd (~2.8)
Wsic – Stillwater complex (2.7 Ma, plume- or rift-related
Wg – granite (~2.6?) Wa Wg
25 km
44N
112W
Crust ~50 km thick, with mafic lower crust, upper meta- sedimentary & volcanic strata, TT and G plutons, & the Stillwater layered intrusion

5. Paleoprot (X) Selway seaway (X) Big Sky orogen
Selway seaway — X crust ( Ga) between Wmh and Wwy blocks
Island-arc diorite (~1.8 Ga) implies subduction to NW? (Vogl et al., ‘04)
Giletti’s line - ages metam. reset from W to X (~ 1.6)
Big Sky orogen ( Ga) active as seaway closed
X island arc thrust over Wyo (Harms et al. ‘04)
Medicine Hat
block (W)
island-arc
diorite (~1.8)
convergence
Subduction
zone
Selway seaway (X)
Big Sky orogen
Wyoming
block (W)
metam
grades
Hi Lo
Giletti’s line
metam
ages~ >2.5
30 km ID
Big Sky orogen was active during assembly of supercont. Nuna (Columbia).

6. Mesoproterozoic Belt-Purcell basin Lemhi sub-basin
Rift Stage — Y1 Yim Y2 Y3
~15 km in 20 m.y. ~ Ga
Sag stage —Y4 Yvm Y5
~5 km in 200 m.y., ( Ga)
Lemhi sub-basin
Rift to sag — Y4L Yg Ygb ~15 km in 50 m.y., (1.45 to ~ 1.37 Ga)
Ydt ~1.15
Yim
Yvm
Ydt Y1 Y2 Y3 Y4 Y5 Y1
Ygb Yg
Yim
Y4L
40 km
West half of rifted Belt basin may be in Siberia. Detrital
zircons ( Ga) in Y1-Y3 may be from Australia (Sears ‘07).

7. 0 km
DeerTrail
basin
Sediment-accumulation curve for the Belt basin (from Sears, 2007), and also for the Lemhi sub-basin and the Deer Trail basin (added here)
Lemhi sub-basin
0 km
2.2 km
12 km
Belt
basin
1454 Ma
1390 Ma
1070 Ma
1270 Ma Ma

8. 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.

9. 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 ~ 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.

10. 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 (~ Ga), but the Laurentia-Australia model may be better for Rodinia and the Windermere rift.

11. Supercontinent Cycle (after Bradley, 2011)
Data
gap
Ages of northern Rocky Mtn orogens and rifts generally fit the global supercontinent cycle.

12. Neoproterozoic to Triassic
ODc
Neoproterozoic to Triassic
ZOr – Windermere upper crustal rift
ZOi – within-plate intrusions
Sr(i) ~ 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
COk
ZOr
inner
miogeocline
Sr(i) 0.706
ZOr
ZOi
TRc Pp Dm Mc
DMc
outer miogeocline
PPNw
Rifted continental margin is overlain by a miogeoclinal
wedge that thickens toward the paleo-Pacific Ocean.

13. Permian to Jurassic accreted island arcs
PJq – Quesnellia island-arc
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.
PJq
Quesnellia was thrust over the Pz miogeocline in Early Jurassic
next
Sr(i)~0.706
Blue Mtns complex was accreted in Cretaceous (~ Ma)
PJb
suture
50km

14. 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 (Ksz) ~ Ma
Sr(i) ~0.706
Ksz
TRls
PJi
PJr
PTRw
JKmi
Ksz mylonite
PTRb
TRof
Jiz
25 km
Blue Mtns island-arcs probably formed in a tectonic setting similar that of the Philippine islands.

15. Cretaceous continental arc
TRJi ~ Ma
Kai – Alk int ≤ 115
Kgk – Kaniksu ~107-67
Kga - Atlanta~90-67
Kgb - Boulder ~79-66
KTgb – Bitterroot ~66-54
KTai - Back-arc hi-K ig rx (≤ 75)
TRJi
retro-arc
foreland basin(rfb)
Kai
fold-thrust
belt(KT)
Kai
KTai
Tmc
grt(K)
Kai
Sr(i)~0.706
Kai
rfb
grt(JK)
accreted
terranes
fold-
thrust
belt(K)
pbb
over-thick
crust (JK)
50 km
Plate convergence, collisional accretion and NE subduction drove crustal thickening, arc-to-backarc magmatism, NE thrusting, and foreland subsidence.

16. Eocene eoTmc – metamorphic core complexes
eoTv – Eocene volcanics (early andesite & later rhyodacite)
eoTi – Eocene intrusions (monzodiorite and monzogranite porphyries)
eoTb – extensional fault-bounded basins
eoTv
eoTi
eoTb
eoTi
eoTv
eoTmc
eoTi
eoTmc
50 km
Bimodal magmatism and extensional tectonism and may have occurred in response to slab-window over-ride, less convergence & steeper subduction.

17. Neogene features CRB - Columbia R. basalt (17-6 Ma)
JD – Joseph dike swarm
CNR – Central Nevada rift & basalt (17-14)
YH - Yellowstone hot-spot track, rhyolitic and basaltic volcanics (16-0.6)
SRP - Snake River Plain, basalt, seds (< 3)
QTS – Basin-fill seds in grabens (<1-3 km)
Qs – Surface sediments
QTs Qs Qs
CRB
QTs JD Y
QTs
SRP YH
10 Ma
CNR
Plume-related volcanism, doming & collapse. Uplift of overthick crust, widely distributed extensional faulting.