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

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-2005-1235 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

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 3.3-2.6 PO >2.6-1.5 K S Great Falls tectonic zone Selway 2.4-1.6 BZ WY Blue Mtns 0.3-0.15 S/W WY 3.5-2.7 B Frm < 2.5 Grouse Cr. >2.5

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 (~3.5-3.4) Wfg - felsic metavolc. gneiss (~3.5-3.3) Wa – orthoamphibolite (~3.2) 46N Wms Wsic Wfg Wttg Intrusions Wttg – Tn-Trnd-Gd (3.0-2.8), 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

Paleoprot (X) Selway seaway (X) Big Sky orogen Selway seaway — X crust (1.9-1.7 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 (1.9-1.6 Ga) active as seaway closed X island arc thrust over Wyo blk @1.6 (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~1.6 >2.5 30 km ID Big Sky orogen was active during assembly of supercont. Nuna (Columbia).

Mesoproterozoic Belt-Purcell basin Lemhi sub-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) 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 (1.6-1.5 Ga) in Y1-Y3 may be from Australia (Sears ‘07).

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

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 Laurentia-Australia 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 ODc Neoproterozoic to Triassic 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 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.

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 (~135-74 Ma) PJb suture 50km

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) ~135-74 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.

Cretaceous continental arc TRJi ~205-162 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.

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.

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.