U.S. Department of the InteriorU.S. Geological Survey

Lithotectonic Maps of the Northern Rocky Mountains —

Archean to Cenozoic Continental Margins

Art BookstromArt BookstromJohn WallisJohn WallisMike ZientekMike Zientek

Reference list available on requestto abookstrom@usgs.gov

LithotectonicMap, 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

Bozeman

Spokane

Boise

Kalispell

Basement- Basement- map underlaymap underlay•MTMT(Sims et al. ‘04) (Sims et al. ‘04) IDID (Sims et al. ‘05)(Sims et al. ‘05)•Terranes & ages (Ga) Terranes & ages (Ga) from Foster et al. ‘06from Foster et al. ‘06•Wyoming, Medicine Wyoming, Medicine Hat, and Grouse Cr. Hat, and Grouse Cr. Blocks (W)Blocks (W)•Selway and Selway and Farmington terranes Farmington terranes (X)(X)•Pend Oreille terrane Pend Oreille terrane (W-Y)(W-Y)•Blue Mtns (P-J)Blue Mtns (P-J)

Medicine Hat 3.3-2.6

Selway 2.4-1.6 WY

Grouse Cr. >2.5

Frm< 2.5

Blue Mtns 0.3-0.15

S

BZ

K

B

WY3.5-2.7

S/W

Gre

at Falls

tectonic

zone

Crust ~50 km thick, with mafic lower crust, upper meta- sedimentary & volcanic strata, TT and G plutons, & the Stillwater layered intrusion

NW part of Wyoming craton — NW part of Wyoming craton — 1 of ~35 known Archean cont. nucleii1 of ~35 known Archean cont. nucleii

25 km

46N

44N112W

Subduction zone

Big Sky orogen was active during assembly of supercont. Nuna (Columbia).

convergence

30 km

ID

Ydt

West half of rifted Belt basin may be in Siberia. Detrital 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). zircons (1.6-1.5 Ga) in Y1-Y3 may be from Australia (Sears ‘07).

40 km

0 km

12 km

Ma

Lemhi sub-basin

DeerTrail basin

0 km2.2 km

Beltbasin

Sediment-accumulation curve for the Belt basin (from Sears, 2007), and also for the Lemhi sub-basin and the Deer Trail basin (added here)

Belt-Sediment Source Areas (Ross and Villeneuve ‘03)

Belt detrital zircon populations match ages of rocksin 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)

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.

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).

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)

Ages of northern Rocky Mtn orogens and rifts generally fit the global supercontinent cycle.

Datagap

Neoproterozoic to TriassicNeoproterozoic to Triassic•ZOrZOr – – Windermere upper Windermere upper crustal rift crustal rift •ZOiZOi – – within-plate intrusionswithin-plate intrusions•Sr(i)Sr(i) ~ 0.706 ~ 0.706 - - rifted rifted continental basementcontinental basement•COkCOk - - Kootenay miogeo.Kootenay miogeo.•ODceODce - - Covada eugeo.Covada eugeo.•DmDm – Milligen basin (blk sh)– Milligen basin (blk sh)•DMcDMc – Copper basin (delta w/ – Copper basin (delta w/ basal Antler-arc cgl)basal Antler-arc cgl)•McMc – Carbonate banks– Carbonate banks•PPNwPPNw – Wood R. delta– Wood R. delta•PpPp – Phosphoria – Phosphoria epicontinental basinepicontinental basin•TRcTRc – Continental redbeds– Continental redbeds

innermiogeocline

Rifted continental margin is overlain by a miogeoclinalwedge that thickens toward the paleo-Pacific Ocean.

outer miogeocline

Permian to Jurassic Permian to Jurassic accreted island arcsaccreted island arcs•PJqPJq – Quesnellia island- – Quesnellia island-arcarc•PJbPJb – Blue Mountains – Blue Mountains island-arc complexisland-arc complex•Westward subduction beneath oceanic island arcs stopped during collisional accretion, and•Eastward subduction began outboard from and beneath the augmented continental margin.

50km

suture

next

25 km

Blue Mtns island-arcs probably formed in a tectonic setting similar that of the Philippine islands.

Cretaceous continental arc•TRJiTRJi ~205-162 Ma ~205-162 Ma•Kai Kai – Alk int – Alk int ≤ 115≤ 115•Kgk – Kaniksu Kgk – Kaniksu ~107-~107-6767•Kga - AtlantaKga - Atlanta~90-67~90-67•Kgb - BoulderKgb - Boulder ~79-~79-6666•KTgb – Bitterroot KTgb – Bitterroot ~66-54~66-54•KTai - Back-arcKTai - Back-arc hi-K ig hi-K ig rx (≤ 75)rx (≤ 75)

Plate convergence, collisional accretion and NE subduction drove crustal thickening, arc-to-backarc magmatism, NE thrusting, and foreland subsidence.

retro-arc foreland basin(rfb)

fold-thrust belt(KT)

50 km

TRJi

rfb

pbb

accretedterranes

fold- thrust belt(K)

50 km

eoTmc

eoTmc

Bimodal magmatism and extensional tectonism and may have occurred in response to slab-window over-ride, less convergence & steeper subduction.

CNR

JD

CRB

Plume-related volcanism, doming & collapse. Uplift of overthick crust, widely distributed extensional faulting.