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 [email protected]
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.
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