THE RISE AND FALL OF THE WYOMING CRATON: 4 BILLION YEARS OF CRUSTAL GENESIS AND EVOLUTION

The Wyoming Craton (WC) records ~4 billion years of episodic crustal genesis and lithospheric evolution through magmatic and tectonic additions, modifications and recycling. The WC has distinct characteristics including 1) three subprovinces defined by lithologic associations, the Beartooth-Bighorn magmatic zone (BBMZ), Montana metasedimentary terrane (MMT), and southern accreted terranes (SAT); 2) an enriched ²⁰⁷Pb/²⁰⁴Pb isotopic signature, and 3) a thick mafic crust (15-20 km thick). Evidence for Hadean and Eoarchean crust is preserved in detrital zircons in quartzites from the northern WC spanning the BBMZ and MMT, dating back to 4.0 Ga, with minor concentrations of ages at 3.9, 3.7, and 3.5 Ga. Lu-Hf isotopic data from these detrital grains and xenocrysts in SAT granitoids indicate derivation of the earliest magmas from undepleted to marginally depleted mantle, resulting from plume-dominated magmatism. The oldest felsic rocks formed across the WC at 3.6-3.5 Ga ago with a major crust forming event at 3.4-3.2 Ga. These rocks are dominantly from the TTG suite, and formed primarily by partial melting of a garnet-bearing mafic source. A period of tectonic quiescence resulted in deposition of platform type sediments between 3.1-2.9 Ga. A second major crust-forming event occurred in the BBMZ 2.9-2.8 Ga ago, emplacing voluminous calc-alkaline and TTG magmas with geochemical characteristics of modern arcs. Emplacement of an Alpine-style nappe complex and the allochthonous Jardine metasedimentary sequence also occurred in the Late Archean. The WC was cratonized ~ 3.0-2.8 Ga ago, with relative tectonic stability demonstrated at 2.7 Ga during emplacement of the Stillwater Complex. Magmatism continued in the SAT from 2.75-2.62 Ga through accretion of modern-day arc crust and local in situ anatexis and metamorphism continued through ~2.55-2.45 Ga. The WC experienced substantial tectonic reworking in the Paleoproterozoic along its margins (Great Falls Tectonic Zone, Cheyenne Belt, Trans-Hudson Orogen). The WC was thick and stable enough to accommodate formation of the Mesoproterozoic Belt Basin (~20 km thickness) and Phanerozoic sedimentary deposits. Flat-slab subduction of the Farallon Plate, Laramide-style deformation, Eocene and Yellowstone hot spot magmatism all have contributed to the erosion of the WC.