Geochemical and geochronologic evidence for a contiguous northeastern Wyoming Province

The extent and nature of the Wyoming Province, an Archean craton in southwestern Laurentia, are poorly understood due to limited exposure between spatially isolated basement-cored uplifts. This lack of exposure has led to debate about whether the northeastern Wyoming Province is underlain by contiguous Archean crust or Proterozoic rocks and suture zone associated with the Trans-Hudson orogeny. To assess these models we analyzed samples recovered from drill cores in the buried northeastern Wyoming Province that straddle the proposed Proterozoic suture. Whole-rock geochemical and Nd-Pb-O isotopic data suggest the rocks formed by partial melting of > 3.5 Ga hydrated mafic to tonalitic sources similar to elsewhere in the northern Wyoming Province. Zircon U-Pb dates record Mesoarchean magmatism and metamorphism (3.0–2.8 Ga). Published whole-rock Rb-Sr, hornblende and biotite K-Ar, and apatite fission track dates suggest these rocks have not been heated above 300 °C since 2.5–2.1 Ga. Geophysical potential field data are consistent across northeastern Wyoming contrasting with major discontinuities associated with documented Proterozoic orogens on all other margins of the Wyoming Province. Hence, geochemical, isotopic, and geochronologic data along with geophysical imaging can be most simply interpreted in terms of continuous Archean crust in the northeastern Wyoming Province. A geophysically-imaged reflector east of the Bighorn Mountains may juxtapose Archean terranes with similar ages and sources, similar to the boundary between the Montana metasedimentary terrane and Beartooth-Bighorn magmatic zone in the northwestern Wyoming Province. This work emphasizes the value of integrating geologic and geophysical constraints to constrain Archean provinces and their tectonic evolution.