Wed 21st November @ noon, Rm 312.222

Abstract:

The Wyoming province consists of Precambrian rocks that are exposed in the Laramide uplifts in the Rocky Mountains of Wyoming.  The province records a long history with rocks dating back to 3.4 billion years ago (Ga) and xenocrystic zircon grains dating to ca. 3.9 Ga.  Lu/Hf ratios on some of the xenocrystic zircons indicate an ancestry that goes back into the Hadean.  The earliest granitic rocks at 3.4 Ga are tonalitic.  Potassium-rich plutons, indicative of granites derived from crustal melting, were emplaced 3.3 Ga, indicating that evolved continental crust in the Wyoming province had formed at that time.  The majority of the province is composed of variably deformed granitic plutons that were emplaced 2.85 Ga, 2.7 Ga., and 2.62 Ga.  Like Phanerozoic continental arc magmas, these plutons contain contributions from both continental and juvenile components.  The formation of early continental crust in the Wyoming province may explain why the Wyoming province records the earliest Himalayan-type orogeny on Earth at 2.7 Ga.  This is evinced by high T granulite metamorphism (>900°C, >10 kbar), juxtaposition of rocks with >3 Ga zircon grains against paragneisses that were juvenile at the time, and post metamorphism leucogranites emplaced in an extensional environments.