Filling the North American Proterozoic Tectonic Gap: 1.60–1.59‐Ga Deformation and Orogenesis in Southern Wyoming, USA

Abstract

Abstract Structural and thermochronologic studies in the Sierra Madre, southern Wyoming, indicate that parts of the 1.78–1.75‐Ga Cheyenne belt, an Archean‐Proterozoic suture, were reactivated at ca. 1.6 Ga. New shear zones, notably the brittle Battle Lake thrust‐tear fault zone, also formed at this time. The Battle Lake fault zone (BLFZ), which displaced parts of the Cheyenne belt at least 30 km to the north, corresponds to the surface expression of a south‐dipping reflector imaged by regional seismic studies (Continental Dynamics of the Rocky Mountains experiment). 40Ar/39Ar and U‐Pb data define age patterns in the Sierra Madre that are delineated by discrete structures. North of the 1.78‐Ga Divide Peak mylonite zone, a foreland structure associated with the Medicine Bow orogeny, 40Ar/39Ar biotite dates suggest cooling below 300°C by 2.0 Ga. South of the Divide Peak mylonite zone but north of the BLFZ, hornblendes yield apparent 40Ar/39Ar ages of ca. 1.80–1.78 Ga that may record tectonic burial and cooli...