Gravitational collapse of a Paleoproterozoic orogen, southern Hualapai Mountains, Arizona

Recent recognition of pervasively migmatized gneisses in the southern Hualapai Mountains raises questions about the origin and consequences of crustal anatexis in Proterozoic rocks of northwestern Arizona. This study uses structural and metamorphic data from a small but well-exposed area of the southern Hualapai Mountains to constrain the tectonic history of and elucidate partial-melting processes in the boundary zone between the Paleoproterozoic Mojave and Yavapai crustal provinces. Based on field observations, structural data, and thermobarometry a multiphase history is inferred for the southern Hualapais. Pre-D1 crust may have experienced heating related to extension. Subhorizontal fabrics (S0/S1) formed initially during thrusting and crustal thickening associated with the regional D1 of the Mojave and Yavapai provinces, which has been recognized elsewhere in northwestern Arizona at 1740–1720 Ma. Supracrustal sediments were buried to depths greater than 26–34 km, where they underwent partial melting at temperatures of 800 °C. Large-volume melting eventually destabilized the D1 crust and promoted gravitational collapse. Rocks from the deepest parts of the D1 orogen were tectonically exhumed to less than 12 km. Subhorizontal fabrics developed during D1 thrusting were reactivated during exhumation (S1/S2). The southern Hualapais field area shows evidence for only minor structural overprinting during later regional D2 event (Ivanpah-Yavapai orogeny).