Mesozoic tectonic evolution of the Twin Buttes Mine area, Pima County, Arizona: implications for a regional tectonic contro of ore deposits in the Pima mining district

Abstract

Ground magnetic data are consistent with the interpretation that Lower Jurassic volcanic rocks of the Twin Buttes mine area (Ox Frame Volcanics) are confined to a distinct block by the northwest trending Sawmill Canyon Fault Zone which was initially active during the Lower Jurassic. Possible reactivation of the Sawmill Canyon Fault zone in the Middle Jurassic as a left-lateral wrench fault is recorded by the deposition of syntectonic red-beds (Rodolfo Formation). Lower Cretaceous rocks (Whitcomb Quartzite, Glance Conglomerate, and Angelica Akrose) were deposited in alluvial environments resulting from additional reactivation of the Sawmill Canyon Fault Zone. Upper Cretaceous (Laramide) deformation involved the formation of northwest trending folds and northwest and northeast trending reverse, tear, and later block faults during the uplift of Precambrian basement. Ore deposits of the Pima mining district are localized along a northeast trending fault zone with evidence for initial activity in the Middle Jurassic and later reactivation during the Laramide.