Abstract

Rocks in the northern Canelo Hills reflect the tectonic settings of southeastern Arizona during Mesozoic time. The stratigraphy of Upper Jurassic rocks records deposition in a terrane of high physiographic relief created by large movements of northwest-striking faults, and lesser offsets on northeast-striking faults. Deposition of these Upper Jurassic rocks included emplacement of large exotic blocks of Paleozoic rocks by gravity sliding. These clastic rocks are approximately 150 million years old and were deposited on a thick sequence of Lower and Middle Jurassic rocks. Recognition of the age and depositional relations between the volcanic rocks and clastic rocks indicates a revision of the mid-Mesozoic regional stratigraphic framework. Compression during Laramide time deformed the northern Canelo Hills into a northwest-trending complexly faulted, upright anticline.

Results of this study, combined with previously published work, provide a new perspective of mid-Mesozoic tectonics of the region. A thick volcanic sequence represents a Lower and Middle-Jurassic continental arc setting that contrasts sharply with the late Paleozoic shallow marine cratonic shelf setting. Large movements, possibly including strike-slip, on northwest-striking faults accompanied the eruption of arc volcanics. The arc setting was succeeded by large block faulting that probably reflect incipient continental rifting associated with the Sonoran Trough. Rocks in the northern Canelo Hills record the transition from arc volcanism and strike-slip (?) faulting to rifting. Deposition of coarse clastic rocks, reflecting rifting continued into Early Cretaceous time. The rift setting was succeeded in Early Cretaceous time (approximately 115 m.y. ago) by a shallow marine trough. Regression of the marine conditions at approximately 100 m.y. ago suggests another change in tectonic setting of the region. The onset of Laramide deformation approximately 85 m.y. ago represents the final Mesozoic change in tectonic and depositional settings in southeastern Arizona.