Cenozoic Extensional Tectonics Revealed Through Seismic Reflection Imaging, SE Arizona

by Wagner, Frank Henry.

The Basin and Range province of western North America is a broad region of irregular topographic expression characterized by various styles of Cenozoic extension. Recent reprocessing and interpretation of a regional suite of industry seismic reflection profiles in southern Arizona, in the southern Basin and Range province of southwestern North America, have illuminated subsurface features related to Cenozoic crustal extension and show a detailed view of extensional processes in the southern Basin and Range. Seismic stratigraphic investigations on these profiles suggest a two-phase model for the evolution of the Catalina-Rincon metamorphic core complex, with an initial stage of isostatic core complex emplacement during detachment faulting that resulted in little topographic expression. This was followed, after a significant tectonic hiatus, by latestage exhumation and flexural uplift of the metamorphic core complex controlled by younger high-angle faulting. Along-strike, upper-plate deformation in response to core complex emplacement was accommodated by the Santa Rita fault, south of the Catalina- Rincon metamorphic core complex. Finite-element models predicts early mechanical failure of the upper-plate of the detachment system to the south of the Catalina core complex. These models suggest that the Santa Rita fault is the result of a perturbation in the regional stress field caused by the Catalina detachment and the associated brittle failure of the upper plate from the extreme crustal extension associated with corecomplex emplacement. These profiles, coupled with geologic and well control, indicate that the southwest-dipping Catalina detachment, the northwest-dipping Santa Rita fault, the east dipping Altar Valley fault, and the highly dissected Sierrita Mountains are all 12 aspects of the same extensional event in the middle-Tertiary. These features all appear to merge into a broad zone of middle-crustal deformation and likely represent heterogeneous upper-crustal deformation in response to middle-to-lower crustal homogeneous deformation. 13