Crustal structure from three-dimensional gravity modeling of a metamorphic core complex: A model for uplift, Santa Catalina Rincon mountains, Arizona

Gravity modeling shows that the observed fluctuations in gravity over the Catalina-Rincon metamorphic core complex of southeastern Arizona are caused primarily by shallow crustal density contrasts. The Wilderness suite granites, the probable source of a 20-mgal low over the central part of the core complex, may extend to depths of 7 12 km below the surface. Seismic refraction information is consistent with the existence of a deep crustal root under the Catalina-Rincon core complex. We hypothesize that the voluminous Wilderness suite granites are related to a crustal thickening event that built the root in early Tertiary time. Modeling of flexural isostatic uplift, resulting from an excess crustal root, predicts two episodes of uplift for the Catalina-Rincon metamorphic core complex: (1) low-relief flexural uplift in the middle Tertiary and (2) complete uplift precipitated by high-angle Basin and Range faulting at 10 15 Ma. The uplift and exposure of core complexes, therefore, can be an isostatically driven process that occurs in regions of locally thickened crust.