EVIDENCE FOR A LOCAL CRUSTAL ROOT BENEATH THE SANTA-CATALINA METAMORPHIC CORE COMPLEX, ARIZONA

We used data from the Tucson, Arizona, broad-band seismic station to a nalyze crustal and mantle structure under and adjacent to the Catalina metamorphic core complex. The data can be modeled with a simple two-l ayer crust having an average Moho depth of approximately 30 km and sei smic velocities consistent with a felsic composition. The lower crust thickens under the Catalina Mountains, depressing the Moho by approxim ately 4.2 km. The crustal root can isostatically compensate the averag e topography of the Catalina Mountains, indicating that the depth of i sostatic compensation is at or below the Moho and that the Catalina Mo untains act as a coherent block bounded by high-angle normal faults. T he presence of the crustal root is not consistent with models that pre dict upward bowing of the Moho under the Catalina metamorphic core com plex. The presence of the root cannot rule out models of lower crustal flow during the formation of the core complex. However, the presence of a root favors a model of metamorphic core complex development descr ibed by crustal thickening in shortening episodes (crustal-welt model) followed by collapse of the crustal welt through extension.