UPDATED ISOPACH MAP OF THE TUFF OF SAN FELIPE IN BAJA CALIFORNIA, MEXICO

The 12.5 Ma Tuff of San Felipe is an ignimbrite layer, often more than 10 m thick, exposed in a number of outcrops throughout Sonora and Baja California, Mexico. If we correctly calculate the volume distribution of the Tuff of San Felipe on either side of the Gulf of California, it will help us to place Baja California to where it once was aligned with Sonora before the opening of the Upper Delfín Basin at 6 Ma. The volume of the Tuff was estimated to be at least 54 cubic km by Stock et al. (JVGR, 1999), although at that point, not all outcrops of the tuff in Baja California had been discovered and none had yet been identified in Sonora. We use the presently known extent and thickness of the Tuff in Baja California, including outcrops identified farther west and south in the stable part of the Baja California peninsula (Bennett, 2009; Olguin-Villa, 2010; Skinner et al., this meeting) to update the volume estimate for the Tuff of San Felipe in Baja California. Outcrops in Sonora are still being investigated by numerous workers, and will not be included in this presentation. Using existing published maps, and GoogleEarth, we can zoom in to identify the Tuff of San Felipe in Baja California and calculate the thicknesses of the outcrops in more locations than were previously reported. With ArcGIS, we create a layer of thicknesses and will present a final distribution and isopach map of the Tuff of San Felipe in Baja California. This result is used to calculate an updated volume estimate, after correcting for geological extension that took place after 12.5 Ma in parts of the region.