CHARACTERIZATION OF THE TUFF OF SAN FELIPE ON ISLA ANGEL DE LA GUARDA, BAJA CALIFORNIA, MEXICO

The Tuff of San Felipe has proven invaluable in reconstructing Isla Tiburon to the Baja Peninsula and constraining the opening of the northern Gulf of California. Recently identified outcrops of the Tuff of San Felipe have doubled its previously known extent. Work on new locations in the Sierra Libre of Sonora, Isla Angel de la Guarda, and various mesas around Cataviña, in Baja California is aimed at locating some of the slip deficit in Pacific – North America plate motion and placing tighter constraints on the timing and location of rifting events. In 2011, a field expedition to Isla Angel de la Guarda sampled the Tuff in 44 locations and returned 362 oriented paleomagnetic cores as well as 14 oriented block samples. Here we present the preliminary paleomagnetic analysis of these samples. Specimens from these cores are measured for a) anisotropy of magnetic susceptibility (AMS) to determine the flow direction, b) paleomagnetic orientation to confirm that they are the Tuff of San Felipe, and c) magnetic mineralogy to aid in interpretation of the AMS results. The stratigraphic transects and dense nature of this sampling campaign will allow us to better constrain flow direction and significant flow variations to aid in vent location and correlation of displaced flows and to test the details of correlation of these outcrops to the Cataviña region of the Baja California Peninsula.