GIS PLATE TECTONIC RECONSTRUCTION OF THE SOUTHERN GULF OF CALIFORNIA OBLIQUE RIFT

We present GIS-based plate tectonic reconstruction maps for the southern Gulf of California oblique rift. The maps track plate boundary deformation in 2 and 1 Myr intervals (6-2 Ma and 2 Ma-present) using a custom ArcGIS add-in tool to close basins and restore slip on dextral faults. The tool takes a set of polygons depicting present day locations of tectonic blocks and sequentially restores displacement of their centroids along a vector specific to that location and time. Tectonic blocks are defined by faults, geology, seismic data, and bathymetry/topography. The blocks move in two steps: 1) rate A motion displaces blocks W of the main plate boundary relative to North America and 2) rate B motion displaces blocks W of the main plate boundary relative to the Baja California microplate, if applicable. Spreading center and fault-slip rates were acquired from geologic data, cross-Gulf tie points, and GPS studies. A recent GPS study indicated that ~92% of modern-day Pacific-North America (PAC-NAM) plate motion (~302° azimuth) is localized between the Baja California microplate and North America. Baja-North America GPS rates agree remarkably with ~6 Ma geologic offsets across the Gulf and are used during reconstruction steps back to 6 Ma. Unpublished GPS data indicate that modern plate motion is partitioned between the plate boundary, Gulf-margin system, and borderland faults west of Baja California. The Alarcon and Guaymas spreading centers initiated at 2.4 Ma and 6 Ma (Lizarralde et al., 2007), respectively, while the Farallon, Pescadero, and Carmen spreading centers began between ~2-1 Ma (Lonsdale, 1989). Therefore, the 2, 4, and 6 Ma reconstruction steps include a long transtensional fault zone along much of the southern Gulf, connecting the Guaymas spreading center with either the Alarcon spreading center or East Pacific Rise. Once the 6 Ma map is finalized, tectonic maps for 8, 10, 12, 14 Ma will be made, and paleogeographic elements will be added to all maps.