Cordilleran Section - 108th Annual Meeting (29–31 March 2012)

Paper No. 1
Presentation Time: 08:30-18:30


SKINNER, Lisa A., School of Earth Sciences and Environmental Sustainability, Geology Program, Northern Arizona University, PO Box 4099, Flagstaff, AZ 86011, UMHOEFER, Paul J., School of Earth Sciences & Environmental Sustainability, Northern Arizona University, 625 Knoles Drive, Box 4099, Flagstaff, AZ 86011, KLUESNER, Jared W., Earth and Planetary Sciences, University of California Santa Cruz, Earth and Marine Sci, Santa Cruz, CA 95064 and NAVA, Richard, USGS, Astrogeology Science Center, 2255 N Gemini Drive, Flagstaff, AZ 86001,

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 Unpublished GPS data indicate that modern plate motion is partitioned between the plate boundary, Gulf-margin system, and borderland faults west of Baja California.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.