Rocky Mountain Section - 64th Annual Meeting (9–11 May 2012)

Paper No. 1
Presentation Time: 8:45 AM


BALDRIDGE, W. Scott, Earth and Environmental Sciences Division, Los Alamos National Laboratory, M.S. D408, Los Alamos, NM 87545, FERGUSON, John F., Geosciences Department, University of Texas at Dallas, PO Box 688, Richardson, TX 75080, BRAILE, Lawrence W., Earth and Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47097-2051, SNELSON, Catherine M., National Security Technologies, LLC, P.O.Box 98521, M/S NLV022, Las Vegas, NV 89193-8521, BIEHLER, Shawn, Dept. Earth Sciences, University of California, Riverside, CA 92521, BAILEY, Bevin L., Department of Geology, University of Kansas, Lawrence, KS 66045, BUENING, Jonathan, Earth and Atmospheric Sciences, Purdue Univ, 550 Stadium Mall Drive, West Lafayette, IN 47907-2051, CHRISTIANSON, Ryan, Geology Department, Centenary College, Shreveport, LA 71104, JUDY, Brett, Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 and PAZOS, Celia S., Geological Sciences, California State Polytechnic University, Pomona, Pomona, CA 91768,

The active late Cenozoic Rio Grande rift of the southwestern U. S. comprises several right-stepping, faulted basins separated by accommodation zones of different types. For several years the SAGE (Summer of Applied Geophysical Experience) Program has conducted a variety of geophysical surveys along the eastern margin of the rift, 10-35 km southwest of Santa Fe, New Mexico. The purpose has been to investigate structures and history of a complex NE-trending accommodation zone (Santo Domingo) separating the larger Española (to north) and Albuquerque rift basins. Crustal extension is transferred dominantly along north- to northwest-trending en echelon faults, creating sub-basins and plunging ramps oblique to the accommodation zone.

SAGE has produced seismic reflection images of two of these faults (“ramp faults”), the La Bajada (LB) and San Francisco (SF) faults, allowing determination of their dips (near 60o down to west). Offset on the basin-bounding LB fault increases from near zero at the south to a maximum of ~3000 m 13 km to the north, where the uplifted footwall comprises the flanking Cerrillos uplift. Initiation of the LB fault is not constrained but vertical offset is only ~200 m since 2.7 Ma. Uplift of the Sandia Mountains ~20 Ma ago warped the hanging wall into a closed northward plunging structural basin. Preliminary gravity data for the intra-rift SF fault are compatible with ~1.3 km of down-to-the west offset. Combining our new seismic, gravity, and other geophysical data, and integrating with industry seismic reflection, geological, and borehole data allows us to estimate extension and block rotation along these faults.

We are able to discriminate pre-rift (Laramide) from post-middle Miocene (rift) structures, and begin to quantify vertical offset across faults and geometry of basin fill. Our overall goal is to infer kinematic development, linkages among faults, growth history, and possible pre-rift structural controls.