SHEARER, DAVID L., and KATE C. MILLER
Department of Geological Sciences, UTEP, El Paso, Texas

Abstract: Tectonics and Subsurface Structure, Playas and Hachita Valleys, southwest Now Mexico

Southwest New Mexico has experienced numerous episodes of orogeny and magmatism since the Proterozoic. Dominant geologic influences on the subsurface structure include the development of Paleozoic-age Pedregosa Basin, compression tectonics of the Laramide, and late Cenozoic Basin and Range extension.

An integrated geophysical investigation was conducted on a 25 by 30 mile area that includes the Playas and Hachita Valleys and Hatchet Mountains. Over 200 closely-spaced (1-3 miles) gravity points with high accuracy GPS coordinates were collected to supplement values (~1000 points) in the UTEP database. Satellite images were correlated to surface geology and analyzed for tectonic trends using Laplacian edge enchancement filters. Synthetic seismograms, compiled from geophysical logs and local stratigraphy, were used to identify subsurface horizons on east-west seismic sections. Gravity, seismic, tectonic trends and surface geology were integrated via forward modeling along east-west profiles.

Residual gravity anomalies show north-south oriented uplifted fault blocks and associated Cenozoic grabens within the Paleozoic-age basin. Several major faults with NW-SE strike trends are present beneath the valley fill. They have high angle (45° average) dips near the surface and low angle dips at depth (>7 km). These basement-involved Laramide compressional faults show displacements of several kilometers. In some cases, listric normal faulting from Basin and Range extension are associated with high angle (~65°) Laramide features near surface but as separate low angle faults at depth.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas