Geophysical Anomalies and New Constraints on Buried Structures, Southern San Luis Basin, Colorado

Benjamin Drenth^1,2 and V. J. S. Grauch¹.  (1) U.S. Geological Survey, Denver, CO 80225 and (2) School of Geology and Geophysics, The University of Oklahoma, Norman, OK 73019  [email protected]

Preliminary interpretations of recently collected high-resolution aeromagnetic data and ground gravity data are combined with subsurface constraints from well and limited seismic data in the southeastern San Luis basin. This region is characterized by widespread mid- to late-Tertiary volcanic rocks within a section of sediments, the Santa Fe Group, related to Rio Grande rift extension. These rocks appear to mostly lie directly on Precambrian basement, which has been deformed by extension along largely preexisting faults and lineaments, leaving behind horst blocks of variable size within the basin. Depth estimates derived from aeromagnetic anomalies show discrete sub-regions with distinct structures, including horst blocks near the eastern basin margin, subcrop extents of surficial volcanic units, buried faults, and regional architecture of the upper portion of the basin. Gravity models using new data and constraints from recently uncovered vintage seismic data reveal a complex relationship between modern horst blocks and basement uplifts. A large north-south-trending horst block near the ColoradoÐNew Mexico border appears to be partially cored by basement rocks and contains a strongly magnetized Miocene volcanic section overlain by younger basalt flows that display variable magnetic polarity. Relationships observed on the surface of this horst are extended into the subsurface of the basin in order to better understand the regionÕs stratigraphy and deformation history.