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GEOREF RECORD

Geophysical expression of buried range-front embayment structure; Great Sand Dunes National Park, Rio Grande Rift, Colorado

Benjamin J. Drenth, V. J. S. Grauch, Chester A. Ruleman and Judith A. Schenk
Geophysical expression of buried range-front embayment structure; Great Sand Dunes National Park, Rio Grande Rift, Colorado
Geosphere (Boulder, CO) (May 2017) 13 (3): 974-990

Abstract

Great Sand Dunes National Park and Preserve (GRSA, Colorado) lies along the eastern margin of the San Luis Basin and the tectonically active Sangre de Cristo fault system that are part of the northern Rio Grande rift. GRSA lies within a prominent embayment in the range front where two separate sections of the Sangre de Cristo fault system intersect. Fault scarps are observed along both intersecting fault zones within older basin-fill alluvium, but have been obscured by the actively migrating dunefield. The dune sand is also strongly magnetic, locally limiting the usefulness of aeromagnetic methods for mapping concealed structure. This study uses airborne geophysical methods, primarily airborne gravity gradient data, along with constraints from geologic mapping and limited subsurface data and groundwater modeling, to interpret the subsurface basin geometry and range-front structure of the embayment. Using forward modeling of the gravity gradient data and locations of faults inferred from gravity gradient and aeromagnetic lineaments, several previously unrecognized tectonic elements are interpreted adjacent to the range front. Some of the largest rift-related fault offsets are demonstrated to be basinward of the normal fault zones mapped at the surface along the range front of the Sangre de Cristo Mountains, along faults concealed under the dunefield and subparallel to the two fault sections. A fault-bounded structural bench, likely composed of Proterozoic rocks, underlies most of the high dunefield at depths of 500 m to 1 km. The bench is truncated on its southwest margin by a northwest-trending, southwest-dipping normal fault. A northeast-trending, northwest-dipping normal fault with approximately 600 m of estimated relief lies under the southern margin of the dunefield and bounds a structurally higher bench of Proterozoic rocks concealed at <400 m depth near the range front. The northwest- and northeast-trending geophysical lineaments generally correspond well with the trends of faults mapped at the surface, and with both pre- and syn-rift structures in the Sangre de Cristo Mountains. Aeromagnetic anomalies are explained by variations in the magnetization of pre-rift rocks, and the strongly magnetic dune sand.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 13
Serial Issue: 3
Title: Geophysical expression of buried range-front embayment structure; Great Sand Dunes National Park, Rio Grande Rift, Colorado
Affiliation: U. S. Geological Survey, Crustal Geophysics and Geochemistry Science Center, Denver, CO, United States
Pages: 974-990
Published: 20170510
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 71
Accession Number: 2017-046440
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 1 table, geol. sketch maps
N37°40'00" - N37°49'60", W105°40'00" - W105°30'00"
Secondary Affiliation: Colorado School of Mines, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201725
Program Name: USGSOPNon-USGS publications with USGS authors
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