Seismic search for evidence of magma beneath the Jemez Mountains in the northern Rio Grande rift. [Abstract only]
- Los Alamos National Lab., NM
The Jemez volcanic field is located at the intersection of the northeast-trending Jemez lineament - a major crustal fracture zone - and the western margin of the Rio Grande rift in north-central New Mexico. Seismic refraction/wide-angle reflection profiles were obtained in 1981. Profiles were designed to map distribution and depth of low velocity anomalies as indicators of possible shallow magma chambers and/or fractured porous regions. Interpretation of records from 6 shotpoints recorded by a 60-station seismic net indicates: (1) There are considerable variations in near-surface seismic velocities and thicknesses overlying the topographically irregular basement (average V approx. 6.0 km/s). (2) The major shallow (2 to 10 km) anomaly is a 10-km-dia, low P-velocity (approx. 5.5 km/s) region directly below the resurgent dome that was uplifted approx. 1 km after the last caldera collapse. This velocity is not low enough to unequivocally indicate still-molten material but instead may be a deeply buried tuff layer. (3) Anomalies in travel times, frequency content, and waveforms of transmitted waveforms from regional and teleseismic sources suggest an approx. 30-km-dia anomaly extends from shallow (approx. 5 km) depth to at least Moho levels (approx. 40 km). (4) Reflections from largely horizontal surfaces (sills, magma chamber roofs, etc.) are not clearly observed, suggesting complicated three-dimensional structure. In contrast to the Jemez, data from the Socorro area (another region where transverse fractures intersect the rift) indicate predominantly horizontal midcrustal structure dominated by a thin (<1 km), complexly laminated, sill-like magma layer.
- OSTI ID:
- 6176855
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 15:5; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
150301* -- Geothermal Exploration & Exploration Technology-- Geophysical Techniques & Surveys
FEDERAL REGION VI
GEOPHYSICAL SURVEYS
GEOTHERMAL SYSTEMS
JEMEZ MOUNTAINS
MAGMA
MAGMA SYSTEMS
MAPPING
MOUNTAINS
NEW MEXICO
NORTH AMERICA
RIO GRANDE RIFT
SEISMIC SURVEYS
SURVEYS
TOPOGRAPHY
USA