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Geophysics

Task Objectives

A high-resolution aeromagnetic and gamma ray survey of BBNP was flown during this USGS study along NE-SW trending lines 400 m apart and 300-1000 m above the ground over BBNP. The magnetic data clearly show linear and circular magnetic highs and lows that delineate lava flows and intrusions. The linear trends mostly likely indicate faults and fractures that localized the volcanism. These data were useful for mapping the distribution of volcanic rocks that dominate BBNP, as well as faults.

Geophysical studies of this task were collaborative with the NPS, USGS, University of Texas, El Paso, and other academic scientists to: (1) interpret the aeromagnetic and aerial gamma-ray data to aid project efforts to map the volcanic stratigraphy and geology of BBNP, (2) merge the Big Bend surveys with adjacent data providing a view of the regional magnetic and gamma-ray characteristics, (3) model magnetic and gravity data in selected locations to estimate volumes of igneous rocks, (4) identify linear volcanic fields that correlate with Precambrian basement structures to investigate the role of inheritance on later magmatic events, and (5) use this information to develop a comprehensive model of the volcanic and tectonic evolution of BBNP in relation to the larger geologic framework of the Trans-Pecos region.

Highlights & Key Findings

The Pine Canyon caldera has a reversely magnetized caldera-filling unit and was likely to have collapsed to the greatest extent in the northeastern portion of the caldera along buried faults. A long-wavelength magnetic high over the broader Chisos Mountains area is interpreted to be sourced by a large (1-4 kilometers thick, 700-3000 cubic kilometers in volume), completely buried intrusion. Results from studies of the Chisos Mountains and the Pine Canyon caldera which were associated with this task, were summarized in an article published in the journal "Geological Society of America Bulletin".

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