GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 204-2
Presentation Time: 9:00 AM-6:30 PM


HOFFMAN, Charles F., MICHELFELDER, Gary S., BOHANNON, Loren A. and PEITZ, Megan R., Department of Geography, Geology, and Planning, Missouri State University, 901 S. National Ave., Springfield, MO 65897

The Mogollon Datil volcanic field of central and southern New Mexico is comprised of Oligocene and Miocene volcanic and volcaniclastic rocks resulting from ignimbrite flare-up in the southwest United States. The associated structure and volcanic stratigraphy record the transition from compression to extension overprinted by caldera collapse and secondary hydrothermal alteration. Geologic mapping of the Bearwallow Mountain 7.5’ quadrangle was conducted to investigate the structural relationships between caldera collapse, crustal extension and hydrothermal mineralization leading to economic deposits to the west and north of the quadrangle.

The quadrangle is comprised of late Oligocene rhyolite and ash-flow tuffs of the Fanney Rhyolite and the Deadwood Gulch member, and andesite to basaltic lava flows of the Mineral Creek and Bearwallow Mountain andesites. Three normal faults orientations are observed within the quadrangle. Normal faults associated with the Bursum caldera, are east-west and northeast-southwest trending. These faults are the result of the collapse of the caldera. Fanney Rhyolite lava flows are oriented along these faults and host secondary mineral deposits. North-south trending faults dipping to the west are younger and are the result of extension related to the Basin and Range to the west. Andesitic to basaltic lava flows of the Bearwallow Mountain Andesite cover the northern section of the quadrangle and postdate normal fault activity. Radial dikes within the Bearwallow Mountain Andesite suggest a volcanic center located at Bearwallow Mountain.

We present a new geologic map of the Bearwallow Mountain 7.5’ quadrangle at 1:24,000 scale, supported by stratigraphic sections, cross sections, and magnetic and very low frequency electromagnetic surveys. We provide an improved geologic framework for understanding the Bursum caldera collapse structure, post-collapse extension, and the possibility of economic deposits related to the Mogollon Mining District.