Regional audiomagnetotelluric study of the Questa Caldera, New Mexico

Abstract

Audiomagnetotelluric (AMT) soundings at Questa caldera were made in the course of a mineral resource study of the Columbine-Hondo and Latir Peak Wilderness areas, New Mexico, in the fall of 1980 and 1981. This regional electrical survey covered an area of approximately 518 km 2 and consisted of 92 AMT stations at an average spacing of approximately 3 km. An AMT apparent resistivity map and one-dimensional models delineate several major lithologic and structural features. A large north-south resistivity high is interpreted to outline a largely concealed batholith 20 km long, 2-6 km wide, and >4 km thick. Two high-resistivity east-west trends coincide with the mapped margins of the Questa caldera, indicating the electrically contrasting rocks at its boundary. Apparent resistivity lows coincide with areas of hydrothermal alteration known to contain stockwork molybdenum deposits.

The plutonic record of a silicic ignimbrite from the Latir volcanic field, New Mexico

“…Gravity lows are commonly found in the subsurface beneath caldera systems [e.g., Davy and Caldwell , 1998; Marti et al , 2008], and whereas some interpretations suggest they represent the plutonic rock from which the ignimbrite was fractionated [ Lipman , 2007], others suggest these anomalies reflect the presence of postcaldera intrusions [ Steck et al , 1998]. Geophysical surveys of the Latir volcanic field suggest that it is underlain by a large pluton or set of plutons with an estimated volume of 4500 km 3 [ Cordell et al , 1985; Long , 1985; Lipman , 1988]. The most recent models for the formation of the plutons beneath the Latir volcanic field demand an episodic intrusive history, but also suggest that the bulk of the intrusive rocks had a short (less than 500 ka) magmatic history [ Lipman , 1988].…”

Geochronology of a Bouguer Gravity Low

“…The felsic intrusions in the region have an average density of 2,600 kg/m 3 , compared to the 2,700 kg/m 3 density of Precambrian wall rock, creating a negative gravity anomaly (Cordell et al, ). These studies indicate that the batholith is defined as an elongate N‐S geometry, bound by N‐S Rio Grande faults on its western margin, and thickest in the region of the southern caldera margin (Figure b; Long, ; Cordell et al, ). In this contribution, we use surface and subsurface mapping, combined with published and new geochronological data, to understand the assembly of the geophysical anomaly defined in earlier studies.…”

Application of structural geology to mineral and energy resources of the Central and Western United States

“…Case histories of the AMT method in mineral and geothermal environments have been described by Strangway and Kozier (1979), Hoover and others (1976), and Hoover and Long (1976). Previous AMT or MT studies investigating the structural and lithologic relations in volcanic areas include those by Hoover and others (1976) and Hermance and others (1984) (Long Valley, California); Leary and Phinney (1974), Stanley and others (1977), and Stanley (1982) (Yellowstone, Wyoming and Idaho);Long (1985) (Questa, New Mexico); and Fitterman and others (1988) (Newberry volcano, Oregon).…”