Age of the Socorro Magma Body: Surface Uplift History from River Terrace Correlation and Cosmochronology

New Mexico Institute Of Mining And Technology, Socorro NM

Investigators

Abstract

The Socorro magma body is one of the largest known midcrustal magma bodies on Earth: it is a sill-like feature, about 3,400 square kilometers in area, about 150 meters thick, and lies at about 19 km depth under the central Rio Grande rift in the Socorro, New Mexico area The Socorro magma body causes surface uplift with a maximum rate of about 2.5-3 mm/yr centered over the northern part of the body. Models of surface uplift due to an elastic crustal response to magmatic inflation at 19 km depth agree well with InSAR interferograms. The age of the magma body and its related surface uplift are controversial. In order to resolve this controversy, the New Mexico Tech research team will carry out a pilot study of terrace remnants to determine the age of onset of surface uplift. They will map the terrace remnants with the aid of Digital Elevation Models and correlate them using soil characteristics (clay and carbonate content), geomorphic characteristics (surface textures, degree of desert varnish, location within flights of terraces), sedimentological characteristics of terrace deposits (clast types, sedimentary structures, grain size), and 36Cl ages. Well-preserved and unaltered surfaces will be dated using 36Cl cosmogenic isotope profile dating. Lateral changes in terrace elevations and vertical terrace spacing will, in turn, allow identification of those terraces affected or unaffected by Socorro magma body inflation. Terrace ages will bracket onset of Socorro magma body -related uplift and constrain long-term rates of uplift and magma-body inflation. The Socorro magma body is one of the largest known midcrustal magma bodies on Earth. Leveling and InSAR studies indicate that the magma body is causing surface uplift at rates of about 2.5 mm/yr (in the central zone of fastest uplift). The Socorro Seismic Anomaly has the highest rate of upper crustal seismicity in New Mexico and lies above the magma body. Microseismicity presumably is triggered by deformation and ascending hydrous fluids above the Socorro magma body. This project seeks to constrain the age of the Socorro magma body, which is relevant to understanding crustal rheology, evolution of the brittle-ductile transition, crustal growth in rifts, magma genesis during rifting, stress evolution during rifting, and volcanic hazard.