A lower-crustal extension to a mid-crustal magma body in the Rio Grande rift, New Mexico

J.W. Schlue, R.C. Aster, R.P. Meyer
Department of Earth and Environmental Science New Mexico Tech Socorro, New Mexico 87801

Abstract:

A prominent and spatially localized phase arriving approximately 4 s after the initial compressional arrival, repeatedly observed on seismograms recorded in the central Rio Grande rift from intermediate- and deep-focus earthquakes at distances near 90, is identified as a probable compressional- to shear-wave conversion from a lower-crustal root of the Socorro mid-crustal magma body (SMB). This phase is inconsistent with previously determined crustal models containing a simple sill-like mid-crustal magam body with a negligible conduit system. Finite-element synthetic seismogram modeling suggests that a partially molten root with a western boundary dipping steeply to the east extends several kilometers from the 19 km-deep upper surface of the magma body down into the lower crust of the southwestern portion of the Albuquerque-Belen basin. The location and geometry of this feature suggest that the intracrustal intrusion of mantle magmas responsible for the ongoing inflation of the SMB and associated seismicity is occurring via an off-axis conduit system located beneath the active margin of the Albuquerque-Belen basin.

AGU Index Terms: 8145 Physics of magma and magma bodies; 7203 Body wave propagation; 7205 Continental crust; 8434 Magma migration
Keywords/Free Terms: Rio Grande rift, magma body, magma migration, finite-element.

JGR-Solid Earth 96JB02464
Vol. 101 , No. B11 , p. 25,283