HR: 0800h
AN: T41A-0359    [Abstracts]
TI: Crustal Structure of the Southern Rio Grande Rift Defined by Wide Angle Reflection Data
AU: Miller, K C
EM: miller@geo.utep.edu
AF: University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968, United States
AU: * Averill, M G
EM: Matthew.Averill@anadarko.com
AF: Anadarko Petroleum Corporation, 1201 Lake Robbins Drive, The Woodlands, TX 77429, United States
AU: Barnes, C G
EM: cal.barnes@ttu.edu
AF: Texas Tech University, Box 41053, 125 Science Building, Lubbock, TX 79409-1053, United States
AB: A new model of crustal velocity structure in the southern Rio Grande Rift across the Potrillo Volcanic Field (PVF) provides new information on the crustal evolution of the region from Laramide to Recent times. The model results from analysis of seismic refraction/wide-angle reflection data acquired from a 205-km-long profile, comprised of 8 shots and 793 receivers. Together, the data and model exhibit 1) a new detailed cross-section of the modern Basin and Range structure of southern New Mexico and far West Texas; 2) evidence for a number of high velocity bodies between 5 and 10 km depth that underlie Basin and Range structure; 3) a dramatic step up in a mid-crustal interface from 15 to 11 km depth that leads to thickening of the mid-crust below the PVF; 4) increased seismic reflectivity within the crust and at the Moho interface concentrated below the PVF and; 5) evidence for thicker crust (~30-31 km) than previously determined. The velocity structure in the upper 3 to 5 km defines the geometry of the late Tertiary basins and ranges. The basin fill has velocities from 2.5 to 4.5 km/s. In the ranges, velocities are 4.7 to 5.3 km/s and represent uplifted Paleozoic sedimentary rock. By contrast, we interpret high velocity bodies and complex lateral velocity variations at 5 to 10 km depth to reflect the signature of Laramide basement uplifts. The transition between the upper and middle crust is defined by an interface that steps up abruptly from a depth 15 km to 11 km beneath the PVF. Velocities range from 6.28 to 6.4 km/s below this transition to velocities of 6.7 to 7.1 km/s at the base of the crust. Crustal thickness varies from 35 km at the western end of the profile to as little as ~30 km beneath the El Paso area. Upper mantle velocities range from 7.75 to 7.9 km/s, which is consistent with a warm upper mantle and high heat flow values of 85 to 125 mWm2 associated with the southern Rio Grande Rift. Near-vertical incidence records show a complicated reflectivity pattern at the Moho, which may be related to recent volcanism. Oligocene-age (ca. 27 Ma) crustal xenoliths from Potrillo Maar crystallized at depth similar to that of the top of the thickened mid-crust. Petrographic features of the xenoliths indicate the presence of a compositionally-extended plutonic complex that underwent ductile shear during and after emplacement. The age and deformation of the xenoliths, velocity structure, and character of seismic reflectivity near the Potrillo Volcanic Field are strongly reminiscent of metamorphic core complexes in southern Arizona.
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting