Crustal Seismic Investigation of the Southern Rio Grande Rift

AVERILL, MATTHEW, K.C. MILLER and S. HARDER, Department of Geological Sciences, University of Texas at El Paso
[email protected] Fax: 915-747-5073

The southern portion of the Rio Grande Rift (SRGR) has undergone a protracted history of volcanism and tectonism culminating in the modern extensional environment. In May of 2003, a seismic refraction survey was carried out to investigate the crustal structure of the SRGR. This experiment was comprised of 7 shots of 1000-2000 lbs. at ca. 25 to 50 km spacing and 793 seismic recorders (TEXANS) deployed at a variable spacing of 100, 200 and 600 m over 205 km.

Preliminary results show energy propagation across the entire length of the array. Tomography results from inversion of first arrival data define Basin and Range style structure including undulating low (< 5.0 km/s) and high (> 5.0 km/s) features in the upper 5 km of the crust. The Hueco basin is marked by low velocities to greater than 3 km depth at the east end of the profile. High velocities (> 6.2 km/s) at approximately 5 km depth underlying the East Potrillo Mountains may be due to a mafic intrusion or a remnant Laramide feature. Future work will involve integrating results with existing reflection seismic, surface geology and well data.

Near vertical reflection data straddling the Potrillo volcanic field (PVF) shows strong intra-crustal reflections, complex PmP reflections at approximately 11 s and a possible PmS reflection at approximately 15 s. Through interpretation of these data in light of xenolith studies in the PVF and previous geophysical work we will develop new insights into the crustal-scale structure and evolution of the SRGR.