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.