TY - JOUR
T1 - Sp receiver function imaging of a passive margin
T2 - Transect across Texas's Gulf Coastal Plain
AU - Ainsworth, Ryan
AU - Pulliam, Jay
AU - Gurrola, Harold
AU - Evanzia, Dominic
N1 - Funding Information:
We thank S. Hansen and K. Dueker for the use of their receiver function imaging software and S.P. Grand for the use of broadband instruments. High school science teachers David Boyd, Michael Arratia, and Craig Weart and students from Southwestern University, Deep Springs College, Texas Lutheran University, and Cornell College, as well as Baylor and Texas Tech, contributed extensively to fieldwork and we gratefully acknowledge their efforts. EarthScope, the Incorporated Research Institutions for Seismology (IRIS), and the U.S. Geological Survey's Advanced National Seismic System (ANSS) contributed significantly to acquiring, archiving, and disseminating broadband seismic data on an unprecedented scale in Texas and Oklahoma. We are indebted to two anonymous reviewers, whose criticisms and suggestions led to an improved manuscript. This research was supported by funding from the National Science Foundation ( EAR 0746321 , EAR 0750711 ), the Norman Hackerman Advanced Research Program of the Texas Higher Education Coordinating Board , NHARP # 003658-0034-2009 , the Gulf Coast Association of Geological Societies , and the W.M. Keck Foundation .
Publisher Copyright:
© 2014 Elsevier B.V.
PY - 2014
Y1 - 2014
N2 - The Gulf Coast of Texas has been the subject of intensive geological and geophysical investigation in pursuit of hydrocarbons but studies that penetrate beyond the upper crust are limited to a few refraction profiles and regional surface wave investigations. The passing of EarthScope's Transportable Array has facilitated regional investigations of the lithosphere but its 70-km station spacing does not allow many important tectonic features to be imaged. A broadband seismic transect across the Texas Gulf Coastal Plain was therefore performed in order to image deep structure beneath this passive margin and the transition to the neighboring craton. A 2D Sp receiver function common conversion point (CCP) stacked image produced for this transect reveals several discontinuities in the sub-crustal lithosphere.The region nearest the shoreline is underlain by an anomalous ~18 km thick low velocity layer that produces a strong negative pulse in the Sp receiver functions. The drop in velocity is too large to be due to any reasonable change in Fe or Mg content but could be produced by partial melt or mantle hydration. It is unlikely that partial melt would still be found in a 160-180-year-old passive margin, such as the Gulf Coast, but hydration, possibly introduced by a through-going Balcones fault system, and resulting serpentinization could produce the observed anomaly.An event with negative polarity appears at a depth of ~110 km, which we interpret to be the lithosphere-asthenosphere boundary (LAB). Thermal variations alone would not produce a sufficiently sharp discontinuity to be imaged by Sp converted phases. Recent shear-wave splitting studies revealed unusually large delay times in this region, along with fast polarization directions that differ from measurements on the Laurentian craton. Large delay times may imply significant flow, which could also produce frictional heating, due to shearing, and partial melt, which would steepen the velocity gradients.An additional layer is bounded by discontinuities at 145-165 km depth (with negative polarity) and 185-205 km depth (with positive polarity). The appearance of these discontinuities suggests that the mantle beneath the LAB is more complicated here than elsewhere and that the transition from lithosphere to asthenosphere occurs over a broad (85-100-km-thick) depth interval.
AB - The Gulf Coast of Texas has been the subject of intensive geological and geophysical investigation in pursuit of hydrocarbons but studies that penetrate beyond the upper crust are limited to a few refraction profiles and regional surface wave investigations. The passing of EarthScope's Transportable Array has facilitated regional investigations of the lithosphere but its 70-km station spacing does not allow many important tectonic features to be imaged. A broadband seismic transect across the Texas Gulf Coastal Plain was therefore performed in order to image deep structure beneath this passive margin and the transition to the neighboring craton. A 2D Sp receiver function common conversion point (CCP) stacked image produced for this transect reveals several discontinuities in the sub-crustal lithosphere.The region nearest the shoreline is underlain by an anomalous ~18 km thick low velocity layer that produces a strong negative pulse in the Sp receiver functions. The drop in velocity is too large to be due to any reasonable change in Fe or Mg content but could be produced by partial melt or mantle hydration. It is unlikely that partial melt would still be found in a 160-180-year-old passive margin, such as the Gulf Coast, but hydration, possibly introduced by a through-going Balcones fault system, and resulting serpentinization could produce the observed anomaly.An event with negative polarity appears at a depth of ~110 km, which we interpret to be the lithosphere-asthenosphere boundary (LAB). Thermal variations alone would not produce a sufficiently sharp discontinuity to be imaged by Sp converted phases. Recent shear-wave splitting studies revealed unusually large delay times in this region, along with fast polarization directions that differ from measurements on the Laurentian craton. Large delay times may imply significant flow, which could also produce frictional heating, due to shearing, and partial melt, which would steepen the velocity gradients.An additional layer is bounded by discontinuities at 145-165 km depth (with negative polarity) and 185-205 km depth (with positive polarity). The appearance of these discontinuities suggests that the mantle beneath the LAB is more complicated here than elsewhere and that the transition from lithosphere to asthenosphere occurs over a broad (85-100-km-thick) depth interval.
KW - Gulf Coastal Plain
KW - Lithosphere-asthenosphere boundary
KW - Passive margin
KW - Sp receiver functions
UR - http://www.scopus.com/inward/record.url?scp=84926278969&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2014.05.056
DO - 10.1016/j.epsl.2014.05.056
M3 - Article
AN - SCOPUS:84926278969
VL - 402
SP - 138
EP - 147
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
SN - 0012-821X
IS - C
ER -