Lithospheric Structure of the Rio Grande Rift - Fig. 1

Lithospheric Structure of the Rio Grande Rift - Fig. 1 Figure 1. The 960-km RISTRA transect across the Rio Grande rift (RGR) region. Areas of Cenozoic extension are hatched.
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The seismic structure of the crust and upper mantle of the southwestern United States has been examined using teleseismic arrivals recorded by IRIS PASSCAL Instruments in LA RISTRA (Colorado PLAteau Rio Grande Rift-Great Plains Seismic TRAnsect). Receiver function estimation and filtering methods developed by Wilson and Aster (2005) produce receiver functions with decreased sensitivity to noise. Crustal thickness and VP/VS are estimated using both direct and reverberated P-to-S receiver function modes. Regularized receiver function migration methods produce a multiple- suppressed image of the velocity discontinuity structure of the subsurface. Crustal thickness averages 44.1 +/- 2.3 km beneath the Great Plains (GP) and 45.6 +/- 1.1 km beneath the Colorado plateau (CP). Crustal thinning beneath the RGR is broadly symmetric about the rift axis, with the thinnest crust (35km) located directly beneath the rift axis, suggesting a pure shear stretched lithosphere beneath the RGR (figure 2). We observe a prominent northwest-dipping discontinuity, ranging from 65-85 km deep beneath the CP, and possible subcrustal discontinuities beneath the GP. These discontinuities, along with recent xenolith data, are consistent with preserved ancient lithospheric structures such as relict suture zones associated with Proterozoic subduction. An upper mantle discontinuity at 220-300 km depth may correlate with similar structure observed beneath eastern North America. Flat discontinuities at 410 and 660 km depth suggest that there is not a large-scale thermal anomaly beneath the RGR at these depths (Wilson et al., 2005b). Research supported by the NSF Geophysics program and Los Alamos IGPP; instruments and field support provided by IRIS PASSCAL.
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West, M., J. Ni, W.S. Baldridge, D. Wilson, R. Aster, W. Gao, and S. Grand, crust and upper mantle shear wave structure of the southwest of the southwest United States: Implications for rifting and support for high elevation. J. Geophys. Res. 109, doi: 101029/2003JB002575, 2004.
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Wilson, D., Aster, R., Imaging the seismic structure of the crust and upper mantle using regularized joint receiver functions, frequency-wave number filtering, and multimode Kirchhoff migration, J. Geophys. Res., in press, 2005.
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Wilson, D., Aster, R., West, M., Ni, J., Grand, S., Gao, W., Baldridge, W.S., Semken, S.,Lithospheric Structure of the Rio Grande Rift, Nature, 433, doi: 10.1038/nature03297, 2005a.
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Wilson, D., Aster, R., Ni, J., Grand, S., West, M., Gao, W., Baldridge, W.S., Semken, S., Imaging the seismic structure of the crust and upper mantle beneath the Great Plains, Rio Grande Rift, and Colorado Plateau, J. Geophys. Res., in press, 2005b.


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