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Cocorp Seismic Reflection Studies of the Rio Grande Rift

2011; American Geophysical Union; Linguagem: Inglês

10.1029/sp014p0169

2771-6929

L. D. Brown, Peter A. Krumhansl, Charles E. Chapin, Allan R. Sanford, Frederick A. Cook, S. Kaufman, Jack Oliver, F. Steve Schilt,

High-pressure geophysics and materials

Major buried intragraben horsts, large intrusive bodies, deformed metamorphic terrains, the crust-mantle boundary, and a midcrustal zone of magma accumulation are among the geological features apparently resolved by seismic reflection profiling in the Rio Grande rift carried out by the Consortium for Continental Reflection Profiling (COCORP). As part of its program to apply advanced, multichannel seismic reflection techniques to the study of major geological problems of the continental crust, COCORP collected 155 km of 24-fold reflection data near Socorro, New Mexico, in 1975 and 1976, including an 80-km traverse across the rift from the Sierra Lucero on the west to the Manzano Mountains on the east. Stacked reflection sections indicate coherent reflected energy from depths of at least 35 km. From these results the Precambrian basement within the rift is seen to be pervasively disrupted by high-angle normal faults, resulting in substantial buried topography. A major buried horst was discovered in the southwestern part of the Albuquerque Basin, probably correlative with the nearby Sierra Ladron block. The western rift boundary is defined by a reflector dipping eastward at a moderate angle (∼40° ) which intersects the surface at the western edge of the Monte Largo embayment. The eastern rift boundary is associated with a high angle, linear (planar ?) zone defined by lack of coherent reflections and extending to the base of the crust. The basement within the rift is characterized by seismically transparent zones devoid of coherent energy, possibly homogeneous plutons, and zones dominated by numerous short (less than 5 km), discontinuous reflector segments. The latter suggest considerable disruption of structural coherence such as might be expected in a deformed metamorphic terrain. At midcrustal depths a strong, complex P-wave reflector corresponds in depth and dip with a previously inferred magma body. Synthetic seismograms and spectral studies indicate that the observed waveforms are consistent with, but not unique to, models of low velocity partially molten material within the crust. The seismic sections show a complex intermittent zone of layered reflection bands at the base of the crust rather than the simple Moho model often inferred from refraction results. The structural variations in the crust mapped by COCORP reflection profiling may have played an important role in the development and subsequent evolution of the Rio Grande rift.