Cocorp Seismic Traverse Across the Rio Grande Rift
L.D. Brown, S. Kaufman, J.E. Oliver, 1983. "Cocorp Seismic Traverse Across the Rio Grande Rift", Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces, A. W. Bally
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COCORP's deep seismic reflection surveys in the Rio Grande Rift of central New Mexico consist of six lines recorded in 1975 and 1976 (Figure 1). Two of these, lines 1 and 1A, constitute an east-west traverse across the southern end of the Albuquerque-Belen basin. Although collected during an early stage of the COCORP program when economic constraints limited the amount of 3D control which could be obtained and data processing was less intensive, these seismic sections clearly map substantial buried structural relief, with the Albuquerque basin separated into two subgrabens by a central buried horst. Normal faulting in the eastern part of the rift may have been influenced by pre-existing Laramide thrust faults. Perhaps the most unique feature of these deep seismic data is evidence of an unusually strong mid-crustal reflection which is interpreted to correspond to an active magma body. This deep magma appears to have accumulated as series of sills beneath a mid-crustal barrier. The following summary is abstracted from a fuller discussion of the COCORP New Mexico results reported by Brown et al (1980).
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Seismic Expression of Structural Styles: A Picture and Work Atlas. Volume 1–The Layered Earth, Volume 2–Tectonics Of Extensional Provinces, & Volume 3–Tectonics Of Compressional Provinces
Until a few decades ago, structural and regional geology were traditionally the preserve of field geologists. They usually mapped areas of outcropping deformed rocks and supplemented their work by laboratory studies of rock deformation and by theoretical work. Structural geology became tied to the geology of uplifts, folded belts, and underground mines, all of which were accessible to direct observation. Since World War II we have witnessed a tremendous development of geophysics in oceanography and in petroleum geology. Academic geophysicists in oceanography led their geological colleagues into modern plate tectonics and industry geophysicists developed reflection seismology into a superb structural mapping tool that penetrated the subsurface.
Today we are facing a situation where instruction and textbooks in structural geology are almost entirely dedicated to rock deformation, analytical techniques in detailed field geology and summaries of plate tectonics. Illustrations based on reflection seismic profiles are virtually absent in textbooks of structural geology. These texts illustrate only the parts of the proverbial elephant, together with some conjecture, but without ever offering a glimpse of the whole elephant.
Some of the reason cited for the relative scarcity of published reflection profiles are: 1) the confidentiality of exploration data; 2) difficulties in the photographic reduction and reproduction of seismic profiles for a book format; 3) the two-dimensional nature of vertical reflection profiles; and 4) the obvious distortions in reflection profiles that are typically recorded in time.
The AAPG leadership felt that it was time to attempt to correct the situation and to produce this picture and work atlas. The first volumes, of what may become a series of volumes, are addressing an audience that includes: petroleum geologists concerned with structural interpretations; exploration companies that provide in-house training; the AAPG continuing education program; and academic colleagues interested in updating their curricula in structural geology by inclusion of reflection profiles from the “real world” in their teaching.
The atlas is not meant to be a textbook in reflection seismology (instead we listed some at the end of this introduction) nor a text in structural and/or regional geology. Our intent is simply to provide a teaching tool.