Geophysical indicators of magmatism and tectonism in the Basin and Range
- Geological Survey, Menlo Park, CA (United States)
Recent seismic measurements provide a wealth of clues about Basin and Range magmatism and tectonism. There are clear differences in the crustal velocity structure and the thickness of the crust east and west of the .706 line in Northern Nevada. Whereas uppermost-crustal layers dip to the west near the area of the 706 line, the deeper crustal layers dip to the east. However, it is difficult to determine if the easterly dip of the deeper layers is a result of extension or accretion. In specific regions of the Basin and Range, there is evidence that the lowermost five kilometers of the crust have been magmatically added to the pre-existing crust. In other regions, there appear to be no magmatic additions, and the crustal structure is like that of normal continental crust. Locally, the apparent lower-crustal magmatic additions are thickest beneath areas that show evidence of intense faulting and these areas are also overlain by Tertiary volcanic rocks at the surface. The regional coincidence of the apparent deep magmatics, observed faulting, and surface volcanics suggests that upper-mantle magmas are transported to the surface through the intensity faulted zones. This relation among volcanics, deep magmas, and faulting lends support to the hypothesis that pure shear is the dominant mode of extension. Paleomagnetic measurements have detected large amounts of rotation in parts of the Basin and Range. The calculated rotations and the observed crustal structure suggest that much of the Basin and Range extension may be related to rotation of large blocks of crust.
- OSTI ID:
- 5342549
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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