Two distinct episodes of Cenozoic extension in the northern Basin and Range Province, as indicated by magmatic and structural characteristics
- Geological Survey, Menlo Park, CA (United States)
Although some workers in the central and southern Great Basin, Nevada and Utah, hold that Cenozoic crustal extension took place as a single, protracted episode that continues today, many studies indicate that two episodes took place. The distinction between episodes is especially clear in the northeastern Great Basin, where initial extension took place about 40--36 Ma, and extension was renewed from about 18 Ma to present. It appears that the early episode of extension was characterized by WSW hyperextension in north-trending linear zones, now about 130 km apart. Extension took place at the time of voluminous calc-alkaline intermediate to felsic magmatism, but magmatism was regional and not limited to the zones of extension. The first episode began later to the south, paralleling the southward progression of Great Basin magmatism as well as arc magmatism near the west coast. Later extension (Basin and Range sensu stricto) was WNW-directed and was initiated between 17 and 13 Ma region wide; it was accompanied by fundamentally basaltic magmatism throughout the region. Striking differences between the two extensional episodes indicates fundamentally different causes. Extensional zones of the early event were not localized by formerly thickened lithosphere, but rather appear to represent a periodic instability with characteristic wavelength of 80--100 km. The Basin and Range event was initiated during reorganization of the former subduction zone at the North American margin into lengthy transform margin, and coincided with the start of the eastern Snake River and Rio Grande rifts. Magmatism involved the crust less than in the early event.
- OSTI ID:
- 5021367
- 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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