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Late Cenozoic crustal extension and magmatism, southern Death Valley region, California

GSA Field Guides

By:
and
DOI: 10.1130/0-8137-0002-7.135

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Abstract

The late Cenozoic geologic history of the southern Death Valley region is characterized by coeval crustal extension and magamatism. Crustal extension is accommodated by numerous listric and planar normal faults as well as right- and left-lateral strike slip faults. The normal faults sip 30°-50° near the surface and flatten and merge leozoic miogeoclinal rocks; the strike-slip faults act as tear faults between crustal blocks that have extended at different times and at different rates. Crustal extension began 13.4-13.1 Ma and migrated northwestward with time; undeformed basalt flows and lacustrine deposits suggest that extension stopped in this region (but continued north of the Death Valley graben) between 5 and 7 Ma. Estimates of crustal extension in this region vary from 30-50 percent to more than 100 percent. Magmatic rocks syntectonic with crustal extension in the southern Death Valley region include 12.4-6.4 Ma granitic rocks as well as bimodal 14.0-4.0 Ma volcanic rocks. Geochemical and isotopic evidence suggest that the granitic rocks get younger and less alkalic from south to north; the volcanic rocks become more mafic with less evidence of crustal interaction as they get younger. The close spatial and temporal relation between crustal extension and magmatism suggest a genetic and probably a dynamic relation between these geologic processes. We propose a rectonic-magmatic model that requires heat to be transported into the crust by mantle-derived mafic magmas. These magmas pond at lithologic or rheologic boundaries, begin the crystallize, and partially melt the surrounding crustal rocks. With time, the thermally weakened crust is extended (given a regional extensional stress field) concurrent with granitic magmatism and bimodal volcanism.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Late Cenozoic crustal extension and magmatism, southern Death Valley region, California
Series title:
GSA Field Guides
DOI:
10.1130/0-8137-0002-7.135
Volume
2
Year Published:
2000
Language:
English
Publisher:
Geological Society of America
Contributing office(s):
Western Geographic Science Center
Description:
30 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
GSA Field Guides
First page:
135
Last page:
164
Number of Pages:
30
Country:
United States
State:
California
Other Geospatial:
Death Valley