{sup 40}Ar/{sup 39}Ar thermochronology and thermobarometry of metamorphism, plutonism, and tectonic denudation in the Old Woman Mountains area, California

Journal Article · Sat Feb 01 04:00:00 EST 1992 · Geological Society of America, Bulletin

DOI:https://doi.org/10.1130/0016-7606(1992)104<0176:AATATO>2.3.CO;2· OSTI ID:543081

Foster, D A ^[1]; Miller, C F ^[2]; Harrison, T M ^[3]; Hoisch, T D ^[4]

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1. State Univ. of New York, Albany, NY (United States)
2. Vanderbilt Univ., Nashville, TN (United States)
3. Univ. of California, Los Angeles, CA (United States)
4. Northern Arizona Univ., Flagstaff, AZ (United States)

Discrimination of individual tectonometamorphic events in polymetamorphosed terranes requires a comprehensive understanding of the relative timing and conditions of metamorphism and plutonism. We have applied a combination of {sup 40}Ar/{sup 39} Ar thermochronology, petrology, and thermobarometry to reconstruct the complex Early Proterozoic through early Cenozoic tectonic and metamorphic evolution of continental crust in the Old Woman Mountains area, southeastern California. Strong Mesozoic thermal events obscure the earlier history in much of the Old Woman Mountains area. In those areas where Early Proterozoic rocks underwent only lower-greenschist-facies metamorphism during the Mesozoic, thermobarometry of pelitic schists indicates that Proterozoic metamorphism occurred at 9 to 11 kbar and {approximately}700 {degrees}C. {sup 40}Ar/{sup 39}Ar ages of hornblende from samples of interbedded Proterozoic amphibolite indicate that this high-grade metamorphism took place before 1600 Ma. The relatively high-pressure conditions of Early Proterozoic metamorphism in the Old Woman Mountains area contrast with the low-pressure granulite-facies metamorphism that occurred elsewhere in the Mojave Desert at this time. {sup 40}Ar/{sup 39}Ar analyses of hornblende from Proterozoic rocks within Mesozoic shear zones and hornblende barometry from Jurassic intrusive rocks suggest that tectonism and burial of Paleozoic strata to >10 km began between 170 and 150 Ma. This tectonism resulted in regional greenschist-facies metamorphism. Late-stage mineral assemblages in Proterozoic and Paleozoic pelitic rocks in the Old Woman Mountains area indicate an increase in metamorphic grade from greenschist to upper amphibolite facies toward Later Cretaceous Plutons of the 73 Ma Old Woman-Piute batholith. Barometric calculations from garnet-bearing metamorphic rocks suggest that this Cretaceous metamorphism took place at 3.5 to 5.0 kbar in the Old Woman Mountains. 68 refs., 11 figs., 3 tabs.

• OSTI ID: 543081
• Journal Information: Geological Society of America, Bulletin, Journal Name: Geological Society of America, Bulletin Journal Issue: 2 Vol. 104; ISSN 0016-7606; ISSN BUGMAF
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
AGE ESTIMATION
ARGON 39
ARGON 40
BAROMETERS
CALIFORNIA
GEOTHERMOMETRY
METAMORPHIC ROCKS
METAMORPHISM
PLUTONIC ROCKS
TECTONICS