Magma accumulation rates and thermal histories of plutons of the Sierra Nevada batholith,CA |
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| Authors: | Jesse W Davis Drew S Coleman John T Gracely Richard Gaschnig Michael Stearns |
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| Institution: | (1) Department of Geological Sciences, University of North Carolina at Chapel Hill, 104 South Road, Mitchell Hall, Chapel Hill, NC 27599, USA;(2) ExxonMobil Exploration Company, P.O. Box 4778, Houston, TX 77060, USA;(3) School of Earth and Environmental Sciences, Washington State University, Webster Physical Science Building, Pullman, WA 99164, USA;(4) Department of Earth Science, University of California, Webb Hall, Santa Barbara, CA 93106, USA;(5) Present address: ExxonMobil Production Company, 396 West Greens Road, Houston, TX 77067, USA |
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| Abstract: | Zircon U–Pb geochronology results indicate that the John Muir Intrusive Suite of the central Sierra Nevada batholith, California,
was assembled over a period of at least 12 Ma between 96 and 84 Ma. Bulk mineral thermochronology (U–Pb zircon and titanite,
40Ar/39Ar hornblende and biotite) of rocks from multiple plutons comprising the Muir suite indicates rapid cooling through titanite
and hornblende closure following intrusion and subsequent slow cooling through biotite closure. Assembly of intrusive suites
in the Sierra Nevada and elsewhere over millions of years favors growth by incremental intrusion. Estimated long-term pluton
assembly rates for the John Muir Intrusive Suite are on the order of 0.001 km3 a−1 which is inconsistent with the rapid magma fluxes that are necessary to form large-volume magma chambers capable of producing
caldera-forming eruptions. If large shallow crustal magma chambers do not typically develop during assembly of large zoned
intrusive suites, it is doubtful that the intrusive suites represent cumulates left behind following caldera-forming eruptions. |
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