Journal of Petrology Advance Access originally published online on October 3, 2007
Journal of Petrology 2007 48(11):2063-2091; doi:10.1093/petrology/egm050
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Development of a Continental Volcanic Field: Petrogenesis of Pre-caldera Intermediate and Silicic Rocks and Origin of the Bandelier Magmas, Jemez Mountains (New Mexico, USA)
1Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712, USA
2Department of Geology, Washington State University, Pullman, WA 99164, USA
3Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
4Department of Geological Sciences, Central Washington University, Ellensburg, WA 98926, USA
5Department of Geological and Environmental Sciences, California State University, Chico, CA 95929, USA
6310 Garver Lane, White Rock, NM 87544, USA
RECEIVED JANUARY 20, 2006; ACCEPTED AUGUST 3, 2007
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Abstract |
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The Miocene–Quaternary Jemez Mountains volcanic field (JMVF) is the site of the Valles caldera and associated Bandelier Tuff. Caldera formation was preceded by > 10 Myr of volcanism dominated by intermediate composition rocks (57–70% SiO2) that contain components derived from the lithospheric mantle and Precambrian crust. Simple mixing between crust-dominated silicic melts and mantle-dominated mafic magmas, fractional crystallization, and assimilation accompanied by fractional crystallization are the principal mechanisms involved in the production of these intermediate lavas. A variety of isotopically distinct crustal sources were involved in magmatism between 13 and 6 Ma, but only one type (or two very similar types) of crust between 6 and 2 Ma. This long history constitutes a record of accommodation of mantle-derived magma in the crust by melting of country rock. The post-2 Ma Bandelier Tuff and associated rhyolites were, in contrast, generated by melting of hybridized crust in the form of buried, warm intrusive rocks associated with pre-6 Ma activity. Major shifts in the location, style and geochemical character of magmatism in the JMVF occur within a few million years after volcanic maxima and may correspond to pooling of magma at a new location in the crust following solidification of earlier magma chambers that acted as traps for basaltic replenishment.
KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements
*Corresponding author. Telephone: 1-512-471-8054. Fax: 1-512-471-9425. E-mail: rowem{at}mail.utexas.edu