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Journal of Petrology Advance Access originally published online on June 19, 2008
Journal of Petrology 2008 49(7):1397-1426; doi:10.1093/petrology/egn030
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Dynamic Magma Systems, Crustal Recycling, and Alteration in the Central Sierra Nevada Batholith: the Oxygen Isotope Record

Jade Star Lackey1,*, John W. Valley2, James H. Chen3 and Daniel F. Stockli4

1Geology Department, Pomona College, Claremont, CA 91711, USA
2Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706, USA
3Science Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
4Department of Geology, University of Kansas, Lawrence, KS 66045, USA

RECEIVED JANUARY 6, 2007; ACCEPTED MAY 27, 2008


  Abstract

Values of {delta}18O of zircon from the central Sierra Nevada batholith (SNB), California, yield fresh insight into the magmatic evolution and alteration history of this classic convergent margin batholith. Direct comparison of whole-rock and zircon (Zrc) {delta}18O provides evidence for modest (0.5{per thousand}), but widespread, alteration, which has complicated interpretation in previous whole-rock {delta}18O studies. Four discrete belts of {delta}18O values are recognized in the central Sierra. A small belt of plutons with relatively low {delta}18O(Zrc) values (5·2–6·0{per thousand}) intrudes the foothills, with a sharp increase of {delta}18O revealing the concealed Foothills Suture; high {delta}18O(Zrc) values (7·0–8·5{per thousand}) dominate the rest of the western SNB. East of the axis of the Sierra, {delta}18O is distinctly lower (6·75–5·75{per thousand}), and decreases monotonically to the Sierra Crest. A sharp 1{per thousand} increase of {delta}18O in the eastern Sierra reveals a second crustal boundary, with the fourth belt hosted in high-{delta}18O North American crust in the White Mountains and Owens and Long Valleys. Correlated O, Sr, and Pb isotope ratios reveal differences in magma generation between the western and eastern Sierra. The western Sierra experienced massive crustal recycling, with substantial melting and mobilization of accreted oceanic and volcanic arc rocks; crustal contamination affects many western SNB plutons. In contrast, the eastern Sierra was dominated by voluminous recycling of the lithospheric mantle and lower crust, with minimal crustal contamination. Batholith-wide shifts in {delta}18O occur between pulses of Cretaceous magmatism that may be linked to tectonic reorganizations of magma sources. Within intrusive suites, {delta}18O may be unchanged (Tuolumne); increase (Sonora and Whitney); or decrease (Sequoia and John Muir) with time. These trends show stable long-lived sources, or those where recycling and contamination may increase or decrease with time. Overall, {delta}18O reveals diverse magma system behavior at a range of scales in the Sierran arc.

KEY WORDS: zircon; crustal growth; granitoids; supracrustal; magma systems; Sierra Nevada

*Corresponding author. Telephone: (909) 621-8677. Fax: (909) 621-8552. E-mail: JadeStar.Lackey{at}pomona.edu


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