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Supracrustal input to magmas in the deep crust of Sierra Nevada batholith: Evidence from high-δ^(18)O zircon

Lackey, Jade Star and Valley, John W. and Saleeby, Jason B. (2005) Supracrustal input to magmas in the deep crust of Sierra Nevada batholith: Evidence from high-δ^(18)O zircon. Earth and Planetary Science Letters, 235 (1-2). pp. 315-330. ISSN 0012-821X.

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Oxygen isotope ratios of zircon (Zc) from intrusives exposed in the Tehachapi Mountains, southern California, reveal large inputs of high-δ^(18)O supracrustal contaminant into gabbroic and tonalitic magmas deep (> 30 km) in the Cretaceous Sierra Nevada batholith. High δ^(18)O(Zc) values (7.8 ± 0.7‰) predominate in the deep parts of the batholith, but lower values (6.1 ± 0.9‰) occur in shallower parts. This indicates a larger gradient in δ^(18)O with depth in the batholith than occurs from west to east across it. Oxygen, Sr, and Nd isotope data show that the supracrustal contaminant was likely young (Paleozoic or Mesozoic), hydrothermally altered upper oceanic crust or volcanic arc sediments. Such rocks were subducted or underthrust beneath the Sierran arc during accretion of oceanic terranes onto North America. This component yielded high-δ^(18)O magmas that were added to the base of the batholith. On average, gabbros in the southern Sierra contain at least 18% of the subducted supracrustal component. Some tonalite and granodiorite magmas were additionally contaminated by Kings Sequence metasedimentary rocks, as evidenced by δ^(18)O(Zc) and initial ^(87)Sr/^(86)Sr that trend toward values measured for the Kings Sequence. Besides high δ^(18)O values in the southern Sierra, xenoliths in the central Sierra also have elevated δ^(18)O, which confirms the widespread abundance of supracrustal material in the sub-arc lithospheric mantle. In contrast to δ^(18)O(Zc), whole rock δ^(18)O values of many samples have undergone post-magmatic alteration that obscures the magmatic contamination history of those rocks. Such alteration previously prevented confident determination of the mass of young, hydrothermally altered mantle rocks that contributed to Sierran granitoids.

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Additional Information:© 2005 Elsevier B.V. Received 26 October 2004; received in revised form 24; January 2005; accepted 4 April 2005; Available online 1 June 2005. This study was supported by DOE 93ER14389, NSF EAR99-02973, and EAR02-07340 to JWV, and EAR 98-15024 to JBS. A Dean Morgridge Distinguished Graduate Fellowship (JSL) supported portions of this work. We thank Mike Spicuzza, for assistance with stable isotope analysis. Reviews by Allen Glazner, Calvin Miller, Ilya Bindeman and Cory Clechenko improved early versions of this paper. We thank Jay Ague and George Bergantz for journal reviews that helped us enhance the overall quality of paper.
Funding AgencyGrant Number
Department of Energy (DOE)93ER14389
NSFEAR 98-15024
Dean Morgridge Distinguished Graduate FellowshipUNSPECIFIED
Subject Keywords:oxygen isotopes; zircon; granitoids; alteration; Sierra Nevada; Tehachapi Mountains
Issue or Number:1-2
Record Number:CaltechAUTHORS:20130508-082324118
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Official Citation:Jade Star Lackey, John W. Valley, Jason B. Saleeby, Supracrustal input to magmas in the deep crust of Sierra Nevada batholith: Evidence from high-δ18O zircon, Earth and Planetary Science Letters, Volume 235, Issues 1–2, 30 June 2005, Pages 315-330, ISSN 0012-821X, 10.1016/j.epsl.2005.04.003.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38341
Deposited By: Tony Diaz
Deposited On:14 May 2013 23:28
Last Modified:03 Oct 2019 04:56

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