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Andradite skarn garnet records of exceptionally low δ^(18)O values within an Early Cretaceous hydrothermal system, Sierra Nevada, CA

Ryan-Davis, J. and Lackey, J. S. and Gevedon, M. and Barnes, J. D. and Lee, C-T. A. and Kitajima, K. and Valley, J. W. (2019) Andradite skarn garnet records of exceptionally low δ^(18)O values within an Early Cretaceous hydrothermal system, Sierra Nevada, CA. Contributions to Mineralogy and Petrology, 174 (8). Art. No. 68. ISSN 0010-7999. doi:10.1007/s00410-019-1602-6.

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Skarn garnets in the Mineral King roof pendant of the south–central Sierra Nevada within Sequoia National Park, California, USA reveal variable fluid chemistry with a significant component of meteoric water during metasomatism in the Early Cretaceous Sierra Nevada Batholith. We focus on andradite garnet associated with Pb–Zn mineralization in the White Chief Mine. Laser fluorination oxygen isotope analyses of δ^(18)O of garnet (δ^(18)O(Grt)) from sites along the skarn show a large range of values (− 8.8 to + 4.6‰ VSMOW). Ion microprobe (SIMS) analyses elucidate that individual andradite crystals are strongly zoned in δ^(18)O(Grt) (up to 7‰ of variation). Total rare-earth element concentrations (∑REE) across individual garnets show progressive depletion of skarn-forming fluids in these elements during garnet growth. These findings support a skarn model of earliest red high-δ^(18)O grandite garnet consistent with a magmatic-dominated equilibrium fluid (δ^(18)O(H_2O) as high as ≈ + 8‰). Later, green andradite crystallized in equilibrium with a low-δ^(18)O fluid indicating a significant influx of meteoric fluid (δ^(18)O(H_2O) ≈ − 6 to − 5‰), following a hiatus in garnet growth, associated with late-stage Pb–Zn mineralization. Latest orange overprint rims have higher δ^(18)O values (δ^(18)O(H_2O) ≈ 0–2‰), and depleted total REEs, suggesting influx of high-δ^(18)O, trace-element depleted fluid derived from regional metamorphism of the carbonate host. Remarkably, low δ^(18)O(Grt) values in the White Chief canyon skarn require a significant proportion of meteoric fluid available during > 400 °C andradite-forming metasomatism. Fluid flow was channelized at the pluton–wallrock contact, evidenced by the narrow extent of skarn.

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Ryan-Davis, J.0000-0001-7048-5937
Alternate Title:Andradite skarn garnet records of exceptionally low δ18O values within an Early Cretaceous hydrothermal system, Sierra Nevada, CA
Additional Information:© 2019 Springer-Verlag GmbH Germany, part of Springer Nature. Received: 2 March 2019; Accepted: 12 July 2019; First Online: 29 July 2019. We thank two anonymous reviewers and Executive Editor O. Müntener for their helpful comments that clarified the manuscript. We thank K. Nydick and G. Bradshaw for assistance with permitting for field work in Sequoia National Park, F. Kyte for assistance on the UCLA electron microprobe, N. Kita, J. Kern and R. Havranek for assistance in the WiscSIMS lab. M. Spicuzza (Wisconsin) and T. Larson (Texas) helped in the LF-IRMS isotope labs. T. Sisson and D. John at the USGS are acknowledged for thoughtful discussions. This work was supported by NSF—OCE-1338842 awarded to Lee, Lackey, Barnes and others as part of the Frontiers in Earth Systems Dynamics program. J. Valley is supported by NSF (EAR-1524336). The WiscSIMS ion microprobe laboratory is supported by the National Science Foundation (EAR-1355590, -1658823) and by the University of Wisconsin–Madison.
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University of Wisconsin-MadisonUNSPECIFIED
Subject Keywords:Skarn; Garnet; Oxygen isotope; Fluid flow; Arc magmatism
Issue or Number:8
Record Number:CaltechAUTHORS:20190729-150159823
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Official Citation:Ryan-Davis, J., Lackey, J.S., Gevedon, M. et al. Contrib Mineral Petrol (2019) 174: 68.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97493
Deposited By: Tony Diaz
Deposited On:30 Jul 2019 15:57
Last Modified:16 Nov 2021 17:32

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