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Coexisting serpentine and quartz from carbonate-bearing serpentinized peridotite in the Samail Ophiolite, Oman

Streit, Elisabeth and Kelemen, Peter and Eiler, John (2012) Coexisting serpentine and quartz from carbonate-bearing serpentinized peridotite in the Samail Ophiolite, Oman. Contributions to Mineralogy and Petrology, 164 (5). pp. 821-837. ISSN 0010-7999. doi:10.1007/s00410-012-0775-z.

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Tectonically exposed mantle peridotite in the Oman Ophiolite is variably serpentinized and carbonated. Networks of young carbonate veins are prevalent in highly serpentinized peridotite, particularly near low-temperature alkaline springs emanating from the peridotite. An unusual feature in some samples is the coexistence of serpentine and quartz, which is not commonly observed in serpentinites. This assemblage is unstable with respect to serpentine + talc or talc + quartz under most conditions. Serpentine in the carbonated serpentinites in this study is more iron rich than in most serpentinites reported in previous studies, and samples with co-existing quartz contain the most iron-rich serpentines. Calculations of thermodynamic equilibria in the MgO–SiO_2–H_2O–CO_2 system suggest that serpentine + quartz may be a stable assemblage at low temperatures (e.g., <~15–50 °C) and is stabilized to higher temperatures by preferential cation substitutions in serpentine over talc. Based on these calculations, serpentine + quartz assemblages could result from serpentinization at near-surface temperatures. Clumped isotope thermometry of carbonate veins yields temperatures within error of the observed temperatures in Oman groundwater for all samples analyzed, while the δ^(18)O of water calculated to be in equilibrium with carbonate precipitated at those temperatures is within error of the observed isotopic composition of Oman groundwater for the majority of samples analyzed. As groundwater geochemistry suggests that carbonate precipitation and serpentinization occur concomitantly, this indicates that both hydration and carbonation of peridotite are able to produce extensive alteration at the relatively low temperatures of the near-surface weathering environment.

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Additional Information:© 2012 Springer-Verlag. Received: 14 November 2011; Accepted: 24 May 2012; Published online: 17 June 2012. Many thanks are owed to everyone at the Geological Survey of Oman and the Directorate General of Minerals in the Ministry of Commerce and Industry, Sultanate of Oman, particularly H. Al-Azri, A. Al-Rajhi, and S. Al-Busaidi. We also extend our thanks to B. Evans for insightful comments, advice, and generosity; to J. Matter, A. Paukert, and E. Mervine for their collaboration in the field and in scientific discussions; to N. Kitchen, M. Bonifacie, K. Bergmann, and others at the laboratories for stable isotope geochemistry at Caltech for assistance with clumped isotope analysis; and to C. Mandeville, J. Bosenberg, B. Goldoff, and others at AMNH for assistance with electron microprobe analysis. This manuscript benefited greatly from the thoughtful comments and suggestions of Othmar Muntener and an anonymous reviewer. This material is based upon work supported by the National Science Foundation, through a Graduate Research Fellowship to E. Streit under Grant No. DGE-0707425 and through a research grant to P. Kelemen under Grant No. EAR-1049905, and by a Columbia Initiative in Science and Engineering Grant to P. Kelemen and J. Matter.
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-0707425
NSF Graduate Research FellowshipEAR-1049905
Columbia Initiative in Science and Engineering GrantUNSPECIFIED
Subject Keywords:Serpentinization; Carbonation; Alteration; Peridotite; Oman; Ophiolite; Clumped isotopes
Issue or Number:5
Record Number:CaltechAUTHORS:20121115-100217914
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35480
Deposited By: Tony Diaz
Deposited On:20 Nov 2012 21:11
Last Modified:09 Nov 2021 23:15

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