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Hydrous, Low-carbon Melting of Garnet Peridotite

Balta, Brian J. and Mosenfelder, Jed L. and Asimow, Paul D. (2011) Hydrous, Low-carbon Melting of Garnet Peridotite. Journal of Petrology, 52 (11). pp. 2079-2105. ISSN 0022-3530.

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The presence of volatile species in the Earth's upper mantle drives the formation of low-degree melts at pressures and temperatures at which volatile-free mantle rocks would be subsolidus. The two most abundant volatile species, given the oxidation state of the Earth's upper mantle, are carbon dioxide and water; each species has a distinct effect on the melting process. We present experimental melting results from 3 GPa and 1375°C on hydrous systems with controlled water contents and rigorously minimized carbon contamination that constrain the independent effects of these volatiles. The hydrous melts in these experiments are in equilibrium with garnet peridotite at pressures reasonable for hydrous melting under mid-ocean ridges. Compared with anhydrous experiments or carbon-rich silicate melting, the addition of water produces a melt with increased SiO_2 content relative to MgO and FeO, tantamount to an increase in the stability of olivine at the solidus relative to the other crystalline phases. We also report a substantial and unexpected change in the composition of clinopyroxene in equilibrium with the melt; the clinopyroxene stability field contracts when water is added to the system, producing clinopyroxenes with higher CaO and lower Al_2O_3 than found at the same pressure without water. The contraction of the clinopyroxene field decreases the bulk partition coefficients of TiO_2, Na_2O, heavy rare earth elements, U, and H_2O, with important implications for hydrous melting of the mantle; for example, initiating hydrous melting deeper in the garnet lherzolite stability field.

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Asimow, Paul D.0000-0001-6025-8925
Additional Information:© 2011 The Author. Published by Oxford University Press. Received June 25, 2010. Accepted July 26, 2011. First published online: August 25, 2011. This work benefited from many enlightening discussions with Sally Newman, George Rossman, Mark Hirschmann, Liz Miura, Ma Chi, and Mike Baker. The authors would like to thank Alex Sessions and Magnus Eek for the use of their Elemental Analyzer, Ed Stolper and John Beckett for the use of their 1atm furnaces, and Claude Herzberg and George Rossman for supplying starting materials. This paper was significantly improved by reviews from Trevor Falloon, Glenn Gaetani, Rajdeep Dasgupta, and Othmar Müntener. This work was supported by the National Science Foundation Ocean Sciences Marine Geology and Geophysics program, grant numbers OCE-0241716 and OCE-0550216.
Funding AgencyGrant Number
NSF Ocean Sciences Marine Geology and Geophysics programOCE-0241716
NSF Ocean Sciences Marine Geology and Geophysics programOCE-0550216
Subject Keywords:mantle; peridotite melting; volatiles; water
Issue or Number:11
Record Number:CaltechAUTHORS:20111128-103324923
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Official Citation: J. Brian Balta, Paul D. Asimow, and Jed L. Mosenfelder Hydrous, Low-carbon Melting of Garnet Peridotite J. Petrology (2011) 52(11): 2079-2105 first published online August 25, 2011 doi:10.1093/petrology/egr040
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:27970
Deposited By: Ruth Sustaita
Deposited On:28 Nov 2011 18:53
Last Modified:03 Oct 2019 03:27

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