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Effect of H_2O on Liquidus Relationships in MgO-Al_2O_3-SiO_2 at 30 Kilobars

Sekine, Toshimori and Wyllie, Peter J. (1983) Effect of H_2O on Liquidus Relationships in MgO-Al_2O_3-SiO_2 at 30 Kilobars. Journal of Geology, 91 (2). pp. 195-210. ISSN 0022-1376. doi:10.1086/628756.

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Dehydrated gels with compositions corresponding to mixtures of pyrope-enstatite, pyrope-quartz, and pyrope-quartz-corundum were sealed in platinum capsules and reacted in half-inch piston-cylinder apparatus at 30 kbar. Samples were pyrope composition with variable H_2O, and other compositions with 7.5 wt % H_2O. Highly aluminous metastable orthopyroxenes nucleated from and persisted in mixtures with compositions near pyrope. There is no univariant fusion curve for pyrope-H_2O. Pyrope dissolves incongruently in H_2O subsolidus, and a trace of liquid is produced near 1000°C. A univariant reaction: pyrope + forsterite + vapor = spinel + liquid was located at 1150 ± 20° C. The liquidus for pyrope with excess H_2O is at 1310°C. Orthopyroxenes coexisting with SiO_2-rich liquids contain 0.8-5.7% excess SiO_2 compared with MgSiO_3-Al_2O_3. Liquidus diagrams dry, with 7.5% H_2O, and with excess H_2O illustrate the effect of H_2O on the liquidus relationships. With increasing H_2O: the liquidus volume for Opx expands greatly at the expense of that for Qz, and slightly at the expense of Py; the volume for Fo expands significantly at the expense of that for Opx, and slightly at the expense of Py; liquid coexisting with Fo + Opx + Py is enriched in SiO_2 and Al_2O_3; liquid coexisting with Opx + Py + Qz is enriched greatly in SiO_2 and slightly in Al_2O_3; the range of liquid compositions coexisting with Opx + Py is greatly increased toward enrichment in SiO_2. These results provide boundaries for corresponding phase relationships in CaO-MgO-Al_2O_3-SiO_2-H_2O with applications to the effect of H_2O on partial fusion of subducted oceanic crust (quartz eclogite) and mantle peridotite.

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Alternate Title:Effect of H2O on Liquidus Relationships in MgO-Al2O3-SiO2 at 30 Kilobars
Additional Information:© 1983 University of Chicago Press. Manuscript received September 30, 1982; revised November 29, 1982. This research was supported by the Earth Sciences Section of the National Science Foundation, NSF Grants EAR 8108626 and EAR 8206178. We thank R. C. Newton for discussion and insights about metastable aluminous orthopyroxenes, and S. A. Morse for critical review.
Funding AgencyGrant Number
NSFEAR 8108626
NSFEAR 8206178
Issue or Number:2
Record Number:CaltechAUTHORS:20160217-113539998
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Official Citation:Toshimori Sekine , and Peter J. Wyllie . "Effect of H2O on Liquidus Relationships in MgO-Al2O3-SiO2 at 30 Kilobars." The Journal of Geology 1983; 91(2), 195-210. DOI: 10.1086/628756
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64538
Deposited By: Tony Diaz
Deposited On:19 Feb 2016 19:15
Last Modified:10 Nov 2021 23:32

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