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Published September 21, 2007 | Supplemental Material + Published
Journal Article Open

Oxygen-isotope and trace element constraints on the origins of silica-rich melts in the subarc mantle


Peridotitic xenoliths in basaltic andesites from Batan island in the Luzon arc contain silica-rich (broadly dacitic) hydrous melt inclusions that were likely trapped when these rocks were within the upper mantle wedge underlying the arc. These melt inclusions have been previously interpreted to be slab-derived melts. We tested this hypothesis by analyzing the oxygen isotope compositions of these inclusions with an ion microprobe. The melt inclusions from Batan xenoliths have δ 18OVSMOW values of 6.45 ± 0.51‰. These values are consistent with the melts having been in oxygen isotope exchange equilibrium with average mantle peridotite at temperatures of ≥875°C. We suggest the δ 18O values of Batan inclusions, as well as their major and trace element compositions, can be explained if they are low-degree melts (or differentiation products of such melts) of peridotites in the mantle wedge that had previously undergone extensive melt extraction followed by metasomatism by small amounts (several percent or less) of slab-derived components. A model based on the trace element contents of Batan inclusions suggests that this metasomatic agent was an aqueous fluid extracted from subducted basalts and had many characteristics similar to slab-derived components of the sources of arc-related basalts at Batan and elsewhere. Batan inclusions bear similarities to "adakites," a class of arc-related lava widely considered to be slab-derived melts. Our results suggest the alternative interpretation that at least some adakite-like liquids might be generated from low-degree melting of metasomatized peridotites.

Additional Information

© 2007 American Geophysical Union. Received 9 October 2006; accepted 19 June 2007; published 21 September 2007. We thank Rene Maury for providing access to the sample examined in this study and for his help and guidance during the early stages of this work. This study benefited from financial support from NSF grant EAR-0337736 and a grant to J.M.E. from the Packard foundation. This work benefited from reviews by P. Kelemen, C. Macpherson, J. Ryan, and G. Gaetani. We thank G. Bebout and V. Salters for their work editing this paper. Auxiliary material for this article contains two sections: (1) the methods of standardization and raw data for ion microprobe analyses of oxygen isotope ratios in minerals and glasses examined in this study and (2) the distribution coefficients and source compositions used in trace element models.

Attached Files

Published - EILggg07.pdf

Supplemental Material - EILggg07.txt

Supplemental Material - EILggg07tableS1.txt

Supplemental Material - EILggg07tableS2.txt

Supplemental Material - EILggg07tableS3.txt

Supplemental Material - EILggg07tableS4.txt

Supplemental Material - EILggg07tableS5.txt

Supplemental Material - EILggg07tableS6.txt

Supplemental Material - EILggg07tableS7.txt

Supplemental Material - EILggg07tableS8.txt

Supplemental Material - EILggg07textS1.txt


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August 22, 2023
October 16, 2023