Report

Melt Production Beneath Mt. Shasta from Boron Data in Primitive Melt Inclusions

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Science  13 Jul 2001:
Vol. 293, Issue 5528, pp. 281-283
DOI: 10.1126/science.1059663

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Abstract

Most arc magmas are thought to be generated by partial melting of the mantle wedge induced by infiltration of slab-derived fluids. However, partial melting of subducting oceanic crust has also been proposed to contribute to the melt generation process, especially when young and hot lithosphere is being subducted. The isotopic composition of boron measured in situ in olivine-hosted primitive melt inclusions in a basaltic andesite from Mt. Shasta, California, is characterized by large negative values that are also highly variable (δ11B = –21.3 to –0.9 per mil). The boron concentrations, from 0.7 to 1.6 parts per million, are lower than in most other arc lavas. The relation between concentration and isotopic composition of boron observed here supports a hypothesis that materials left after dehydration of the subducting slab may have contributed to the generation of basaltic andesite lavas at Mt. Shasta.

  • * Present address: Institute for Study of the Earth's Interior–PML, Okayama University at Misasa, Tottori-ken, 682-0193, Japan.

  • To whom correspondence should be addressed. E-mail: erose{at}pheasant.misasa.okayama-u.ac.jp

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