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Boron depletion during progressive metamorphism: Implications for subduction processes

Authors :
Virginia B. Sisson
William P. Leeman
Ann E. Moran
Source :
Earth and Planetary Science Letters. 111:331-349
Publication Year :
1992
Publisher :
Elsevier BV, 1992.

Abstract

Systematic differences in trace element compositions of volcanic arc versus intraplate magmas are commonly attributed to involvement of subducted sediments and/or seawater-altered oceanic crust in arc magma genesis. The exact contributions from these materials is poorly understood. Metamorphic processes may significantly modify subducted oceanic slabs before they reach subarc depths. The nature and magnitude of such compositional modifications, as exemplified by the element boron, are investigated in metamorphic suites having protoliths analogous to subducted marine sediments and basalts. Our results indicate that in addition to protolith type, B content depends on metamorphic temperature. Greenschist and amphibolite facies metasediments generally have B contents at least a factor of two lower than in equivalent unmetamorphosed sediments. Moreover, four low-pressure pelitic to semipelitic metasediment suites display progressive loss of B with increasing peak metamorphic temperature (ca. 200–750°C). Metabasalts of greenschist and higher grades also have consistently lower B contents (

Details

ISSN :
0012821X
Volume :
111
Database :
OpenAIRE
Journal :
Earth and Planetary Science Letters
Accession number :
edsair.doi...........72baea6ff78a9013e9e7809715327b7b