Publication Date:
2022-10-26
Description:
© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Le Roux, V., & Liang, Y. Ophiolitic pyroxenites record boninite percolation in subduction zone mantle. Minerals, 9(9), (2019): 565, doi: 10.3390/min9090565.
Description:
The peridotite section of supra-subduction zone ophiolites is often crosscut by pyroxenite veins, reflecting the variety of melts that percolate through the mantle wedge, react, and eventually crystallize in the shallow lithospheric mantle. Understanding the nature of parental melts and the timing of formation of these pyroxenites provides unique constraints on melt infiltration processes that may occur in active subduction zones. This study deciphers the processes of orthopyroxenite and clinopyroxenite formation in the Josephine ophiolite (USA), using new trace and major element analyses of pyroxenite minerals, closure temperatures, elemental profiles, diffusion modeling, and equilibrium melt calculations. We show that multiple melt percolation events are required to explain the variable chemistry of peridotite-hosted pyroxenite veins, consistent with previous observations in the xenolith record. We argue that the Josephine ophiolite evolved in conditions intermediate between back-arc and sub-arc. Clinopyroxenites formed at an early stage of ophiolite formation from percolation of high-Ca boninites. Several million years later, and shortly before exhumation, orthopyroxenites formed through remelting of the Josephine harzburgites through percolation of ultra-depleted low-Ca boninites. Thus, we support the hypothesis that multiple types of boninites can be created at different stages of arc formation and that ophiolitic pyroxenites uniquely record the timing of boninite percolation in subduction zone mantle.
Description:
This study was supported by National Science Foundation grants EAR-1220440 to V.L.R. and EAR-1624516 to Y.L. We thank the reviewers for their helpful suggestions, as well as Taylor Hough, Gretchen Swarr, Alberto Saal, Soumen Mallick, and Nilanjan Chatterjee for help with LA-ICP-MS and EPMA analyses, and Mark Kurz for help with sample collection.
Keywords:
Ophiolite
;
Boninite
;
Pyroxenite
;
Josephine peridotite
;
REE temperatures
;
Diffusion
;
Melt percolation
;
Subduction zones
Repository Name:
Woods Hole Open Access Server
Type:
Article
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