Mantle Evolution from Ocean to Arc: The Record in Spinel Peridotite Xenoliths in Mt. Pinatubo, Philippines

Betchaida Payot,Akihiro Tamura,Shoji Arai,Mitsuru Okuno,Masako Yoshikawa,Danikko Rivera

doi:10.3390/min8110515

Betchaida Payot, Akihiro Tamura + Show 4 more

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https://doi.org/10.3390/min8110515

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Abstract

A suite of peridotite xenoliths were collected from lahar flow deposits located close to the summit of Mt. Pinatubo. Spinel harzburgite is the most dominant lithology among dunites, pyroxenites and websterites. A rare spinel lherzolite xenolith (P12-7) is also present in this suite. The spinel lherzolite has well-preserved protogranular texture with very minimal presence of secondary amphibole, low Cr# in the chromian spinel, and depleted and hump shaped patterns of chondrite-normalized rare earth element (REE) patterns for the clinopyroxenes. In contrast, the spinel harzburgites contain abundant secondary amphiboles and orthopyroxenes, higher Cr# in the spinel, and slightly elevated patterns for the chondrite-normalized REE patterns for the amphiboles. The spinel lherzolite also exhibits higher olivine Fo content for a given spinel Cr# compared to the spinel harzburgites. The spinel lherzolite is interpreted as a typical residue from partial melting of abyssal peridotites whereas the spinel harzburgites may have formed via partial melting with subsequent modification during the influx of fluids in the mantle wedge. Our results suggest that fragments of MOR-derived lithosphere exist in the mantle wedge beneath the Philippine island arc. This work provides evidence for the conversion of abyssal to arc peridotites in the mantle wedge.

Highlights

Sandwiched between the overlying oceanic lithosphere and the subducting slab, the mantle wedge at a subduction zone is an important locus for magma generation
Though direct observation of the mantle wedge is not possible, information on the probable characteristics of the mantle wedge can be obtained from the mantle peridotites in obducted ophiolites [1,2,3], and xenoliths brought by arc lavas to the Earth’s surface [4,5,6]
Arai and others [11] argued that the wide variability of Cr# in detrital chromian spinels from the northern portion of the Oman Ophiolite implies generation of the mantle peridotites at a fast-spreading center

Summary

Introduction

Sandwiched between the overlying oceanic lithosphere and the subducting slab, the mantle wedge at a subduction zone is an important locus for magma generation. The nature of the mantle wedge remains to be poorly elucidated due to its location and depth. Mantle peridotites in ophiolites can be used to determine the tectonic setting in which the ophiolites were formed [7,8,9]. The mineral chemical variations in mantle peridotites of the Oman Ophiolite point to formation at a mid-oceanic ridge [10]. Arai and others [11] argued that the wide variability of Cr# in detrital chromian spinels from the northern portion of the Oman Ophiolite implies generation of the mantle peridotites at a fast-spreading center

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