TY - JOUR

T1 - AMPHIBOLE IN ULTRA-DEPLETED PERIDOTITES FROM THE HOROKANAI OPHIOLITE, HOKKAIDO, JAPAN

T2 - BONINITE MELT TRAPPED IN THE MANTLE WEDGE

AU - Tamura, Akihiro

AU - Nishio, Ikuya

AU - Iwata, Yuya

AU - Arai, Shoji

AU - Morishita, Tomoaki

N1 - Publisher Copyright: © 2024, Edizioni ETS. All rights reserved.

PY - 2024

Y1 - 2024

N2 - Ultra-depleted peridotites have been reported from the mantle sections of a number of ophiolitic complexes (e.g., Papua New Guinea and New Caledo-nia). Such rocks are residues derived from boninitic melts in supra-subduction zones, particularly in forearcs. In the mantle wedge, slab-derived fluid-melt containing H2O increases the degree of melting and metasomatizes the peridotites. However, the relationship between high-degree melting under hydrous conditions and metasomatism is not well understood. In this paper, we report petrological features of amphibole-bearing ultra-depleted peridotites from the Horokanai ophiolite, Hokkaido, Japan. The peridotite complex in the Horokanai ophiolite consists of clinopyroxene-free harzburgite, orthopyroxene-poor harzburgite, and dunite. The harzburgites contain high-Cr# spinel (0.70-0.85) and orthopyroxene with very low abundances of incompatible elements (e.g., Y < 0.01 µg/g; Ti ~ 2 µg/g). Pargasitic-edenitic amphibole occurs as spinel-hosted inclusions and as an interstitial phase to olivine and orthopyroxene. The harzburgite is a residue formed by the high-degree melting caused by fluid flux. The hydrous conditions cause incongruent melting of orthopyroxene, producing a depleted Si-rich melt (i.e., a boninitic melt). Because such Si-rich melt can coexist with Cr-rich spinel under these conditions, amphibole is ultimately crystallized in the harzburgite. Such amphibole formation is important in producing secondary sodic amphibole during alteration of ultra-depleted peridotites.

AB - Ultra-depleted peridotites have been reported from the mantle sections of a number of ophiolitic complexes (e.g., Papua New Guinea and New Caledo-nia). Such rocks are residues derived from boninitic melts in supra-subduction zones, particularly in forearcs. In the mantle wedge, slab-derived fluid-melt containing H2O increases the degree of melting and metasomatizes the peridotites. However, the relationship between high-degree melting under hydrous conditions and metasomatism is not well understood. In this paper, we report petrological features of amphibole-bearing ultra-depleted peridotites from the Horokanai ophiolite, Hokkaido, Japan. The peridotite complex in the Horokanai ophiolite consists of clinopyroxene-free harzburgite, orthopyroxene-poor harzburgite, and dunite. The harzburgites contain high-Cr# spinel (0.70-0.85) and orthopyroxene with very low abundances of incompatible elements (e.g., Y < 0.01 µg/g; Ti ~ 2 µg/g). Pargasitic-edenitic amphibole occurs as spinel-hosted inclusions and as an interstitial phase to olivine and orthopyroxene. The harzburgite is a residue formed by the high-degree melting caused by fluid flux. The hydrous conditions cause incongruent melting of orthopyroxene, producing a depleted Si-rich melt (i.e., a boninitic melt). Because such Si-rich melt can coexist with Cr-rich spinel under these conditions, amphibole is ultimately crystallized in the harzburgite. Such amphibole formation is important in producing secondary sodic amphibole during alteration of ultra-depleted peridotites.

KW - boninite

KW - harzburgite

KW - hydrous melting

KW - mantle wedge

KW - pargasite

U2 - 10.4454/ofioliti.v49i1.568

DO - 10.4454/ofioliti.v49i1.568

M3 - Journal article

AN - SCOPUS:85184389324

VL - 49

SP - 37

EP - 54

JO - Ofioliti

JF - Ofioliti

SN - 0391-2612

IS - 1

ER -