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Mineral chemistry and petrogenesis of chromitites from the K hoy ophiolite complex, N orthwestern I ran: I mplications for aggregation of two ophiolites
Author(s) -
Zaeimnia Fatemeh,
Kananian Ali,
Arai Shoji,
Mirmohammadi Mirsaleh,
Imamalipour Ali,
Khedr Mohamed Zaki,
Miura Makoto,
AbbouKebir Khadidja
Publication year - 2017
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12211
Subject(s) - ophiolite , geology , geochemistry , partial melting , chromitite , peridotite , mantle (geology) , paleontology , tectonics
Abstract The K hoy ophiolitic complex in N orthwestern Iran is a part of the T ethyan ophiolite belt, and is divided into two sections: the E astern ophiolite in Q eshlaq and K alavanes ( J urassic– C retaceous) and the W estern ophiolite in B arajouk, C huchak and H essar ( L ate C retaceous). Our chromitites can be clearly classified into two groups: high‐ A l chromitites ( Cr # = 0.38–0.44) from the E astern ophiolite, and high‐ C r chromitites ( C r# = 0.54–0.72) from the W estern ophiolite. The chromian spinels in high‐ A l chromitite include primary mineral inclusions mainly as N a‐bearing diopside and pargasite with subordinate rutile and their formation was probably related to reaction between a MORB (mid‐ocean‐ridge basalt)‐like melt with depleted harzburgite, possibly in a back‐arc setting. Their host harzburgites contain clinopyroxene with higher contents of A l 2 O 3 , N a 2 O , C r 2 O 3 , and T i O 2 relative to W estern harzburgites and are possibly residue after moderate partial melting (~15 %) whereas the Western harzburgite is residue after high partial melting (~25 %). The chromian spinel in the W estern K hoy chromitites contains inclusions such as clinopyroxene, olivine and platinum group mineral‐bearing sulfides. These W estern chromitites were possibly formed at two stages during arc growth and are divided into the moderately high‐ C r# chromitites ( B arajouk and H essar) and the high‐ C r# chromitites ( C huchak A and C ). The former crystallized from island‐arc‐tholeiite ( IAT ) melts during reaction with the host depleted harzburgites, whereas the latter crystallized from boninitic melts (second stage melt) during reaction with highly depleted harzburgite in a supra‐subduction‐zone environment. Based on the mineral chemistry of chromian spinels, pyroxenes, and mineral inclusions, the chromitites and the host peridotites from the E astern and W estern K hoy ophiolites were formed in a back‐arc basin and arc‐related setting, respectively. The K hoy ophiolitic complex is a tectonic aggregate of the two different ophiolites formed in two different tectonic settings at different ages.