Na-rich character of metasomatic/metamorphic fluids inferred from preiswerkite in chromitite pods of the Khoy ophiolite in Iran: Role of chromitites as capsules of trapped fluids

Zaeimnia, Fatemeh; Arai, Shoji; Mirmohammadi, Mirsaleh

doi:10.1016/j.lithos.2016.11.021

Cited by 10 publications

(4 citation statements)

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“…Higher Al 2 O 3 (3.6 wt%), Na 2 O (0.8 wt%) and TiO 2 (0.5 wt%) of clinopyroxene inclusions in the Eastern Khoy chromitites also suggest that they were produced by interaction between MORB‐like magma and a wall harzburgite or crystallized from MORB‐like melts (Akizawa, Arai, & Tamura, ). The occurrence of presiwerkeit (Na–Al Mica) in the Eastern Khoy Chromitite is related to the involvement of slab‐derived fluid responsible for serpentinization (Zaeimnia, Arai, & Mirmohammadi, ).…”

Section: Discussionmentioning

confidence: 99%

Mineral chemistry and petrogenesis of chromitites from theKhoy ophiolite complex,NorthwesternIran:Implications for aggregation of two ophiolites

et al. 2017

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The Khoy ophiolitic complex in Northwestern Iran is a part of the Tethyan ophiolite belt, and is divided into two sections: the Eastern ophiolite in Qeshlaq and Kalavanes (Jurassic–Cretaceous) and the Western ophiolite in Barajouk, Chuchak and Hessar (Late Cretaceous). Our chromitites can be clearly classified into two groups: high‐Al chromitites (Cr# = 0.38–0.44) from the Eastern ophiolite, and high‐Cr chromitites (Cr# = 0.54–0.72) from the Western ophiolite. The chromian spinels in high‐Al chromitite include primary mineral inclusions mainly as Na‐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 Al2O3, Na2O, Cr2O3, and TiO2 relative to Western 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 Western Khoy chromitites contains inclusions such as clinopyroxene, olivine and platinum group mineral‐bearing sulfides. These Western chromitites were possibly formed at two stages during arc growth and are divided into the moderately high‐Cr# chromitites (Barajouk and Hessar) and the high‐Cr# chromitites (Chuchak 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 Eastern and Western Khoy ophiolites were formed in a back‐arc basin and arc‐related setting, respectively. The Khoy ophiolitic complex is a tectonic aggregate of the two different ophiolites formed in two different tectonic settings at different ages.

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Section: Discussionmentioning

confidence: 99%

Mineral chemistry and petrogenesis of chromitites from theKhoy ophiolite complex,NorthwesternIran:Implications for aggregation of two ophiolites

et al. 2017

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“…7,10). Crystallization of such inclusions may be triggered by late fluid circulation in the subduction zone (Zaeimnia et al 2017;Johan et al 2017;Xiong et al 2018). The rutile and ilmenite inclusions in the chromite grains can be explained by post-formation high-grade metamorphism of their host rocks.…”

Section: Magnesium Isotopic Compositions Of the Purang Ophiolitic Rocksmentioning

confidence: 99%

Microchemistry and magnesium isotope composition of the Purang ophiolitic chromitites (SW Tibet): New genetic inferences

Xiong

Zoheir

Robinson

et al. 2023

American Mineralogist

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New petrographic and microanalytical studies of mineral inclusions in the Purang ophiolitic chromitites (SW Tibet) are used to scrutinize the evolution of the associated Cretaceous sub-oceanic lithospheric mantle section. Silicate inclusions in the chromite grains include composite and single-phase orthopyroxene, clinopyroxene, amphibole, and uvarovite. Most inclusions are sub-rounded or globular, whereas a few inclusions exhibit cubic/octahedral crystal morphologies. The latter are randomly distributed in the large chromite grains, though discrete aggregates are consistently confined to the grain centers. Abundant micron-scale, clinopyroxene inclusions are topotaxially aligned along crystallographic planes. Less abundant sulfide, wüstite, apatite and uvarovite inclusions are observed in some samples.The trace element geochemistry of the Purang chromitite evoke parental MORB-and boninite-like melts, consistent with the supra-subduction zone setting. The δ 26 Mg values of the high-Cr and high-Al chromitites range from -0.25 to -0.29‰ and -0.05 to -0.32‰, respectively. The associated harzburgite has nearly overlapping δ 26 Mg values of -0.13 to -0.37‰, but pyroxenite sills show a rather wider range of the δ 26 Mg values (-0.61 to -0.67‰).The variable Mg isotope signatures, combined with abundant exotic, ultra-high pressure and super reduced (UHP-SuR) mineral inclusions in the chromite grains, suggest that recycling and recrystallization under different mantle conditions played an important role in the genesis and evolution of these rocks. Further, discrete silicate, sulfide, and metal alloy inclusions in the Purang chromitites are comparable to those reported in other Tethyan ophiolites, and collectively suggest a common geodynamic evolution.

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“…This dismembered ophiolite belt is exposed in a number of locations. It mainly shows mid-ocean ridge and island-arc, geochemical signatures and is widely exposed in the Khoy area, with some massive-sulfide mineralization and chromite deposits (Zaeimnia et al, 2017). In the Khoy area, the ophiolite members in the east have been classified as the main ultramafic parts of the mantle and comprise dunite and harzburgite (Khalatbari-Jafari et al, 2003).…”

Section: Osk Ophiolitesmentioning

confidence: 99%

The Van Microplate: A New Microcontinent at the Junction of Iran, Turkey, and Armenia

Azizi

Tsuboi

2021

Front. Earth Sci.

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In northwestern Iran, magmatic activity occurred during three main intervals: The Cretaceous, Eocene, and Miocene-Quaternary. The first two phases of magmatic activity are more consistent with arc-type magmatism on an active continental margin; whereas the last phase, which has calc-alkaline and alkaline affinities, shows more similarity to postcollisional magmatism. Magmatic belts are mostly situated in the northern and eastern parts of the Oshnavieh–Salmas–Khoy ophiolite belt (OSK-Ophiolite) in northwestern Iran. The OSK-Ophiolite is known as the Neotethys, an ocean remnant in northwestern Iran, and extends to eastern Turkey and surrounds the Van area. This configuration shows that the Van microplate and surrounding ocean have played an important role in the evolution of magmatic activity in northwestern Iran, eastern Turkey, and the Caucasus since the Cretaceous. The Van microplate is situated among the Arabian plate to the south, northwestern Iran to the east, and Armenia to the north. The subduction of the northern branch of the Neotethys oceanic lithosphere beneath southern Eurasia has been critical in flare-up magmatism in the southern Caucasus since the Late Cretaceous. Considering the Van area as a new microplate makes understanding the geodynamic evolution of this area easier than in the many tectonic models that have been suggested before. When regarding the Van microplate, the main suture zone, which is known as the Bitlis–Zagros zone, should be changed to the Zagros–Khoy–Sevan–Akera suture zone, which extends to the eastern and northern Van microplate and western Iran.

show abstract

Na-rich character of metasomatic/metamorphic fluids inferred from preiswerkite in chromitite pods of the Khoy ophiolite in Iran: Role of chromitites as capsules of trapped fluids

Cited by 10 publications

References 58 publications

Mineral chemistry and petrogenesis of chromitites from theKhoy ophiolite complex,NorthwesternIran:Implications for aggregation of two ophiolites

Mineral chemistry and petrogenesis of chromitites from theKhoy ophiolite complex,NorthwesternIran:Implications for aggregation of two ophiolites

Microchemistry and magnesium isotope composition of the Purang ophiolitic chromitites (SW Tibet): New genetic inferences

The Van Microplate: A New Microcontinent at the Junction of Iran, Turkey, and Armenia

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