Mineral Inclusions in Chromite from the Chromite Deposit in the Kudi Ophiolite, Tibet, Proto‐Tethys

Abstract

High‐Al chromite from the Kudi chromitites contains a wide range of mineral inclusions. They include clinopyroxene, amphibole, phlogopite, olivine, orthopyroxene, apatite, base‐metal sulfides, calcite and brucite. The modal abundance of inclusions vary greatly among different grains of chromite. The common inclusions are clinopyroxene and amphibole, which occur as monomineral or polymineral associated with other minerals. The shapes of these inclusions tend to follow the growth plane of host chromite. Mineral assemblages and textures demonstrate that some inclusions (olivine, clinopyroxene) are trapped during magmatic stage, and most of the inclusions (e.g., amphibole, phlogopite) are trapped during recrystallization of chromite. Sulfide inclusions are pentlandite, chalcopyrite and cubanite. They occur either as isolated grains or together with silicate minerals, and formed from the separation of sulfide‐bearing liquid from silicate magma. The parental magma of chromitites contains Al2O3 15.0wt%–16.5wt%, TiO20.30wt%–1.05wt% based on calculation with the composition of chromite, similar to parental magma of high‐Al chromitites from elsewhere and the estimated melt composition is comparable with that of MORB. Considering the high‐Mg olivine in disseminated chromitite and abundant hydrous inclusions, we propose that Kudi chromitites formed beneath a volcanic front during the subduction initiation of Proto‐Tethys.

Mantle peridotites of ophiolites rarely preserve reliable records of paleo-oceanic lithospheric mantle

“…These hydrous minerals can be found as interstitial grains between major constituent minerals of chromitites and peridotites or as inclusions in chromite/spinel. Amphibole is the predominant hydrous mineral reported in the literature (Melcher et al, 1997;Rollinson, 2008;Uysal et al, 2009;Liu et al, 2010Liu et al, , 2017Borisova et al, 2012;Khedr et al, 2014;Huang et al, 2017b;Rospabé et al, 2017;Çelik et al, 2018;Qiu et al, 2018;Slovenec and Šegvić, 2018;Xiong et al, 2018;Wojtulek et al, 2019;Pan et al, 2022a). In this context, we aim to summarize the compositional characteristics of amphibole in mantle peridotites and compare them to those in chromitites and in Moho dunitic transition zones of ophiolites.…”

Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis

“…Among various solid inclusions in chromite from chromitites [40][41][42], the polymineralic inclusions characterized by hydrous, Na-rich minerals are noteworthy. They occur in various types of chromitites and are similar in mineral assemblage and chemistry ( Figure 2) [43].…”