Chromite as a key player on highly siderophile elements and osmium isotope compositions of the refractory mantle

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta Pub Date : 2025-05-02 DOI:10.1016/j.gca.2025.04.026

Ben-Xun Su, Ibrahim Uysal, Recep Melih Akmaz, Qi-Qi Pan, Yılmaz Demir, Lukáš Ackerman, Paul T. Robinson

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引用次数: 0

Abstract

Chromitites in ophiolites are recognized for their high concentrations of highly siderophile elements (HSE), notably IPGE (Os, Ir and Ru). However, the effects of this enrichment on ophiolitic rocks and mantle heterogeneity remain poorly understood and to address this issue, we investigated chromitites from the Pozantı-Karsantı and Kızıldağ ophiolites in Türkiye. The results reveal HSE enrichment, particularly IPGE, in chromite separates compared to matrix, with indistinguishable Os isotope compositions between the two phases. This observation aligns with the presence of platinum-group minerals (PGM) occurring as inclusions within chromite grains. The IPGE enrichment and similar Os isotope compositions are also present in chromitites relative to dunites, suggesting close affinity of HSE with chromite fractions relative to silicate melts during chromite crystallization and aggregation. A global compilation of data on chromitites in ophiolites demonstrates covariations of HSE and their ratios with chromite Cr# values, indicating that chromite composition modulates its capacity to retain HSE. Peridotites containing chromite with low-Cr# (<45) exhibit consistent HSE concentrations and a decrease in 187Os/188Ost ratios as chromite Cr# values increase, reflecting different partial melting degrees. In contrast, the refractory peridotites (with chromite Cr# > 45) show more scattered HSE variations and distinct trends with chromite Cr#, generally trending towards the chromitite field. This variability likely reflects the compositional effects of chromite on HSE variations, suggesting significant metasomatism and interaction with parental melts of chromitites or evolved melts. Therefore, chromite plays a critical role in the variations of HSE contents and 187Os/188Os within the refractory mantle.

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铬铁矿是高亲铁元素和难熔地幔锇同位素组成的关键因素

蛇绿岩中的铬铁矿以其高浓度的高亲铁元素（HSE）而闻名，特别是IPGE （Os， Ir和Ru）。然而，这种富集对蛇绿岩和地幔非均质性的影响仍然知之甚少，为了解决这个问题，我们研究了 rkiye蛇绿岩Pozantı-Karsantı和Kızıldağ中的铬铁矿。结果表明，与基体相比，铬铁矿分离物中HSE富集，特别是IPGE富集，两相之间的Os同位素组成难以区分。这一观察结果与铂族矿物（PGM）的存在一致，这些矿物以包裹体的形式出现在铬铁矿颗粒中。在铬铁矿中IPGE富集且Os同位素组成相似，表明在铬铁矿结晶和聚集过程中，HSE与相对于硅酸盐熔体的铬铁矿组分具有密切的亲和关系。蛇绿岩中铬铁矿的全球数据汇编表明，HSE及其比值与铬铁矿Cr#值的共变化，表明铬铁矿成分调节了其保留HSE的能力。含低Cr# （<45）铬铁矿的橄榄岩HSE浓度一致，随着铬铁矿Cr#值的增加，187Os/188Ost比值减小，反映了不同的部分熔融程度。难熔橄榄岩(含铬铁矿Cr# >；（45） HSE变化较为分散，随铬铁矿Cr#变化趋势明显，总体趋向于铬铁矿场。这种变化可能反映了铬铁矿的成分对HSE变化的影响，表明其与铬铁矿母质熔体或演化熔体有明显的交代作用和相互作用。因此，铬铁矿对难熔地幔内HSE含量和187Os/188Os的变化起着至关重要的作用。

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来源期刊

Geochimica et Cosmochimica Acta 地学-地球化学与地球物理

CiteScore

9.60

自引率

14.00%

发文量

437

审稿时长

6 months

期刊介绍： Geochimica et Cosmochimica Acta publishes research papers in a wide range of subjects in terrestrial geochemistry, meteoritics, and planetary geochemistry. The scope of the journal includes: 1). Physical chemistry of gases, aqueous solutions, glasses, and crystalline solids 2). Igneous and metamorphic petrology 3). Chemical processes in the atmosphere, hydrosphere, biosphere, and lithosphere of the Earth 4). Organic geochemistry 5). Isotope geochemistry 6). Meteoritics and meteorite impacts 7). Lunar science; and 8). Planetary geochemistry.