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Diffusion-driven Ca-Fe isotope fractionations in the upper mantle: implications for mantle cooling and melt infiltration
Geochimica et Cosmochimica Acta ( IF 4.5 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.gca.2020.08.033 Jin-Ting Kang , Chen Zhou , Jing-Yi Huang , Yan-Tao Hao , Fang Liu , Hong-Li Zhu , Zhao-Feng Zhang , Fang Huang
Geochimica et Cosmochimica Acta ( IF 4.5 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.gca.2020.08.033 Jin-Ting Kang , Chen Zhou , Jing-Yi Huang , Yan-Tao Hao , Fang Liu , Hong-Li Zhu , Zhao-Feng Zhang , Fang Huang
Abstract This study reports Ca-Fe isotope compositions of mineral separates in a set of peridotite xenoliths including ten lherzolites, one harzburgite, and one wehrlite from Hainan Island, south China. Iron isotope compositions show a small variation ( 2‰) in previous studies should be dominated by disequilibrium sub-solidus Ca redistribution between cpx and opx, which is driven by the changes of mantle temperature and chemical composition in pyroxene. The wehrlite, which was formed by reaction of peridotite with an evolved, silica-undersaturated melt, has δ44/40Ca of 3.22‰ and δ56/54Fe of 0.22‰, significantly heavier than the value of fertile mantle. Such heavy isotope signatures in the wehrlite are best explained by diffusion during the metasomatic melt percolating the refractory mantle. In summary, this study reveals that significant kinetic Ca isotope fractionations could occur in the mantle by inter-mineral Ca diffusion during re-equilibration upon cooling and Ca diffusion from melt into peridotite during melt percolation.
更新日期：2020-12-01
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