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Silicate mineral inclusions in chromite from the Eastern Bushveld complex: Implications for the origin and evolution of hydrous melt during chromite mineralization in the Critical Zone

文献类型：期刊论文

作者Tang, Dongmei1,2; Qin, Kezhang1,2,3; Fang, Linru1,2,3; Evans, Noreen J.4
刊名LITHOS
出版日期2023-02-01
卷号438页码:16
ISSN号0024-4937
关键词Chromitite Silicate mineral inclusion H 2 O content Hydrous melt Bushveld
DOI10.1016/j.lithos.2022.106997
英文摘要In this work, we systematically describe silicate mineral inclusion morphology and genesis in chromite from UG3, MG2 and LG6 chromitite layers of the Eastern Limb of the Bushveld Complex. Rounded to subhedral in-clusions of phlogopite, amphibole and, to a lesser extent, olivine and orthopyroxene, are concentrated at or near the center of chromite grains. The most common occurrences are tabular amphibole forming planar contact with orthopyroxene, phlogopite, and phlogopite surrounding amphibole and olivine. Several features indicate re-equilibration reactions between the host chromite and the inclusions including high Mg# values in orthopyr-oxene inclusions (81.9 to 88.4; average of 85.0), low MgO (5.16 to 8.15 wt%) and high FeO (28.66 to 32.54 wt%) contents in the host chromite, and higher Cr2O3 content in amphibole (0.32 to 3.60 wt%) and phlogopite (0.29 to 2.29 wt%) inclusions relative to cumulus orthopyroxene, amphibole and phlogopite in the silicate rocks. Furthermore, the high H2O (4.16 to 4.45 wt%) and Na2O (0.07 to 6.12 wt%) contents in phlogopite inclusions, low transition element (V, Ni, Co and Zn) contents in the orthopyroxene from chromitite seams, and the devi-ation from mantle 818O values (5.7 to 6.7 %o) in inclusions, indicates alteration by or reaction with, hydrous melt. In addition, the similar orthopyroxene 818O (5.7-6.8 %o) in the MG2 and LG6 hanging wall and footwall, and in amphibole inclusions (818O = 5.9-6.7 %o) from the LG6, MG2 and UG3 chromitite seams, suggest that the hy-drous melt which formed hydrous mineral inclusions in chromite, and in the hanging wall and footwall silicate minerals, had a similar origin. The high 818O values, LG6 olivine inclusions, and the lower H2O and Li contents in Critical Zone (CZ) orthopyroxene from chromitite compared to orthopyroxene from the overlying and underlying rocks, as well as previous experiments and chemical data, all indicated that a pyroxene remelted hydrous alkali-melt was probably the main source of the trapped melt in chromite. Compatible transition metal element (Ni and Co) contents in orthopyroxene from chromitite seams are lower than those in orthopyroxene from mafic rocks, indicating the former intensely reacted with interstitial liquid. Conversely, there is a low but narrow range in H2O content (8.7 ppm to 28.1 ppm) in orthopyroxene from the CZ chromitite relative to orthopyroxene from norite in the overlying and underlying rocks (3.0 ppm to 46.1 ppm), and a lower Li content in orthopyroxene from chromitite (2.4 ppm to 4.2 ppm) relative to the overlying and underlying norite rocks (2.5 ppm to 8.7 ppm). Coupled low H2O-Li contents in the orthopyroxene from chro-mitite seams and reaction with interstitial liquid suggest that chromite selectively captured hydrous silicate melt during grain formation. Capture of hydrous melt related to remelted pyroxene is a likely mechanism of inclusion formation, and was a common phenomenon in chromite from the Eastern Limb of the Bushveld Complex.
WOS关键词PLATINUM-GROUP ELEMENT ; OXYGEN-ISOTOPE ; QUANTITATIVE-ANALYSIS ; STILLWATER COMPLEX ; TRACE-ELEMENTS ; UG2 CHROMITITE ; ORTHO-PYROXENE ; MERENSKY REEF ; MARGINAL ROCKS ; SOUTH-AFRICA
资助项目National Natural Science Foundation of China[42073039]
WOS研究方向Geochemistry & Geophysics ; Mineralogy
语种英语
出版者ELSEVIER
WOS记录号WOS:000916026900001
资助机构National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China
源URL[http://ir.iggcas.ac.cn/handle/132A11/106818]  
专题地质与地球物理研究所_中国科学院矿产资源研究重点实验室
通讯作者Tang, Dongmei
作者单位1.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Mineral Resources, Beijing 100029, Peoples R China
2.Chinese Acad Sci, Inst Earth Sci, Beijing 100029, Peoples R China
3.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
4.Curtin Univ, John De Laeter Ctr, Perth, WA 6845, Australia
推荐引用方式
GB/T 7714		 Tang, Dongmei,Qin, Kezhang,Fang, Linru,et al. Silicate mineral inclusions in chromite from the Eastern Bushveld complex: Implications for the origin and evolution of hydrous melt during chromite mineralization in the Critical Zone[J]. LITHOS,2023,438:16.
APA Tang, Dongmei,Qin, Kezhang,Fang, Linru,&Evans, Noreen J..(2023).Silicate mineral inclusions in chromite from the Eastern Bushveld complex: Implications for the origin and evolution of hydrous melt during chromite mineralization in the Critical Zone.LITHOS,438,16.
MLA Tang, Dongmei,et al."Silicate mineral inclusions in chromite from the Eastern Bushveld complex: Implications for the origin and evolution of hydrous melt during chromite mineralization in the Critical Zone".LITHOS 438(2023):16.

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来源：地质与地球物理研究所

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