Rhenium-Osmium isotope systematics of an Early Mesoproterozoic SEDEX polymetallic pyrite deposit in the North China Craton: Implications for geological significance and the marine osmium isotopic record
Rhenium-Osmium isotope systematics of an Early Mesoproterozoic SEDEX polymetallic pyrite deposit in the North China Craton: Implications for geological significance and the marine osmium isotopic record
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DOI：
10.1016/j.oregeorev.2020.103331
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发表时间：
2020-02
影响因子：
3.3
通讯作者：
Bingyu Gao;Lianchang Zhang;Xindi Jin;Zhiquan Li;Wenjun Li
中科院分区：
文献类型：
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作者：
Bingyu Gao;Lianchang Zhang;Xindi Jin;Zhiquan Li;Wenjun Li
古海底热液硫化物沉积物中保存的铼锇（Re-Os）同位素系统可以用来了解古海水的Os组成。特别是，通过测量同沉积黄铁矿（SEDEX矿床的共同成分）中的Re-Os同位素，可以确定沉积喷发（SEDEX）矿床的年龄。本文报道了华北克拉通北缘中段高玉庄组中以沉积为主的多金属黄铁矿矿床。同沉积黄铁矿的Re-Os同位素数据显示，等时线年龄为1505±55 Ma，限制了原生成矿的时间，以及寄主沉积物的最小年龄为中元古代。黄铁矿初始187os /188Os （Osi）值为0.181±0.066，表明成矿流体为海水和海底热液混合流体，其中Os主要来源于海水。奥西值略高于古元古代海水的奥西值（~0.13），表明当时有一个放射性成因的河流通量进入海洋，而当时大气中的氧含量一定足够高，以驱动这种增加的大陆放射性成因的氧输入到海洋。我们认为，SEDEX沉积物记录的Re-Os同位素系统可能为研究整个前寒武纪海水Os同位素组成的变化提供关键的见解。
The rhenium-osmium (Re-Os) isotopic system preserved in ancient seafloor hydrothermal sulfide deposits can be used to gain insight into the Os composition of ancient seawater. In particular, the age of sedimentary exhalative (SEDEX) deposits can be determined by measuring Re-Os isotopes in syn-depositional pyrite, a common constituent of SEDEX deposits. Here we report on the Gaobanhe sediment-hosted, polymetallic pyrite deposit which is hosted within the Gaoyuzhuang Formation in the central part of the northern margin of the North China Craton (NCC). Re-Os isotopic data from syn-depositional pyrite yield an isochron age of 1505 ± 55 Ma, constraining the timing of primary mineralization, as well as the minimum age of the host sediments to the Mesoproterozoic. Analyzed pyrite grains indicate an initial187Os/188Os (Osi) value of 0.181 ± 0.066, suggesting that the mineralizing fluids were an admixture of seawater and submarine hydrothermal fluids, with the Os being primarily derived from seawater. The Osivalue is slightly higher than that of Paleoproterozoic seawater (~0.13), suggesting that there was a radiogenic riverine flux to the oceans and that atmospheric oxygen must have been sufficiently high at that time to drive this increased, continental radiogenic Os input to the oceans. We propose that the Re-Os isotopic system, as recorded by these SEDEX deposits, may provide key insights when examining changes in the Os isotopic composition of seawater throughout the Precambrian.