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A geochemical and isotopic perspective on tectonic setting and depositional environment of Precambrian meta-carbonate rocks in collisional orogenic belts
Gondwana Research ( IF 6.1 ) Pub Date : 2021-04-23 , DOI: 10.1016/j.gr.2021.03.013
M. Satish-Kumar , M. Shirakawa , A. Imura , N. Otsuji-Makino , R. Imanaka-Nohara , S.P.K. Malaviarachchi , I.C.W. Fitzsimons , K. Sajeev , G.H. Grantham , B.F. Windley , T. Hokada , T. Takahashi , G. Shimoda , K.T. Goto

In this contribution we review the possibility of establishing the depositional age and tectonic settings of metamorphosed carbonate rocks from continental collision zones in the East African-Antarctic Orogen. The geochemical characteristics of regionally distributed meta-carbonate rocks from the Highland Complex (HC) in Sri Lanka are considered in detail and compared with similar occurrences in East Antarctica, India, Madagascar and Africa. The variations seen in the Highland Complex of Sri Lanka imply that carbonate deposition was younging from west to east, spanning apparent ages from Mesoproterozoic to Neoproterozoic. In the case of East Antarctica, such variations are within the Neoproterozoic, whereas in southern India, Madagascar and Mozambique they have a broader age range possibly from the Paleoproterozoic to Mesoproterozoic. There is also clear evidence that some carbonates were deposited in an open ocean surrounding volcanic islands in the Mesoproterozoic. Shale-normalized REE patterns have typical signatures of open ocean deposition in a passive continental margin with variable continental input in platforms nearby to island arcs. In comparison to Phanerozoic equivalents, the absence of a Ce anomaly is most significant, whereas other parameters such as (Pr/Yb)SN, (Pr/Tb)SN, and (Tb/Yb)SN were used to evaluate relative enrichments of the LREE, MREE and HREE fractions that are characteristic of ambient seawater. Pronounced La, and Y anomalies with minor Eu and Gd anomalies and correlations of REE parameters and anomalies with carbon and oxygen isotopes, 87Sr/86Sr initial ratios and εNd values are evaluated for meta-carbonate rocks in the Proterozoic collision zone. The εNd values and Sr initial ratios suggest that basins in the western Mozambique Ocean that separated the East Gondwana from West Gondwana received contributions from Archean continental crust and ambient seawater, whereas the eastern Mozambique Ocean had REE contributions from specific cratonic continents in passive margins or from continental/volcanic island arcs in active margins.



中文翻译:

碰撞造山带前寒武纪准碳酸盐岩的构造环境和沉积环境的地球化学和同位素视角

在本文中,我们回顾了建立东非-南极造山带大陆碰撞带变质碳酸盐岩的沉积年龄和构造背景的可能性。详细考虑了斯里兰卡高地综合体(HC)的区域分布的偏碳酸盐岩的地球化学特征,并将其与南极东部,印度,马达加斯加和非洲的类似事件进行了比较。在斯里兰卡高地综合体中看到的变化表明,碳酸盐沉积物从西向东呈年轻化趋势,从中元古界到新元古代都存在明显的年龄。就南极东部而言,这种变化是在新元古代之内,而在印度南部,马达加斯加和莫桑比克,它们的年龄范围可能很宽,从古元古代到中元古代。 页岩归一化REE模式 在被动大陆边缘具有典型的开放海洋沉积特征,在岛弧附近的平台上具有可变的大陆输入。与生代等效物相比,没有Ce异常是最重要的,而其他参数(如(Pr / Yb )SN,(Pr / Tb)SN和(Tb / Yb)SN )用于评估铁矿石的相对富集。 LREE,MREE和HREE馏分是周围海水的特征。明显的La和Y异常,具有较小的Eu和Gd异常,以及REE参数和异常与碳和氧同位素的相关性,87 Sr / 86 对元古代碰撞带中的碳酸盐岩的Sr初始比和εNd值进行了评估。 εNd值和Sr初始比值表明,在莫桑比克西部将东冈瓦纳与西冈瓦纳分开的盆地得到了古宙大陆壳和周围海水的贡献,而莫桑比克东部则是特定克拉通大陆的被动贡献或来自稀土的贡献。活跃边缘的大陆/火山岛弧。

更新日期:2021-05-25
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