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首页> 外文期刊>Journal of Asian earth sciences >Geochemistry of lower Vindhyan clastic sedimentary rocks of Northwestern Indian shield: Implications for composition and weathering history of Proterozoic continental crust
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Geochemistry of lower Vindhyan clastic sedimentary rocks of Northwestern Indian shield: Implications for composition and weathering history of Proterozoic continental crust

机译：西北印度盾构下温迪扬碎屑沉积岩的地球化学：对元古代大陆壳的成分和风化历史的启示

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摘要

The western margin of the ~1600 Ma Vindhyan basin of the Indian shield is marked by the presence of lower Vindhyan Group (LVG) comprising shales and sandstone with minor limestone, conglomerate and mafic volcanic flows at the base. Major and trace element compositions of sandstones and shales of the LVG have been investigated to infer the nature of provenance, weathering processes, and tectonic setting. Provenance analysis using trace elements and petrography suggests that the Archaean Banded Gneissic Complex (BGC) of Rajasthan is most likely the source of these clastic rocks. The shale and sandstone comprising lower part of LVG namely Khardeola Formation are distinctive in having high LILE such as Th, Rb, and K_2O, high ferromagnesian trace elements and also higher values of K_2O/Na_2O, Rb/Sr and (La/Yb)n ratios in comparison to succeeding sedimentary units comprising upper formations of the LVG. The significantly different geochemical characteristics of Khardeola Formation suggest change in provenance with sediments in the lower formation being derived from proximal source and those of upper formations from distal source. Based on REE patterns and Eu/Eu* values, the clastic sediments of Khardeola formation can be modeled by a mixture of 60% Berarch Granite and 40% mafic volcanic rocks of Hindoli belt. On the other hand, the upper formations are best modeled with a mixture of 60% BGC granitic gneisses, 20% BGC mafic enclaves and 20% Berach Granite. CIA (chemical index of alteration) values and A-CN-K plot suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions. The shift of sediment source from local in the beginning to distal during later period suggests sedimentation in a tectonically active basin.
机译：印度盾构〜1600 Ma Vindhyan盆地的西缘以下部Vindhyan组（LVG）的存在为标志，该组由页岩和砂岩组成，底部有少量石灰岩，砾岩和镁铁质火山岩流。研究了LVG砂岩和页岩的主要和微量元素组成，以推断物源，风化过程和构造环境的性质。使用微量元素和岩相学进行的物源分析表明，拉贾斯坦邦的古生带状片麻岩复合体（BGC）最有可能是这些碎屑岩的来源。 LVG下部即Khardeola组的页岩和砂岩的特点是具有较高的LILE（例如Th，Rb和K_2O），高铁镁微量元素以及较高的K_2O / Na_2O，Rb / Sr和（La / Yb）n与包括LVG上部地层的后续沉积单元的比率Khardeola组的地球化学特征明显不同，表明下层的沉积物来源有所变化，下层的沉积物来自近端，上层的沉积物来自远端。根据REE模式和Eu / Eu *值，可以用60％的Berarch花岗岩和40％的Hindoli带镁铁质火山岩混合物模拟Khardeola形成的碎屑沉积物。另一方面，最好用60％BGC花岗岩片麻岩，20％BGC黑镁岩飞地和20％Berach花岗岩的混合物模拟上部地层。 CIA（化学变化指数）值和A-CN-K图表明，源区在温暖和潮湿的条件下经历了中度到高度的化学风化。沉积物来源从开始时的局部向后期的远侧转移，表明构造活动盆地中的沉积。

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  • 来源
    《Journal of Asian earth sciences》 |2010年第2期|p.51-61|共11页
  • 作者

    Mahshar Raza; A.M. Dayal; Abdullah Khan; V.R. Bhardwaj; Sarwar Rais;

  • 作者单位

    Department of Geology, Aligarh Muslim University, Aligarh 202002, India;

    Department of Geology, Aligarh Muslim University, Aligarh 202002, India National Geophysical Research Institute, Uppal Road, Hyderabad 50007, India;

    Department of Geology, Aligarh Muslim University, Aligarh 202002, India;

    Department of Geology, Aligarh Muslim University, Aligarh 202002, India;

    Department of Geology, Aligarh Muslim University, Aligarh 202002, India;

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  • 正文语种 eng
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  • 关键词

    geochemistry; Indian shield; vindhyan basin; rajasthan; proterozoic;

    机译：地球化学印度盾长春盆地拉贾斯坦邦元古代;

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