Research highlights

The clay fraction of the sediments in 15 rivers along the east coast of India showed

• Mixed-mineral assemblages in accordance with dominant geology and chemical weathering.

• High CIA and PIA, and low Ca, K, Na and Sr values indicating moderate to intense chemical weathering on source rocks.

• Enriched transition metals and depleted high-field strength elements supporting dominance of mafic component.

• Ratio–ratio plots of trace metals indicating intermediate provenance between mafic and felsic sources.

Abstract

The clay fraction of sediments in the lower reaches of 15 rivers along the east coast of India showed high kaolinite followed by illite and smectite for the rivers dominantly draining the Archaean–Precambrian Terrain (APT), high smectite followed by illite and kaolinite for those draining the Deccan Trap Volcanic Terrain (DVT) and, high illite followed by kaolinite, smectite or chlorite for those draining through Mixed-Lithology Terrain (MLT). The CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) values, depletion of Ca, K, Na and Sr and enrichment of Al, Fe and Ti, high Rb/Sr and Th/U ratios of sediments relative to the Upper Continental Crust indicate moderate to intense chemical weathering on source rocks. The average composition of clays exhibits slight enrichment of Fe, Mg, Sc, V, Co, Cr and Ni and depletion of Nb, Zr, Hf, Y and Ta relative to the Post-Archaean average Australian Shale. The Cu, Zn and Pb contents were in the range ‘significantly polluted to moderately polluted’ in APT- and DVT-sediments. The plots of TiO₂ vs. Fe₂O₃+MgO, Th/Sc vs. Sc and La–Th–Sc showed sediment composition intermediate between granite and basalt, while the plots of TiO₂ vs. Zr, Th vs. Sc and V–Ni–Th indicate intermediate provenance between mafic and felsic sources. The mineralogy of the sediments indicates mixed sources, but their chemical composition is affected by weathering and the provenance is intermediate between mafic and felsic sources.

中文翻译：

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印度东海岸河流的沉积物的矿物学和地球化学：关于风化和物源的推论

研究重点

印度东海岸的15条河流中沉积物的黏土含量显示

• 根据主要地质和化学风化的混合矿物组合。

• 较高的CIA和PIA，以及较低的Ca，K，Na和Sr值，表明烃源岩具有中等至强烈的化学风化作用。

• 富集的过渡金属和贫乏的高场强元素，支持了镁铁矿成分的主导地位。

• 痕量金属的比例比率图表明镁铁质和长英质来源之间的中间出处。

抽象的

在印度东海岸的15条河流的下游，沉积物的黏土含量显示出高岭土，其次是伊利石和蒙脱石，以河流为主要排放古生－前寒武纪地形（APT），高蒙皂石接着是伊利石和高岭石，用于排水对于通过混合岩性地形（MLT）排空的井，则采用Deccan陷阱火山地形（DVT）和高伊利石，然后是高岭石，蒙脱石或绿泥石。CIA（化学变化指数）和PIA（陈旧橡胶质变化指数）值，Ca，K，Na和Sr的耗竭以及Al，Fe和Ti的富集，相对于沉积物的高Rb / Sr和Th / U比的沉积物上部大陆壳表明烃源岩有中等至强烈的化学风化作用。黏土的平均成分表现出少量的Fe，Mg，Sc，V，Co，Cr和Ni富集和Nb的耗竭，Zr，Hf，Y和Ta相对于后Archaean澳大利亚平均页岩。在APT和DVT沉积物中，Cu，Zn和Pb的含量在“严重污染至中等污染”范围内。TiO的地块₂ vs. Fe ₂ O ₃ + MgO，Th / Sc vs. Sc和La–Th–Sc表示沉积物组成介于花岗岩和玄武岩之间，而TiO _2图 相对于Zr，Th vs. Sc和V–Ni–表示在镁铁质和长素体来源之间的中等来源。沉积物的矿物学表明混合来源，但其化学组成受风化的影响，物源介于镁铁质和长英质之间。