Sediments from stable sand bars along a 40 km section of the Brahmaputra River in northern Bangladesh were analyzed for their major, trace and rare earth element contents to determine their provenance, compositional maturity, source area weathering and tectonic setting. Geochemically, the sediments were classified as litharenites and the Index of Compositional Variability (ICV) varied between 1.4 and 2.0, indicating low compositional and mineralogical maturity. A high mean SiO₂ concentration (72.9 wt.%) and low Al₂O₃ (11.1 wt.%) were consistent with a low abundance of shale and clay components. The depletion of the oxide components Na₂O, CaO and K₂O relative to average upper crustal compositions (UCC) reflected loss of feldspar during chemical weathering in the source region. Average TiO₂ values for most samples were higher than average crustal levels, consistent with the northern section of the Brahmaputra River being a potential resource for valuable Fe-Ti oxide heavy minerals. Major and trace element ratios indicated the sediments represented erosional products from typical felsic upper continental crustal materials with contamination (30%–40%) from more intermediate/mafic compositions. The rare earth element patterns showed negative Eu anomalies (0.57–0.71), indicating they were derived mainly from fractionated felsic rocks. Resemblance of the sediment compositions to mean compositions from Higher Himalaya crystalline rocks pointed to these being potential source rocks but with components from a mafic source also present. Major element chemistries and low to intermediate weathering indices for all sediments indicated a lack of substantial chemical weathering. Evidence from tectonic discrimination diagrams suggested the Brahmaputra River sediments were derived from rock types that formed in a transitional tectonic setting ranging from an ancient passive margin to an active continental margin. Deposition occurred under cool to semi-arid climatic conditions in an oxic environment.

中文翻译：

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雅鲁藏布江最近沉积物的地球化学：物源，构造，源区风化和沉积环境

分析了孟加拉国北部布拉马普特拉河40公里处稳定沙洲的沉积物的主要，痕量和稀土元素含量，以确定其出处，成分成熟度，源区风化和构造环境。从地球化学角度来看，沉积物被分类为锂钙石，组成变异指数（ICV）在1.4到2.0之间变化，表明组成和矿物学成熟度较低。较高的平均SiO ₂浓度（72.9 wt。％）和较低的Al ₂ O ₃（11.1 wt。％）与低含量的页岩和粘土组分相一致。氧化物组分Na ₂ O，CaO和K ₂的耗竭相对于平均上地壳成分（UCC）的O反映了源区化学风化过程中长石的损失。平均TiO ₂大多数样品的水汽含量都高于平均地壳水平，这与布拉马普特拉河北部是有价值的Fe-Ti氧化物重矿物的潜在资源一致。主要元素和微量元素的比值表明，沉积物代表典型的长英质上地壳物质的侵蚀产物，而来自更多中/基性成分的污染（30％–40％）。稀土元素模式显示出负的Eu异常（0.57–0.71），表明它们主要来自于分馏的长英质岩石。沉积物成分类似于来自喜马拉雅山高级结晶岩的成分，表明它们是潜在的烃源岩，但也含有镁铁质烃源。主要化学成分和所有沉积物的中低风化指数表明缺乏实质的化学风化。构造判别图的证据表明，雅鲁藏布江的沉积物是从过渡构造环境中形成的岩石类型衍生而来，从古代被动边缘到活跃大陆边缘。沉积发生在有氧环境中的凉爽至半干旱气候条件下。