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首页> 外文期刊>Applied Geochemistry: Journal of the International Association of Geochemistry and Cosmochemistry >Geochemistry of major and trace elements and Pb-Sr isotopes of a weathering profile developed on the Lower Cambrian black shales in central Hunan, China
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Geochemistry of major and trace elements and Pb-Sr isotopes of a weathering profile developed on the Lower Cambrian black shales in central Hunan, China

机译：湖南中部下寒武统黑色页岩中风化剖面的主要和微量元素及铅-锶同位素地球化学

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This paper reports a geochemical study on the major and trace elements and Pb-Sr isotopes of a weathering profile developed in the Lower Cambrian black shales in central Hunan (China). Six weathering horizons were identified and sampled vertically throughout the profile. The chemical composition of the profile consists of variable concentrations of the major elements Fe_2O_3, FeO, MnO, MgO, CaO, Na_2O, and P_2O_5 and of less variable concentrations of SiO_2, TiO_2, Al_2O_3, and K_2O. The chemical change caused by weathering is estimated by mass-balance calculations, and the results show that the element mobility is characterised by substantial loss of SiO_2, FeO, CaO, K_2O, Na_2O, LOI, Cr, V, Ba, Cs, Rb, Sr, U, and Th, and moderate loss of Al_2O_3, MgO, Fe_2O_3, Ni, Cu, Pb, Tl, Sn, Sc, Ge and REE (Y). The high field strength elements TiO_2, Sn, Sc, U, Ga, Ge, Zr, Hf, Nb, and Ta were immobile during weathering. The chemical changes and the Pb-Sr isotopic data suggest that four types of chemical reactions occurred: the oxidation of sulphide minerals (e.g., pyrite) and organic carbon (OS), the dissolution of less resistant clinochlore-Ia, calcite, and P-bearing minerals (DL), the dissolution of detrital albite and microcline (DA), and the transformation of clay (TC) minerals (e.g., muscovite and illite-smectite). These chemical reactions then led to two stages of geochemical processes, an early stage of chemical differentiation and a later stage of chemical homogenisation. The chemical differentiation dominated by the OS, DL, and DA reactions, led to the leaching of mobile elements (e.g., MgO, Na_2O, K_2O, P_2O_5, Sr, and REE) and the redistribution of some less mobile elements (e.g., SiO_2 and Al_2O_3). In contrast, the chemical homogenisation, which was caused by TC reactions, led to the leaching of both mobile and less mobile elements from the system and ultimately transformed the weathered black shales into soil. Soils derived from black shales in South China might result from the above two geochemical processes.
机译：本文报道了湖南中部下寒武统黑色页岩中风化剖面的主要，微量元素和Pb-Sr同位素的地球化学研究。确定了六个风化层位，并在整个剖面上垂直采样。轮廓的化学成分由主要元素Fe_2O_3，FeO，MnO，MgO，CaO，Na_2O和P_2O_5的可变浓度以及SiO_2，TiO_2，Al_2O_3和K_2O的可变浓度组成。通过质量平衡计算估算了由风化引起的化学变化，结果表明元素迁移率的特征在于SiO_2，FeO，CaO，K_2O，Na_2O，LOI，Cr，V，Ba，Cs，Rb， Sr，U和Th，以及Al_2O_3，MgO，Fe_2O_3，Ni，Cu，Pb，Tl，Sn，Sc，Ge和REE的中等损耗（Y）。高场强元素TiO_2，Sn，Sc，U，Ga，Ge，Zr，Hf，Nb和Ta在风化过程中不动。化学变化和Pb-Sr同位素数据表明发生了四种类型的化学反应：硫化物矿物（例如黄铁矿）和有机碳（OS）的氧化，抗性较弱的斜绿石-Ia，方解石和P-含矿物质（DL），碎屑钠长石和微斜岩（DA）的溶解以及粘土（TC）矿物质（例如白云母和伊利石-蒙脱石）的转变。这些化学反应随后导致了地球化学过程的两个阶段，即化学分化的早期阶段和化学均质化的后期阶段。在OS，DL和DA反应中占主导地位的化学差异导致了流动元素（例如MgO，Na_2O，K_2O，P_2O_5，Sr和REE）的浸出以及一些较少活动元素（例如SiO_2和Al_2O_3）。相反，由TC反应引起的化学均质化导致系统中的可移动和不可移动元素均被浸出，最终将风化的黑色页岩转化为土壤。中国南方黑色页岩的土壤可能是上述两个地球化学过程的结果。

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