黔西北地区二叠纪玄武岩古风化壳常量元素的地球化学特征

通过对峨眉山玄武岩古风化壳进行野外调查、取样和分析测试工作,认为:①贵州西部广泛出露峨眉山玄武岩,晚二叠世古气候温润潮湿,利于峨眉山玄武岩风化形成含Fe、Ti的黏土矿物和铝质黏土矿物的古风化壳,该风化壳受古地理环境和峨眉山玄武岩控制。②相对玄武岩而言,铝质黏土岩主量元素含量特征表现为富TiO_2、Al_2O_3,轻度亏损SiO_2,明显亏损TFe,其他主量元素大量流失;铁质黏土岩主量元素含量特征表现为富TFe、TiO_2,轻度富Al_2O_3,但相对于铝质黏土岩,TiO_2的富集程度偏低,SiO_2亏损明显,其他元素亦大量流失。③由于晚二叠世频繁的海侵作用,水位较高的区域,风化壳下部处于较还原的条件下,Fe被还原成易溶的二价状态或在有机质的作用下迁出风化壳,而Ti由于存在形式较为稳定,继续保存在黏土矿物中,与Fe发生分异;局部水位较浅的氧化环境及重力分异作用下,黏土矿物与铁矿物由于比重差异而分选开来,形成Fe与Al、Ti的分异,并伴随铁矿、钛矿和铝土矿的富集。该富集规律的发现对寻找该区铁、钛和铝土矿有一定的理论指导意义。

Geochemical characteristics of paleo-weathering crust of Permianbasalt in northwestern Guizhou

Through the field investigation, sampling and test of basalt paleo-weathering crust in Emei Mountain, this paper has the following conclusions:(1) Emei basalt is widely outcropped in western Guizhou. The ancient climate of Late Permian is warm and wet, so it is helpful for the formation of paleo-weathering crust containing clay minerals of iron, titanium and aluminum. This weathering crust is controlled by the paleogeographic environment and the Emei basalt. (2) Compared to basalt, major elements in aluminum clay is characterized by rich TiO2, Al2O3, mild loss of SiO2, obvious loss of TFe and other main elements shows a great loss. And major elements in iron clay is characterized by rich TFe, TiO2, mild rich Al2O3. But compared to the aluminum clay, the TiO2 concentration is low, and SiO2 and other elements shows an obvious loss.(3)Due to frequent transgression of Late Permian, the lower part of paleo-weathering crust in areas with higher ground water levels, is in the reduction conditions. Fe is restored in soluble bivalent state or gets out of paleo-weathering crust under the effect of organic matter. Due to a stable state, Ti continues to save in clay minerals and is differentiated from Fe. Clay minerals and iron are sorted to form the differentiation of Fe and Al, Ti due to the density difference under the gravity differentiation in oxidation environment of local shallow water, along with the enrichment of titanium ore, iron ore and bauxite. The discovery of the enrichment regularity is of theoretical guiding significance to the exploration of the iron, titanium and aluminum ore.