塔中地区志留系砂岩元素地球化学特征与物源判别意义

Element Geochemistry of sandstones in the Silurian of central Tarim basin and the significance in provenance discrimination.

通过分析塔中地区志留系砂岩的某些常量元素和微量元素含量的变化,研究了该地区砂岩的地球化学以及其物源特征。结果表明塔中地区志留系的沉积构造环境为活动大陆边缘和被动大陆边缘,物源主要来自再循环造山带。砂岩的矿物成分主要在石英、钾长石、斜长石、伊利石、绿泥石等矿物之间变化。化学风化作用指标(CIW)和化学蚀变作用指标(CIA)反映了该地区砂岩的碎屑成分受到了强烈的风化作用,风化作用强度为:依木干他乌组>塔塔埃尔塔格组>柯坪塔格组。化学组分变化指标(ICV)反映了有些砂岩中含有第一次旋回沉积物。A-CN-K三角图反映了砂岩的碎屑源岩中斜长石含量要高于钾长石含量,主要在花岗闪长岩和花岗岩之间变化,砂岩的碎屑成分在风化过程中受到了钾的交代作用,长石以及长石中的高岭石发生了伊利石化。稀土元素及其比值(La/Yb)_N、(La/Lu)_N等也反映了该地区砂岩来源于花岗闪长岩和花岗岩的混合物。

The geochemistry and provenance characteristics of sandstones in the Silurian of central Tarim basin have been studied by analyzing the selected major element and trace element compositions. Petrographic results suggests that the tectonic setting is active continental margin and passive continental margin, the provenance is recycling orogenic belt mainly. The sandstones mainly consist of quartz, K-feldspar, plagioclase, illite and chlorite etc. The chemical index of weathering ( CIW) and the chemical index of alteration ( CIA) parameters of the sandstones suggest the weathering of the clastic constituents is intense in the area. The intensity of weathering: Yimugantawu Formation > Tataertage Formation > Kepingtage Formation. The index of compositional variability ( ICV) suggests some sandstones contain first cycle material. The A-CN-K diagram indicates that a high average plagioclase to K-feldspar ratio in the provenance, range from granodiorite to granite, the clastic constituents of sandstones under-went K-metasomatisim during weathering processes, illite replaced feldspar and thus perhaps the original kaolinite in the feldspar. The trace element and ratios, for example (La/Yb)(N), (La/Lu)(N) et al., suggest a mix of a granodiorite granite source for the sandstones in this area.