北羌塘盆地沃若山地区早侏罗世雀莫错组砂岩地球化学特征与物源判别意义

出露于羌塘盆地沃若山地区的雀莫错组砂岩是北羌塘盆地早侏罗世的沉积物,对研究早侏罗世沉积盆地的演化特征具有重要的意义。通过对其地球化学特征的分析研究,结果表明该组砂岩为被动大陆边缘裂陷期的沉积产物,岩性主要为岩屑砂岩,岩石矿物成分主要在钾长石、斜长石、伊利石、绿泥石以及石英之间变化。化学风化作用指标(CIW)、化学蚀变作用指标(CIA)和A-CN-K图解,反映该组砂岩的碎屑成分受到了强烈的风化环境,并在风化过程中发生钾交代作用,长石发生伊利石化。化学组分指标(ICV)表明岩石碎屑为近源的第一次旋回沉积物,受沉积分选和再循环作用影响不大;A-CN-K图解还反映出砂岩碎屑源岩中斜长石含量高于钾长石含量,主要在花岗岩和花岗闪长岩之间变化;稀土元素特征表明该组砂岩具有同源性,其成分主要受源区岩石成分控制,为酸性火山岩类。

Geochemical characteristics and tectonic significance of Early Jurassic Quemo Co Formation inWoruoshan area, north Qiangtang basin

Early Jurassic Quemo Co Formation is very important for studying the sedimentary evolution form the late Triassic to the early Jurassic in Qiangtang basin. Geochemistry and provenance characteristics of sandstones in the Quemo Co Formation of Woruo Mmountain area were studied by analyzing the selected major element and trace element compositions. The results suggest that the sandstone deposited in the chasmic stage of the passive continental margin. The sandstones are the lithic sandstone which mainly consist of K-feldspar,plagioclase,illite, chlorite and quartz. The chemical index of weathering (CIW), the chemical index of alteration (CIA) parameters and the A-CN-K plot of the sandstones suggest that weathering of the elastic constituents has been intense in the area,the elastic constituents of sandstones underwent K-metasomatisim during weathering processes,illite replaced feldspar and perhaps the original kaolinite in the feldspar. The index of compositional variability (ICV) suggests that some sandstones contain first cycle materials The A-CN-K diagram indicates that a high average plagioclase-to-K-feldspar ratio in the provenance,varying from granodiorite to granite. The REE characteristics suggest only one source of acid igneous rock for the sandstones in this area.