藏西南札达白垩纪Albian期海绿石的矿物学特征及地质意义

The Mineralogical Characteristics of Cretaceous Albian Glauconite in Zanda,Southwestern Xizang(Tibet) of China and Its Geological Implications

海绿石是海相沉积的指相矿物,通常形成于海进系列,与低的沉积物供应速率有关。本文利用岩相和扫描电子显微镜(SEM)对样品进行了详细的观察,并运用X射线粉晶衍射(XRD)、傅立叶变换红外吸收光谱(FTIR)、电子探针微分析(EPMA)等技术,对藏西南札达县波林地区夏拉剖面中的海绿石砂岩和含海绿石灰岩样品进行了系统的分析与研究。上述分析表明砂岩和灰岩中的海绿石均为高演化的海绿石,砂岩中的海绿石为原地海绿石,而灰岩中的海绿石则源于下伏砂岩。通过沉积环境分析和区域地层对比,笔者等认为札达地区砂岩中海绿石的出现可能与Albian晚期印度大陆从澳大利亚—南极大陆的彻底裂解而造成的该地区的海进有关。持续的海进过程导致了该地区高演化的海绿石的形成。

Glauconite as a typical facies mineral is generally regarded as accompanied with transgression sequence,with a low sedimentation rate. Glauconite in the Xiala section from Zanda,southwestern Xizang（Tibet） of China,has been studied by observation under both petrographical microscope and Scanning Electron Microscope（SEM）,and the analysis by X-ray Diffractometry（XRD）,Fourier Transform Infrared spectroscopy（FTIR）,Electron Probe Micro-analysis（EPMA）. The above analyses reveal that the glauconites both in sandstone and limestone are highly evolved. The glauconite in sandstone is autochthonous origin,but the glauconite in limestone may come from the underlying glauconitic sandstone.Based on the analysis of sedimentary environment and comparing of glauconite-bearing strata with others in adjacent areas,we conclude that the glauconitization in Zanda may be associated with the transgression which caused by final separation of the Indian Continent from the Australian—Antarctic Continent in the Late Albian. Long-term transgressive trend is indicated by the occurrence of the highly evolved glauconite.