南羌塘盆地江鱼玛洛地区中侏罗统雀莫错组砂岩地球化学及源区环境

南羌塘盆地江鱼玛洛地区发育中侏罗统雀莫错组,通过岩石地球化学分析,对砂岩源区环境进行恢复. 化学风化作用指标(CIW)、化学蚀变作用指标(CIA)和A-CN-K图解反映砂岩的碎屑成分遭受过较强烈的风化. 化学组分指标(ICV)和Th/Sc-Zr/Sc图解指示主要为第一沉积旋回产物,伴有少量沉积再循环物质. 岩石元素Al₂O₃/TiO₂、Th/Sc、Cr/Zr比值和La/Th-Hf源岩判别图解反映砂岩的碎屑主要来源于上地壳长英质源区,并混入少量基性铁镁质岩石. 砂岩的微量元素特征及SiO₂-K₂O/Na₂O、La-Th-Sc、Co-Th-Zr/10、Sc-Th-Zr/10判别图解均表明该砂岩形成于大陆边缘裂陷构造背景.

GEOCHEMISTRY AND SOURCE AREA ENVIRONMENT OF THE MIDDLE JURASSIC SANDSTONE IN SOUTHERN QIANGTANG BASIN

The sandstone of Middle Jurassic Quemocuo Formation is developed in Jiangyumaluo area of southern Qiangtang Basin. The environment of sandstone source area is restored through petrogeochemical analysis. The chemical index of weathering (CIW), chemical index of alteration (CIA) parameters and A-CN-K diagram of sandstones show that the clastic compositions are intensely weathered. The index of compositional variability(ICV) and Th/Sc-Zr/Sc diagram indicate that the sandstone contains mainly the first sedimentary cycle materials, with a little recycled sediment. The Al₂O₃/TiO₂, Th/Sc and Cr/Zr ratios of rock elements and La/Th-Hf discrimination diagram of source rocks suggest that the clastics of sandstone are mainly from the felsic source area of upper crust, mixed with a small number of basic femic rocks. The characteristics of trace elements and SiO₂-K₂O/Na₂O, La-Th-Sc, Co-Th-Zr/10, Sc-Th-Zr/10 diagrams all indicate that the sandstones were formed in the continental margin rifting tectonic setting.