羌塘角木日地区中二叠统龙格组泥岩地球化学特征及其地质意义

沉积岩物源分析对揭示盆地物质组成、储集岩性质及古环境恢复等研究具有重要指示意义。文中对藏北羌塘盆地角 木日地区中二叠统龙格组的钙质泥岩样品进行了微量元素地球化学测试分析，系统地研究了微量元素含量、特征比值及稀 土元素配分方式。结果表明研究区龙格组钙质泥岩样品具有中等轻稀土元素分异（（La/Sm）N =2.50~5.41），重稀土元素比较 平坦（（Gd/Yb）N=1.32~2.47），具有微弱的Eu负异常；Sr/Ba，V/Cr，Ni/Co，Ceanom及δEu等相关参数综合显示，研究区中二 叠纪时期整体表现为海相氧化环境；样品Rb/Sr比值及La/Th-Hf，La/Sc-Co/ Th，Th/Sc-Zr/Sc关系图解综合说明龙格组钙质 泥岩物源区风化作用较弱，源岩主要为安山岩；通过对沉积岩La/Sc-Ti/Zr，La-Th-Sc和Th-Sc-Zr/10等构造环境判别图 解分析，综合表明区钙质泥岩物源区的构造背景主要为大洋岛弧型。
Provenance analysis of sedimentary rocks has an important significance on revealing the composition of basins, qualities of reservoirs and sedimentary environment. Trace elements of Middle Permian carbonaceous mudstone samples in Jiaomuri area, Qiangtang Basin were analyzed and discussed. The study of trace element content，characteristic ratios and REE distribution indicates that the samples are moderately differentiated in LREE((La/Sm)N=2.50~5.41), while the HREE shows flat pattern ((Gd/Yb)N=1.32~2.47) and all samples have slight Eu abnormity. The ratios of Sr/Ba, V/Cr, Ni/Co, Ceanom and δEu values are used to reveal the redox of paleo-ocean. Our data show that the Middle Permian sedimentary environment where mudstones deposited was mainly oxidizing marine conditions. Ratio of Rb/Sr and La/Th-Hf, La/Sc-Co/Th, Th/Sc-Zr/Sc diagrams show that the provenance area underwent weak weathering and the source rocks are probably mainly andesitic rocks. La/Sc-Ti/Zr，La-Th-Sc and Th-Sc-Zr/10 discrimination diagrams suggesting that the carbonaceous mudstone of the Longge Formation formed probably in an oceanic island arc tectonic setting.