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通过对扬子克拉通北缘西乡-碑坝小区寒武纪-侏罗纪碎屑沉积岩的Mo、Nd同位素进行测定,结合微量元素数据分析,结果表明,该区寒武纪-侏罗纪碎屑沉积岩的δ98Mo变化范围在?0.65‰~+1.87‰之间,εNd(t)变化范围在?1.46~?10.90之间.茅口组晚期一个样品(4820)具有相对偏正的δ98Mo和εNd(t)(0.97‰,?1.46),有可能与二叠纪晚期峨眉山地幔柱的喷发过程中,扬子克拉通北缘古海水中富集的大量硫化氢有关,此时海水中的MoO42?转变为MoS42?,并具有偏正的Mo同位素组成.晚二叠世长兴期样品(4814)也具有明显偏正的δ98Mo(1.87‰),但εNd(t)相对偏负(?10.90),并具有相对较高的总有机碳(TOC)含量和总硫含量(TS)(分别为1.52%,2.02%),暗示该时期具有较高的初级生产力和有机碳埋藏量,似乎表明脱硫酸还原作用产生的大量HS?,H2S与同期海相沉积岩明显偏正的δ98Mo有一定的耦合性.研究显示,古大陆边缘碎屑沉积岩的Mo同位素变化,与区域构造活动及产生的环境效应存在一定的相关性,可以作为指示区域古环境演化的有效示踪剂.
Through the determination of Mo and Nd isotopes of Cambrian-Jurassic clastic sedimentary rocks in the Xixiang-Beiba district, the northern margin of the Yangtze craton, and the analysis of trace element data, the results show that the Cambrian-Jurassic broken The δ98Mo range of sedimentary rocks is between 0.65 ‰ and 1.87 ‰, and εNd (t) varies between 1.46 and 10.90. A late Maokou Formation sample (4820) has relatively normal δ98Mo and εNd t) (0.97 ‰, 1.46) may be related to the large amount of H2S enriched in the ancient seawater at the northern margin of the Yangtze Craton during the Emeishan plume plume in the Late Permian. At this time, the MoO42? MoS42 ?, and has a positive Mo isotope composition.The Late Permian Changxing Period sample (4814) also has a significantly positive δ98Mo (1.87 ‰), but εNd (t) is relatively negative (1010.90) The higher total organic carbon (TOC) and total sulfur (TS) (1.52% and 2.02%, respectively) suggest a higher initial productivity and organic carbon burial during this period, which seems to indicate that the desulfuric acid reduction A large number of HS ?, H2S and over the same period marine sedimentary rocks significantly positive? 98Mo coupling has shown that the ancient continental margin sediment Mo isotopic variation of rocks has some correlation with regional tectonic activities and environmental effects, which can be used as an effective tracer to indicate paleoenvironment evolution in the area.