Strontium and Sul f ur Isotope Compositions and the Significance of the Pal ao-Oceanic Geol ogy in the Middl a Cretaceous in the South Tibet
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摘要: 讨论了西藏南部中白垩世海相碳酸盐锶同位素组成和黑色页岩中黄铁矿硫同位素组成的主要特征及其古海洋地质意义。主要结论是:①该区中白垩世海相碳酸盐的锶同位素组成在0.7084~0.7090之间,大陆壳来源的锶占28%~30%,陆源物质输入的影响高于其它地区;火山熔岩中锶的同位素组成为0.7095,高于同期玄武岩的平均值,火山熔岩中大陆壳来源的锶约为65.2x10-6,占总锶量的34%左右,火山熔岩形成过程中,同化了大量的壳源物质。②该区中白垩世黑色页岩中的黄铁矿的硫同位素组成为27‰~31.6‰,它来源于同期海水硫酸盐,且系中晚期成岩作用的产物,不同时间、不同沉积环境中形成的黄铁矿,其δ34S值差异明显,它们动态地反映成岩作用中环境的演化过程。Abstract: Discussed the principal features of the strontium isotope composition in oceanic carbonates and the sulfurisotope composition (pyrites)in the black shale,as well as the significance of the palao-oceanic geology in theMiddle Cretaceous in the South Tibet, as follows. 1. The 87Sr/8Sr ratio in the oceanic carbonate was about 0. 708 4-0. 709 0. Strontium originated fromthe crust amounted to 28%一3000.The influence inputted from the continental materials in the studied areawas greater than that in the other areas. The 87Sr/86Sr value in the volcanic lava was 0. 709 5,and higher thanthe average value of the synchronous basalt. The strontium,originated from the crust,in the volcanic lave ac-counted for 65.2 X 10-6 , amounting to 34%in the total. A large number of the crust origin materials was as-similated in the forming process of the volcanic lava. 2. The sulfur isotope composition (pyrites) in the black shale was 27%-31. 6%.The sulfur originatedfrom the synchronous seawater sulfate,and the pyrite was the diagenetic product in the middle— late diage-nesis. The δ34S (pyrites),formed in the different time and environment, was very different. The sulfur iso-topes could reflect the environment evolution process in the diagenesis.
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Key words:
- visotope composition /
- material origin /
- environment evolution /
- palao-oceanic geology
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[1] 1 余光明,王成善·西藏特提斯沉积地质·见:地质专报,矿物岩石,地球化学:第12号·北京:地质出版社,1990. 10-38
2 Burke W H,Denison It E,Hetherington E A,et al. Variation of sea-water 87Sr/86Sr throughout phanerozole time. Geology,1982, 10,516-519
3 Faure G. Principies of Isotope GeologyCthe second edition),NewYorke,John Wiley Sons. 1986. 141-151.161-164,183-193,523--531
4 格里年科BA,格里年科πH.著.硫同位素地球化学·赵瑞译北京:地质出版社,1980.58-59,64,67 -

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