The Petrographic and Geochemical Signatures and Implication of Origin of the Middle and Upper Cambrian Dolostone in Eastern Margin Tarim: Comparative Studies with the Whirlpool Point of the Western Canada Sedimentary Basin
详细信息
- 责任者：Qian YiXiong(Wuxi Institute ; Exploration & Production Research Institute ; SINOPEC ; Wuxi 214151 ; China) ; You DongHua
- 刊名：Acta Petrologica Sinica
- 出版年：2012
- 卷期：28(8)
- 关键词：白云岩 ; dolostone ; 塔里木盆地 ; Tarim Basin
- 页码：p.2525-2541
- 图表：illus.,4 tables,42 refs.
- 分类号：0803
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Comparative studies fault/fracture controlled the hydrothermal dolomitization, occurred pervasively in Cambrian at the Whirlpool point outcrops, the Western Canada Sedimentary Basin, with regard to petrographic, geochemical, isotopic and fluid inclusion demonstrated that three major dolomitization events in the Middle Cambrian Moheshan Group and Upper Cambrian Tereshakeitaga Group at Wuzilitaga outcrop, Northeast Tarim basin, have been recorded. (1) Near-micritic dolostone and fine-medium crystalline dolostone, formed at low temperatures during early stages of diagenesis, similar to the replaced host rock ("matrix") in their succession and geochemical signatures; with negative value δ13CPDB (-0.47‰~-0.28‰) and δ18OPDB values (-7.3‰~-7.43‰) as well as the lower Sr contents (42.75×10-6), rather higher content of Mn (312×10-6~506×10-6) and Fe (0.2650%~0.403%); 87Sr/86Sr=0.71085; REE=18.84×10-6, δEu=0.66, δCe=0.81, the estamted temperature 47.6℃ for near-micritic dolostone and 55.12℃ for fine-medium crystalline dolostone. (2) Fine-medium and medium-coarse crystalline dolostone supposed to formed during intermediate or deep burial condition, with depleted δ13CPDB (-1.5‰) and δ18OPDB (-8.5‰) as well as the lower Sr contents (56.27×10-6), Mn (312×10-6) and Fe (0.13%); with rather higher homogenization temperatures (up to 108.34℃ at average temperature) and estimates of low and medium salinities (4%~13.7%NaCleqv). (3) Fractures and vugs-lining coarse or saddle dolomite precipitation, with the lowest Sr (29.1×10-6~49.9×10-6), the highest content Mn (498×10-6~754×10-6) and Fe (0.15%~1.14%), δ13CPDB=-0.48‰ and depleted δ18OPDB=-8.82‰, 87Sr/86Sr=0.70996; REE=15.08×10-6, δEu =0.70, δCe=0.78; formed under either relatively deeper burial conditions or possibly from hydrothermal fluids, which is supported by elevated homogenization temperatures (120~150℃) and estimates of slightly higher salinities (5%~12%NaCleqv) for saddle dolomites; and highest homogenization temperatures (140~180℃) and estimates of medium to higher salinities (5%~18%NaCleqv) for coarse and huge crystal dolomitse, in which completely occludes the fractures, breccias and vugs. Compare with the Cambrian hydrothermal dolomite (HTD) occurred at the Whirlpool point outcrops, the Western Canada Sedimentary Basin, which has been related to the hydrothermal fluids, expelled from the Rocky Mountain fold-and-thrust belt during the Laramide orogeny. The coarse-huge crystal and saddle dolomite in fractures and vugs at Wuzilitaga outcrop have a feature of higher δ13C, δ18O, REE and HREE/HREE with a little lower contents of sequentiality (degree of order), δEu and δCe, in addition to the presence of rather lower homogenization temperatures and salinity in fluid inclusions, suggested to intimately associated with a slightly hot basinal saline, presumably mostly derived from re-circulated of formation water, which have been funnelled upward along strike-slip faults and fractures,developed and facilitated during the Late Permian (Late Hercynian) or from the Yansha to Himalaya (Late Cretaceous to Quaternary) in Northeast Tarim.