关键词: 塔中地区, 奥陶系, 碳酸盐岩, 埋藏溶蚀, 地球化学特征

Abstract: The geological background and rock geochemistry characteristics of carbonate burial dissolution in the Ordovician system of the northwestern Tazhong area were analyzed. The results show that the burial dissolution has an important role in the development of carbonate rock reservoir. The magmation and thermal fluid alternation in the Middle-Late Permian and the multistage tectonic movement are the basic conditions for developing burial dissolution. The hypogenic diagenesis is characterized by the minor volumes of critical fingerprints of pyrite, chlorite, quartz, fluorite, ferrodolomite, solid bitumen and the bright orange-yellow luminescent calcites with rather low contents of iron elements and high richness of manganese contents existing in fracture-filling oscillatory-zoned calcites. The chemical analysis also indicates that the fracture-filling calcites have very high contents of manganese, strontium and magnesium elements. The isotope data show that the mean value of δ¹⁸O_PDB is -6.6‰ and δ¹³C_PDB is -2.0‰ . In addition, the most striking feature in histograms of micro-thermometric measurements for aqueous inclusion in the Ordovician reservoirs is characterized by homogenization temperature from 115℃ to 130℃ and from 170℃ to 210℃. The calculated salinity of the inclusion ranges from 5% to 7% , from 8% to 9% and from 12% to 13% . It is concluded that the multistage and original hypersaline formation water overlapped by the magmatic-hydrothermal fluid in a large scale of strong epigenic dissolution exists in the northwestern Tazhong area.

Key words: Tazhong area, Ordovician, carbonate rocks, buried dissolution, geochemical characteristics