GEOCHEMICAL CHARACTERS OF DOLOSTONE RELATED TO LACUSTRINE EXHALATIVE HYDROTHERMAL ACTIVITES OF THE PERMIAN, SANTANGHU BASIN, XINJIANG

Santanghu basin ,which was in the period of extension behind collision in Permian,is a superimposed basin formed over the Paleozoic orogenic basement. Because of the extension, mental fluid intruded into lithosphere, which established the foundation for the exhalation of hydrotherm and the formation of exhalative hydrothermal rocks.

The dolostone is mainly produced in Permian Lucaogou Formation (LF), Santanghu basin. Researches of 4 bisects show that the averge content of dolomite in dolostone is 60%. According to the results of geochemical analysis , ①the values of δ¹³C_PDB in dolostone are between -5.7‰ to 4.5‰ (1.07‰ in average), which fits the point of view that the range of typical lacustrine primary carbonate in δ¹³C_PDB is -2‰ to 6‰ (Kelt K.1990). ②The values of ¹⁸O_PDB in dolostone are -1.99‰ to -6.1‰ (1.07‰ in average).Calculated by the equation: T=13.85 -4.54 δ¹⁸O_PDB +0.04(δ¹⁸O_PDB)² (XuZhiwei,1999), the formation temperature of Permian Lucaogou Formation (LF) is higher than 42.59℃ but less than 128.25℃,and the average temperature is 67.92℃，which means a lacustrine hydrothermal environment.③The values of ⁸⁷Sr/⁸⁶Sr in doloston are 0.704605~0.70722 (0.706006 in average), which is less than average crustal source ⁸⁷Sr/⁸⁶Sr: 0.7119 (Palmer M R, et al，1989), showing the characteristics of the mantle fluid.

In conclusion: geochemistry characters show that the dolostone in Permian Lucaogou

Formation (LF) deposited in a lacustrine hydrothermal environment with the participation of the mantle hydrotherm. In a sense, the characters represent a kind of new type primary dolostone related to lacustrine exhalative hydrothermal activites.