Comprehensive Research On Primary Dolostone Related To Lacustrine Exhalative Hydrothermal Activites Of The Permian Yuejingou Section, Xinjiang, NW China

In this paper, we do detailed research on petrography and geochemistry of laminated primary "dolostone" and "ankerite rock"developed in measured section in Permian Lucaogou Formation,Yuejingou Section, Santanghu Area, Xinjiang. Conclusions are summarized as follow:①The mineral composition of lacustrine exhalative hydrothermal rocks represented by laminated micrite "ankerite rock" and "dolostone" are mianly carbonate minerals related with hydrothermal activity(ankerite, dolomite, calcite), aluminosilicate minerals(alkali feldspar, analcime), silicate minerals(quartz) and small amount of metal sulfides, apatite and halite et.al. Hydrothermal minerals act as certain rules of paragenetic association and can be identified by combination type of ankerite, dolomite, alkali feldspar, analcime and quartz.②Electron Probe and geochemistry analysis shows this hydrothermal minerals are objective existence and have the same material source despite of their different texture and structure.③This set of lacustrine "white smoke type" exhalative hydrothermal rocks is mostly with microcrystal-cryptocrystal structure and we can find structure of hydrothermal intraclastic, hydrothermal exhalative breccia and syngenetic deformation bedding locally.④Carbon and oxygen isotope analysis infers that diagenesis environment was in characteristic of closed lacustrine facies with high temperature and salinity. Strontium isotope analysis suggests that hydrothermal fluids that formed exhalative hydrothermal rocks was originated from mantle.⑤Two sets of volcanic rocks underlying and overlying Permian Lucaogou Formation in Santanghu area indicate that strong and persistent volcanic activity in this area which reflects the activity of mantle material in Permian. And REE analysis reveals that the characteristics of exhalative hydrothermal rocks in Permian Lucaogou Formation in Santanghu area are similar to upper crust, which explans hybridism occur between hydrothermal fluids origaneted from mantle and crustal material.⑥Comprehensive tectonic setting analysis suggests that Santanghu basin enter into intracontinental evolution after Upper Carboniferous. Early-Middle Permian was in stage of regional extension, intracontinental fault basin, depression basin and developed a large number of high angle normal faults and contemporaneous faults that provided channels for the eruption and activity of hydrothermal fluids. Besides, multi-stages volcanic activity in this period urged hydrothermal fluids circulate easily.⑦Sedimentary model of exhalative hydrothermal rocks is inferred to be as follow. In magmatism period, alkaline magma overflowed and formed alkaline rock represented by analcime and alkali feldspar. And in magma intermission period, different compositions of hydrothermal fluids which dominated by carbonate alternative exhaled and urged the spray explosion of early originated rocks. Near the vents, hydrothermal exhalative breccia and intraclastic structure were formed. Far away from the vents, laminated micrite "ankerite rock" and "dolostone" were formed.⑧This paper discusses the genetic type of primary dolostone in Permian Lucaogou Formation in Santanghu area.⑨The discocery of exhalative hydrothermal rocks offer new ideas for oil and gas exploration in Santanghu basin.