The Model of Dolomitization Jointly Controlled by Two-episode Fluids in Maokou Formation in Central Sichuan Basin

Key words: 
• central Sichuan Basin /
• Lower Permian /
• Maokou Formation /
• petrographic characteristics /
• geochemical analysis /
• dolomitization fluids /
• model of dolomitization

Abstract: Petrographic characteristics and geochemical analysis reveal that there exist three types of dolomites in dolostones in Maokou Formation, Lower Permian, central Sichuan Basin:①idiotopic fine crystal-dolomite(IFD)(δ¹³C_PDB=3.06‰, δ¹⁸O_PDB=-6.81‰; Fe:1×10^-6, Mn:negative, Sr:150×10^-6);②xenotopic coarse crystal-saddle dolomite(XCSD)(δ¹³C_PDB=3.22‰, δ¹⁸O_PDB=-7.82‰; Fe:149×10^-6, Mn:185×10^-6, Sr:85×10^-6); ③xenotopic fine crystal-dolomite(XFD)(δ¹³C_PDB=3.49‰, δ¹⁸O_PDB=-9.45‰; Th=123℃, S=133‰~139‰NaCl; Fe:58×10^-6, Mn:59×10^-6, Sr:76×10^-6).This study demonstrates that two episodes of dolomitization fluids in the study area:①early burial-dolomitization fluid formed by compaction(T=37.4℃; S=29.8‰NaCl); ②late hydrotherm-dolomitization fluid controlled by structure(Th=114.8℃; S=153‰~226‰NaCl).The origin of the dolostone is illustrated that:①IFD is replacive by early burial-dolomitization fluid; ②XFD is the product of hydrothermal alteration on IFD; ③XCSD is precipitated directly from hydrothermal fluid.Based on the achievement, corresponding model of dolomitization has been established.