LA-ICP-MS U-Pb Age, Clumped and Stable Isotope Constraints on the Origin of Middle Permian Coarse-Crystalline Dolomite Reservoirs in Northwest Sichuan Basin, Southwest China

摘要

Objective The recent discovery of commercial natural gas accumulations in the Middle Permian coarse-crystalline dolomites in the northwest Sichuan Basin has attracted attention to the formation mechanism of these deep-burial carbonate reservoirs.Due to their temporal relationship to the flooded basalts that represent the end-Middle-Permian Emeishan Large Igneous Province(ELIP),the Middle Permian dolomites were prev iously thought to be products of hydrothermal dolomitization related to the ELIP magmatism.Field and core observations,however,show that the occurrence and distribution of these dolomites are not controlled by faults,the supposed conduits for hydrothermal fluids.Conversely,they are somewhat strata-bound.Hence,the objective of this study,by employing LA-ICP-MS U-Pb dating,clumped isotope thermometry(047)and routine stable isotope geochemistry(C carbon,O oxygen and Sr strontium isotopes),is to re-evaluate the genesis of these dolomite reservoirs,with special attention focusing on the diagenetic environment and timing of dolomitization,and the attributes of dolomitizing fluids.