Meso-Cenozoic Tectono-thermal History Of Shiwandashan Basin, South China

Field structural, sedimentological as well as indoor inorganic geochemistry, fission trackdating and fluid inclusion analysis are carried out for Meso-Cenozoic Shiwandashan basin inSouth China, which is an important target basin for oil exploration during the past years. Theobjectives of this study include the reconstruction of the tectono-thermal history of the basinas well as the understanding of the relationship between tectonics and sedimentary process aswell as the estimation of amount of erosion.The tectonic history of Shiwandashan basin since Paleozoic can be divided into 5 stages,i.e.,. Passive margin-arc collision (Canbrian-Silurian), passive margin (closure ofQinzhou-Fangcheng sea trough, Devonian-Early Permian), retro-arc foreland basin (LatePermian-Middle Triassic), collisional foreland basin (Late Triassic-Cretaceous) andStrike-slip-compressional inversion (Tertiary). Fore sedimentary cycles can be identifiedfrom Late Triassic to Tertiary, with the depocenter and the subsidence center migratednorthward to northeastward. Fission track analysis is carried out for 37 apatite samples and6 zircon samples from Mesozoic strata in Shiwandashan basin. Fission track ages for allapatite samples are younger than their respective strata ages, which shows that the maximumburial temperatures for these samples exceeded the total annealing temperatures of the fissiontracks. Time-temperature history modeling based on apatite fission track analytical datashows that these samples experienced similar low temperature history. These samplesreached their maximum burial temperature (ranging between 98~C-175~C) during the periodof 41-85Ma, which was followed by a period of monotonous cooling and uplifting. Vitrinitereflectance (Ro) measurements on the source rock from the basin show that the basinexperienced two stages of thermal event: Early/Late Permian and Early-Middle Triassic. Thepaleo-thermal gradient of Mesozoic and Cenozoic are 4℃/100m and 3～2.5℃/100m,respectively.Integrated analysis on fission track, fluid inclusion, R_o data and geologicalhistory shows that the basin has experienced three stages of erosion since Mesozoic: LateTriassic-Middle Jurassic, Late Jurassic-Early Cretaceous and Late Cretaceous-Cenozoic, withthe last period being the major period of erosion.