摘要
Five evolutional phases are found from Mesozoic basin-fill sequences in the northern Jianghan basin, the south foot of the Dabie Mountains: (i) Early Triassic to the early period of Late Triassic showing continental shelf marine and paralic deposits; (ii) the middle-late period of Late Triassic indicating the uplift and erosion in compressional tectonic setting; (iii) the late period of Late Triassic to Early-Middle Jurassic showing peneplain terrestrial and fluvial clastic deposits interlayered with coal-seams; (iv) Late-Jurassic to Early-Cretaceous characterized by cycle fills of acidic volcanic rocks interstratified with pyroclastic rocks in intracontinental extension tectonic regime; (v) a lot of coarse clastic deposits similar to molasses occur in Late-Cretaceous mainly. Based on the compositions of detrital sandstones and conglomerates, combined with the analysis of sedimentary facies, it is indicated that most clasts sourced from the Yangtze continent from phase one to phase three, whose provenances are attributed to “recycled orogenic belt” types. On the other hand, detrital assemblages of the fifth phase deposits are mainly related with pre-Mesozoic metamorphic rocks of the Dabie Mountains, subjected to “arc orogenic belt” provenance types. In the Mesozoic basins of the south foot of the Dabie Mountains, it is proved that there are no direct depositional records corresponding to “Late Triassic syn-collisional orogenesis”. Molasse depositional records of Upper Cretaceous distinctly reflect post-collisional orogenesis of the Dabie Mountains (intracontinental orogenesis) and intensive exhumation in extensional tectonic regime. This paper further discusses the inconsistent relations existing between basin-fill records at the south and north feet of the Dabie Mountains and the uplift models of the Dabie Mountains published, and indicates their key problems.
Five evolutional phases are found from Mesozoic basin-fill sequences in the northern Jianghan basin, the south foot of the Dabie Mountains: (i) Early Triassic to the early period of Late Triassic showing continental shelf marine and paralic deposits; (ii) the middle-late period of Late Triassic indicating the uplift and erosion in compressional tectonic setting; (iii) the late period of Late Triassic to Early-Middle Jurassic showing peneplain terrestrial and fluvial clastic deposits in-terlayered with coal-seams; (iv) Late-Jurassic to Early-Cretaceous characterized by cycle fills of acidic volcanic rocks interstratified with pyroclastic rocks in intracontinental extension tectonic re-gime; (v) a lot of coarse clastic deposits similar to molasses occur in Late-Cretaceous mainly. Based on the compositions of detrital sandstones and conglomerates, combined with the analysis of sedimentary facies, it is indicated that most clasts sourced from the Yangtze continent from phase one to phase three, whose provenances are attributed to 搑ecycled orogenic belt?types. On the other hand, detrital assemblages of the fifth phase deposits are mainly related with pre- Mesozoic metamorphic rocks of the Dabie Mountains, subjected to 揳rc orogenic belt?provenance types. In the Mesozoic basins of the south foot of the Dabie Mountains, it is proved that there are no direct depositional records corresponding to 揕ate Triassic syn-collisional orogenesis? Molasse depositional records of Upper Cretaceous distinctly reflect post-collisional orogenesis of the Dabie Mountains (intracontinental orogenesis) and intensive exhumation in extensional tectonic regime. This paper further discusses the inconsistent relations existing between basin-fill records at the south and north feet of the Dabie Mountains and the uplift models of the Dabie Mountains pub-lished, and indicates their key problems.
基金
This work was supported by the Innovative Project of the Chinese Academy of Sciences (Grant No. KZCX1-07) and the National Key Fundamental Research Project (Grang No. G1999043303).
