Oceanic plate stratigraphy and tectonic evolution of the Nujiang-Lancangjiang-Jinshajiang area in southwestern China

The present paper focuses on the preliminary study of the distribution and tectonic evolution of the oceanic plate stratigraphy,including the successive evolution,stepwise amalgamation and plate-accretion,and final subduction, consumption and closure of the Proto- and Palaeo-Tethys ocean in the Nujiang-Lancangjiang-Jinshajiang area in southwestern China. The Garze-Litang back-arc ocean basin has gone through the initiation during the Early Carboniferous,culmination during the Permian to the Middle Triassic,decline and westward subduction during the Late Triassic,and finally preservation of only a part of the ocean during the latest Late Triassic. The Ailaoshan back-arc ocean basin was formed no later than the Early Carboniferous,fully expanded during the the period from the Early Carboniferous to the Early Permian,subducted westwards at the end of the Early Permian or at the beginning of the Late Permian,and finally terminated during the Late Triassic. The Jinshajiang ocean basin was opened and expanded into an ocean during the Early Carboniferous,began subduction at the end of the Early Permian,culmianted during the period from the Carboniferous to the early Early Permian, and came to the subduction and collapse during the period from the end of the Early Permian to the Early and Middle Triassic. The Lancangjiang back-arc basin began expansion during the Middle to Late Devonian,developed into a mature ocean basin during the period from the Carboniferous to the Early Permian. Then an intra-oceanic arc was created through intra-oceanic subduction,and finally the Lancangjiang back-arc basin was closed as a result of birectional subduction during the period from the Late Permian to the Early and Middle Triassic. The Changning-Menglian ocean as the major part of the Tethys ocean which represents the geological records of Proto- and Palaeo-Tethys oceanic evolution began subduction eastwards and consumption during the Late Ordovician,and finally closed due to the arc-continent collision during the period from the latest Permian to the Early Triassic.