Reassessment of petrogenesis of Carboniferous—Early Permian rift-related volcanic rocks in the Chinese Tianshan and its neighboring areas

The Carboniferous-Early Permian rift-related volcanic successions, covering large areas in the Chinese Tianshan and its adjacent areas, make up a newly recognized important Phanerozoic large igneous province in the world, which can be further divided into two sub-provinces： Tianshan and Tarim. The regional unconformity of Lower Carboniferous upon basement or pre-Carboniferous rocks, the ages （360--351 Ma） of the youngest ophiolite and the peak of subduction metamorphism of high pressure-low temperature metamorphic belt and the occurrence of Ni-Cu-bearing mafic-ultramafic intrusion with age of ~352 Ma and A-type granite with age of ~358 Ma reveal that the final closure of the Paleo-Asian Ocean might take place in the Early Mississippian. Our summation shows that at least four criteria, being normally used to identify ancient asthenosphere upwelling （or mantle plumes）, are met for this large igneous province： （1） surface uplift prior to magmatism; （2） being associated with continental rifting and breakup events; （3） chemical characteristics of asthenosphere （or plume） derived basalts; （4） close links to large-scale mineralization and the uncontaminated basalts, being analogous to those of many ＂ore-bearing＂ large igneous provinces, display Sr-Nd isotopic variations between plume and EMI geochemical signatures, These suggest that a Carboniferous asthenosphere upwelling and an Early Permian plume played the central role in the generation of the Tianshan--Tarim （central Asia） large igneous province.

Late Carboniferous-Early Permian Volcanic Event Deposits and Stratigraphic Correlation in Shandong Province and Its Adjacent Regions

Deposits of 10 volcanic events of 6 stages have been discovered by the authors after detailed field and lab studies of the Benxi and Taiyuan Formations in Shandong Province and its adjacent regions. They show certain temporal-spatial distribution characteristics. Volcanic fragments were probably derived from two different volcanic sources north and south of the North China Platform, while the magma of the two volcanic sources was probably derived from the lower crust. A new stratigraphic correlation scheme is put forward for the Benxi and Taiyuan Formations in this region on the basis of previous biostratigraphic work with the regionally widespread volcanic event layers as the marker bed for the isochronous stratigraphic correlation on a super-regional scale and in conjunction with the maximum transgressive event layers.