Late Mesozoic orogenesis along the coast of Southeast China and its geological significance

Abstract：The Changle-Nan’ao zone is situated along the southeastern margin of the Southeast China continent, hence it may hold a key to understanding the interactions between the Eurasian and Paleo-pacific plates and geological evolution of the coastal areas in Late Mesozoic. The T3-J1 sedimentary rocks in the coastal zone are unconformably overlain by Lower Cretaceous Nanyuan Formation or occur as amphibolite facies enclaves in late Jurassic-early Cretaceous gneissic granites. The metasedimentary rocks (T3-J1) enclaves with penetrative migmatization were deformed together with the wall rocks (gneissic granites) and intruded by insignificantly deformed Cretaceous granitic plutons or dykes. Metamorphism and deformation in the late Triassic to early Jurassic (T3-J1) metasedimentary rocks are characterized by cratonward (NW) weakening. The Lower Cretaceous Nanyuan Formation is characterized by extensive folding and greenschist facies metamorphism and unconformably covered by the Upper Cretaceous Shimaoshan Group, showing no signs of metamorphism. The major stratigraphic units and tectonics in the Changle-Nan’ao zone indicate that the continental margins underwent two stages of compression (orogenesis) in Late Mesozoic. During the first episode of orogenesis, the late Triassic to early Jurassic (T3-J1) continental sediments were folded and metamorphosed. Subsequently, the folded and metamorphosed T3-J1 sedimentary rocks were exhumed together with other rocks from the depth of middle and upper crusts in early Cretaceous, accompanied by large scale synkinematic magmatism (147-135 Ma) and regional migmatization. During the second stage of compression in Late Mesozoic, the Nanyuan Formation was folded and metamorphosed. The 110-100 Ma magmatic complex, the 100-90 Ma A-type granites, and the 90-80 Ma bimodal igneous rocks in coastal areas of Southeast China might be correlated with the middle Cretaceous crustal contraction and the subsequent crustal extensions, respectively. Consequently, the two Late Mesozoic magmatic cycles (165-120 Ma and 110-80 Ma) might be controlled by the two synchroneous tectonic cycles (165-120 Ma and 115-80 Ma). Each of the Late Mesozoic tectonic cycles includes a crustal contraction and a subsequent crustal extension. It should be noted that the Late Mesozoic tectonics and magmatism in the coastal areas of Southeast China seem to be comparable with those that simultaneously occurred in the hinterland of the continent.