Classification of Yanshanian volcanic cycle and the related mineralization in the coast area of southeastern China

Subduction of the Paleo-Pacific plate in Late Mesozoic resulted in intense volcanism and the formation of giant volcano-intrusive complex in the coastal area of southeastern China.Based on the rock association, time-space distribution, regional unconformity, tectonic background and mineralization type, the volcanic activities can be classified into four cycles.The first cycle (200~165 Ma) is represented by a set of nearly EW-trending bimodal volcanic rocks consisting of tholeiitic basalt and rhyolite.The basalt was mainly originated from asthenospheric mantle under the Indosinain post-tectonic plate extensional environment.During this period, the mineralization was weak.The second cycle (165~145 Ma) is the transition from peak compression to extension of epicontinental arc because of subduction, represented by the scattered calc-alkaline series andesitic dacite with association of low-temperature hydrothermal gold deposits and other non-metallic deposits, such as pyrophyllite.The third cycle (145~115 Ma) reflects extension stage of South China after subduction of paleo-Pacific plate, in which large areas of volcanic rocks consisting of high potassium calc-alkaline series rhyolite and dacite were formed in Mesozoic due to intensive volcanism.It was associated with abundant metallic, nonmetallic and rare earth minerals, dominated by hydrothermal type.In the fourth cycle(115~85 Ma), volcanism weakened and migrated toward east to the coastal area, dominated by the central eruption accompanied by A-type granite.It is a set of bimodal volcanic rocks with peralkaline rhyolite in the post-orogenic environment and developed porphyroclastic lava in the late period.In this stage, abundant metals and non-metallic minerals such as alunite and phyllite were formed, and the epithermal hydrothermal type was dominant, followed by porphyry type.