Tracing an Early Jurassic magmatic arc from South to East China Seas

Drilling has revealed suites of magnesian granite and diorite emplaced in Early Jurassic time (198–195 Ma) and an arc-related low-temperature (678 to 696°C) magmatism in NE South China Sea. These rocks have 87Sr/86Sri (0.705494 to 0.706623) and εNdt (−0.9 to +2.2) as evidence of evolved mantle-derived magmas, coupled with enriched fluid-mobile elements Cs to K and Pb implying involvement of subduction-zone fluids. Another Early Jurassic granodiorite (zircon U-Pb 187 Ma) drilled from the SW East China Sea, a magnesian high-K calc alkaline, is comparably confined to a range of low-temperature (~675°C) arc-related granite, characterized by enrichment of fluid-mobile elements and Nb-Ta depletion. Its Sr-Nd isotopes (87Sr/86Sri = 0.705200, εNdt = 1.1) suggest a product of evolved mantle-derived melts. Together with detrital igneous zircons from Paleocene sequences, these observations reveal an Early Jurassic arc-related low-temperature (600 to 740°C) magmatism in the SW East China Sea. These arc-related granitoids, along with those from SE Taiwan, could define an Early Jurassic NE-SW trending Dongsha-Talun-Yandang magmatic arc zone along the East Asian continental margin paired with Jurassic accretionary complexes from SW Japan, East Taiwan to the West Philippines. This arc-subduction complex assembly was associated with oblique subduction of the paleo-Pacific slab beneath Eurasia, presumably responsible for Early Jurassic lithospheric extension in south China block.