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 eNdt (−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, is 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, eNdt = 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, E Taiwan to the W 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.