The Northeast Mindoro block is the conjugate margin of the southern East China Sea Basin: Insight from detrital zircon data

There is a hot debate over whether the initial opening of the South China Sea (SCS) took place in continental crust or oceanic crust. In this study, we present new detrital zircon U–Pb ages from late Eocene sedimentary rocks in the East China Sea Basin (ECSB). Our results reveal a broad U–Pb age spectrum with a substantial proportion of grains dating >1500 Ma. Notably, the provenance characteristics of the late Eocene ECSB are markedly distinct from other regions along the South China margin, as evidenced by kernel density estimation, nonmetric multidimensional scaling, and cumulative age distribution plots. The ECSB shared nearly identical provenance features with the northeast Mindoro block on the southern SCS margin during the late Eocene. Considering the previously proposed widespread breakup unconformity across the southern ECSB and the slab-based plate reconstruction from tomography of the SCS, we propose that northern Mindoro was the conjugate margin of the southern ECSB and underwent southward drifting during the SCS opening. This study provides a new plate reconstruction model of the SCS and evidence supporting the contention that the initial breakup of the SCS occurred within the continental crust.