A New High-resolution Oceanic Crustal Age Model and Plate Reconstruction of the South China Sea

The South China Sea (SCS) is a crucial part of the tectonic framework of Southeast Asia. Due to sparse magnetic data and a lack of microfossil or radiometric ages, the crustal age and tectonic evolution of the SCS have been debated. The latest high-resolution sea surface magnetic data with a total length of 40,000 km in the SCS were collected from 1999-2014. Constrained by ages from recent International Ocean Discovery Program (IODP) Expeditions 349, 367 and 368, we identify 1136 magnetic anomaly picks that are four times the number of that presented in previous studies. We then present a new, high-resolution oceanic crustal age model for the SCS based on the identified magnetic anomaly picks. The crustal age model suggests that the spreading ages of the east, northwest, and southwest sub-basins are C13n-C5Cr (33.2-17.0 Ma), C12n-C10r (30.7-29.0 Ma), and C6Cr-C5Cr (24.4-17.0 Ma), respectively. The flowlines based on the oceanic crustal ages indicate that the spreading directions underwent a conspicuous counterclockwise rotation (by 34°) at anomaly C6Ar (~21.5 Ma), causing an elongate S-shaped boundary between the east and southwest sub-basins. Further plate reconstructions of the SCS reveal that the entire SCS basin gradually propagated from northeast to southwest and that the continental margins of the southwest sub-basin are conjugated in the NNW-SSE direction.