Seafloor spreading anomalies in the South China Sea revisited

We present an updated interpretation of seafloor spreading anomalies in the South China Sea based on new magnetic data from two RN Sonne cruises. Great efforts were made to correct the data for the magnetic daily variations arising from ionospheric currents which are particularly strong in the surveyed area. Our interpretation is that symmetric seafloor spreading of 5.6 cm/year full rate began at similar to31 Ma at an E-W trending ridge in the central part of the South China Sea. After a ridge jump of similar to50 km to the south at 25 Ma spreading accelerated to 7.3 cm/year full rate. At the same time or shortly thereafter a second spreading center became active in the southwestern part of the South China Sea which we believe remained separated from the original spreading axis. The full rate was somewhat higher at 8.0 cm/year at this spreading ridge. The formation of oceanic crust ended at 20.5 Ma simultaneously at both spreading axes. This interpretation provides a convincing correlation of high quality measured data and synthetic magnetic profiles. It differs significantly from the findings of earlier studies.