Using olivine to constrain the mechanism for the opening of the South China Sea
Mantle plumes and plate tectonics represent two fundamental geodynamic mechanisms that play crucial roles in Earth's geological processes.The South China Sea(SCS)is located at the intersection of the Hainan mantle plume and the convergent subduction zone within Southeast Asia.The role of the Cenozoic mantle plume in the opening of the SCS remains a subject of debate.Given that basalts genetically linked to mantle plumes in the SCS and its surrounding areas share a pyroxenite mantle source,we used olivine from mid-ocean ridge basalts(MORBs)recovered from the northern SCS during the International Ocean Discovery Program(IODP)Expedition 367 to constrain the lithology of the mantle source for this nascent ocean and testify the involvement of mantle plumes in its initial opening.The olivine phenocrysts in the U1500B MORB exhibit a range of compositions of Fo=76.4～89.4,NiO=0.09％～0.26％,CaO=0.25％～0.34％and MnO=0.16％～0.33％.The concentrations of NiO,CaO and MnO and the FeO/MnO ratio of the olivine phenocrysts are similar to those observed in the MORBs recovered from Site U1433B near the fossil ridge of the southwest subbasin of the SCS and MORBs from mid-ocean ridges off mantle plumes.The peridotite source is inferred for the initial opened SCS,suggesting the absence of the Hainan mantle plume for the initial opening of the SCS.This result aligns with the previously estimated normal mantle potential temperature for the U1500B mid-ocean ridge basalts(～1380℃).The initial ridge of the SCS exhibits high magmatic productivity but shows little mantle thermal anomaly or fusible components such as pyroxenite,suggesting an abundance of recycled volatile from subducted slabs.Therefore,it is plausible that lithospheric extension resulting from the rollback of subducted slabs may serve as the primary mechanism for the opening of the SCS.
South China SeaOlivineSource lithologyMantle plumeMid-ocean ridge basalts
万方数据
维普
