Plume-ridge interaction in the South China Sea: Thermometric evidence from Hole U1431E of IODP Expedition 349

Abstract

Testing the hypothesis that the Hainan mantle plume triggered the opening of the South China Sea (SCS) and interacted with the spreading ridge is important for the purpose of understanding the dynamics of the evolution of the SCS. This study examined the most primitive olivine (Fo = 83.1–87.1) and spinel (Cr# = 28–60%) in the basalt and glassy samples collected from Hole U1431E of International Ocean Discovery Program (IODP) Expedition 349, with the goal of estimating the crystallization temperature. Spinels mostly enclosed by olivines have low Fe3+ and Ti contents and show compositional equilibrium with the host olivines. The application of the Al-in-olivine thermometer provided crystallization temperatures for the studied samples, which varied from 1208 ± 29 °C to 1287 ± 29 °C. When extrapolating to primitive olivine of Fo = 90, the crystallization temperature of primitive olivine is approximately 1350 °C, which is much higher than that of other primitive mid-ocean ridge basalt (MORB) but comparable to that of Iceland oceanic island basalt (OIB). Therefore, the mantle potential temperature at the extinct ridge of the SCS at ~16 Ma is much higher than that beneath a normal mid-ocean ridge, manifesting the mantle plume-ridge interaction during the last spreading of the SCS. Given the lack of thick oceanic crust, seamount chains or lineaments in the SCS, we propose that this plume impacted on the SCS might be eclogite-rich and of low buoyancy.