Research Starting From The Feature Of Late Neogene WPB In The Northwest Of The SCS

The lithology、major element、trace element、transtion element and Rb-Sr、147Sm/144Nd、143Nd/144Nd、206pb/204Pb isotopic ratios of the basalts from Leiqiong area of china and KonTum area of Viet Nam were determined in this paper. The basalts are quartz tholeiites、olivine tholeiites、alkali olivine basalts and mantle xenoliths (Mg#:89.77-92.48), The main conclusions in this paper are as follows:(1) The high field strength elements(HFSE) of the basalts in the northwest margin of the SCS in late neogene, such as Nb, Ta, Hf, e.g., are enriched, The features of geochemistry are similar to OIB, and the basalts are WPB. Based on its geological characteristics and other information, the Leiqiong area has the higher regional geothermal anomalies. So the northwest margin of the SCS should have a larger scale mantle plume.(2) The volcanic eruptions leaded by the mantle plumes began in the late Miocene, it occurred after the spreading of the SCS. It is no obvious connection with the spreading of the SCS.(3)The basalt physicochemical properties in Sanshui basin in the Eocene epoch are similar to the basalts of Leiqiong and Kon Turn area. Especially, the basalts of the Kon Turn in Late Miocene are more similar to the basalts of Sanshui basin in the Eocene epoch, it hints that the position of mantle plume in the SCS and northwest margin area has possibly changed in time and space.(4) The isotopic data suggest that the origin composed by DM&EMII, the transition element and isotopic indicates that the formation of a large number of basaltic magma may be contaminated by the ocean crust component.