ON THE PROBLEM ABOUT THE CRUST'S ATTRIBUTION OF SOUTH CHINA SEA BASIN——DISCUSSION FROM COMPARATIVE STUDY ON BASALTS OF SEAMOUNTS IN SOUTH CHINA SEA BASIN AND THE NEIGHBORING AREAS
ZOU Heping (Changsha Institute of Geotectonics, A cademia Sinica, Changsha, 410013)
According to a comparative study on the basalts from seamounts in the South China Sea Basin (SCSB) and those from Leizhou Peninsula-North Hainan and Reed Bank Seamount, this paper takes a sceptical attitude to the view that the crust oF SCSB is an oceanic crust.The seamounts in SCSB arc not all formed by the post-spreading volcanism. Some were formed calier than the period or the same time when the so-called sea-floor spreading took place. In the same type of basalts from the seamounts in SCSB and from Leizhou Peninsula-North Hainan and Reed Bank Seamount, the content of major elements, the value of K_2O/Na_2O and KO_1(KO_1=MgO+2TiO_2-3K_2O), the variance of (La/Yb)_N, Zr/Nb, Rb/Sr, Nb/Yb, La/Nb, and the patterns of trace elements and REE are quite similar. Also, the rocks have similar Sr-Nd-Pb isotopic ratios and variants. It is shown that the basalts of seamounts in SCSB have a closer affinity to continental basalt than to oceanic basalt. And therefore, the author believes that the data of lithology and geochemistry, also chronology of the basalts do not support the view that the crust of SCSB is an oceanic crust. At least, the crust of SCSB does not belong to the typical new-born oceanic crust generally recognized.