Oxygen isotope and trace element compositions of peridotite xenoliths from Panshishan volcano, SE China.

Oxygen isotopic compositions and trace element contents of minerals from 8 peridotite xenoliths hosted by Cenozoic basalts in Panshishan, SE China have been obtained by laser fluorination method and ICP-MS respectively. delta O-18 values of peridotie minerals fall into the range of "normal" mantle minerals, and isotopic equilibrium have been achieved among coexisitng minerals. Elevated incompatible element (U, Nb, Ta, LREE) contents of clinopyroxenes demonstrate that some Panshishan samples have undergone cryptical metasomatism. Combined with oxygen isotopic data, it is suggested that the metaomatic agent was melt originated within the mantle without involvement of crustal component. The previous studies have shown that the peridotites from Nushan, 100km north of Panshishan, have undergone metasomatism induced by fluid/melt with crustal component from paleo-subduction before the collision between South China and North China blocks at Triassic. Therefore, the deep boudary between South China and North China blocks is suggested to be just between Nushan and Panshishan.