Geochemical characteristics of Early Palaeozoic plagioclase granite from ophiolitic cumulate in central Qiangtang, northern Tibet, China

Taoxinghu ophiolite was an important discovery of Longmu Co-Shuanghu suture zone in recent years. This discovery has given an answer to the doubt that there was not a complete ophiolite section in Longmu Co-Shuanghu suture zone, and it is an important evidence of the existence of this suture zone and at the same time it is one of the main foundations to confirm the time of the decomposition of Paleo-tethys Ocean. The plagiogranite′s petro-geochemistry characteristics have indicated the attribute of oceanic ridge granite, including high Al2O3 content, from medium-aluminous to super-aluminous (12.56%~16.19%), high Na2O, low K2O (Na2O/K2O>3), low content of major elements, trace elements and rare-earth elements. However, the REE distribution patterns and trace element patterns of plagiogranite were different from the standard oceanic ridge plagiogranite, which displays obvious differentiation of LREE and HREE and intensely Eu positive anomaly (Eu/Eu?鄢=1.92~9.19, mean value is 5.18). Preliminary estimation is that this is due to complete Ca separation during the rapid rising process of magma and non-uniform distribution of garnet in the samples. According to former research results, the preliminary conclusion was that the magma of plagiogranite came from mantle，which is the same as metamorphosed peridotite, cumulate gabbro and basic lava of Taoxinghu ophiolite. It is the remains of basic magmatic differentiation and a component unit of ophiolites.