Geochemical characteristics and LA-ICP-MS zircon U-Pb geochronology of Guogangjianan Carboniferous ophiolite in central Qiangtang, the Tibetan Plateau

In order to investigate the evolution of the Lungmu Co-Shuanghu plate suture zone and the tectonic history of central Qiangtang, the authors studied Guoganjianian ophiolite in the aspects of petrology, geochemistry and geochronology. The cumulate in Guoganjianian ophiolite was recently discovered during 1∶50000 regional geological survey of the Gemuri area. Geochemical studies show that the cumulate gabbro has low REE content and flatten REE patterns with slight enrichment of LREE, and the degree of differentiation between LREE and HREE is low. These samples are enriched in large ion lithophile elements (LILE) such as Rb and Ba, and depleted in Nb, Ta and Ti, suggesting that they were probably formed in a subduction zone. LA-ICP-MS technique was applied to U-Pb zircon dating of the cumulate gabbro from Guoganjianian ophiolite. The result shows that the ages of cumulate gabbro is 354.8Ma±2.4Ma, suggesting that Lungmu Co-Shuanghu Ocean already began its subduction in Early Carboniferous. The study of Guoganjianian cumulate gabbro provides important basic data for investigating the evolution of Lungmu Co-Shuanghu plate suture zone and the tectonic history of central Qiangtang.