GEOCHEMISTRY OF THE OPHIOLITE AND ISLAND ARC VOLCANIC ROCK IN THE MIANXIAN-LUEYANG SUTURE ZONE, SOUTHERN QINLING AND THEIR TECTONIC SIGNIFICANCES
Lai Shaocong; Zhang Guowei (Northwest University. Xian 710069)Yang Yongcheng; Chen Jiayi(Regional Geological Surveying Team Bureau of Geology and Mineral Resources of Shaanxi Province.Xianyang 712000)
The ultlabasic rocks in the Mianxian-Lueyang ophiolitic melange include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly. The diabase dike swarm show LREE enrichment but slightly slightly Eu anomaly. Metamorphosed volcanic rocks can be divided intO two groups in terms of their REE geochemistry and trace element ratios of Ti / V, Th / Ta, Th / Yb and Ta /Yb. One is the MORB-type basalt with LREE depletion, representing the fragments of oceanic crust The other is the island-are volcanic rocks including tholeiitic and cafe-alkaline associations. They were formed in the continental margin.