Tectonic attributes of the Northern part of the Middle Gangdise Belt in the Early Cretaceous: evidences of zircon U-Pb dating and lithogeochemistry of volcanic rocks from the Zenong Group

The genesis of the widely distributed volcanic rocks of the Zenong Group in the Middle Gangdise Belt, Tibet, has been controversial. By carrying out zircon U-Pb dating of the volcanic rocks from the Zenong Group in Laiduo are, the authors believe that the volcanic rocks of the Zenong Group were formed during 124.0～114.7Ma.The geochemical analyses of volcanic rocks from the Zenong Group show that their SiO₂ contents range from 54.53% to 78.35%，and the aluminum saturation index A/CNK is between 0.77 and 3.75, suggesting the volcanic rocks of the Zenong Group belong to the aluminum-peraluminous rocks, enriching in LREEs and LILEs such as Rb、Ba、Th and U, depleting in HFS elements such as Nb and Ta, and with an obvious negative anomaly of Eu. Evidences of the both Zircon U-Pb dating and lithogeochemisty indicate that the Zenong Group may be the product of the southward subduction of the Slainajap ocean which is now in the form of Shiquanhe-Yongzhu-Namucuo-Jiali ophiolite belt during the Early Cretaceous.