GEOCHRONOLOGY AND GEOCHEMISTRY OF THE ANDESITES FROM TAMULANGOU FORMATION IN BADAGUAN AREA, INNER MONGOLIA

The paper analyzes the zircon U-Pb chronology and whole-rock geochemistry of the andesites from Tamulangou Formation in Badaguan area of northern Hailar to reveal the tectonic setting and petrogenesis of the andesites, and discusses tectonic evolution history of Mongolia-Okhotsk suture zone. The LA-ICP-MS zircon U-Pb dating results show the rocks were formed in 160.9-164.0 Ma. The lithogeochemical characteristics indicate the andesites belong to high-K calc-alkaline rock with notable fractionation of LREE and HREE, (La/Yb)_N of 9.97-26.85, and slight negative-weak positive Eu anomaly (δEu=0.71-1.11); The trace elements are characterized by enrichment of LILEs (Rb, U, Th and K), severe depletion of Sr, P and Ti, and relative depletion of Nb and Ta. The magma may be derived from the fluid-metasomatized mantle wedge and experienced obvious fractional crystallization during evolution. Combined with the regional evolution history, it is believed that the andesites in the study area were formed in the lithospheric extension environment after the closure of Mongolia-Okhotsk Ocean.