Geochronology, geochemistry and tectonic setting of volcanic rocks from Manketouebo Formation in Wulagai area, southern Da Hinggan Mountains

This paper is the result of geological survey engineering.

Objective By finding out the age and geochemical characteristics of volcanic rocks in Wulagai area of Da Hinggan Mountains, this paper discusses the age, genesis and tectonic background of volcanic rocks, so as to provide a basis for the study of magmatic activity and tectonic evolution in the south of Da Hinggan Mountains.

Methods Our project carried out systematically study the LA-MC-ICP-MS zircon U-Pb chronology and rock geochemistry from the volcanic rocks of Manketouebo Formation in Wulagai area of Da Hinggan Mountains.

Results The volcanic rocks of Manketouebo Formation in the study area were formed in the middle Late Jurassic ((154.8±1.2)-(164.96±0.71)Ma). The volcanic rocks of this region belong to alkali series rocks, with characteristics of high silicon, rich in alkali and potassium, low magnesium and calcium. The rare earth distribution curves of all samples have similar characteristics. The total amount of rare earth is medium, the fractionation of light and light rare earth is obvious, which belongs to light rare earth enrichment type, and the negative Eu anomaly is significant. The rocks are relatively enriched in the large ion lithophile elements Rb, K, Th and U, and have a strong deficit in the high-field strong elements such as Nb, Ta, Ti, P; the volcanic rocks have the characteristics of low Sr, high Yb and A-type granite.

Conclusions The studies on trace elements and rare earth elements indicate that the volcanic magma are derived from the melting of the crust and have the same magmatic source. The volcanic rocks of Manketouebo Formation originated in the post orogenic extensional tectonic background, which was possibly related to the lithosphere extension after the closure of the Mongol-Okhotsk Ocean.