Tenth Institute of Geological and Mineral Exploration and Development, Inner Mongolia Autonomous Region, Chifeng 024000, Inner Mongolia, China

The geochronological and geochemical characteristics of volcanic rocks of Manketouebo Formation are of great significance for the study of large?scale volcanic activities, petrogenesis and regional stratigraphic corre? lation in the south?central sector of Great Xing??an Range. In this paper, zircon U??Pb geochronology and geochemis? try of orthostratigraphic section volcanic rocks of the Manketouebo Formation are analyzed. The ages of the five dat? ing samples collected are (162. 3 ± 1. 4) Ma, (163. 4 ± 1.3) Ma, (160.9 ± 1.8) Ma, (157.0 ± 1.1) Ma, (162.3 ± 2.2) Ma, respectively, belonging to Late Jurassic. The volcanic rocks in the study area are character? ized by high silica, alkali enrichment and aluminum, calcium, magnesium deplement, which belong to the paralu? minous?peraluminous high potassium?calcium alkaline series. It is enriched in large ion lithophile elements (Rb,K, Ba) and light rare earth elements (LREE), and depleted in high field strength elements (Nb, Ta, P, Ti) and heavy rare earth elements (HREE), with obvious negative europium anomalies. It is suggested that the magma was derived from partial melting of the lower crust, and experienced the fractional crystallization of plagioclase and apa? tite. Based on the geochronology, geochemistry and regional geological data of volcanic rocks in the area, it is con? sidered that the volcanic rocks in the orthostratigraphic section of the Manketouebo Formation are characterized by A2 type granite and are formed in a post?collision environment, which is related to post?orogenic extension of the Mongolia??Okhotsk ocean closure.