Geological and geochemical characteristics and tectonicsetting of Late Mesozoic volcanic rocks in the southern margin of Mongolia-Okhotsk orogenic belt

Extensive Mesozoic volcanic rocks are distributed in the southern margin of Mongolia-Okhotsk tectonic belt, exhibiting NE-trending occurrences in the northern of Daxing'anling Range in China and adjacent areas of the China-Mongolia and China-Russia borders. The volcanic rocks are mainly trachyte basalt, basaltic trachyandesite, trachyandesite, trachyte and rhyolite. In this paper, zircon U-Pb of volcanic rocks and whole rock matrix Ar-Ar geochronological data are systematically collected, revealing that the volcanic rocks are mainly formed during 114.5-162.4 Ma, corresponding to Late Jurassic-Early Cretaceous. Statistical analysis of 32 geochemical datasets suggests that the volcanic rocks exhibit an alkaline-subalkaline transitional affinity. In addition, Sr-Nd isotopic signatures indicate their derivation from a mantle wedge or lithospheric mantle which was metasomatized by fluids. Combined with regional tectonic evolution, it is proposed that the Mesozoic volcanic rocks in the southern margin of MongoliaOkhotsk were formed in a post-orogenic extensional setting.