Ar-Ar age, geochemistry and petrogenesis of Late Mesozoic volcanic rocks in the northern marginal region of Erlian basin, Inner-Mongolia

The studied area is located in the northern margin of Erlian basin, NE of China. The Late Mesozoic volcanic rocks in this area are mainly composed of rhyolite, basalt, trachy-basalt and basaltic andesite. 40Ar-39Ar dating of Chagannuoer Formation rhyolite and Bulagenhada Formation basaltic andesite give a plateau age of 141.57 +/- 1.59Ma and 129.05 +/- 1.86Ma, respectively, indicating that these volcanic rocks were formed in Early Cretaceous. The geochemical characteristics of the volcanic rocks show that the earlier Chagannuoer Formation rhyolites origined from lower crustal magma, which experienced high degrees fractional crystallization or assimilation and fractional crystallization. The magma origination of Daotenuoer Formation rhyolites were middle-upper crust or lower crustal magma suffered strong asiimilation of upper crust. Bulagenhada Formation basic volcanics origined from the metasomatized lithospheric mantle modified by previous subducted ocean slabs, and Combining previous studies, we suggest that the tectonic environment of Early Cretaceous was intense lithopheric extension and thinning, related to Northern China lithopheric thinning geological event in Late Mesozoic.