Characteristics and geological impli-cations of the Late Permian adakitic volcanic rocks from Bairin Right Banner area, Inner Mongolia

Permian adakitic volcanic rocks are distributed in Bairin Right Banner, southeast Inner Mongolia. This set of adakitic volcanic rocks is mainly outcropped in Dayushu, Shanhoutun and Handaba, with rock association being andesite, trachyandesite, dacite and augite andesite. The LA-ICP-MS zircon U-Pb age is 256.7±2.7Ma, indicating that the rocks were formed in the Late Permian. This set of volcanic rocks belongs to the quasi-aluminum-weak aluminium and medium-K-Calcalkaline rock series, with the following geochemical characteristics:rich Si (SiO₂>56%), high Al (Al₂O₃>15%), rich Na, poor K (Na₂O=4.32%~4.73%, K₂O=4.32%~2.49%), higher Sr and lower Yb and Y (Sr > 400×10^-6, Yb < 1.9×10^-6, Y < 18×10^-6), Na₂O/K₂O=2.33~3.90, Mg^#=35.3~60.8, the to-tal amount of rare earth elements 96.69×10^-6~192.4×10^-6, light and heavy REE exhibiting obvious fractionation ((La/Yb)_N=6.27~13.82) and positive anomalies δEu (1~1.67). Enrichment of LILE (Rb, Ba, U) and depletion of HFSE(Nb, Ta) are displayed in the primitive mantle normalized multielement variation diagram, indicating geochemical characteristics of O-type adakitic volcanic rocks. Based on regional information, adakitic volcanic rocks distributed in Bairin Right Banner were formed by contamination of the partly molten remnants of Paleo-Asian oceanic crust and the mantle peridotite, suggesting the existence of subduction extinction event of Paleo-Asian oceanic crust toward the North China Plate in Late Permian.