Recycling of supra-crustal materials in the rhyolites from north Sonid Youqi: implications for the crustal evolution in the southeast Central Asian Orogenic Belt

Whole-rock geochemistry, zircon U–Pb ages and Hf–O isotopes of the volcanic rocks from Tegusiaobao, north of Sonid Youqi, southeast Central Asian Orogenic Belt, were presented to trace their origin and the associated crustal evolution process. The Tegusiaobao volcanic rocks are composed of trachyandesite and per-aluminous rhyolites. Precise SHRIMP and LA-ICP-MS zircon U–Pb dating of rhyolite samples reveal that the Tegusiaobao volcanic rocks erupted during the Latest Permian to Triassic (c. 257–231 Ma), which is coeval with the emplacement of post-collision-related dikes and granites in the southeast Central Asian Orogenic Belt. Geochemical and isotopic analysis implies that a crust-mantle magma mixing model is likely responsible for the genesis of the Tegusiaobao trachyandesite-rhyolite suite. Nine zircon grains from a rhyolite sample exhibit variable δ18O values, with one mantle-like value (5.10‰) and eight values (6.42–8.77‰) that are akin to the supra-crustal materials. Zircons from this sample show depleted Hf isotopic composition (εHf(t) =  + 10.91 to  + 15.81). The high δ18O values of the rhyolite reveal the interaction of their protolith and surface water at low temperatures, and the preceding subduction caused the recycling of the supra-crustal materials and the closure of the Solonker–Linxi Ocean. The generation of the Tegusiaobao volcanic rocks also suggests that reworking of the supra-crustal materials is a potential way to operate the crustal evolution in the Central Asian Orogenic Belt.