Net growth of the continental crust during the process of accretionary orogeny: Constraints from igneous rocks, southern margin of the middle section of the Central Asian Orogenic Belt

The upwelling of the asthenosphere mantle is an important way for the net growth of the continental crust. While the geological performance of crust-mantle interaction in the process of accretion and orogeny still needs further research. The Juyanhai area in western Inner Mongolia locates in the southern margin of the middle section of the Central Asian Orogenic Belt (CAOB), where it bridges the northern Beishan Orogenic Belt and the northern margin of the Alxa block. Based on the granitoids with crust-mantle interaction characteristics encountered in four wells of Juyanhai, this paper systemically analyzes the contribution of the asthenosphere mantle material and its specific geological performance during the accretion and orogeny. We have determined the dioritic microgranular enclaves of granodiorite rich in needle-like apatite. Furthermore, the granitoids yield Pb-206/U-238\ magmatic crystallization ages of 306 similar to 313Ma, which display extremely depleted Hf isotopic signatures (epsilon(Hf),(t) = similar to + 13. 0 + 14. 3) and show relatively young two-stage Hf model age (t 2 = 410 similar to 588 Ma), reflecting a remarkable continental crustal growth event. The zircon EHf (t) value reveals that the granitic magma source includes remelting of juvenile continental crust and injection of depleted mantle. The corresponding Late Carboniferous crustal growth implies geodynamics of mid-ocean ridge subduction or slab roll-back in Juyanhai area, in the southern margin of middle part of CAOB.