Zircon U-Pb age and Hf isotopic characteristics of the Diebusige Complex in Langshan area, Inner Mongolia, and its constraints on the tectonic evolution of the Alxa Block

The Alxa Block is located in the western part of the North China Craton (NCC), and its Precambrian geological evolution has been long controversial.In this study, the in-situ zircon U-Pb dating and the Lu-Hf isotope analysis were conducted on the Precambrian basement at the northeast margin of the Alxa Block, which called the Diebusige Complex.The Diebusige Complex consists mainly of metamorphic supracrustal rocks and metamorphic plutonic rocks, including high grade metamorphic gneiss, marble, quartzite, amphibolite and intruded K-felspar granite.LA-ICP-MS zircon U-Pb dating results of three paragneiss samples show that the detrital zircons from the Diebusige Complex yielded ²⁰⁷Pb/²⁰⁶Pb ages range from 2.60 Ga to 2.10 Ga, and the Diebusige Complex subjected to high grade metamorphic events at 1.98~1.90 Ga and 1.90~1.79 Ga, suggesting that the protoliths of the Diebusige Complex may be deposited at 2.10~1.98 Ga.There is no evidence of Archean rocks exposed in Langshan area, but the possibility of Archean rocks exist at deeper crustal levels cannot be ruled out.Zircon Lu-Hf isotopic data shows that the diagenetic material of the Diebusige Complex was originated from the reworking of Early-Middle Archean crust (3.42~2.79 Ga).Comparing the Diebusige Complex with the Yinshan Block and the Khondalite Belt in magmatic-metamorphic events and the Hf isotopic charateristics.We speculate that the Precambrian basements of the Alxa Block are probably part of the Khondalite Belt in Paleoproterozoic.