LA-ICP-MS zircon U–Pb dating of the Langshan Group in the northeast margin of the Alxa block, with tectonic implications

• The Langshan Group in the northeastern Alxa block formed in the Neoproterozoic.
• The provenance of the Langshan Group came from both the Alxa block and the NCC.
• The Alxa block and the NCC were connected until the Neoproterozoic.

The relationship between the Alxa block and the North China Craton (NCC) is one of the controversial tectonic issues in China. The age spectra of detrital zircons from sedimentary rocks may help resolve the tectonic affinity of the Alxa block. The Langshan terrane is located in the northeast margin of the Alxa block which is connected to the northwest margin of the NCC. Detailed U–Pb dating of zircon from the meta-volcanic rocks and meta-sedimentary rocks of the Precambrian Langshan group shows that the Langshan Group formed in the Neoproterozoic. The evidence includes the zircon age of 804.1 ± 3.5 Ma for the meta-volcanic rocks and the youngest detrital zircon age peak at 1187-810 Ma for the meta-sedimentary rocks. The detrital zircon age patterns of the Langshan group and Precambrian strata of the Alxa block and the NCC are similar. The older and younger detrital zircon age peaks of the Langshan group are comparable to those of the NCC and the Alxa block, respectively. The 1.7-1.5 Ga detrital zircons in the Langshan Group, which might be derived from the “Zhaertai-Bayan Obo-Huade” Mesoproterozoic rift system in the northern margin of the NCC, are not found in the Precambrian strata of the Alxa block. The detrital zircon age peaks of the Langshan group are well correlated to the known Precambrian tectono-thermal events that affected both the Alxa block and the NCC. The development of the Langshan Neoproterozoic rift system is shown by the contemporaneous magmatism in the Alxa block and the adjacent NCC. The results from this study indicate that the Alxa block and the NCC were together in the Neoproterozoic.