Attribution of the Langshan Tectonic Belt: Evidence from zircon U-Pb ages and Hf isotope compositions

This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 +/- 8 Ma. The youngest UePb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 +/- 33 Ma, 1187 +/- 3 Ma and 1189 +/- 39 Ma, suggesting that the depositional age of the protolith of the schist was between 908 +/- 8 Ma and 1118 +/- 33 Ma. In addition, 436 UePb age data and 155 Lu-Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The UePb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date. Moreover, two-stage Hf model ages of the northern flank feature three age peaks at similar to 900 Ma, similar to 1700 Ma and similar to 2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at similar to 2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the UePb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the UePb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton (NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon UePb age of 860 +/- 7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts (i.e., the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian. (C) 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license.