The detrital zircon LA-ICP-MS U-Pb ages and its significance of Benbatu Formation in Xiwuzhumuqinqi, Inner Mongolia, China

Based on the previous research, the authors investigated the field geological characteristics, lithologies, rock assemblages and zircon LA-LCP-MS U-Pb data from the Benbatu Formation. The sandstone in this formation are chiefly of lithic-crystal pebbled sandstone. The zircons from sandstone show oscillatory growth zoning or striped absorption in cathodoluminescence images, together with their high Th/U ratios (0.06-1.03). These features indicated a magmatic origin. The zircon U-Pb dating results show that 39 analyzed spots can be divided into five groups, i.e., 319~451 Ma (peak at 363 Ma), 457~543 Ma (peak at 513 Ma), 724~996 Ma (peak at 945 Ma), 1031~1836Ma (peak at 1572 Ma) and 2469-2505Ma (peak at 2487 Ma). These ages indicate that: (1) Benbatu Formation was deposited after 319 Ma; (2) the presence of the detrital zircons with the ages of 457~543 Ma, indicating the Pan-African tectonic events, suggested that these rocks were sourced from the Jiamusi-Mongolia massif; (3) the others age population, such as 945 Ma, 1572 Ma and 2487 Ma, should display the age information of the basement of the Jiamusi-Mongolia massif.