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.