内蒙古西乌珠穆沁旗本巴图组碎屑锆石LA-ICP-MS U-Pb年龄及其意义

在前人研究的基础上，对本巴图组的野外地质特征、岩石类型、岩石组合、锆石年代学等进行了研究。镜下特征显示本巴图组砂岩主体为岩屑晶屑含砾砂岩；碎屑锆石阴极发光图像显示，它们多具有震荡生长环带或条痕状吸收，Th/U比值为0.06~1.03(平均0.55)，具有岩浆锆石的典型特点。应用LA-ICP-MS测年技术对本巴图组进行了碎屑锆石分析，其206Pb/238U年龄可以分为5组：①319~451Ma，峰期年龄为363Ma；②457~543Ma，峰期年龄为513Ma；③724~996Ma，峰期年龄为945Ma；④1031~1836Ma，峰期年龄为1572Ma；⑤2469~2505Ma，峰期年龄为2487Ma。年龄分布的意义：研究区本巴图组沉积的时间下限应为319Ma之后；457~543Ma发生泛非期构造热事件，沉积物源主要来源于佳-蒙地块；另外几组峰值年龄945Ma、1572Ma和2487Ma主要反映了佳-蒙地块基底的年龄信息。

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.