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

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

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。

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 fi：om 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.