DETRITAL ZIRCON U-Pb CHRONOLOGY OF THE LINXI FORMATION IN ZHALANTUN AREA, NORTHERN DAXINGANLING MOUNTAINS: Geological Implications

The Late Permian Linxi Formation in Zhalantun area, Inner Mongolia, is characterized by the assemblage of sandstone and slate. The LA-ICP-MS zircon U-Pb dating results of two samples, silty argillaceous slate and siltstone, show that 150 age data are mainly distributed in six ranges, namely 259.7-281.9 Ma (n=18), 291.3-311.5 Ma(n=110), 319.2-334.5 Ma (n=10), 340.3-375.2 Ma (n=9), 399.7-400.7 Ma (n=2) and 728.5-765.4 Ma (n=2) with the weighted average ages of 273.3, 298.1, 327.0, 356, 400.2 and 750.0 Ma, respectively. The above six groups of age peaks are basically consistent with the time of regional magmatic activities. The Early Permian intrusive rocks and volcanic rocks from Dashizhai Formation make up 85% of total clastic materials for the sedimentary rocks of Linxi Formation, while the Paleozoic intrusive rocks(earlier than Late Carboniferous) and geologic bodies like Zhalantun Group offer a few clastics as well. Two important regional uplift events occurred in Late Paleozoic 250-270 and 310-325 Ma are recorded respectively by the Linxi and Baoligaomiao formations.