LA-ICP-MS U-Pb dating of detrital zircon from Lingguanmiao basin in North Qinling

A number of T3-J1 rift basins were developed in the Qinling orogen after the main orogenic episode of the Indosinian orogeny. Selecting grayish green and moderate-fine grained sandstone metamorphosed to low-greenschist facies from the Lingguanmiao basin of the North Qinling orogenic belt in Danfeng County of Shaanxi Province and conducting LA-ICP-MS detrital zircon U-Pb isotope analysis, the authors attempted to establish the age structure of the sedimentary rocks in the basin and infer the provenance and its variation. The result reveals that the 85 analytical points of the magma-genetic detrital zircons yielded five age groups: 426~605Ma, 661~1174Ma, 1494~1789Ma, 2113~2261Ma and 2826~3298Ma. Among the ages, the youngest age is 426Ma±5Ma, and the oldest is 3298Ma±70Ma. The major age groups are 426~605Ma and 661~1174Ma. The age structure reflects the tectono-magmatic events occurring in the source region during the Caledonian and Grenvillian orogenic periods, respectively. In addition, the lack of the ages from the Middle Silurian to Late Triassic can be attributed to the assumption that the widespread Indosinian magmatic bodies failed to make contribution to the source due to their poor development in North Qinling. In comparison with the age data from the surrounding terranes and in conjuction with other geological evidence, the authors hold that the provenance of the Lingguanmiao basin might mainly have come from the Neoproterozoic Kuanping Group and the Caledonian granites which had intruded into Erlangping and Qinling Groups, with the addition of a small amount of material from the Paleozoic Erlangping and Proterozoic Qinling complex. After the formation of Lingguanmiao basin, the sedimentary rocks in the basin suffered strong metamorphism and deformation, which might record the new intracontinental orogeny that Qinling experienced since the ending of the Indosinian orogeny set forth by plate tectonics.