Timing and Location of the Collision between North China Craton and Siberian Plate: New Evidence of Zircon U-Pb ages of Linxi Formation and its intrusion in Linxi region, Inner Mongolia

The amalgamation of Siberian Plate with North China Craton (NCC) is an important issue on study of tectonic frame of China and the whole eastern Asia. Different researchers have different understanding about the timing and location for the collision and final closure of Siberian Plate and NCC. Some researchers believe that Hegenshan-Sunitzuoqi-Soren Obo line in the northern Inner Mongolia is the final suture zone, but the timing for final closure has been in debating. Some other researchers believe that the Xar Moron River-Changchun-Yanji fault is the final suture, however they failed to reach a consensus regarding the suture time. To solve this problem, based on field studies, we collected detrital zircons in argillaceous rocks and magmatic zircons in granodiorite intrusions from the dynamic metamorphic belt to carry out LA-ICP-MS U-Pb dating in the northern side of Tongbu County, Linxi region, Inner Mongolia, where is tectonically located between the Xar Moron River suture belt and Erenhot-Hegenshan suture belt. LA-ICP-MS study on 40 detrital zircons in the dynamically metamophosed biotite schists in the Linxi Formation from Linxi region suggests that their U-Pb ages can be roughly divided into two groups; Group-I in the range of 397-482 Ma with the peak at 424 × 4 Ma and Group-II in the range of 261-358 Ma with the peak at 313.2 × 3.7 Ma. The youngest age, 261 × 3Ma, is interpreted to maximum depositional age of the protoliths of these schists and has limited the Linxi Formation to be formed at Late Permian. The age distribution patterns for detrital zircons in Linxin Formation suggest that the sedimentary materials are mainly from the NE China block rather than NCC, which has thus put constraint on the final collision location of Siberian plate with NCC to be at the Xar Moron River-Changchun suture belt, south of Linxi area, and on the timing for collision after the sedimentation of Linxi Formation sequences. The veined granodiorite that intruded into Linxi Formation has magmatic zircon age of 245.9 × 1.7 Ma and captured zircon age of 300.0 × 2.1 Ma (Their Th/U ratios of zircons are greater than 0.3 and show features of magmatic origin). The magmatic zircon age represents the granodiorite emplaced at Early-Middle Triassic, while the age of captured zircons is consistent with the peak age of 313.2 × 3.7 Ma for the detrital zircons in Linxi Formation. Speculated from the outcrop of the Triassic magmatic rocks, this collision event formed nearly EW-trending giant mountains from Beishan in Xinjiang Province to central Jilin Province across the southern Inner Mongolia. Thus the granodiorite is regarded as post-collisional or late-orogenic granite which likely formed in response to the collision of the Siberian plate with NCC, therefore provides further constraint that the final collision of Siberian plate with NCC occurred at Early-Middle Triassic.