LA-ICP-MS zircon U-Pb dating of the Upper Carboniferous volcanic rocks from northern Beishan region in Gansu Province and its tectonic significance

Much information remains to be discovered concerning the Late Paleozoic ocean-land transition in Beishan region. The Late Paleozoic strata can provide important evidence for this subject. However, the research on the age of the upper Carboniferous volcanic rocks from northern Beishan region is insufficient. This paper shows that the LA-ICP-MS zircon U-Pb ages of the "Early Carboniferous Baishan Formation" from Heiyinghsan area are 308.6Ma±1.0Ma and 299.1Ma±2.4Ma, which belong to the Late Carboniferous Ganquan Formation. The Ganquan Formation is widely distributed and unconformably overlies the Lower or Middle Devonian strata in northern Beishan region, which implies the closure of the Paleoasian Ocean before Late Carboniferous. The age revision of the Baishan Formation in some sense provides evidence to the tectonic evolution of the Beishan region.