Zircon U-Pb ages of quartz vein rocks in Tuanliangzi Formation complex of southwestern Yunnan Province: Regional metamorphism deformation age restriction of Late Triassic Lancang River tectonic belt

Abundant tectonic hydrothermal quartz veins were found, which are parallel to the regional foliation (S2) in Mesoproterozoic Tuanliangzi Formation in southwest Yunnan, and those ancient mixtites of Tuanliangzi Formation are important tectonic rocks in southern Lancang River tectonic belt and along the west Yangtze block. Three zircon samples of quartz dykes and one zircon sample of green dyke were selected and analyzed using laser ablation inductively coupled plasma mass spectrometry (LAICP-MS). The ²⁰⁶Pb/²³⁸U ages can be divided into three groups, i.e., 395~461Ma, 240~260Ma and 222~228Ma, with most of them concentrated on 222~228Ma. The quartz dykes ages indicate two stages of regional metamorphism deformation (M₁D₁, M₂D₂):the first stage of metamorphism deformation(M₁D₁) was the result of pro-Tethys eastward subduction in Early Paleozoic(395~461Ma); the second stage of metamorphism deformation(M₂D₂) occurred in late Paleozoic-Mesozoic which could be divided into two periods of metamorphism deformation(M_2aD_2a, M_2bD_2b):the early period was Late Paleozoic to Early Mesozoic (240~260Ma) when the Paleo-Tethys experienced eastward subduction, whereas the late period of metamorphism deformation was caused by the closure of Paleo-Tethys Ocean basin in early Late Triassic (222~228Ma). The quartz dykes in Tuanliangzi Formation were impacted by tectonic hydrothermal event in the early Late Triassic, and were formed later than Lincang granite and the volcanic rocks of Manghuan Formation(229~235Ma), but earlier than stretch volcanic rocks of Xiaodingxi Formation and Manghuihe Formation (210~222Ma), which indicates that these syn-emplacement quartz dykes were the results of rapid exhumation that happened later than the Paleotethys ocean eastward collision with Yangtze block; in addition, the ancient Tethys Ocean had been closed earlier than early Late Triassic, suggesting minimum age limitation of quartz dykes in Tuanliangzi Formation.