Zircon U–Pb Age of Volcanic Rocks from the Langmusi Formation in the Western Qinling Mountains and Its Tectonic Significance

Volcanic rocks are wide spread in Langmusi area of western Qinling, which is an important window to study the Indosinian magmatism of the Qinling Orogen. However, the formation age of langmusi volcanic rocks is not well constrained. In this contribution, a detailed study of LA−ICP−MS zircon U−Pb geochronology for the hornblende andesites from Langmusi Formation was conducted. CL images show that the internal structures of zircon from hornblende andesites show typical magmatic origin. Zircon U−Pb dating results demonstrate that the horndiorite andesites have slightly different ages, with weighted average ages of (221.8±1.2) Ma and (210.6±2.1) Ma respectively. Therefore, the horndiorite andesites of langmusi Formation were formed the Late Triassic period. Combining with previous studies, we argue that the volcanic rocks of the Langmusi Formation represent an important magmatic event of the Qinling Indosinian orogeny, which were formed in a syn−collisional tectonic setting.