LA-ICP-MS zircon U-Pb dating of the gabbro from Longwu Gorge ophiolite, Jianzha-Tongren area, Qinghai, China and its geological significance

Longwu Gorge ophiolite belt located in Tongren Area, Qinghai Province, is at the jointing part of West Qinling and South Qilian orogenic belts. The ophiolite geochronology is very important for the study of tectonic evolution of orogenic belt and the reconstruction of the ancient ocean-land and plate tectonic framework. LA-ICP-MS zircon U-Pb dating of gabbro from the Longwu Gorge ophiolite suggests an isotopic age of (250.1±2.2)Ma (MSWD=0.7), which indicates that the Longwu Gorge ophiolite was the product of magmatic activitiy during the process of extension of paleo-ocean basin along the jointing part of West Qinling and South Qilian in the late Permian to early Triassic. Zircons from the granodiotite intruding the ophiolite yielded an age of 244±1.4Ma, which was younger than the formation of ophiolite, but it is significantly older than the Indosinain collisional granitoids in the region. Therefore, it may reflect the emplacement age of the Longwu Gorge ophiolite.