U-Pb geochronology, Hf isotopes of zircons from the volcanic rocks along the eastern margin of Lanping basin, Sanjiang orogenic belt.

Several volcanic belts developed in the Sanjiang orogenic belt, southeast of Tibetan Plateau. Recently published new geochronological and geochemical data gradually revealed the spatial and temporal relationship among these belts. However, these belts are commonly covered by Mesozoic to Cenozoic sediments of the Lanping basin, which have led to some erroneous tectonic interpretations. Basement rocks expose very well in Misha regions, eastern margin of the Lanping basin. The basement consists of two tectono-stratigraphic units: an upper one consisting of Late Triassic fine-grained elastic and bioclastic and a lower volcanic one. The lower one has a thickness of ca. 150m, which is made of three volcanics-sediments sequences. Each sequence is composed of ignimbrite and crystal-lithic tuff in lower and reddish or dark shale and limestone in upper. LA-ICP-MS U-Pb results of zircon from the volcanic rocks demonstrated that the volcanism started at least since 258Ma, and continued to 248Ma. In-situ zircon Lu-Hf isotopic data revealed a significant contribution of mantle-derived material to the earlier magmatic rocks, while the latter stage magmatic rocks seem to have completely resulted from partial melting of Precambrian crustal rocks. These new data indicate that the volcanic rocks along the eastern margin of the Lanping basin have the same geochronological framework and identical isotopic variation trend as other Paleo-Tethyan volcanics in the Sanjiang belt, suggesting they all form an entire continental arc belt developed along the western margin of Cathaysian affinity block(s).