The discovery of Early Jurassic volcanic rocks along the Southern Lancangjiang tectonic magmatic belt in southwest Yunnan, with a discussion on the upper limit of Indosinian tectonic cycles in Yunnan Province

The ages of rhyodacite in Jiangqiao-Nalan area of Pu'er City was determined by utilization of zircon-LA-ICP-MS in south Lancangjiang zone, and the result of U-Pb dating yielded (196.7±2.3)Ma and (198.1±3.5)Ma, which indicates that rhyolite in this area was formed in early Jurassic instead of in Late Triassic. The data fill in the record of volcanic-sedimentary activity in Jurassic's geological history. The analysis of the major elements, REE and trace elements of rocks shows that the volcanic rocks of lower Jurassic in South Lancangjiang zone were formed under the extensional tectonic background after collision, and were probably related to the subducted lithosphere plates or orogenic belt of Yamane delamination, and that they occurred after the closure of lower Cretaceous in this area were typically associated with the POG (post-orogenic granite) or A₂ granite. These data constrain the final time of Indosinian cycle. The granite has the feature of post-orogenic granite or "A" type granite, and it indicates the termination time of Indo-Chinese cycle in southwestern Yunnan.