Multiphase tectonic events in the Lancangjiang tectonic belt

The Lancangjiang tectonic belt (LTB) along the southern margin of the Tibetan Plateau serves as a pivotal archive of the Late Palaeozoic to Cenozoic tectonic evolution. It provides critical insights into Tethyan dynamics, the India-Eurasia collision, and plateau uplift. In this study, we reconstruct the multi-stage tectonic history of the LTB by integrating structural analysis and petrology with zircon and apatite U-Pb geochronology and geochemistry. Four distinct tectono-thermal events were identified: 234-200 Ma, 80-69 Ma, 57-38 Ma, and 20-19 Ma. Geochronological data from granitoids reflect magmatic pulses related to the evolution of the Paleo-Tethys Ocean, while results from mylonites and gneisses constrain the timing of superimposed tectonic-metamorphic deformation. Combined with the regional geological framwork, the evolution of the LTB is divided into four stages: (1) a Triassic post-period of tectonic quiescence following the closure of the Paleo-Tethys Ocean; (2) a Late Cretaceous metamorphic-thermal event induced by the far-field effects of the Neo-Tethys subduction-collision system; (3) a Paleogene phase of intracontinental convergence and crustal shortening triggered by the India-Eurasia collision; and (4) an Early Miocene stage of large-scale sinistral ductile shearing developed under a regional extensional regime. This study establishes a temporal framework for major tectonic events along the southeastern boundary of the Tibetan Plateau, providing key geochronological constraints for deciphering the evolutionary history of the Tethyan realm and deep geodynamic processes.