Abstract:

Studying the Lincang terrane is essential to understand the tectonic evolution of the Proto-Tethys in the Sanjiang region of Southwest China.However, there have been ongoing debates about its tectonic characte-ristics.This study focuses on the Lancang Group, which serves as the basement of the terrane.Our study presents zircon U-Pb chronology and whole-rock elemental composition of altered metavolcanic rocks in the area.The zircon U-Pb dating results indicate that these rocks formed during the Late Ordovician period, specifically at (457±2) Ma and (455±2) Ma.The protoliths of the 22 chlorite schists are from the low-potassium tholeiite series, while the protoliths of the six albite chlorite schists are basaltic-andesites from the high-potassium calc-alkaline-potassium basalt series.These rocks share similar characteristics with typical arc volcanic features, such as strong enrichment of light rare earth elements (LREEs), large-ion lithophile elements (LILEs), and negative anomalies of high field strength elements (HFSE).This evidence supports the idea that the Huimin magmatism was formed through the subduction of the Proto-Tethys Ocean to the Simao Block during the Ordovician-Silurian period.Therefore, we propose that the Lincang terrane may not be a distinct block with Precambrian basement, but rather a continental arc that formed through the subduction of the Proto- and Paleo-Tethys at the margin of the Simao Block.

Key words: Proto-Tethys, magmatic arc, Lincang terrane, Lancang Group