The discovery of Late Triassic subvolcanic dacite porphyry in the eastern margin of the Baoshan terrane, western Yunnan Province, and its geodynamic implications

Geochronology, petrogenetic type and tectonic significance of the Hezhu subvolcanic dacite porphyry in the eastern margin of the Baoshan terrane were studied in this paper. In situ U-Th-Pb geochronology indicates that the porphyry has an age of 216.8Ma±2.2 Ma, suggesting Late Triassic emplacement instead of Early Cenozoic emplacement as proposed by previous researchers. This means that the abundance and distribution of magmatism of the Cenozoic intrusive province in the south of Baoshan terrane should be re-evaluated. This is also the first discovery of Late Triassic subvolcanic dacite porphyry in the west of the Changning-Menglian suture zone. Petrographic observation and petrochemical data suggest that the Hezhu porphyry has both S- and I-type characteristics, and was formed by mixing of mantle-derived mafic and crustal felsic magmas. The participation of mantle components in Hezhu porphyry further implies that mantle upwelling prevailed in Tengchong and Baoshan terrane in the Late Triassic period.