Petrogeochemistry and zircon U-Pb chronology of the Niuzhi monzonitic porphyry in southern segment of Ailao Mountain tectonic belt

This study presents bulk petrogeochemistry and zircon U-Pb dating results for the Niuzhi monzonitic porphyry in Mojiang, Yunnan. LA-ICP-MS zircon U-Pb dating results show that the Niuzhi monzonitic porphyry formed in the Late Permian (263.5±1.7 Ma). The Niuzhi monzonitic porphyry is characterized by SiO₂ content of 55.30%-74.37%, alkali (Na₂O+K₂O) 2.56%-7.57%, and Na₂O higher than K₂O. It is enriched in LREE and Sc, Co, Cs, As, and depleted in Cr, Ni, Zn, Rb, Sr, Ba, Zr, Ta, Th, U, W, with negative Eu anomalies (δ Eu 0.74-1.06). According to the diagrams, the Niuzhi monzonitic porphyry formed in the tectonic environment of island arc-continent or continental-arc collision, indicating that the branch of Paleo-Tethys Ocean or arc basin in Ailaoshan tectonic belt may have been closed in the Late Permian (263.5±1.7 Ma).