Objective The Lianhuashan pluton is located on the western margin of the Cenozoic potassic magmatic suite in western Yunnan and along the southeastern margin of the Lanping–Simao Basin in the northern Indochina Block. Quartz monzonite from this pluton was investigated to constrain its source characteristics and petrogenetic dynamic processes, thereby improving the understanding of the genesis of the potassic magmatic suite.

Methods Zircon U−Pb geochronology, zircon Hf−O isotopes, whole−rock geochemistry, and Sr−Nd−Pb isotopic compositions were systematically analyzed to constrain its petrogenesis and tectonic setting.

Results Zircon U−Pb dating indicates that the Lianhuashan pluton emplaced at ca. 36 Ma, with magmatic activity lasting from 36 to 34 Ma. The Lianhuashan quartz monzonite belongs to the shoshonitic series and is characterized by alkali− and K−rich compositions, enrichment in large−ion lithophile elements (e.g., Rb, Pb, and Sr), depletion in high field strength elements (e.g., Ta and Zr), and pronounced negative Nb−Ta−Ti anomalies. Zircon Ɛ_Hf(t) values range from +2.74 to +4.77, zircon δ¹⁸O values from 7.76‰ to 9.04‰, and whole−rock Ɛ_Nd(t) values from −3.92 to −3.76.

Conclusions These geochemical and isotopic features suggest that the parental magma was derived from a lithospheric mantle metasomatized by Paleo−Tethyan subduction. During magma ascent and emplacement, the magma experienced fractional crystallization and crustal contamination. The formation of the Lianhuashan pluton was related to delamination of the thickened lithosphere triggered by the India−Asia collision, representing a magmatic response to lithospheric delamination within the Indochina Block.