Petrogenesis of the Cenozoic Lianhuashan pluton (SW China): Constrained by zircon U-Pb geochronology, Lu-Hf isotope, and geochemistry

Potassic magmatic rocks provide significant insights in understanding of mantle composition, evolution, and interaction with crust. Potassic magmatism along the Jinshajiang-Ailaoshan Paleo-Tethyan suture has drawn much attention. Whereas igneous intrusion in the Simao terrane, west to Jinshajiang-Ailaoshan potassic magmatic belt has rarely been investigated. Hence, we present zircon U-Pb ages and Lu-Hf isotope and whole-rock geochemistry for the Lianhuashan pluton. Zircon U-Pb dating from monzonite and quartz monzonite porphyry yield ages of 33.6 +/- 0.2 and 33.5 +/- 0.3 Ma, respectively. Monzonites are characterized by high K2O (4.93-5.16%) and K2O/Na2O (1.46-1.71), high Y (22.90-23.80 ppm), and Yb (1.87-2.21 ppm), relatively enrichment of light rare earth element (LREE). Zircons from monzonites show epsilon(Hf)(t) values ranging from -1.1 to +0.6 and crustal model ages (T-DM (c)) between 1.04 and 1.15 Ga. These geochemical features suggest that parent magmas of the rocks originated from a metasomatized lithospheric mantle. Quartz monzonite porphyries are characterized by high Sr (836.00-1,529.00 ppm), Sr/Y (70.85-99.93) and La/Yb (32.31-49.83), low Y (11.80-15.60 ppm), and Yb (0.95-1.30 ppm), enrichment in LREE and depletion in heavy rare earth elements (HREE). Quartz monzonite porphyries have higher Mg-#, MgO, Ni, and Cr contents than the lower crust-derived adakite-like rocks. It is suggested that they were derived by variable degree of mixing between lower-crustal melts and mafic magmas. Based on petrology and geochemistry features, the following evolution process are concluded. During the Neoproterozoic, metasomatic-enriched mantle magma resulted from the bisubduction of oceanic plate; meanwhile, the crust thickened, and juvenile lower crust formed. During late Eocene, hot asthenosphere upwelled and K-rich mafic magmas resulted from the decompression of delamination, followed by magmatism emplacing, crystallizing, and the forming of the Lianhuashan pluton.