Genesis of Quartz Monzonite Porphyry in Xiaping, Shitouping Heavy Rare Earth Mining Area, Southern Jiangxi Province: Zircon U-Pb Chronology, Geochemistry and Lu-Hf Isotope Characteristics

Previous studies on Xiaping quartz monzonite porphyry in Shitoping heavy rare earth mining area, southern Jiangxi province have been relatively limited. Therefore, comprehensive geochemical, chronological and Lu-Hf isotope analyses were conducted to elucidate the rock mass genesis, the properties of magmatic source and tectonic environment. The rock geochemistry shows that the SiO₂ content ranges from 62.46% to 64.55%, with total alkali (K₂O+Na₂O) content varies between 8.13% and 8.61%. Additionally, Mgo, CaO, FeO and A/CNK value fall within the range of 1.03 to 1.15. Furthermore, it shows enrichment in Ba, K, La, Nd, Zr, Gd, while display depletion in Nb, Ta, Sr, P, Ti. Light rare earths are enriched and heavy rare earths are in deficit, with LREE/HREE ranges from 10.54 to 14.92, exhibiting a positively skewed distribution pattern; the fractionation of light and heavy rare earth elements is obvious, with (La/Yb)_N ranging from 14.72 to 21.46, δEu ranging from 1.10 to 1.31, indicating weak positive Eu anomalies are present. The zirconium saturation temperatures ranged from 893 ℃ to 917 ℃, while the Zr+Nb+Ce+Y values ranged from 572.2×10^-6 to 648.7×10^-6. Geochemical characteristics show A-type granite characteristics. LA-ICP-MS zircon U-Pb dating indicates that the diagenetic age of Xiaping pluton is 142.9 Ma±1.6 Ma. The <italic>ε</italic>_Hf(<italic>t</italic>) values range from -10.64 to -8.06, while two-stage model age (<italic>T</italic>_DM2) ranges from 1707 Ma to 1871 Ma, and the magma source area is composed of lower crustal metasedimentary rock. It is concluded that the Xiaping pluton were formed in an extensional tectonic environment, which is related to the lithospheric extension caused by the subduction and retreat of the Early Cretaceous Paleo-Pacific Plate.