Genesis of the Guanxi Pluton in Southern Jiangxi: Constraints from Zircon U-Pb Ages and Sr-Nd Isotopes

关西岩体位于华南板块，为讨论关西岩体的岩石成因，文章进行了LA-ICP-MS锆石U-Pb定年、岩石地化及Sr-Nd同位素研究。LA-ICP-MS锆石U-Pb同位素年龄测定结果表明赣南关西岩体的年龄为199.3 ± 2.6 Ma (MSWD = 1.5, n = 9)。关西花岗岩高硅、富碱，贫铁、镁、钙，富集Nb、Ta、Zr、Hf等高场强元素，具有显著的Eu负异常并强烈亏损Ba、Sr、P、Ti等元素；具有较高的全岩锆饱和温度(TZr = 811℃~1074℃，平均值为966℃)，10,000 × Ga/Al > 2.6，表明关西岩体为A型花岗岩。关西花岗岩Sr-Nd同位素分析显示具有较低(87Sr/86Sr)i值(0.703518~0.677420)和较高的εNd(t)值(0.33~1.09)，强烈的Eu负异常和高Rb/Sr比值，结合全岩主微量元素特征，它的源区可能为亏损地幔演化形成的新生地壳。The Guanxi Pluton is situated within the South China Block. To discuss the petrogenesis of the Guanxi Pluton, this study conducted LA-ICP-MS zircon U-Pb dating, petrogeochemical analysis, and Sr-Nd isotopic investigations. LA-ICP-MS zircon U-Pb isotopic age determination results indicate that the age of the Guanxi Pluton in southern Jiangxi is 199.3 ± 2.6 Ma (MSWD = 1.5, n = 9). The Guanxi granite is characterized by high silica and alkali content, low iron, magnesium, and calcium, enrichment in high-field-strength elements such as Nb, Ta, Zr, and Hf, significant Eu negative anomalies, and strong depletion in elements like Ba, Sr, P, and Ti. It exhibits high whole-rock zircon saturation temperatures (TZr = 811˚C ~1074˚C, average of 966˚C) and 10,000 × Ga/Al ratios greater than 2.6, indicating that the Guanxi Pluton is an A-type granite. Sr-Nd isotopic analysis of the Guanxi granite reveals low initial (87Sr/86Sr)i values (0.703518~0.677420) and high εNd(t) values (0.33~1.09), along with strong Eu negative anomalies and high Rb/Sr ratios. Combined with the whole-rock major and trace element characteristics, its source region is likely juvenile crust formed through the evolution of depleted mantle.