赣南沙地花岗岩体LA-ICP-MS锆石U-Pb年龄、地球化学特征及构造意义 LA-ICP-MS Zircon U-Pb Ages and Geochemical Characteristics of the Shadi Granitic Pluton in Southern Jiangxi and Their Tectonic Significance

本文对赣南沙地地区沙地花岗岩体中的正长花岗岩进行了LA-ICP-MS锆石U-Pb定年、岩石学和地球化学研究。结果表明：正长花岗岩锆石U-Pb年龄为428.3 ± 5.9Ma，表明沙地花岗岩体形成于早志留世；地球化学特征显示：沙地花岗岩体的铝饱和指数为1.07~1.19, K2O/Na2O为1.07~1.73，属过铝质岩石；稀土元素总量为(169~244) × 10−6，轻稀土元素富集，稀土配分模式呈明显的右倾型；δEu为0.10~0.40，Eu亏损中等偏高；岩体中Rb、Th、U、La、Ce、Nd、Zr、Hf及Sm相对富集，Ba、Sr及Ti相对亏损；岩体Rb/Sr为2.90~7.28，平均值为5.12，明显高于大陆地壳平均值和上地壳平均值，具壳源花岗岩特征。沙地花岗岩体形成于早古生代晚期的加里东构造运动，是华夏地块与扬子地块在新元古代碰撞拼贴之后发生裂解，在奥陶纪至志留纪上地壳部分熔融形成的S型花岗质岩浆，在碰撞到后碰撞过渡期上升至上地壳形成的花岗岩体。 This study conducted analysis on the Shadi granitic pluton in the Shadi area, southern Jiangxi Province using LA-ICP-MS zircon U-Pb dating, petrological and geochemical methods. The results show that the zircon U-Pb ages of the positive long granite in the studied areas are 428.3 ± 5.9 Ma, indicating the Shadi granitic pluton formed in Early Silurian. Geochemical result shows that the Shadi granitic pluton has ACNK of 1.07 - 1.19 and K2O/Na2O of 1.07 - 1.73, suggesting that they belong to peraluminous rock. The pluton has a total REE content of (169 - 244) × 10−6, and is enriched in LREE, with distinct right oblique REE patterns, Eu values of 0.10 to 0.40 and obvious negative Eu anomaly. The REE analysis shows the pluton is enriched in Rb, Th, U, La, Ce, Nd, Zr, Hf and Sm, and depleted in Ba, Sr and Ti, with Rb/Sr ratio of 2.90 - 7.28 (averaging 5.12) obviously higher than the average values of continental crust and the upper crust, suggesting that the pluton is of the characteristics of crust derived granite. The Shadi granite pluton might result from the Caledonian movement of late Early Paleozoic, and broke up after collision matching between Cathaysian land mass and Yangtze land mass. S-type granitic magmas, formed by partial melting of the upper crust in the period of Ordovician to Silurian, ascended to the upper crust and yielded the Shadi granite pluton in the period of collision to post-collision.