广西岑溪地区糯垌岩体中岩石包体的岩石学、地球化学特征及其意义

Petrological and geochemical characteristics and geological significance of inclusions in Nuodong pluton in Cenxi area,Guangxi Province

为探讨广西岑溪地区糯垌岩体及其岩石包体的成因,对糯垌岩体的岩石包体进行详细的岩相学、LA—ICP—MS锆石U—Pb年代学和地球化学分析。岩相学研究表明糯垌岩体的岩石包体主要为斑状黑云母钾长花岗岩、黑云斜长片麻岩、黑云二长片麻岩、二长变粒岩、钾长变粒岩和花岗闪长岩,按成因分为捕掳体和残浆包体两类。斑状黑云母钾长花岗岩包体(样品F16—7—6)和黑云斜长片麻岩包体(样品F16—13—4)的LA—ICP—MS锆石U—Pb定年结果分别为(152. 3±2. 2) Ma和(252. 7±4. 4)Ma;斑状黑云母钾长花岗岩与寄主岩石形成时代一致,黑云斜长片麻岩与大冲花岗闪长岩的侵位时代一致。岩石包体和寄主岩石在hark图解、稀土元素配分曲线和微量元素蛛网图中具有相似的演化趋势,表明寄主岩石经历了一定程度的同化混染作用。

The petrography,LA-ICP-MS zircon U-Pb chronology and geochemical analysis of inclusions in Nuodong pluton are studied to explore the genesis of Nuodong pluton and its inclusions in the Cenxi area of Guangxi Province. The results of petrographic study show that the rock inclusions of Nuodong pluton are mainly composed of porphyritic biotite feldspar granites,biotite plagiogneiss,biotite monzognesiss,fine-grained monzognesiss,k-feldspar granulite and granodiorite. The inclusions can be divided into xenolith and residual magma inclusions according to the petrogenesis. The zircon U-Pb dating results of the porphyritic biotite feldspar granites inclusions( Sample F16-7-6) and biotite plagiogneiss inclusions( Samples F16-13-4) by LA-ICP-MS are 152. 3 ± 2. 2 Ma and 252. 7 ± 4. 4 Ma,respectively. The age of porphyritic biotite feldspar granite is consistent with that of the host rocks,and the age of biotite plagiogneiss is consistent with the emplacement age of Dachong granodiorite pluton.The inclusions and the host rocks have similar evolutionary trend in the hark diagram,the REE distribution curves and spider diagram,indicating that the host rocks had undergone some degrees of assimilation and mixing.