扬子板块西北缘大安花岗岩体锆石U-Pb年代学、地球化学特征及其地质意义

位于扬子板块西北缘宁强地区的大安花岗岩体，岩石类型主要为黑云母花岗闪长岩，但其形成时代却有一定的争议，成因及地质意义尚未明确.对大安花岗岩体进行详细的LA-ICP-MS锆石U-Pb年代学和岩石地球化学研究.结果表明，花岗闪长岩年龄为212.3±1.6 Ma和212.48±0.43 Ma，属晚三叠世.地球化学特征显示花岗闪长岩相对高硅（67.61%~69.02%）、高Al₂O₃（16.14%~16.80%），Na₂O > K₂O，富集大离子亲石元素（Cs、Ba）和轻稀土元素，Eu负异常不明显，强烈富集Sr（538×10-6~907×10-6）和亏损Y（3.10×10-6~3.90×10-6），高Sr/Y比值（138~291），表现出明显的埃达克质岩石的地球化学特征.综合区域地质资料认为，大安花岗岩体形成于后碰撞构造环境，是在华北板块与扬子板块碰撞后期伸展体制下，由于地幔物质上涌带来的热量导致加厚基性下地壳脱水熔融，形成了具有埃达克质性质的岩浆. 

Zircon U-Pb Geochronology,Geochemistry and Geological Significance of Daan Granite in Northwestern Margin of Yangtze Block

Located in the Ningqiang area of the northwest margin of the Yangtze block, the Daan granite consists mainly of biotite granodiorite. However, the petrogenesis and geological significances of the Daan pluton remain unclear in addition to the controversial formation age. In this paper, a detailed study of LA-ICP-MS zircon U-Pb geochronology and geochemistry is presented for the Daan granite.The results show that the age of granodiorite is 212.3±1.6 Ma and 212.48±0.43 Ma, belonging to the Late Triassic. Geochemically, the Daan granites have relatively high SiO₂ (67.61%-69.02%) and Al₂O₃ (16.14%-16.80%) contents, and are enriched in LILE (Cs, Ba) and LREE. The samples display an insignificant negative Eu anomaly, low Y (3.10×10-6-3.90×10-6) contents, and high Sr contents (538×10-6-907×10-6) and Sr/Y ratios (138-291), exhibiting marked geochemical features of adakite. Combined with regional geological data, it is proposed that the Daan granite was formed in a post-collisional tectonic environment. The extensional regime after collision between the North China block and the Yangtze block induced the upwelling of mantle material, resulting in the dehydration and melting of thickened basic lower crust and formed the adakitic magma.