福建太姥山位于中国东南沿海地带,是晚中生代太平洋板块与欧亚板块相互作用的重要地区.野外和岩相学分析表明该地区花岗岩岩类分布广泛,岩性以钾长花岗岩为主.岩石中发育典型的显微文象结构,缺少暗色矿物.岩石具高硅、富碱、贫钙镁和高分异指数等特点,属高钾钙碱性系列和准铝质-弱过铝质花岗岩类.岩石稀土元素含量较高,配分模式呈轻稀土富集并缓向右倾斜、重稀土较为平坦、呈明显铕负异常的海鸥型展布；多数花岗岩具有Rb、U、Th、La等元素强烈富集而Ba、Sr、P、Ti等元素相对亏损的特点.锆石LA- ICP-MS U-Pb同位素定年结果表明,太姥山地区花岗岩的成岩年龄为96.6±1.6 Ma(MSWD= 0.65),属燕山晚期岩浆活动的产物.岩石学、岩相学和地球化学特征均表明太姥山地区花岗岩属于A型花岗岩范畴.其岩浆来源为地壳物质的部分熔融,并可能有少量地幔物质的加入.结合多组地球化学图解、野外地质和区域背景及年代学判定该地区花岗岩形成于后碰撞的伸展构造环境.在早、晚白垩世之交,中国东南大陆边缘处于不断伸展之中,导致大量的构造-岩浆活动,太姥山地区A型花岗岩正是在这样的背景下形成的.%Located on the southeast coast of Fujian Province, Taimushan granite was formed as a result of the interaction between the Pacific plate and the Eurasian plate during the late Mesozoic. Field work and petrographic analysis show that granite rocks are extensively distributed in this area, and most of them are K-feldspar granite. Rocks mostly show subhedral granular texture and typical micrographic texture, and the main minerals include alkali feldspar (mainly perthite and subordinately a small amount of microcline) and quartz, with very rare dark minerals. The SiO2 content of rocks is in the range of 76.93% ~79.47%, the total alkalis content (K2O+Na2O)is in the range of 7.47% ~8.88% , and the K2O content of most rocks is higher than Na2O content. A/CNK ratios are in the range of 0.95 ~ 1.01, TFeO/MgO ratios are in the range of 8.11 ~ 17.83, and the differentiation index is in the range of 96.79-98.11. On the whole, the rocks are characterized by high silicon, enrichment of alkali, low calcium and magnesium, and high differentiation index, thus belonging to high-K calc-alka-line and metaluminous to weakly peraluminous granitoids. The rocks have high and remarkably varying REE, ranging from 94.98×10-6 to 446.85×10-6; LREE/HREE ratios range from 3.71 to 17.47, and (La/Yb)N range from 3.8 to 10.53. Seu values range from 0.08 to 0.80, and their distribution patterns show LREE enrichment with gentle right oblique deviation, relative flat HREE and a seagull model characterized by significant negative Eu anomaly, suggesting characteristics of A-type granitic rocks. Most of the granites are strongly enriched in Rb, U, Th and La and considerably depleted in Ba, Sr, P and Ti. 104 Ga/Al ratios are distributed between 2.74 and 3.46 (3.14 on average), which are higher than the 104 Ga/Al low limit ratio of A-type granites in the world. The trace element spider diagrams of the granites generally show four V-shaped valleys for Ba, Sr, P, Ti depletion, similar to trace element spider diagrams of the Nanling granites. Zircon LA-ICP-MS U-Pb dating result indicates that Taimushan granite, whose diagenetic age is 96.6 ± 1.6 Ma (MSWD = 0.65), is the product of magmatic activity in late Yanshanian period. Its petrogenic age is similar to rock-forming ages of the adjacent Sanshao (91.5 + 1.5 Ma), Dacengshan (93.1+2.4 Ma) and Nanzhen intrusive bodies (96.1 + 2.7 Ma), suggesting that they may be products of the same magmatism. Petrography, geochemistry and discrimination diagrams show that the Taimushan granitoids belong to A-type granite with metaluminous to weakly peraluminous characteristics. Magma originated from partial melting of crustal materials, probably with the participation of a small portion of mantle materials. Integrated with multiple geochemical diagrams, field geology, regional background and geochronology, it is inferred that the granitic rocks of this area were formed in a post-collision and tensile tectonic environment. Between early and late Cretaceous, the continental margin of southeast China was constantly stretching, resulting in a large number of magmatic activities, and hence A-type granites were formed in Taimushan area under this background.
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