南秦岭华阳花岗岩LA—ICP—MS锆石U-Pb年龄、地球化学和Hf同位素组成——对五龙岩体群成因的约束

华阳岩体位于南秦岭中部地区，岩体主体岩性为黑云母二长花岗岩。对中粒黑云母二长花岗岩和细粒黑云母二长花岗岩的LA—IcP—MS锆石u—Pb定年分别获得214Ma±2Ma和228Ma±2Ma的年龄，表明该岩体形成于晚三叠世。华阳花岗岩属于弱过铝质和高钾钙碱性系列，具有I—A型花岗岩过渡的特征，A／CNK值为1．01-1．14，Na2O为3．15％～3．83％，K2O为3．04％～5，70％，K2O／Na2O为0．84-1．80，Mg^n为0．24-0．48；稀土元素配分曲线表现为右倾型，轻、重稀土元素分馏明显，具有显著的Eu负异常。该花岗岩富集Rb、K、Pb、Sr等大离子亲石元素，亏损zr、Hf、Ta、Nb、P、Ti等高场强元素，表明华阳花岗岩的物源以壳源物质为主。锆石饱和温度和Ti温度计等的估算显示，华阳岩体岩浆源区的初始温度为750-8000C。花岗岩的锆石εHt（t）值变化范围较小，为-6．17～2．27，平均值为-3．19；二阶段模式年龄孔。为1．65-1．12Ga，加权平均值为1．46Ga，结合区域地质背景和前人研究成果认为，华阳花岗岩是早—中元古代古老地壳物质部分熔融的结果，伴有少量幔源物质的加入；岩体的形成与华南板块和华北板块碰撞有关．是同碰撞向后碰撞构造体制转变或后碰撞伸展早期的产物。

LA-ICP-MS zircon U-Pb age,geochemistry and Hf isotope ofthe granitoids from Huayang pluton in South Qinling orogen： Constraints on the genesis of Wulong plutons.

Huyang pluton is located at the center of the South Qinling orogenic belt in Central China and belongs to Wulong plutons. The granitoid is of weak peraluminous and high-K calc-alkaline nature with A/CNK being 1.01-1.14, Na20 3.15%-3.83%, K20 3.04%-5.70%, K20/Na2O 0.84-1.80, and Mg# 0.24-0.48. The rocks are enriched in LREE and depleted in HREE with negative Eu anomalies. LA-ICP-MS dating yielded zircon U-Pb ages of 214Ma＋2Ma and 228Ma±2Ma, with the zircons separated from medi-urn-grained and fine-grained monogranite respectively; the εHt（t） values are -6.17-2.27, -3.19 on average. The two-stage Hf-isotope model ages （TDDM2） range from 1116Ma to 1366Ma, 1464Ma oll average. 111 combination with regional geology and previous research achievements, the authors hold that Huyang pluton was formed by partial melting of the lower crnst of Neo- or Meso-Pro- terozoic epoch, with the addition of a certain proportion of mantle-derived materials. It is also considered that the pluton was fonned during the continental collision between North China and South China plates, followed by tectonic transition from compression to extension; in this period, the tectonic setting was converted from syn-collision to post-collision or was at the beginning of the extension of the post-collision period .