安徽繁昌浮山钾长花岗岩成因及其构造意义——来自锆石U-Pb年龄、岩石地球化学和Hf同位素的证据

安徽繁昌地区是长江中下游铜铁金多金属成矿带的重要组成部分。对繁昌浮山钾长花岗岩开展了详细的岩石学、岩石地球化学、锆石U-Pb 年代学和Lu-Hf 同位素分析，并在此基础上探讨了岩石成因及动力学背景。岩石地球化学研究表明，浮山钾长花岗岩为硅过饱和的准铝质-弱过铝质富碱富钾岩石，具有较高的Ga/Al 值、TFeO/MgO 值、Zr+Nb+Ce+Y 和稀土元素含量，显示出A 型花岗岩的地球化学特征。此外，浮山钾长花岗岩具有低(87Sr/86Sr)i、高δ18O、负εNd(t)和εHf(t)、负Eu 异常等地球化学特征。繁昌浮山钾长花岗岩LA-ICP-MS 锆石206Pb/238U 年龄为124.9±2.0Ma（n=15，MSWD=0.20），被解释为钾长花岗岩的形成年龄。与长江中下游地区A 型花岗岩带中的其他岩体为同期岩浆活动的产物，均形成于早白垩世。结合岩石学和区域地质资料，表明浮山钾长花岗岩可能是新生下地壳物质部分熔融作用形成的，形成浮山钾长花岗岩的新生下地壳可能由来源于富集地幔岩石圈的玄武质-安山质岩浆和少量结晶变质基底物质组成。根据锆石U-Pb 年龄，结合区域地质资料分析，晚侏罗世—早白垩世，长江中下游地区经历挤压向伸展构造应力场的转变，随时间推移，伸展作用逐渐增大，至125Ma 左右该区岩石圈可能达到了伸展的高峰期。

Petrogenesis and tectonic implications of the Fushan moyite in the Fanchang area,Anhui Province-Evidence from zircon U-Pb age,geochemistry and Hf isotopes

The Fanchang area is one of the important components of the Middle-Lower Yangtze Valley metallogenic belt. The Fushan moyite is one of the most representative and important granitic intrusions. In this paper, LA-ICP-MS zircon U-Pb dating, petrographic observations and geochemical and Hf isotopic analysis were carried out for the Fushan moyite in the Fanchang area, with the emphasis placed on the analysis of petrogenesis and tectonic implications of the Fushan moyite. The Fushan moyite has a clear A-type geochemical signature, e.g., it is of metaluminous to weakly peraluminous nature (A/CNK=0.91~1.11) and has high SiO2 (averagely 71.52%), total alkalis (Na2O+K2O=8.85%~9.60%), K*(K2O/Na2O=1.06~1.57), Fe*(TFeO/MgO=2.49~10.2), rare earth elements (ΣREE=278×10-6~376×10-6), Ga/Al ratio (2.90~3.31) and HFSE (Zr+Nb+Ce+Y=421.8×10-6~655.0×10-6). LAICP-MS zircon U-Pb dating yielded a concordant weighted mean 206Pb/238Pb age of 124.9±2.0Ma, which is similar to ages of other A-type granites in the Middle-Lower Yangtze Valley metallogenic belt, indicating that all A-type granites were formed in the Early Cretaceous. Zircons from this pluton yielded εHf(t) values between -5.8 and -10.0, which, together with U-Pb age,(87Sr/86Sr)I, δ18O and εNd(t) values of the Fushan moyite, suggest the importance of juvenile material in the magma source, and the juvenile material was composed of the basaltic andesitic magma from enriched mantle lithosphere and minor crystalline metamorphic basement. These data, together with other accurate dating data of intermediate-acid plutons and volcanic rocks in the Middle-Lower Yangtze Valley metallogenic belt, support the peak time of crustal extension at ~125Ma in this area.