胶东金矿集区是我国最重要的金矿集区,大规模金成矿作用发生于125~110 Ma.本文选择了与成矿作用同期的早白垩世晚期大泽山岩体为研究对象,通过详细的岩相学、岩石地球化学、锆石LA-ICP-MS U-Pb年代学研究,识别出中粒二长花岗岩和细粒二长花岗岩两种主要的侵入岩类型,它们具有相似的岩相学和岩石地球化学特征,呈现同源岩浆演化特征.定年结果表明,中粒二长花岗岩中锆石U-Pb年龄分别为119.8±0.8 Ma和119.3±0.9 Ma,细粒二长花岗岩中锆石U-Pb年龄分别为109.2±0.7 Ma和109.9±0.7 Ma.岩石地球化学研究表明,二长花岗岩具有高的全碱(K2O+Na2O=8.14%~8.72%),高的Al2O3(12.42%~15.32%),属过铝质高钾钙碱性系列,轻稀土(LREE)富集、重稀土(HREE)相对亏损(LREE/HREE=8.46~18.87),具明显的稀土元素分馏((La/Yb)N=8.52~24.08)和较强的Eu负异常(δEu=0.33~0.58).大泽山岩体锆石εHf(t)值为-26.4~-16.2,亏损地幔二阶段模式年龄(TDM2)为2 812~2 173 Ma,物源主要是古元古代和新太古代陆壳的部分熔融,有少量幔源物质的加入.大泽山岩体成岩期与胶东金矿的主成矿期一致,暗示岩浆活动与金成矿具有统一的地球动力学背景.
The Jiaodong Peninsula is one of the most important gold mineralization areas in China,and the large-scale gold mineralization occurred from 125 Ma to 110 Ma.In this paper,the Early Cretaceous Dazeshan pluton,emplaced coevally with the gold mineralization,is selected to reveal its petrogenesis using detailed lithography,petrogeochemistry and zircon LA-ICP-MS U-Pb chronology.Medium grained monzogranite and fine grained monzogranite are identified in Dazeshan pluton.They have similar petrographic and geochemical characteristics,showing the characteristics of homologous magmatic evolution.Zircon U-Pb dating yields 119.8± 0.8 Ma and 119.3±0.9 Ma for the medium grained monzogranite,109.2±0.7 Ma and 109.9±0.7 Ma for the fine grained monzogranite.Petrogeochemistry studies show that:monzogranite possess high total alkalis(K2O+Na2O=8.14%~8.72%),with high Al2O3 content(12.42%~15.32%),the granites belong to peraluminious high-K calc-alkaline feature,enrichment in LREEs,relative depletion in HREEs(LREE/HREE=8.46~18.87),as well as significant rare earth element fractionation((La/Yb)N=8.52~24.08)and with pronounced negative Eu anomalies(δEu=0.33~0.58).The Dazeshan pluton has low zircon εHf(t)values of-26.4~-16.2,and two-stage Hf model ages(TDM2)vary in range of 2 812~2 173 Ma.The diagenetic material is mainly derived from the partial melting of the Paleoproterozoic and Neoarchean crustal materials with the addition of some mantle materials.The diagenetic period of Dazeshan pluton is consistent with the main metallogenic period of Jiaodong gold deposit,suggesting that magmatism and gold mineralization have the same geodynamic setting.