胶北地体西涝口地区牧牛山二长花岗岩锆石U-Pb和Lu-Hf同位素研究——指示华北克拉通古元古代岩浆作用及地壳演化  

Zircon U-Pb and Lu-Hf isotopes of Muniushan monzogranite in Xilaokou area,Jiaobei Terrane——Indicating Paleoproterozoic magmatism and crustal evolution of the North China Craton

作　　者：周晓萍 吕军阳 胡秉谦 康恺 姜帆 胡亮 张娜 ZHOU Xiaoping;LÜJunyang;HU Bingqian;KANG Kai;JIANG Fan;HU Liang;ZHANG Na(No.6 Geological Team of Shandong Province Bureau of Geology and Mineral Resources,Weihai,Shandong,264209;No.3 Geological Team of Shandong Province Bureau of Geology and Mineral Resources,Yantai,Shandong,264000)

机构地区：[1]山东省地质矿产勘查开发局第六地质大队,山东威海264209 [2]山东省地质矿产勘查开发局第三地质大队,山东烟台264000

出　　处：《地质论评》2022年第3期891-906,共16页Geological Review

基　　金：山东省地矿局科研项目“鲁东中生代盆地构造岩浆演化及盆缘金属矿床成矿机制(编号:202004)”;山东地矿六院青年科技基金项目“胶莱盆地东北缘西涝口金矿床成因机制”的成果。

摘　　要：胶北地体古元古代花岗岩位于胶—辽—吉带南部,是华北克拉通东部陆块东缘的重要古元古代造山带。西涝口地区牧牛山二长花岗岩作为胶北地体出露的少数古元古代花岗岩之一,也是西涝口、辽上、郭城等大型金矿床的赋矿围岩,有重要研究价值。笔者通过岩石地球化学、锆石U-Pb年代学及Lu-Hf同位素分析,讨论了其形成时代及成因机制。经研究发现,该岩体富硅(SiO_(2)=75.79%~76.10%),富碱(Na_(2)O+K_(2)O=6.88%~7.18%),为准铝质钙碱性岩系列(A/CNK值为0.86~0.95);Rb、U、Ta、Pb相对富集,Ba、Nb相对亏损,Sr强烈亏损,岩石10000Ga/Al值为2.88~3.50,属A型板内花岗岩;岩体中岩浆锆石具明显振荡环带结构,相对亏损LREE并逐步富集HREE,具明显正Ce异常和负Eu异常,加权平均年龄为2113±22 Ma,代表其侵位时间为古元古代;变质增生锆石的HREE富集程度明显高于核部岩浆锆石,且具更加强烈的正Ce异常和稍弱负Eu异常,加权平均年龄为1850±24 Ma,代表区内变质事件年龄;ε_(Hf)(t)值为-3.75~+5.17,T_(DM2)值为2450~2712 Ma,该岩体与胶北地体2.5 Ga TTG岩石具相同的地壳演化趋势,暗示其源自太古宙陆壳的重熔。The Paleoproterozoic granite of Jiaobei terrane(northern part of eastern Shandong) is located in the south of Jiao—Liao—Ji(eastern Shandong—Liaoning—Jilin) belt. It is an important Paleoproterozoic orogenic belt in the eastern margin of the eastern continental block of the North China Craton. As one of the few Paleoproterozoic granites exposed in Jiaobei terrane, muniushan monzogranite in Xilaokou area is also the host rock of Xilaokou, Liaoshang, Guocheng and other large gold deposits, which has important research value. This paper discusses its formation age and genetic mechanism through rock geochemistry, zircon U-Pb chronology and Lu-Hf isotope analysis. It is found that the monzogranite is rich in silicon(SiO_(2)=75.79%~76.10%) and alkali(Na_(2)O+K_(2)O=6.88%~7.18%), which is a quasi aluminous calc alkaline rock series(A/CNK value is 0.86~0.95);trace elements Rb, U, Ta, Pb are relatively enriched, Ba and Nb are relatively depleted, Sr is strongly depleted, and the rock 10000·Ga/Al value is 2.88~3.50, belonging to A-type intra-plate granite;The magmatic zircon in the rock mass has an obvious oscillatory ring structure, relatively lacks light rare earth elements(LREE) and gradually enriches heavy rare earth elements(HREE), with obvious positive Ce anomaly and negative Eu anomaly. The weighted average age is 2113±22 Ma, indicating that its emplacement time is Paleoproterozoic;The heavy rare earth elementsenrichment of metamorphic accretionary zircon is significantly higher than that of magmatic zircon in the core, and has stronger positive Ce anomaly and slightly weak negative Eu anomaly. The weighted average age is 1850±24 Ma, representing the age of metamorphic events in the region;ε_(Hf)(t) value is-3.75~+5.17 and T_(DM2)value is 2450~2712 Ma. This rock mass has the same crustal evolution trend as the 2.5 Ga TTG rocks of Jiaobei terrane, indicating an origin by partial melting of Archean continental crust.

关 键 词：胶北地体 西涝口地区 牧牛山二长花岗岩 锆石U-Pb年代学 Lu-Hf同位素分析 

分 类 号：P597[天文地球—地球化学] P534.3[天文地球—地质学]