胶东西北部北截岩体岩石成因:锆石U-Pb年龄、岩石地球化学与Sr-Nd-Pb同位素制约  

Petrogenesis of the Beijie pluton from the northwestern Jiaodong Peninsula:Constraints from zircon U-Pb age,petrogeochemistry and Sr-Nd-Pb isotopes

作　　者：宋英昕 于学峰 李大鹏 耿科[1,2] 尉鹏飞 左晓敏 王秀凤 SONG YingXin;YU XueFeng;LI DaPeng;GENG Ke;WEI PengFei;ZUO XiaoMin;WANG XiuFeng(Ministy of Naturul Resaurces Key Laboralory of Giold Minelsntion Poeeses and Recources Uilintion,Key Laborutory of Mellogenic-Geologic Proeses and Comprehensine Unilisution of Minerals Resources in Shundong Prurince,Shaundong Insitude of Geological Sciences.Jinan 250013,China;Shandong SHRIMP Center,Jinwn 250013,China;Suate Key Iaboralury of Geological Preses and Mineral Resources,Chinu Uniersiy of Geosxiences,Beijng 00083.China;Shandong Geological Museumn,Jiran 250014,China)

机构地区：[1]自然资源部金矿成矿过程与资源利用重点实验室,山东省金属矿产成矿地质过程与资源利用重点实验室,山东省地质科学研究院,济南250013 [2]山东离子探针中心,济南250013 [3]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [4]山东省地质博物馆,济南250014

出　　处：《岩石学报》2020年第5期1477-1500,共24页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41772076、4672084、41372086、41503038);国家重点研究研发计划项目(2016YFC0600105-04、2016YFC0600606);山东省重点研发计划项目(2017CXGC1601、2017CXGC1602、2017CXGC1603);山东省泰山学者项目联合资助.

摘　　要：胶东半岛西北部是我国最重要的金矿集区,95%以上的金资源储量赋存于晚侏罗世玲珑型和早白垩世郭家岭型花岗岩中。然而,对郭家岭型花岗岩形成的大地构造背景及其与金成矿的关系,尤其是岩石成因仍存有争议。本文通过对归属于郭家岭型花岗岩的北截岩体开展详细的岩相学、岩石地球化学、锆石U-Pb年代学和Sr-Nd-Pb地球化学研究,识别出细粒花岗闪长岩、含斑细粒花岗闪长岩、斑状中粒花岗闪长岩、斑状粗粒花岗闪长岩和花岗伟晶岩脉5种侵入岩类型,它们具有相似的地球化学特征和同位素组成,呈连续演化关系,为同一期岩浆活动的产物。电子探针分析显示,样品中的黑云母具有富FeOT、MgO、高Al2O3低TiO2的特点,为岩浆成因的富铁黑云母,Mg和Al元素的负相关性表明结晶过程中二者可能发生了置换。岩石地球化学研究表明,花岗闪长岩具有高的全碱(K2O+Na20=6.92%~9.31%)、Ba(518×10-6~3330×10-6)、Sr(305×10-6~1371×10-6),低的Al2O3(14.41%~15.82%)、MgO(0.19%~0.77%)、Rb(39.3×10-6~105×10-6)、Y(1.2×10-6~6.05×10-6)、Yb(0.08×10-6~0.40×10-6)含量特征,轻稀土(LREE)富集、重稀土(HREE)相对亏损(LREE/HREE=13.13-21.40),轻、重稀土元素分馏明显[(La/Yb)N=18.39~45.76],Rb、Sr、Ba、Pb等大离子亲石元素(LILE)富集,Nd、Ta、Zr、Hf等高场强元素(HFSE)明显亏损,具有高Ba-Sr花岗岩的地球化学特征。锆石LA-ICP-MS定年结果表明,斑状粗粒花岗闪长岩形成于131.53±0.86Ma,花岗伟晶岩脉形成于127.4±1.3Ma,说明其形成于早白垩世早期,伟晶岩脉应该是本次岩浆活动后期的产物。Sr-Nd同位素分析表明,初始87Sr/86Sr(ISr)和εNd(t)分别为0.710658-0.711568和-18.53^-11.17,二阶段亏损地幔模式年龄(tDM2)为2107-2425Ma,与胶东群变质岩年龄一致,指示了其原始岩浆有部分熔融的胶东群参与;Pb同位素分析表明,初始206Pb/204Pb和初始208Pb/204Pb分别为17.047~17.945和37.744~38.38The northwestern Jiaodong Peninsula is the most important gold mineralization area in China.The majority of gold resources C> 95% D in Jiaodong are hosted in the Late Jurassic Linglong-type and Early Cretaceous Guojialing-type granitoids.However,there is still controversy over the geotectonic setting of Guojialing-type granitoids and its relationship with gold mineralization,especially its petrogenesis.This paper systematically investigated the Beijie pluton which belongs to Guojialing-type granitoids to analyse its petrography,petrogeochemistry,zircon U-Pb age,and Sr-Nd-Pb geochemistry.Fine-grained granodiorite,porphyritic finegrained granodiorite,porphyritic medium-grained granodiorite,porphyritic coarse-grained granodiorite and granite pegmatite are identified in Beijie pluton.They have the similar geochemical characteristics and isotope compositions,and present continuous evolution tendency.All these suggest the five intrusive rocks are the product of the same magmatic activity.Electron probe analysis shows the biotites in granodiorites have high MgO,FeOT,Al2 O3 and low TiO2,indicating the Fe-rich biotite is magmatic origin.Negative correlation with Mg and A1 implicit they may be displaced during crystallization.Petrogeochemistry studies show that:C1 D the Beijie granodiorites possess high total alkalis CK2 O+Na2 O=6.92%~9.31% D,Ba C518×10-6~3330×10-6 D,Sr C305×10-6~1371×10-6 D,with low Al2 O3 C14.41%~15.82% D,MgO CD.19%~0.77% D,Rb C39.3×10-6~105×10-6 D,Y C1.2×10-6~6.05×10-6 D,Yb G0.08×10-6~0.40×10-6 D,enrichment in LREEs,relative depletion in HREEs CLREE/HREE=13.13~21.40 D;C2 D the fractional distillation of the LREEs and HREEs is obvious [CLa/YbDN=18.39~45.76];C3 D the LILE Ce.g.,Rb,Sr,Ba and PbD is enriched,while the HFSE Ce.g.,Nd,Ta,Zr and HfD is obviously depleted.All these features suggest that the rocks are similar to the Ba-Sr granites.Zircon LA-ICP-MS U-Pb dating yield 131.53±0.86 Ma for the granodiorite and 127.4±1.3 Ma for the granitic pegmatite,indicating they are formed in Early Creta

关 键 词：北截岩体 锆石U-PB年龄 SR-ND-PB同位素 岩浆混合成因 花岗闪长岩 胶西北 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]