华北地块南缘老牛山杂岩体时代、成因及地质意义--锆石年龄、Hf同位素和地球化学新证据  

Geochronology and origin of the Laoniushan complex in the southern margin of North China Block and their implications:New evidences from zircon dating,Hf isotopes and geochemistry

作　　者：齐秋菊 王晓霞[2] 柯昌辉[2] 李金宝[3] 

机构地区：[1]有色金属华东地质勘查局资源调查与评价研究院,南京210007 [2]中国地质科学院矿产资源研究所,国土资源部深部成矿作用与资源评价重点实验室,北京100037 [3]长安大学地球科学与资源学院,西安710054

出　　处：《岩石学报》2012年第1期279-301,共23页Acta Petrologica Sinica

基　　金：地质调查项目(1212010012012、1212010811033、1212010611803);公益性行业专项课题(200911007-09)联合资助

摘　　要：老牛山杂岩体位于华北地块南缘。野外侵入关系和锆石LA-ICP-MSU-Pb定年显示,其由晚三叠世(印支期)和晚侏罗(燕山期)花岗质岩石组成。印支期岩石类型为石英二长岩、石英闪长岩和粗粒黑云母二长花岗岩,年龄分别为223±1Ma、222±1Ma和214±1Ma;燕山期为中粒-中粗粒黑云母二长花岗岩和细粒-中细粒黑云母二长花岗岩,年龄分别为152±1Ma和146±1Ma。印支期石英闪长岩、石英二长岩的SiO2相对含量低、富碱、高铝,为钾玄系列,准铝质Ⅰ型花岗岩;印支期粗粒黑云母二长花岗岩具富硅、碱、高铝、低镁的特点,属于高钾钙碱性系列,为准铝质-过铝质Ⅰ型花岗岩;燕山期黑云母二长花岗岩具高硅和铝、富碱,低镁的特点,为高钾钙碱性系列,准铝质Ⅰ型花岗岩。组成老牛山杂岩体的花岗岩从早到晚SiO2含量由低变高,MgO、CaO和Na2O由高变低。各期次岩石均表现出稀土元素总量较高,轻稀土元素明显富集,轻、重稀土元素分馏明显,具有较弱的铕异常。两期花岗质岩石均富集大离子亲石元素(K、Rb、Ba、Sr),而相对亏损高场强元素(Nb、Ta、P)。印支期花岗质岩石的全岩εNd(t)为-11.3～-14.87,tDM为1.7～1.9Ga,锆石的εHf(t)为-9.57～-25.11,tDM2为1863～2841Ma;燕山期花岗岩的全岩εNd(t)为-13.32～-16.83,tDM为1.7～1.9Ga,锆石的εHf(t)为-18.28～-24.79,tDM2为2360～2767Ma,表明该杂岩体的源区物质以壳源物质为主,可能与太古宙太华群相似,印支期有年轻地幔物质贡献。The Laoniushan granitoid complex is located in the southern margin of North China Block.Field work and LA-ICP-MS zircon dating suggest that this complex consists of Late Triassic(Indosinian)and Late Jurassic(Yanshanian)granitoids.The rock types of the Indosinian granitoids are adamellite,quartz diorite and coarse-grained biotite monzogranite with ages of 223±1 Ma,223±1 Ma and 21 4±1 Ma,respectively.The Yanshanian granitoids are mid-coarse-grained,mid-grained biotite monzogranite and fine- grained biotite monzogranite with ages of 1 52±1 Ma and 1 46Ma,respectively.The Indosinian adamellite and quartz diorite are low in SiO2 but rich in Al2 O3 and Na2 O+K2 O,showing Shoshonite series and metaluminous I-type granite;coarse-grained biotite monzogranite are rich in SiO2,Al 2 O3 and Na2 O+K2 O,but poor in MgO with the features of high-K calc-alkalic series and metaluminous to peraluminous I-type granite.The Yanshanian biotite monzogranite with high SiO2,Al 2 O3 and Na2 O+K2 O also show the nature of high-K calc-alkalic series and metaluminous I-type granite.From Late Triassic to Late Jurassic SiO2 content of these granitoids increase,but MgO,CaO and Na 2 O decrease.The total REE contents of the granitoids are very high,especially LRRE, suggesting obvious LRRE and HRRE fractionation,and weakly negative Eu anomalies.The granitoids of Indosinian and Yanshanian are all rich in large ion lithophile elements(K,Rb,Ba,Sr),and relative depleted in high-field strength elements(Nb,Ta,P).The Indosinian granitoids withεNd(t)=-1 1.3～-1 4.87,t DM =1.7～1.9Ga,ε Hf (t)=-9.57～-25.11,t DM2 =1 863～2841 Ma,and the YanshanianεNd(t)=-1 3.32～-1 6.83,t DM =1.7～1.9Ga,ε Hf (t)=-18.28～-24.79,t DM2 =2360～2767 Ma,indicate that their sources are dominated by old crust component related to the Archaean Taihua Group and the sources of the Indosinian granitoids is with more juvenile component contributed.

关 键 词：锆石U-Pb定年 SR-ND-HF同位素 物质源区 花岗质杂岩体 华北地块南缘 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]