北秦岭马河钼矿区花岗岩类的锆石U-Pb年龄、地球化学特征及其地质意义  

Geochronology and geological significance of the granites from the Mahe Mo deposit in the North Qinling

作　　者：柯昌辉[1] 王晓霞[1] 李金宝[2] 齐秋菊[3,4] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]长安大学地球科学与资源学院,西安710054 [3]有色金属华东地质勘查局资源调查与评价研究院,南京210007 [4]中国地质大学,北京100083

出　　处：《岩石学报》2012年第1期267-278,共12页Acta Petrologica Sinica

基　　金：中国地质调查项目(1212010012012、1212010811033);国土部公益性行业科研专项(200911007-09、201111007-2)联合资助

摘　　要：本文对北秦岭马河钼矿区桃官坪中-细粒二长花岗岩和西沟斑状二长花岗岩进行了LA-ICP-MS锆石U-Pb年龄测定,分别获得了157±1Ma(NSWD=13)和153±1Ma(NSWD=14)的谐和年龄,表明其为晚侏罗世侵入体。马河钼矿的形成与这两个侵入体密切相关,据此限定该钼矿床成矿时代略晚于157～153Ma,为侏罗世晚期成矿。桃官坪和西沟花岗岩具有高硅(68.12%～76.33%),富碱(Na2O+K2O=6.35%～10.38%)的特征,K2O/Na2O变化较大(0.91～1.89),A/CNK在0.85～1.14之间,为准铝质-弱过铝质高钾钙碱性系列。微量元素上富集U、Pb、Hf等高场强元素,亏损Rb、Ba、K、Sr、P等大离子亲石元素。稀土元素配分曲线为轻稀土相对富集的右倾型,多数具有弱的负铕异常(δEu=0.5～0.9),少数样品具有弱正铕异常(δEu=1.05～1.08)。与华北地块南缘与钼矿有关的花岗岩相比,二者均具有高硅、高钾、富碱的特征。但马河钼矿区成矿花岗岩比华北地块南缘的稍基性,这可能是导致马河钼矿的矿床规模比华北地块南缘较小的原因之一。LA-ICP-MS U-Pb dating for the granites from the Taoguanping and Xigou plutons in the Mahe Mo deposit in the North Qinling yields concordant ages of 1 57±1 Ma（NSWD=1 3）and 1 53±1 Ma（NSWD=1 4）respectively indicating that the two plutons were formed at late Jurassic.The Mahe Mo deposit is closely related to the two plutons.Therefore these ages may suggest the Mo deposit formed at Late Jurassic appreciably later than 1 57～1 53 Ma.The granites from the Taoguanping and Xigou plutons are characterized by high in silica（68.1 2%～76.33%）and alkali（Na 2 O＋K2 O=6.35%～1 0.38%）with the A/CNK of 0.85～1.1 4 and lager variation of K2 O/Na2 O（0.91～1.89）,showing that they are metaluminous or weakly peraluminous and high-K calc-alkaline series.The Taoguanping and Xigou granites are enriched in U,Pb,Hf,but depleted in Rb,Ba,K,Sr and P.The REE patterns are characterized by enrichment in LREE with weak negative abnormal of Eu（0.5～0.9）,but a few samples have weak positive Eu anomalies（1.05 to 1.08）.The granites are similar to the molybdenum deposits related granites in the southern margin of the North China Block in enriched in SiO2 and Na2 O＋K2 O.However,these granites are lower in SiO 2 ,Na 2 O＋K2 O and higher in CaO and MgO than the granites in the southern margin of the North China Block.It may be one reason that the Mahe Mo deposit is not as larger as the deposits in the southern margin of the North China Block.

关 键 词：花岗岩 LA-ICP-MS锆石U-PB年龄 地球化学 马河钼矿 北秦岭 

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