冀北水泉沟岩体西段锆石U-Pb年代学及Hf同位素研究  

Zircon U-Pb chronology and Hf isotope in the western part of the Shuiquangou alkaline complex,northern Hebei Province

作　　者：李长民[1,2] 邓晋福[1] 苏尚国[1] 刘翠[1] 刘新秒[3] 

机构地区：[1]地质过程与矿产资源国家重点实验室中国地质大学地球科学与资源学院,北京100083 [2]中国地质大学长城学院地球科学与资源系,保定071000 [3]天津地质矿产研究所,天津300170

出　　处：《岩石学报》2014年第11期3301-3314,共14页Acta Petrologica Sinica

基　　金：国家“973”项目(2006CB403508);中国地质调查局地质大调查项目(1212011121075、1212010711814);国家自然科学重点基金项目(40234048)联合资助

摘　　要：冀北水泉沟碱性正长杂岩体位于华北克拉通北缘中段,主要岩性为正长岩、石英正长岩、碱性正长岩、角闪正长岩、角闪二长岩和碱长花岗岩等。为了避开后期热液蚀变作用的影响,作者采集了远离东坪-后沟金矿田的水泉沟岩体西段无蚀变的角闪二长岩、角闪正长岩样品,并对这些代表性岩石进行了锆石U-Pb年代学和锆石Hf同位素研究。LA-ICP-MS锆石U-Pb年龄表明,角闪二长岩结晶年龄为372.7±2.5Ma,角闪正长岩结晶年龄为372.7±2.4Ma,二者年龄结果一致,表明水泉沟碱性杂岩体西段形成于晚泥盆世。角闪二长岩的锆石εHf(t)=-12.4^-8.9,两阶段Hf模式年龄为1.93~2.16Ga,平均2.05Ga。角闪正长岩的锆石εHf(t)=-13.2^-11.1,两阶段Hf模式年龄为2.07~2.21Ga,平均2.13Ga。考虑到两种岩石的模式年龄与华北基底变质岩的形成年龄相近,我们初步认为水泉沟碱性杂岩体西段角闪二长岩和角闪正长岩可能主要来源于富集岩石圈地幔部分熔融形成的镁铁质岩浆与古老的中下地壳变质岩部分熔融形成的长英质岩浆混合的结果。野外地质和地球化学数据表明,水泉沟碱性杂岩体形成于晚造山阶段的张性构造环境。The Shuiquangou alkaline syenitic complex in the northern Hebei Province is located in the northern margin of the North China craton. The dominant rock types include syenite,quartz syenite,alkli-syenite,hornblende syenite,hornblende monzonite and alkli-feldspar granite. To avoid the effect of the later-period hydrothermal alteraton,the authors took the not-altered hornblende monzonite and hornblende syenite as samples from the western segment of the Shuiquangou complex far from Dongping-Hougou gold deposit field. In this paper,we present a systematic study of zircon U-Pb geochronologic and Hf isotopes research for these two samples. LA-ICP-MS zircon U-Pb dating gives the emplacement age of 372. 7 ± 2. 5Ma for the hornblende monzonite,and 372. 7 ±2. 4Ma for the hornblende syenite. The two samples have the same age in the range of allowable error,indicating that the western part of the complex formed during the Late Devonian. In-situ Hf analyses of zircons show that the zircons from the hornblende monzonite have εHf（ t） values from- 12. 4 to- 8. 9 and Hf crustal model ages from 1. 93 Ga to 2. 16 Ga with an average of 2. 05 Ga,the zircons from the hornblende syenite have εHf（ t） values of- 13. 2 to- 11. 1 and Hf crustal model ages of 2. 07 Ga to 2. 21 Ga with an average of 2. 13 Ga. All things considered,their model ages are similar to the formation ages of those of basement metamorphic rocks in the North China craton. Therefore,Hf isotopic compositions of zircons suggest that hornblende monzonite and hornblende synite from the western part of the complex indicate that the complex were produced by the magmatic mixing between mafic magma derived from enriched mantle and felsic magama derived from partical melting of the ancient metamorphic rocks of the middle-lower crust. Integrated geological and geochemical data suggest that the complexes are formed in extentional tectonic setting during the late orogenic episode.

关 键 词：碱性杂岩体 锆石U-Pb年龄 锆石HF同位素 MASH模型 岩石成因 冀北水泉沟 

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