摘要
辽东岫岩地区位于胶—辽—吉古元古代造山/活动带内,区域内广泛存在花岗质伟晶岩脉或岩体,对其进行研究具有重要的构造意义。研究区出露大量古元古代花岗伟晶岩,前人将其统一划归到花岗质混杂岩和辽河岩群内。本文通过详细的野外地质调查和室内综合研究,将该套花岗伟晶岩脉解体为出来,重新厘定为新的填图单元。本文对研究区2件花岗伟晶岩样品进行岩石学、岩石地球化学、锆石LA-ICP-MS稀土微量元素和U-Pb定年的综合研究,获得花岗伟晶岩的原岩年龄,并对其岩石地球化学、成因和构造环境进行了探讨。花岗伟晶岩主要矿物组合为钾长石+斜长石+石英±白云母±电气石,花岗伟晶结构,块状构造。岩石地球化学分析结果显示其均匀具有一致的地球化学特征。它们均显示高的SiO2(72.1%~75.3%)、Al2O3(13.5%~16.4%),低CaO(1.42%~2.03%)、MgO(0.15%~0.76%)、P2O5(0.01%~0.02%%)、TiO2(0.06%~0.17%)等含量;稀土元素总量偏低,稀土富集、重稀土亏损,稀土配分曲线右倾型,明显的正δEu异常;微量元素富集大离子亲石元素(Cs、Rb、Ba、U),相对亏损高场强元素(Nb、Ta、Ti)等特征。样品(DST-TW1和WJG-TW1)锆石CL图像强度均较弱,前者大部分锆石不能反映矿物内部结构,后者大部分锆石能显示弱振荡环带,这一特征与锆石U含量均较高(1253.1×10-6~12861.5×10-6、874.5×10-6~5319.1×10-6)相吻合。锆石虽具有岩浆锆石的自形特征,但其Th/U值(0.01~0.26和0.01~0.62)较低,稀土配分模式显示热液锆石特征,在(Sm/La)N—La和Ce/Ce*—(Sm/La)N图解上偏热液锆石区域,此花岗伟晶岩脉可能是母岩浆高度结晶分异后的残余岩浆热液结晶而成,偏热液性质。本文研究的2件样品(DST-TW1和WJG-TW1)年龄分别为1864±20 Ma(MSWD=0.19)和1903.6±4.7 Ma(MSWD=0.041),其侵位时间介于1.9~1.86 Ga之间。从岩石地球化学、形成时代推测其物源与研究区周围~1.87 Ga的S型花�
As the inside of Jiao—Liao—Ji(i.e.Eastern Shandong—Liaoning—Jilin)Paleoproterozoic orogenic/mobile belt of North China Craton,granitic pegmatites are widely outcropped in Xiuyan area,eastern Liaoning Province.To study these granitic pegmatites is of important tectonic significance.A large number of Paleoproterozoic granitic pegmatites were found in Xiuyan area,which were uniformly classified into granitic melanges and Liaohe Rock Groups.In this paper,through detailed field geological survey and indoor comprehensive study,this set of granitic pegmatitic dykes is disintegrated into a new mapping unit.In this paper,petrology,petrogeochemistry,zircon LA-ICP-MS rare earth and trace elements and U-Pb dating of two granitic pegmatite samples in the study area were comprehensively studied to obtain the proto-rock age of granitic pegmatite and to discuss its petrogeochemistry,genesis and tectonic environment.Granitic pegmatites have the main mineral assemblages of K-feldspar+plagioclase+quartz±muscovite±tourmaline with pegmatitic texture and massive structure.The results of geochemical analysis of rocks show that they have uniform geochemical characteristics.They all showed high contents of SiO2(72.1%~75.3%),Al2O3(13.5%~16.4%),low contents of CaO(1.42%~2.03%),MgO(0.15%~0.76%),P2O5(0.01%~0.02%)and TiO2(0.06%~0.17%);the total amount of rare earth elements is low,rare earth enrichment,heavy rare earth loss,the distribution curve of rare earth tilting to the right,obviousδEu anomaly;the trace elements were enriched with large ionic lithophile elements(Cs,Rb,Ba,U)and relatively deficient elements with high field strength(Nb,Ta,Ti).The strength of the zircon CL images of the samples(DST-TW1 and WJG-TW1)was relatively weak,most of the zircons of the former could not reflect the internal structure of the mineral,while most of the latter could show weak oscillating bands,which was consistent with the high U content of the zircons(1253.1×10-6~12861.5×10-6,874.5×10-6~5319.1×10-6).Zircon has since the shape characteris
作者
杨仲杰
YANG Zhongjie(Geological and Mineral Survey Institute Co.LTD of Liaoning Porvince,Shenyang,110031)
出处
《地质论评》
CAS
CSCD
北大核心
2021年第2期523-542,共20页
Geological Review
基金
中国地质调查局沈阳地调中心委托的区调项目“辽宁1∶5万王家堡子(K51E022013)、苏子沟(K51E022014)、黄花甸子(K51E021014)、岫岩县(K51E023014)幅区域地质矿产调查(编号:DD20160049-8)”的成果。
