中国东北地区西部～500Ma泛非期孔兹岩系地球化学特征及其地质意义  

Geochemistry of ～500Ma Pan-African khondalite series in west of NE China and its tectonic implications

作　　者：董策[1] 周建波[1] 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2012年第9期2866-2878,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金(40872121);国家重点基础研究发展规划项目(2009CB825008)联合资助

摘　　要：最近在兴安、额尔古纳地块均发现原岩为中基性-中酸性火山岩、陆源碎屑沉积岩及碳酸盐岩组合组成的孔兹岩系,岩石组合主要分为富铝片岩-片麻岩类和斜长角闪岩两类。岩石地球化学特征表明,富铝片岩-片麻岩类的原岩为泥岩和砂岩,主量和微量元素的分配形式接近澳大利亚后太古宙页岩(PAAS)和北美页岩(NASC),稀土元素的分布特征与NASC相似,显示轻稀土元素富集及Eu负异常,(La/Yb)N=4～17,δEu=0.32～0.79。其Cr/Ti(0.01～0.03)、Zr/Y(1.2～13.3)、Cr/Th(0.1～8.63)、Cr/Zr(0.02～0.47)、Th/U(1.5～7.7)、CIW(68～99)表明物源区以花岗岩类为主,并可能含有碎屑沉积岩。其Ceanom(-0.04～-0.01)、Ce/Ce#(0.90～1.30)表明富铝片岩-片麻岩类原岩沉积环境为亚稳定的大陆边缘沉积。斜长角闪岩原岩为玄武岩或安山质玄武岩,其富Fe2O3(1.83%～12.37%)、MgO(4.28%～7.29%)、贫SiO2(47.06%～56.13%),呈低碱性。轻稀土元素相对富集,MORB标准化的微量元素配分型式为大隆起型,Zr/Nb、Hf/Th值均类似于板内拉斑玄武岩的特征。因此,研究区孔兹岩系应形成于裂谷沉积背景。这与佳木斯地块麻山群孔兹岩系形成环境一致,表明东北地区各地块的变质基底均为孔兹岩系,其原岩均形成于裂谷沉积环境,并统一经历～500Ma泛非期变质事件,这为研究我国前寒武纪的大陆演化、再造我国东北地区的构造格局及其在Gondwana大陆重建中的位置都将具有重大的理论意义。The khondalite series are discovered in Xing’an and Erguna block,its protoliths are medium-mafic to medium-acidic volcanic rocks,terrigenous clastic sedimentary rocks and carbonate.They are dominantly composed of aluminiferous schist-gneiss and amphibolite.The protoliths of aluminiferous schist-gneiss are clay and sandstone.The major element and trace element distribution diagram of aluminiferous schist-gneiss are close to PAAS.REE distribution patterns of aluminiferous schist-gneiss incline NASC,showing the LREE content enrichment and negative Eu abnormality,（La/Yb）N=1~17,δEu=0.32~0.77.The characteristic of Cr/Ti（0.01~0.03）,Zr/Y（1.2~13.3）,Cr/Th（0.1~8.63）,Cr/Zr（0.02~0.47）,Th/U（1.5~7.7）,CIW（68~99） suggest the source region,from which the aluminiferous schist-gneiss were derived,constitute dominantly granitic and sedimentary rocks.Deposit of sub-steady continental margin can be inferred from Ceanom（-0.04^-0.01）,Ce/Ce#（0.90~1.30） of aluminiferous schist-gneiss.The protoliths of amphibolite are basalt or andesitic basalt,with higher Fe2O3（1.83%~12.37%）,MgO（4.28%~7.29%）,lower SiO2（47.06%~56.13%） and worse alkalinity.LILE and HFS elements enrich in MORB-normalized trace element spidegram,combined with the characteristic of LREE content enrichment and Zr/Nb and Hf/Th value,suggesting that the protoliths of amphibolite were derived from an intraplate rift setting.So the protolith of khondalite series in Xing’an and Erguna block probably developed in rift valley deposit which is analogous to that of Mashan Complex.It is concluded that the basement rocks of all the blocks in NE China,including the Erguna,Xing’an,Songliao and Jiamusi-Khanka blocks,constitute khondalite series whose protolith form in rift valley deposit and experience ~500Ma Pan African metamorphic event.The results from this study provide new idea for researching the Precambrian continental evolution in China and reconstructing tectonic framework in the NE China and Gondwana.

关 键 词：孔兹岩系 泛非期 地球化学 原岩特征 沉积背景 中国东北 

分 类 号：P618.51[天文地球—矿床学]