冀西北晚太古代岩石单元的地质关系:对早期陆壳形成的指示  

Geological relation of Late Archean lithologic units in Northwest Hebei,North China Craton:Implication for building of early continental crust

作　　者：彭澎[1] 李云[1] 刘富[1] 王芳[1] 

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029

出　　处：《岩石学报》2012年第11期3531-3544,共14页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划973项目(2012CB416601);国家自然科学面上基金项目(41072146);岩石圈演化国家重点实验室联合资助

摘　　要：冀西北地区出露晚太古代桑干杂岩和崇礼杂岩构成的灰色片麻岩(TTG片麻岩)-麻粒岩地体和红旗营子群角闪岩相变质火山沉积岩系。本文对尚义地区红旗营子群中变质火山岩中的变玄武安山岩(角闪斜长片麻岩)进行了锆石LA-MC-ICPMS定年,获得207Pb/206Pb加权平均年龄2528±12Ma(2σ,MSWD=0.1,n=34),这一年龄代表了该岩石的形成时代。虽然这一年龄非常接近灰色片麻岩的形成时代,野外地质关系指示红旗营子群的形成早于灰色片麻岩及其中的闪长质侵入体。在灰色片麻岩分布区,红旗营子群和一些变质辉长质岩石呈岩片、透镜体或者"岩墙"状分布。变质辉长质透镜体或者"岩墙"状岩片以周边发育串珠状小透镜体,以及不见细粒边部和岩墙"手指"可以与该区分布的早元古代变质基性岩墙相区别。这些变辉长质岩石可能是红旗营子群火山岩系根部或者岩浆房的残留体,也可能部分是更早期地壳的残片。红旗营子群火山岩系的岩石化学特征可以和灰色片麻岩及闪长质片麻岩岩体分别进行对比。地质关系和岩石化学特征表明,这些岩石可能具有相似的成因。根据冀西北地区相关岩石单元的地质关系,火山沉积岩系(红旗营子群)和灰色片麻岩-麻粒岩地体(桑干杂岩和崇礼杂岩)组成了该地区晚太古代大陆二维地壳结构。认识这种地壳结构在空间上的延续性,并识别相关地质单元在时代和物质上的演化关系,可以揭示华北克拉通晚太古代大陆地壳的形成机制。In Northwest Hebei Province, North China Craton, the Late Archean units include grey gneisses-dominated Sanggan and Chongli complexes and amphibolite-facies volcano-sedimentary sequence, the Hongqiyingzi Group. In this paper, zircon grains from a meta-basaltic-andesite sample （amphibole plagioclase gneiss） from the Hongqiyingzi Group in Huangtuyao-Wushijia area, Shangyi, was dated using LA-MC-ICPMS method. A weighted mean 207Pb/206Pb age of 2528±12Ma （2σ, MSWD=0.1, n=34） was obtained, and this age is interpreted as igneous age of the rock. Although this age is close to the ages of the grey gneisses in this area, field relations clearly show that the Hongqiyingzi Group has formed earlier. In the grey gneiss domain, pieces of the Hongqiyingzi Group and other meta-gabbros appear as sheets, lens or ＂dyke＂-like bands. These lens and bands sometimes have numbers of lined smaller lens around the main bodies, with no fine-grained margins and intrusive branches, which can distinguish from the Paleoproterozoic mafic dykes （also metamorphosed） in this same area. These gabbroic sheets could be roots or partly the magma chamber relics of the Hongqiyingzi Group, or they could also be partly the remanents of ancient crust. Element and isotope geochemistry show that the volcanics are akin of grey gneisses or dioritic intrusions in the grey gneisses in this area. Both geological relations and geochemistry show that these volcanic rocks may have similar origins with the grey gneisses and dioritic rocks. According to the geological relationships of the Late Archean units in this area, the volcano-sedimentary sequence （the Hongqiyingzi Group） and the grey gneiss complex （Sanggan and Chongli complexes） composed a 2-dimension Late Archean crust structure. Identifying the spatial continuity of such crustal structure, as well as the time and material evolution of the related units, can reveal the forming mechanism of Late Archean continental crust in the North China Craton.

关 键 词：华北克拉通 晚太古代 地壳结构 变质火山沉积岩系 灰色片麻岩(TTG片麻岩) 红旗营子群 

分 类 号：P588.14[天文地球—岩石学]