早前寒武纪地质构造和分辨率大于120km的长波航磁异常特征表明:塔南—华北—朝鲜北部(狼林地块)具有类似的太古宙结晶基底,它们可能曾经是太古宙统一克拉通的组成部分。20~120km分辨率的中波航磁异常凸现一组北东东—北北东走向、改造太古宙高级变质结晶基底的线性航磁异常,它们分别对应于地壳尺度的长寿断裂。古元古代阶段沿着它们发生了大规模的左行韧性伸展剪切运动,在使塔南、朝鲜北部陆块分别向南西和北东伸展拆离的同时,华北克拉通内部也出现了有限的裂解,并伴随着硅铝壳内活动带的发育。本文将这些古元古代阶段韧性伸展剪切带划分为塔南与华北陆块之间的西部剪切带系统、华北与狼林陆块之间的东部剪切带系统和华北陆块内部的青龙—太行山—中条山等3个独立的剪切带系统。西部韧性剪切系统由阿尔金、大同—环县、以及它们之间的狼山—吉兰泰、雅布赖山等次级剪切带组成,控制古元古代阿拉善群和上集宁群的孔兹岩系为代表的硅铝壳内活动带的沉积—构造演化。东部韧性剪切系统包括沂水和新宾—桦甸等韧性剪切带,相关的古元古代活动带以胶东地区的粉子山群、荆山群和辽吉地区的辽河群为代表。中部韧性剪切带系统以太行山地区阜平群、赞皇群中出现的角闪岩相糜棱片麻岩、眼球状糜棱岩带为代表,发育b-型线理,指示近水平或低角度斜滑性质的左行韧性剪切,相关的古元古代活动带包括双山子—青龙河、五台—滹沱、甘陶河—东焦、吕梁、中条以及济宁等。不同规模的古元古代活动带彼此并不相连,以发育变质沉积—火山岩建造为主体,岩石磁化率明显低于太古宙高级变质结晶基底,与之相关的韧性剪切带则以其透入性矿物线理产生了增强的磁化率各向异性,两者共同构建了地壳尺度北东东—北北东向线性航磁异常带。古元古代末的中条运动使上述硅铝壳内活动带褶皱回返,塔南—华北—朝鲜北部陆块重新焊接,形成近纬向展布逐渐稳定的中轴大陆克拉通,上述地壳尺度的韧性伸展剪切带在中元古代以后的地质历史中,大多被后期不同性质的脆性断裂所追踪。
【作者单位】：
中国地震局地质研究所 北京100029(张家声;
黄雄南);
中国石油勘探开发研究院 北京100083(李燕)【关键词】：
伸展剪切;
硅铝壳内活动带;
航磁异常;
线理;
古元古代;
中国北部【基金】：
国家自然科学基金资助项目(批准号:40472114,49070133)研究成果【分类号】：P542
【DOI】：CNKI:ISSN:0563-5020.0.2007-02-004
【正文快照】：
1前言由于地表岩石露头的不连续性,重建地壳尺度的构造样式缺乏依据。航磁异常样式反映了岩石磁性和磁化率各向异性特征在现今地球磁场中的感应磁化效果,不受弱磁性沉积覆盖的影响,是分析地壳磁性基底构造样式的重要手段之一。伸展转换(transtensional)或挤压转换(transpressio
Geologic and structural records in Early Precambrian and features of long wave(>120 km) aeromagnetic anomaly indicated that southern Tarim, Central North China and northern Korean(Rangrim terrain) had similar Archean crystalline basements, and probably had been parts of a united Archean craton in NW-SE stretching. Medium wave(20～120 km) aeromagnetic anomaly demonstrated a series of NEE-NNE striking linear aeromagnetic anomalies, which reconstructed the Archean high-graded crystalline basement. Results of geologic and structural investigations showed that they were responding to crust-scale long live faults individually. Along them, large-scale left-lateral transtensional ductile shearing had occurred during Paleoproterozoic period. Series insialic mobile belts formed when the southern Tarim, and the northern Korean continental blocks were detached to SW and NE separately from Central North China block. According to the roles of the ductile transtensional shear zones in the reconstruction process of the Archean craton, we divided them into three independent shear systems as western system between southern Tarim and Central Northern China blocks, eastern system between Central Northern China and Rangrim blocks, and Qinglong-Taihangshan-Zhongtiaoshan system in the inner part of the Central Northern China block. The western system was composed by Altyn, Datong-Huanxian shear belts and secondary Langshan-Jilantai and Yabulaishan shear belts between them, controlling the sedimentary and structural evolution of the Paleoproterozoic Alaxa group and the upper Jining Group characterized as khondalite suites. The eastern system included the Yishui, Xinbing-Huadian and the other ductile shear belts, and the related mobile belts presented as Fenzishan Group and Jinshan Group in Jiaodong region, and the Liaohe Group in Liaoning-Jilin region. The Qinglong-Taihangshan-Zhongtiaoshan system appeared as amphibolite-phased mylonitic gneiss and augen mylonites as a result of reworked Fuping and Zanhuang Archaen gneisses in Taihangshan area. Typical b-type lineations, developed in the mylonites, indicated sub-horizontal or low angle left-lateral ductile shearing. The related Paleoproterozoic mobile belts were represented by Shuangshanzi-Qinglonghe, Wutai-Futuo, Gantaohe-Dongjiao, Lüliang and Jining belts composed mainly of sedimentary and volcanics in different scales, and did not join each other in space. Magnetic susceptibility of these formations was obviously lower than the Archean high-graded metamorphic crystalline basements, while the responding ductile shear zones created enhanced anisotropy magnetic susceptibility attributed to their penetrative mineral lineations, both of them contributed to the crustal scale NEE-NNE striking linear aeromagnetic anomalies. The insialic mobile belts mentioned above were folded and inverted during the Zhongtiao movement at the end of the Paleoproterozoic, meanwhile southern Tarim, Central North China and northern Korean Archean blocks joined again to form a latitudinal stretching central continent which were gradually stabilized. The crust-scale transtensional ductile shear belts were mostly traced by later brittle faults in different natures during the geological history after Mesoproterozoic.
【Keyword】：
Transtensional shearing, Insialic mobile belts, Aeromagnetic anomaly, Lineation, Paleoproterozoic, North China
