摘要
将大别造山带西段划分为 7个二级构造单元 ,从北向南依次为 :(1)马畈褶皱带 ;(2 )凉亭混杂岩带 ;(3)牢山褶皱带 ;(4 )苏家河滑覆席 ;(5)熊店 -浒湾韧性剪切带 ;(6 )卡房片麻岩穹窿和(7)彭店韧性剪切带。其中马畈褶皱带属华北板块南缘 ,凉亭混杂岩带可能代表碰撞缝合带位置。野外构造变形特征反映有 4期依次发生的构造作用 :(1)近南北向的褶皱作用 ;(2 )从南向北的韧性推覆剪切作用 ;(3)右旋走滑韧性剪切作用 ;(4 )垂向隆升作用和与其有关的伸展滑脱作用。
From our detail structural investgation in the Xinxian area of the northwestern Dabie, seven structural units have been recognized, which include : (1) Mafan fold belt (MFB), (2) Liangting melange belt (LMB), (3) Laoshan fold belt (LFB), (4) Sujiahe thrust sheet (STS), (5) Xong?Huwan shear belt (XHB), (6) Kafang gneiss dome (KGD), and (7) Pengdian shear belt (PSB)(Fig. 1). The MFB is the northernmost unit and consists of foliated amphibolites, quartzofeldspathic schists, and intercalated leptynites and marbles called the Erlangping Group. The MFB is pervasively affected by middle?small scale, tight to isoclinal folds. Dominant foliations are S?dipping. Petrologic affinities indicate that the MFB protolith may have originated from a Palaeozoic arc developed along the southern margin of the Sino?Korean craton. The LMB is characterized by a chaotic block assemblage and penetrative shear deformation. Blocks include marble, chert, gneissic amphibolite, and garnet?plagiogneiss . The melange matrix is mylonitic and exhibits mineral assemblages indicating greenschist?facies recrystallization. Shear fabrics include S?C structure, mica fish, asymmetric recrystallized tails of quartz lenses, together with the south?dipping shear foliation and small asymmetric fold structures, all indicating a top?to?north shear sense. Thses have been overprinted by a dextral shear deformation. The LFB forms the hanging wall of the LMB. The section reaches a maximum structural thickness of 6 km and is composed of interbedded mica?quartz schists and schistose amphibolites of the upper Proterozoic Guishan Formation. Moderate?to tight?folds and penetrative south?dipping foliations are prevalent. These folds are generally asymmetric, exhibiting north vergence and E?W striking, subhorizontal fold axes. The STS is bounded by a folded thrust dipping to the south from the LFB and dipping to the north from the XHB. It consists of Devonian unmetamorphosed to lower greenschist facies rocks that are affected by predominately south?vergent thrust faults, inclined to recumbent folds, and slaty cleavage that all exhibit a top?to?south shear sense. Structurally underlying the STS, the XHB is defined by a 3～5 km thick zone of mylonitic gneisses that contains sheared eclogite. Mylonitic foliations affecting the XHB generally dip to the north. Two generations of S?C mylonitic fabrics consisting of top?to?north thrust sense overprinted by subhorizontal dextral shear have been recognized. With a NWW?SEE strike, the PSB consists of gneisses intercalated with sheared eclogite and ultramafic rocks. Top?to?NE shear fabrics defined by mica?fish and S?C structures are largely obliterated by steep dipping foliations, subhorizontal lineation defined by phengite and amphibole, and boudinage of eclogite, which all clearly indicate a dextral shear sense. The final unit (KGD) consists of gently domed gneiss and intercalated eclogites and occupies a triangle area of over 500 km 2 bounded by the XHB to the north and by the PSB to the southwest. The shallowly inclined foliation within the KGD contrasts markedly with the >45° dip angles that characterize the XHB and PSB. A domal structure is centered approximately on Kafang. The MFB may belong to a Paleozoic southern margin of the Sino?Korean craton. The LMB has been interpreted as the suture position between the Sino?Korean and Yangtze cratons. History of deformation in the western Dabie has been suggested: (1) folding with W?E strike followed by (2) top?to?north shear, (3) later dextral strike?slip faulting and (4) doming event related to extension.
出处
《高校地质学报》
CAS
CSCD
2000年第3期389-395,共7页
Geological Journal of China Universities
基金
国家自然科学基金资助项目(49372100)
国家重点基础研究发展规划项目(G1999075511)
教育部留学回国人员科研启动基金
