大别造山带西段构造单元

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。

Tectonic Units in the Western Dabie Orogenic Belt

From our detail structural investgation in the Xinxian area of the nor thwestern Dabie, seven structural units have been recognized, which include : (1) Mafan fold belt (MFB), (2) Liangting melange belt (LMB), (3) Laoshan fold b elt (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, quart zofeldspathic schists, and intercalated leptynites and marbles called the Erlan gping Group. The MFB is pervasively affected by middle-small scale, tight to iso clinal 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 ch a otic block assemblage and penetrative shear deformation. Blocks include marble, chert, gneissic amphibolite, and garnet-plagiogneiss. The me lange matrix is mylo nitic and exhibits mineral assemblages indicating greenschist- facies recrystalli zation. Shear fabrics include S-C structure, mica fish, asymmetric recrystall i zed tails of quartz lenses, together with the south-dipping shea r 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 schistos e amphibolites of th e upper Proterozoic Guishan Formation. Moderate-to tight JX*7〗-folds and penetrative south-dipping foliations are prevalent. These folds are gen erally asymmetric, e xhibiting north vergence and E-W striking, subhorizontal fold axes. The STS is b ounded by a folded thrust dipping to the south from the LFB and dipping to the n orth from the XHB. It consists of Devonian unmetamorphosed to lower greenschist facies rocks that are affected by predominately south-vergent th rust faults, inc lined to recumbent folds, and slaty cleavage that all exhibit a top-to-south she ar 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 f abrics consisting of top-to-north thrust sense o verprinted by subhorizontal dext ral shear have been recognized. With a NWW-SEE strike, the PSB consists of gnei s ses intercalated with sheared eclogite and ultramafic rocks. Top-to-NE shear fab rics defined by mica-fish and S-C structures are largely oblitera ted by steep-dipping foliations, subhorizontal lineation d efined by phengite and amphibole, and boudinage of eclogite, which all clearly indicate a dextral shear sense. The f i nal unit (KGD) consists of gently domed gneiss and intercalated eclogites and oc cupies a triangle area of over 500 km2 bounded by the XHB to the north a nd 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 exten sion.