Material Composition,Syn-collision And Post-collision Tectonic Deformation Research Of The West Part Of The Erenhot-hegenshan Suture Zone,Inner Mongolia

As an important part of Xing'an-Mongolian orogenic belt,the Erenhot-Hegenshan suture zone has attracted extensive attention for its material composition,formation time,deformation features,and forming process.Among these predecessors study about it,deformation characters during and after the formation have rarely been revealed.In this study,we have done some researches on the the following issues through systematic field observation and Chronology test on key geological bodies:(1)the material composition and its formation time of the ophiolitic melange in the west part of this suture zone,which lies in the northeast part of Erenhot;(2)the structural deformation in the Late Carboniferous Benbatu formation,which is the matrix of the ophiolitic melange(syn-collision stage);(3)the structural deformation and its formation time of the Early Permian Zhesi formation(post-collision stage).This paper aims at clarifing the material composition of the west part of the Erenhot-Hegenshan suture zone,and revealling its structural deformation characters during the syn-collision and post-collision stage.This research have acquired achievement and cognition as follows:The ophiolitic mélange is an essential component of in the west part of the suture zone.It contains discontinuous mafic-ultramafic block,which are scattered in strongly deformed and low-grade metamorphosed carbonaceous-silty slate of the Late Carbonaceous benbatu formation.It is composed dominately of serpentinized ultramafic rocks,gabbro,silicalite,plagiogranite and mafic lavas.The latest emplacement age of the mélange is likely to be older than the Early Permian.Two stages of structural deformation have been recognized in the Late Carboniferous Benbatu formation.The early stage is intense regional NE-SW trending complicated folds whose hinge are gentle dipping.The NE-SW trending axial plane cleavages are well developed in regional,outcrop and micro scale,which are characterized by intensive transposition of foliation stucture.The deformation age is 319-282 Ma(Late Carboniferous).In the late stage,the age of nearly E-W trending left-lateral strike slip deformation is no early than early Early Permian(282 Ma)and no later than Early Jurassic,it reprinted on the early formed folds and led to the formation of dissymmetric plunging vertical folds.The Early Permian Zhesi formaition developed two-phase deformation.The early phase formaition was mainly complicated nearly E-W folding and faulting,which formed during the late early Permian(P₁²).The late phase formation was mainly NW-SE strike-slip faulting,which formed after the late early Permian(P₁²).The syn-collision fold deformation of the Benbatu Formation shows that the orientation of maximum principal stress during the formation of collision mélange belt was NW-SE,which was nearly orthogonal to distribution direction of the Erenhot-Hengenshan suture zone,suggesting that terrane collages of the collision beit was frontal collision and the late left-lateral slipping shear deformation was likely to reflect the lateral escaping function of the post-collision.The main fold deformation of the Early Permian Zhesi formaition showed that the orientation of maximum principal stress was nearly S-N,Which indicates that the interactions of the terranes on both sides of the collision zone after formation of the suture zone mainly manifested nearly S-N convergence,but it presented more oblique compression,which was consistent with the late left-lateral slipping shear deformation of the late Carboniferous Benbatu Formation.On the basis of that,the west part of the Erenhot-Hegenshan tectonic belt took place outstanding sinistral strike-slipping after the frontal collision.