The sub-vertical meso-and micro-structures and fabrics developed in coesite-bearing foliated eclogites in the Taohang (桃行) area,southeastern Shandong (山东),China. The diagnostic structures and fabrics,including penetrative foliation or mylonitic foliation containing mineral and stretching lineations,as well as sheath-like folds,appear to be the development of anastomosing UHP eclogite-facies shear belt arrays hosting massive eclogites. Textural relationships and mineral assem-blages indicate that the deformation of foliated eclogites developed closely after the formation of the massive eclogite,prior to the development of the granulite/amphibolite-facies symplectites and coronas,occurring over a very wide pressure range of (31-8)×102 MPa. It presents the structural records of the tectonometamorphic processes as being responsible for the earliest stages of exhumation of the UHP metamorphic rocks. Extensive regional field observations show that the meso-and micro-structures and fabrics recognized in the foliated eclogites at Taohang are remarkably similar or consistent in the whole Dabie (大别)-Sulu (苏鲁) UHP metamorphic belt. This article,thus,supports the idea that the earliest stages of exhumation of the UHP metamorphic rocks,from mantle depths to the Moho or the mantle-crust boundary layering,may be attributed mainly to a sub-vertical extrusion and ductile flow along the subduction channel,belonging to a syn-collision exhumation at about 235 to 220 Ma.
Two fresh types of eclogites,namely the massive eclogite and foliated eclogite,are discernible in large eclogite bodies surrounded by country rock gneisses from the Dabie (大别)-Sulu (苏鲁) UHP metamorphic zone.They are different in mineral assemblage,texture and structure at various scales.The massive eclogite has a massive appearance with a metamorphic inequigranular and granoblastic texture,which consists mainly of nominally anhydrous minerals such as garnet,omphacite,rutile with inclusions of coesite and rare microdiamond.Massive eclogites which formed at the peak UHP metamorphic conditions (～3.1-4.0 GPa,800±50 ℃)within the coesite to diamond stability field recorded the deep continental subduction to mantle depths greater than 100 km during the Triassic (～250-230Ma).The diagnostic UHP minerals,mineral assemblages and absence of notable macroscopic deformation indicate the peak metamorphic 'forbidden-zone' P-T conditions,an extremely low geothermal gradient (≤7℃·km-1) and low differential stress.The foliated eclogite is composed of garnet+omphacite+rutile+phengite+kyanite+zoisite+talc+nyb ite±coesite/quartz pseudomorphs after coesite.It is quite clear that the foliated eclogite bears relatively abundant hydrous mineral,and shows well-developed penetrative foliation carrying mineral and stretching lineation reflecting intense plastic deformation or flow of eclogite minerals.The foliated eclogite occurred at mantle levels and recorded the earliest stages of exhumation of UHP metamorphic rocks.At a map scale,the foliated eclogites define UHP eclogite-facies shear zones or high-strain zones.Asymmetric structures are abundant in the zones,implying bulk plane strain or dominant non-coaxial deformation within the coesite stability field.The earliest stages of exhumation,from mantle depths to the Moho or mantle-crust boundary layering,were characterized by a sub-vertical tectonic wedge extrusion,which occurred around 230-210 Ma.The threedimensional relationship between the massive and foliated eclogi
