大别地区的变质作用及与碰撞造山过程的关系

大别造山带从南到北可分为５个变质构造单元：扬子北缘蓝片岩带、突松变质杂岩带、南大虽碰撞杂岩带、北大别变质杂岩带和北淮阳变质带。各个变质构造单元中不同岩石的变质作用可划分为３种类型：（１）超高压型。以含柯石英（及金刚石）的榴辉岩为代表，仅见于南大别碰撞杂岩带中，这类岩石的ＰＴ轨迹反映洋壳Ｂ型俯冲的特点。（２）高压型。见于大别山南部的蓝片岩带、宿松变质杂岩带和南大别杂岩中的变质沉积岩及部分片麻岩中，与

METAMORPHISM OF DABIE MOUNTAINS AND ITS RELATIONSHIP WITH THE COLLISIONAL OROGENY

The Dabie orogenic belt can be divided into 5 meta-tectonic units from south to north,i.e.,the northern Yangtze blueschist belt,Susong metamorphic complex,southern Dabie collisional complex,northern Dabie metamorphic complex and northern Huaiyang metamorphic belt. The rocks of these different units have undergone three types of metamorphism:(1) The ultrahigh pressure type is repressented by the coesite (and/or diamond)-bearing eclogites and only found in the southern Dabie collisional complex,the matamorphic PT path of which implies an oceanic B-type subduction.(2) The high pressure type occurs in the blueschist belt,Susong complex and metasediments and some gneisses in the southern Dabie complex and is probably related with the continental A-tpe subduction of Yangtze Plate.The increase of metamorphic grades from south to north suggests the increase of depth in this direction of subduction. (3) The medium-low pressure metamorphism widespread in the Dabie Mountains may be related to the thermal relaxation in thickened crustal regions caused by large-scale collision,with the metamorphic grade being as high as amphibolite facies (locally to granulite facies) in the northern Dabie complex,and declining southwards and northwards, to epidote amphibolite facies and greenschist facies. The boundaries between different facies are consistent with the strike-slip faults and decollement faults of a late stage. This late stage of meium-low metamorphism has modified to different extents the high and ultrahigh pressure metamorphic rocks of early stages. The southern Dabie collisional complex comprises rocks at least of these three metamorphic types having different metamorphic histories or PT paths. These three type of metamorphism together with the spatial distribution of metamorphic facies belts in Dabie Moutains give the orogenic evolution through oceanic B-type subduction-continental A-type subduction-thrusting arising from continent-continent collision to decollement due to uplifiting.