摘要
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、宿松变质杂岩带、南大别碰撞杂岩带、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 ,与扬子陆壳的 A型俯冲有关 ,由南向北变质作用的 PT条件递增 ,反映陆壳俯冲作用的方向及不同深度。 ( 3)中低压型变质作用。在大别造山带广泛分布 ,与大规模的碰撞作用形成的地壳加厚区出现的热松弛效应有关。变质程度以北大别变质杂岩带最高 ,为角闪岩相 (局部出现麻粒岩相 ) ,向南和向北都有规律地递减为绿帘角闪岩相和绿片岩相 ,不同变质相带之间的界线与晚期走滑和滑脱断层一致。这期变质作用不同程度地改造了早期的高压、超高压变质岩。南大别碰撞杂岩带至少由这 3种不同变质历史或 PT轨迹的岩石混杂而成。大别地区的这 3类变质作用以及变质带的分布记录了大别造山带从洋壳 B型俯冲→陆壳 A型俯冲→陆壳碰撞推覆→隆起滑脱的演化历史。
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.
出处
《地质力学学报》
CSCD
2000年第3期25-38,共14页
Journal of Geomechanics
基金
国家自然科学基金项目!编号 :4 970 2 1 0 4
关键词
榴辉岩
变质作用
大别造山带
碰撞造山过程
ecologite
high\|ultrahigh pressure metamorphism
medium\|low pressure metamorphism
Dabie orogenic belt
