苏鲁变质带北部的岩石构造单元及结晶块体推覆构造

虽然苏鲁变质带北部的超高压变质岩石的类型及其特征与大别山超高压带相似,但是要划出与大别山相对应的岩石构造单元是困难的。详细的区域地质、岩石学、同位素年代学及地球化学的研究已将超高压带的西界大致圈定在牟平断裂至米山断裂的范围内。特别需要提出的是,在荣成超高压变质岩石分布区的南北两侧,出露有3 种不同成因的麻粒岩,即榴辉岩化的麻粒岩;由超高压变质岩经高压升温变质作用生成的麻粒岩;以及未经过榴辉岩相变质的麻粒岩。它们有规律地成带分布。这些麻粒岩带以及在荣成地区出露的未经过麻粒岩相叠加变质的超高压变质带,各自都有着完全不同的变质历史,并且都以深大韧性剪切带为其边界。由此笔者将苏鲁变质带北部由南向北划分为海阳所变质地块(榴辉岩化扬子陆块基底变质单元)、荣成变质地块(超高压变质单元)、威海变质地块(麻粒岩相叠加变质的超高压构造岩片)、昆嵛山边界杂岩带。这些来源于地壳深层的结晶块体是超高压带形成和演化的产物,在后来的进一步碰撞挤压中,这些来源于深层而就位于中上地壳水平的结晶块体,有可能发生了与薄皮构造机制(thin-skin thrust)类似的构造过程。它们有如一系列的推覆体挤压叠置,使华北和华南陆块最后挤压在一起。

DIVISION OF PETROLOGICAL-TECTONIC UNITS IN THE NORTHERN SULU ULTRA-HIGH PRESSURE ZONE: AN EXAMPLE OF THICK-SKIN THRUST OF CRYSTALLINE UNITS

The characteristics of ultra high pressure metamorphic (UHPM) rocks in the Sulu zone are similar to those in the Dabieshan zone.zowever,the corresponding petrological tectonic units in Dabieshan (the northern Andean type magmatic are complex,central UHPM rock bearing melange zone,southern mobilized metamorphic complex of Yangtze margin) are difficult to be established in the Sulu zone.On the basis of the detailed study on regional geology,petrology,geochemistry and isotopic geochronology,the western boundary of the Sulu UHPM zone is roughly defined in the area between the Muping fault and Mishan fault.It is important that three individual granulite units have been distinguished in the area east to the Muping fault,which are eclogitized granulite unit,retrogressive granulite unit from UHPM eclogites,and high pressure granulite unit.These three granulite units as well as UHPM unit in Rongcheng area ,which was suffered metamorphism of amphibolite facies instead of granulite facies,have different metamorphic and deformed history and are bounded by deep large scale ductile shear zones to each other.Therefore,the northern Sulu UHPM zone can be divided into four petrological tectonic units from southeast to northwest:Haiyangsuo metamorphic complex (eclogitized crystalline basement of the Yangtze craton),Rongcheng UHPM complex,Weihai metamorphic complex (granulites retrograded from UHPM eclogites) and Kunyushan boundary metamorphic magmatic complex.These high grade metamorphic crystalline units come from deep crust,and are products relative to UHPM process including its formation,evolution and exhumation.At present,they are imbricated and superimposed upon each other by late tectonics as crystalline nappes,similar to thin skin thrusting.