中国东北黑龙江杂岩体蓝闪石片岩岩石学研究(英文)

Petrology of Blueschists of Heilongjiang Complex in Northeast China

黑龙江杂岩主要由蓝闪石片岩构成,蓝闪石片岩主要包括绿帘石、绿泥石、钠长石、钠质角闪石、多硅白云母和石英以及为数不多的榍石、钛铁矿和黑硬绿泥石。其中,钠质角闪石包括蓝闪石和镁质钠闪石。变质条件的压力（P）温度（T）评价条件为400－425℃和0.69－0.86 MPa,对应岩相为绿帘蓝闪石片岩相。黑龙江杂岩蓝闪石片岩的地球化学研究表明,其原岩是可与洋岛型（OIB）玄武岩和一些洋中脊型（E-MORB）玄武岩相对比的大洋玄武岩,这说明黑龙江杂岩蓝闪石片岩的玄武岩原岩是在海底山或者在大洋隆起条件下由富集源形成的;具有洋岛型玄武岩地球化学特征的变质玄武岩以及富锰的变质燧石、大理石、变质硬砂岩和蛇绿岩鳞片的加入证明黑龙江杂岩是消减—增生杂岩,它含有变形洋壳的碎块和在被改造的前震旦纪佳木斯岩体西边缘上形成于侏罗纪的增生楔岩石;黑龙江杂岩在原岩成分上可与活动大陆边缘许多增生的杂岩相当。

The Heilongjiang Complex contains blueschists composing of epidote,chlorite,albite,sodic amphibole,phengite,quartz,with minor amounts of titanite,ilmenite,and stilpnomelane.Sodic amphiboles are glaucophane to magnesioriebeckite.The Pressure（P）-Temperature（T） metamorphic conditions are estimated to be 400-425 ℃ and 0.69-0.86 MPa,which correspond to epidote-blueschist facies.Geochemical study of blueschists from the Heilongjiang Complex showed that their protoliths were oceanic basalts,which were comparable with oceanic island basalt（OIB） or some types of basalts from plume-influenced regions（E-MORB）.This suggests the formation of basalt protolith of the Heilongjiang blueschists from enriched source in seamount or oceanic uplift setting.The presence of metabasalts with geochemical features typical of ocean island basalts,as well as Mn-rich metacherts,marbles,metagraywackes and ophiolite slices,indicates that the Heilongjiang Complex is a subduction-accretionary complex,containing fragments of deformed oceanic crust and rocks of an accretionary wedge,which was formed at the western part of reworked Pre-Sinian Jiamusi Massif in the Jurassic.The complex is comparable in protolith compositions with many accretionary complexes of active continental margins.