江苏东海前寒武纪变质花岗岩

On Metamorphic Granitoid Gneisses in Donghai Area, Jiangsu

东海变质岩区广泛分布多种类型的长英质片麻岩,构成片麻岩杂岩区。这一套长英质片麻岩,前人曾认为是变质的火山岩、火山-沉积岩经混合岩化作用形成的混合岩,并根据岩石类型、混合岩化作用程度以及所含表壳岩包体的多少,按沉积地层学原理划分了地层单位,建立了群、组、段。近年来,有关国内外这方面的研究成果表明,无论是在太古宙花岗—绿岩地体,还是麻粒岩一片麻岩地体中,花岗岩类侵入体均占主导地位。

The felsic gneisses cover 60-70％ of the surface in Donghai area which had been considered as metamorphic volcanic—sedimentary series. The latest study shows its initial rocks are granites by abyssal intrusion.It has weakly gneisses — blocking structure and macro—meso grained granoblastic texture in weakly deformed sections and gneissic stripped structure in strongly deformed zones. There are some differentiations in composition,attitude,metamorphism between granitoid gneisses and enclosures of supracrustal rock series. Many initial intrusive features have been preserved from metamorphisms such as hypidiomorphic granular texture, subhedron of albite, tablet, Carlsbad twin, albite twin, albite—Carlsbad twin, which formed in magma crystallized period. Based on the rock chemical composition analysis, the relative parameters all drop into the granite area in many kinds of schemes or diagrams which show that the granite formed after orogenic movement in the borderland or hinterland. Its rare earth element patterns are characterized by right dip with LREE enrichment and Eu negative anomalous.