苏北高压变质带绿片岩中石榴石内文石包裹体的发现

New mineral evidence of high-pressure metamorphism of the Subei high-pressure belt——Aragonite inclusions in garnet from greenschist

苏北高压变质带位于苏鲁超高压变质带东南缘,露头多为绿片岩相的中—晚元古代云台岩群,典型的蓝片岩仅见于灌云县杨集的钻孔岩心中。本文通过拉曼光谱研究,在连云港地区的绿片岩内石榴石中发现文石(CaCO3)包裹体。文石呈细小包裹体残留于细粒半自形石榴石斑晶中。这些石榴石作为低扩散的刚性矿物,经历了多期变质变形作用,变质反应证据保存在石榴石的成分环带及包体矿物组合中。文石包裹体的存在证明苏北高压变质带北部的、即本区出露的这套岩系是早期经历了高压变质作用、晚期又叠加了绿片岩相变质作用的高压变质地体。

The Subei high-pressure(HP )metamorphic belt lies on the southeastern margin of the Sulu ul-trahigh-pressure(UHP )metamorphic belt,northern Jiangsu.Most of its outcrops consist of greenschist-fa-cies rocks of the Meso-to Neoproterozoic Yuntai Group-complex.In this belt,however,the typical blueschist is only found in drill cores from Yangji Town ,Guanyun County,northern Jiangsu.The laser Raman(LRM)spectrum shows that there occur micron-sized aragonite(CaCO 3 )inclusions in fine-grained subhedral garnet phenocrysts from greenschist of the group-complex in Lianyungang,northern Jiangsu.These garnets as a low-diffuse rigid mineral have undergone multi-stage deformation and metamorphism.The ev-idence of the metamorphism is preserved in the compositional zoning of garnet and the inclusion mineral assemblage.The appearance of aragonite inclusions indicates that the greenschist-facies rocks in the northern part of the Subei HP metamorphic belt,i.e.the outcrops in the study area,are part of a HP terrane which was overprinted by greenschist facies metamorphism in the late stage.