摘要
华北板块东南缘五河杂岩属于前寒武纪变质基底,出露于蚌埠及相邻地区,主要由变质的镁铁质和长英质火成岩以及表壳岩系组成,并伴生有古元古代片麻状花岗岩和中生代花岗岩类,构成了"蚌埠隆起"。五河杂岩中主要有石榴斜长角闪岩/榴闪岩、石榴麻粒岩、异剥钙榴岩、石榴斜长角闪片麻岩、花岗片麻岩、云母片岩、大理岩和变质砂岩等岩石类型。这些不同类型的变质岩具有类似的峰期变质矿物,如石榴子石、单斜辉石、斜长石、金红石和石英等;结合其锆石U-Pb年龄,表明它们共同经历了古元古代高压麻粒岩相变质作用。石榴斜长角闪岩的石榴子石包体中存在钾长石+斜长石+石英+黑云母等矿物交生体,指示早期花岗质熔体的存在,证明五河杂岩在古元代变质过程中发生了部分熔融作用。此外,部分变基性岩中存在方解石、绿帘石和绿泥石等蚀变矿物,沿石榴子石的裂隙中分布有钾长石+斜长石+石英+黑云母+角闪石等矿物,表明它们经历了含碳酸盐的熔/流体交代作用以及绿帘石化和绿泥石化作用等。遭受过古元古代含碳酸盐的熔/流体交代作用的变基性岩表现为高放射成因Pb同位素组成,而未遭受含碳酸盐的熔/流体交代作用的变基性岩则表现为典型华北板块前寒武纪麻粒岩地体和下地壳包体岩石的低放射成因Pb同位素组成。
The Wuhe complex is located at the southeastern margin of the North China Block and belongs to the Precambrian metamorphic basement.It is exposed in the Bengbu area and its neighbourhood.The Wuhe complex consists of the metamorphosed igneous mafic and felsic rocks and supracrustal rocks associated with the Paleoproterozoic foliated K-feldspar granites andMesozoic granitoids,constituting the ＂Bengbu uplift＂.Its main rock types comprise a variety of lithologies,including garnet amphibolite,garnet granulite,rodingite,garnet-plagioclaseamphibolite gneiss,granitoid gneiss,micaschist,marble,quartzite and meta-sandstone.These rocks contain similar peak metamorphic minerals such as garnet,clinopyroxene,plagioclase,rutile and quartz.As a result,combined with their zircon U-Pb ages,it is suggested that they suffer from a common high pressure granulite facies metamorphism in Palaeoproterozoic.The multiphase solid inclusions within garnet porphyroblasts are discovered from the garnet amphibolite.Some multiphase solid inclusions consist of quartz,calcite,hornblende and chlorite,with quartz and calcite showing a secondary rim of hornblende and chlorite.The intergrowths of quartz,K-feldspar,plagioclase and biotite,and related MS inclusions in garnet show that the Wuhe complex experiences the high pressure granulite facies metamorphism,accompanying closeto-coeval partial melting and heterogeneous carbonate metasomatism.In addition,there are late altered minerals such as calcite,epidote and chlorite,and K-feldspar,plagioclase,quartz,biotite and amphibole distribute along fractures of garnets in the meta-basites.It is suggested that the rocks undergo heterogeneously carbonate-bearing hydrous melt/fluid metasomatism, and epidotization and chloritization.The carbonate metasomatism at the Palaeoproterozoic is likely responsible for the exceptionally high Pb-isotopic compositions registered by some of the metabasic rocks in the metamorphic basement in the area,quite different from those of typical Precambrian granulite terrains or
出处
《地球科学与环境学报》
CAS
2015年第1期1-11,共11页
Journal of Earth Sciences and Environment
基金
国家自然科学基金项目(41273036)
高等学校博士学科点专项科研基金项目(20133402130008)
