内蒙古大青山地区古元古代早期榴云片麻岩(大青山表壳岩)深熔作用：地质、锆石年代学和地球化学研究  

Anatexis of Early Paleoproterozoic garnet-biotite gneisses (Daqingshan supracrustal rocks) in Daqingshan,Inner Mongolia: Geology,zircon geochronology and geochemistry

作　　者：马铭株[1] 董春艳[1] 徐仲元[2] 谢士稳[1] 刘敦一[1] 万渝生[1] 

机构地区：[1]中国地质科学院地质研究所、北京离子探针中心,北京100037 [2]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2015年第6期1535-1548,共14页Acta Petrologica Sinica

基　　金：国家973项目(2012CB416600);中国地质调查局项目(12120113013700;12120114021301;1212010811033;1212011120142)联合资助

摘　　要：大青山位于华北克拉通西部孔兹岩带中段,古元古代晚期孔兹岩系（上乌拉山岩群）十分发育。近年来,在上乌拉山岩群中分辨出一套古元古代早期变质碎屑沉积岩（大青山表壳岩,榴云片麻岩）,它们遭受强烈变质变形和深熔作用改造,形成古元古代早期石榴石花岗岩。包头哈德门沟是古元古代早期榴云片麻岩典型出露区,并有古元古代早期石榴石花岗岩（哈德门沟石榴石花岗岩）形成。由榴云片麻岩经深熔榴云片麻岩再到石榴石花岗岩,浅色体增多,石榴石增多且颗粒增大,黑云母减少,石榴石包裹黑云母、石英、斜长石等矿物。石榴石岩的锆石呈浑圆状,普遍具核-幔-边或核-边结构,碎屑锆石年龄为~2.5Ga,变质锆石年龄为~2.45Ga和~1.90Ga。锆石形态、内部结构和年龄与榴云片麻岩、深熔榴云片麻岩和石榴石花岗岩中的锆石类似,但记录了古元古代晚期变质事件年龄。石榴石花岗岩与榴云片麻岩和深熔榴云片麻岩的地球化学组成特征总体上类似,高Al2O3含量和FeO T/MgO比值,CaO含量和K2O/Na2O比值存在较大变化,富集轻稀土和大离子亲石元素,亏损Nb、Ta、P和Ti。研究表明：1）浅色体和石榴石花岗岩中的石榴石是黑云母转熔的产物,并非岩浆结晶形成的;2）石榴石岩是在石榴石花岗岩岩浆形成之后进一步演化过程中石榴石不断地发生运移、分异和聚集的结果;3）尽管哈德门沟石榴石花岗岩具有一定或较大的规模,但具有深熔岩浆的性质;4）石榴石花岗岩地球化学组成变化与熔融母岩组成变化和深熔及岩浆演化过程中残余矿物相石榴石、锆石局部变化有关。Late Paleoproterozoic khondalites of the Upper Wulashan Subgroup are well developed in the Daqingshan area,central segment of the Khondalite Belt,western North China Craton. Early Paleoproterozoic metasedimentary rocks,named as the Daqingshan supracrustal rocks,have recently been identified from the Upper Wulashan ＂Subgroup＂. They underwent strong metamorphism and anatexis,resulting in formation of Early Paleoproterozoic garnet granite. Hademengou is a typical area where,both the garnet-biotite gneisses（ the Daqingshan supracrustal rocks） and garnet granite（ Hademengou garnet granite） extensively occur. From garnet-biotite gneiss,through anatectic garnet-biotite gneiss,to garnet granite,garnet grains increases both in content and size,whereas biotite is getting less,with leucosomes becoming more abundant. Garnetite in the garnet granite is mainly composed of garnet with biotite,quartz and plagioclase inclusions and contains rounded to elliptical zircon grains commonly with core-mantle-rim or core-rim textures. Detrital cores recorded an age of ~ 2. 5Ga,whereas the metamorphic zircon domains recorded ages of ~ 2. 45 Ga and ~ 1. 90 Ga,respectively.The zircon grains are similar in shape,texture and age to those from the garnet-biotite gneiss,anatectic garnet-biotite gneiss and garnet granite,but with the metamorphic age of the late Paleoproterozoic（ ~ 1. 90Ga）. Similar to the garnet-biotite gneiss and anatectic garnet-biotite gneiss,the garnet granite is high in Al2O3 content and Fe OT/ Mg O ratio and has a large variation in Ca O content and K2 O / Na2 O ratio,characterized by enrichment of light REE and large ion lithophile elements and depletion of Nb,Ta,P and Ti.Combined with early studies,main conclusions can be drawn as follows. 1） Garnet in the leucosome and garnet granite is formed by dehydration melting of biotite（ Bt ＋ Qz ＋ Pl→Grt ＋ Kfs ＋ Melt）,instead of being crystallized from magma; 2） the garnetite was formed as a result of the migration,differentiation and accumulatio

关 键 词：深熔作用 榴云片麻岩 石榴石花岗岩 石榴子岩 SHRIMP定年 地球化学 大青山地区 

分 类 号：P588.345[天文地球—岩石学] P597.3[天文地球—地质学]