冀北康保晚古生代花岗岩的岩石学、锆石年代学及构造意义

发布时间：2018-04-05 15:00

  本文选题：花岗岩　切入点：华北克拉通　出处：《成都理工大学》2015年硕士论文

【摘要】：本研究以冀北康保晚古生代花岗岩类为研究对象,识别出了8个具有不同类型花岗岩的岩体,并且进行了野外的地质观察、室内的镜下鉴定、电子探针测试以及锆石U-Pb定年等方面的细致工作,取得了以下认识:(1)不同岩体的花岗岩矿物含量差别较大,西五福堂岩体、新村岩体、李生宝沟岩体、三老虎岩体和前孟家地岩体,花岗岩中暗色矿物依次逐渐减少,粒度由细粒到粗粒,岩石类型由花岗闪长岩-二长花岗岩-正长花岗岩。小西沟岩体、石柱梁岩体、大盘沟岩体,花岗岩中斜长石均较少,碱性长石含量依次逐渐增加,由正长花岗岩到碱长花岗岩,结构由斑状-含斑-似斑状变化。矿物电子探针测试数据可以得西五福堂岩体的中细粒含角闪黑云花岗闪长岩中,斜长石(An=39.6~43.4)应属于中长石;新村岩体的中粒含角闪黑云二长花岗岩的斜长石中,斜长石(An=25.1~28.9)为更长石;李生宝沟岩体的中细粒二长花岗岩中的斜长石的特征相似,斜长石牌号应均为更长石-钠长石(An=2.9~16.8)。石柱梁和大盘沟岩体的花岗岩所含的斜长石为钠长石(An=0~1.6)。西五福堂岩体花岗岩中黑云母为镁铁质黑云母,显示出壳幔混染的来源和造山带花岗岩中黑云母的特征。其他岩体花岗岩均为铁质及富铁黑云母,物质来源于地壳,为碱性花岗岩中黑云母的特征。角闪石属于钙角闪石((Ca+Na)B≥1.00,NaB0.50)。进一步分别是浅闪石、镁绿钙闪石和绿钙闪石,也显示出了幔源物质混染的特征。(2)花岗岩中锆石Ti温度计测算结果表明,康保晚古生代花岗质岩浆的形成、结晶的平均温度均大于750℃,这些花岗岩和花岗闪长岩均起源于地壳下部。锆石Ti温度与Zr/Hf、Th/U的相关性分析认为,岩浆冷凝时整个岩浆系统处于开放的系统下,而后期多期的流体或者岩浆以富U、Hf为特点(3)石柱梁岩体花岗岩LA-ICP-MS锆石U-Pb年龄为260.6±1.6Ma、小西沟岩体花岗岩LA-ICP-MS锆石U-Pb年龄为264.1±1.7Ma、前孟家地岩体花岗岩LA-ICP-MS锆石U-Pb年龄为269.5±2.7Ma、三老虎岩体花岗岩LA-ICP-MS锆石U-Pb年龄为276.3±1.9Ma、新村岩体花岗岩LA-ICP-MS锆石U-Pb年龄为280.4±2.0Ma、西五福堂岩体花岗岩LA-ICP-MS锆石U-Pb年龄为284.7±1.7Ma。西五福堂岩体的中细粒含角闪黑云花岗闪长岩和新村岩体的中粒含角闪黑云二长花岗岩形成于大陆边缘弧环境向同碰撞转换阶段,其他岩石岩体的花岗岩岩性上为二长花岗岩和偏碱性花岗岩,应是同碰撞后期到后碰撞环境下形成的。
[Abstract]:In this study, eight granites with different types of granites were identified from the late Paleozoic granites in Kangbao, northern Hebei Province, and field geological observations were carried out.The detailed work of electron probe test and zircon U-Pb dating has obtained the following understanding: the content of granite minerals in different rock masses is quite different, the West Wufutang, Xincun, Li Shengbaogou, etc.The dark minerals in the granites are gradually reduced from granulite to coarse-grained, and the rock types are from granodiorite to monzogranite to syenite.There are less plagioclase in Xiaoxigou rock body, Shizhouliang rock body, Dapanggou rock mass and granite, and the content of alkaline feldspar increases gradually, from syenite to alkali feldspar granite, and the structure changes from porphyry, porphyry to porphyry.From the mineral electron probe data, it can be concluded that the plagioclase of the medium and fine grained amphibole granodiorite of the West Wufutang rock body, the plagioclase of the plagioclase Anjiao 39.6n43.4) should belong to the plagioclase containing hornblende monzogranite in the Xincun rock mass.The plagioclase contained in the granite of Shizhulliang and Dapangou is albite.The biotite in the granites of the West Wufutang granite is magnesia-iron biotite, which shows the origin of crust and mantle mixing and the characteristics of biotite in the granites of the orogenic belt.The other granites are ferric and iron-rich biotite, derived from the crust and characterized by biotite in alkaline granites.Hornblende belongs to calcium hornblende (Ca Na)B 鈮，

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