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吉林省敦化市西北岔地区中生代岩浆岩年代学与地球化学
Geochronology and Geochemistry of Mesozoic Magmatic Rocks in Xibencha Area of Dunhua Jilin Province
【作者】 王政；
【作者基本信息】 吉林大学 ， 工程硕士（专业学位）， 2018， 硕士
【摘要】 本文以吉林省敦化市西北岔地区中生代岩浆岩为研究对象,通过对岩浆岩中锆石的LA-ICP-MS U-Pb年代学和岩浆岩的主量元素、微量元素地球化学研究,确定了研究区岩浆岩的形成时代,讨论了研究区不同时代岩浆岩的岩石组合及其形成的构造背景。最终结合区域地质资料,探讨了研究区中生代区域构造演化历史。西北岔地区位于吉林省敦化市额穆镇,大地构造分区属于西伯利亚板块（Ⅰ）,兴蒙古生代造山带（Ⅰ-8）,松佳兴联合地块南缘复合造山亚带（Ⅰ-84）,塔东-黄松新元古代残留构造片南缘（Ⅰ-841）。区内岩浆岩发育,出露面积约占总面积70%以上,岩石类型以花岗岩为主。研究区中生代岩浆岩中的锆石均为自形—半自形,发育典型的岩浆振荡生长环带的特点。定年结果表明,研究区中生代岩浆作用可以进一步划分为两期:晚三叠世（218213Ma）和早侏罗世（188185 Ma）。根据岩石全分析结果,两个侵入单元分别集中落在花岗岩（Gr）和花岗闪长岩（Gd）与奥长花岗岩（Tr）的交汇线上,岩石化学特征区别明显。根据岩石鉴定结果,结合肉眼和显微镜观测岩石的结构、构造等,对岩石进一步命名。晚三叠世花岗岩体的岩石单元的岩石基本类型为:正长花岗岩、二长花岗岩,代表性岩石有黑云母二长花岗岩、黑云母正长花岗岩等。早侏罗世花岗岩体的岩石单元的岩石基本类型为花岗闪长岩,代表性岩石有黑云母花岗闪长岩。晚三叠世（218213Ma）岩浆作用主要由高钾钙碱性岩浆岩组合所构成,对应的构造演化历史事件:晚古生代末期—早中生代,额尔古纳—兴安—松嫩—佳木斯地块与华北板块碰撞拼合的构造事件,在大地构造演化的晚期,由挤压环境转变为舒展环境的构造体质转换阶段;早侏罗世（188185 Ma）花岗闪长岩,形成于板块俯冲环境,岛弧花岗岩发生在碰撞前,是板块构造的一部分。对应的构造历史事件:早—中侏罗世太平洋板块向欧亚大陆俯冲,早侏罗世俯冲挤压使岩石圈加厚,岩浆底侵,在板块前缘形成钙碱性花岗岩带。
【Abstract】 This paper takes mesozoic magmatic rock in Xibeicha Area Dunhua Jilin as object of study,through geochemistry study for LA-ICP-MS U-Pb chronology of zircon in magmatic rock and bulk element and microelement in magmatic rock,determines the formation age of magmatic rock in research area,and discuss the rock association of magmatic rock with different age in research area and its structural setting for formation.In the end,combining with regional geological data,discuss the Mesozoic regional structure evolution history in the research area.Xibeicha area is located in Emu town Dunhua Jilin,the geotectonic classification belongs to Siberian plate（I）,Xingmeng Paleozoic orogenic belt（Ⅰ-8）,compound orogenic subzone in southern margin of Song Jiaxing combined block（Ⅰ-84）,and the southern margin of Taton-Huangsong Neoproterozoic vestigital tectonic slice（Ⅰ-841）.The magmatic rocks are developed in the area,the outcropped area accounts for above70%of total area,the main rock type is granite.In the research area,the zircon in Mesozoic magmatic rock is automorphic-hypautomorphic,and has typical features of magma oscillatory growth zone.Datable results show that in the research area,Mesozoic magmatism can be further divided into two periods,late Triassic epoch（218213Ma）and early Jurassic（188185 Ma）.According to total analysis results for rock,two intrusive units are located in the crossed line of granite（Gr）,Granodiorite（Gd）and trondhjemite（Tr）respectively,and the chemical feature of rock has obvious difference.According to rock identification results,observe the structure and tectonics of the rock combining with naked eye and microscope,and name the rock further.The base types of the rock in rock unit of late Triassic epoch granitic pluton are:syenogranite and monzonitic granite,and the representative rocks are biotite adamellite,biotite syenogranite etc.The base types of the rock in rock unit of early Jurassic granitic pluton are granodiorite,and the representative rocks are biotite granodiorite.In late Triassic epoch（218213Ma）,the magmatism mainly consists of high potassium calcium alkali magmatic rock combination,the corresponding tectonic evolution history events:last phase of neopaleozoic–early Mesozoic,tectonic events of collision and suturing between Erguna-Xing’an-Songnen-Kiamusze blocks and North China Blocks,in the later period of geotectonics evolution,the transformation phase of structural constitution from extruded environment to stretched environment;In early Jurassic（188185 Ma）,the granodiorite was formed in plate subducting environment,island arc granite occurred before the collision,which was a part of plate tectonics.The corresponding tectonic evolution history events:early-middle Jurassic pacific plate dived into Eurasia,the subduction and extrusion in early Jurassic made the lithosphere thicken,magma underplating,and formed calcium alkali granite zone at leading edge of the plate.