中亚蒙古造山带东段造山事件的40Ar-39Ar同位素年代学证据
40Ar-39Ar isotope chronological evidence for the orogeny in the eastern segment of the Central Asian-Mongolian orogenic belt
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摘要: 提要：位于中亚蒙古造山带东段的吉林省中南部呼兰群变质岩中，发现含多硅白云母的蓝晶石片岩带。采用40Ar-39Ar连续阶段升温的方法，对呼兰群下部层位的黑云母片麻岩和上部蓝晶石片岩中的云母类变质矿物进行测定，分别获得（223.57±0.80）Ma、（224.41±4）Ma的坪谱年龄和（221.90±2.79）Ma、（223.27±4.53）Ma的等时线年龄。相同的方法得到侵位于呼兰群地层中、化学成分类似于岛弧拉斑玄武岩的角闪橄榄岩（302.00±6.30）Ma和(246.00±5.70) Ma不一致坪谱年龄，从而确定了该地区古亚洲—蒙古洋缝合及中生代碰撞造山的时限范围在302～225 Ma，且造山作用可能经历了由碰撞造山到陆-陆叠覆造山的连续过程。
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关键词:
- 中亚蒙古造山带 /
- 40Ar-39Ar 同位素年龄 /
- 吉林省中南部
Abstract: Abstract：A kyanite schist belt containing phengite is found in metamorphic rocks of the Hulan Group in the Hongqiling area of south-central Jilin, tectonically in the eastern segment of the Central Asia-Mongolia orogenic belt. Plateau ages of 223.57±0.8 and 224.41±4.0 Ma and isochron ages of 221.9±2.79 Ma and 223.27±4.53 Ma of micas in biotite gneiss of the Lower Member and phengite in kyanite schist of the Upper Member of the Hulan Group are obtained by the continuous stepwise 40Ar-39Ar heating method. The same method also gives discordant plateau ages of 302±6.3 and 246.00±5.70 Ma for hornblende peridotites of island-arc tholeiite type intruded into the Hulan Group. These ages thus confine the time limits of the closing of the Paleo-Asian-Mongolian ocean and Mesozoic collisional orogeny to at least 302-225 Ma and suggest that the area probably underwent a continuous process from continent-continent collisional orogeny to overlapping. -
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