【摘要】 三根河林场新民组火山岩主要由流纹岩、流纹质熔结凝灰岩组成,U-Pb定年结果表明流纹岩形成于165.71±0.83 Ma的中侏罗世.岩石地球化学分析结果显示,SiO₂含量71.05%～76.77%,Na₂O+K₂O含量6.66%～8.49%,铝饱和指数（A/CNK） 1.02～1.17,相对富硅、碱、过铝质,稀土元素总量中等,轻、重稀土元素分馏明显,具有较强的Eu负异常（δEu=0.39～0.66）和Dy负异常,大离子亲石元素Ba、Sr相对亏损,高场强元素Th、U相对富集,Nb、Dy、Ti相对亏损,岩石具有A型流纹岩的特征.岩石地球化学研究表明,岩浆来源于地壳物质的部分熔融作用.空间上,新民组沿大兴安岭火山岩带中北段均有分布,显示大兴安岭火山岩带于中侏罗世处于张性构造环境.更多还原

【Abstract】 The volcanic rocks of Xinmin Formation in Sangenhe forest farm are mainly composed of rhyolites and rhyolitic ignimbrites. The U-Pb dating results indicate the rhyolites were formed in Middel Jurassic,with the age of165.71 ±0.83 Ma. The petrogeochemical analysis shows that the rhyolites are characterized by relatively high silicon,alkali and peraluminous,with the SiO₂ content of 71.05%-76.77%,Na₂ O+K₂ O of 6.66%-8.49% and A/CNK of 1.02-1.17. The rocks present medium total REE content,significant fractionation of HREEs and LREEs,strong negative Eu anomaly （δEu=0.39-0.66）and negative Dy anomaly,relative depletion of LILEs（Ba and Sr）,enrichment of HSFEs（Th and U）and relative depletion of Nb,Dy and Ti,with the characteristics of A-type rhyolites. The study shows the magma is derived from partial melting of crustal materials. The Xinmin Formation is spatially distributed along the middle-north section of Daxinganling volcanic belt,revealing the volcanic belt was in a tensional tectonic environment in Middle Jurassic.更多还原