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辽西义县组火山岩^(40)Ar/^(39)Ar、K-Ar法年龄测定 被引量:69

^(40)Ar/^(39) and K-Ar dating of the Yixian Formation volcanic rocks,western Liaoning Province,China
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摘要 义县组为辽西地区广泛分布的陆相火山-沉积地层,义县火山旋回分为4个亚旋回。含珍稀化石的湖相沉积层与第二亚旋回火山岩伴生。运用激光微区40Ar/39Ar法、常规40Ar/39Ar阶段升温测年法和K-Ar法,对义县旋回火山岩进行了系统的年龄测定,结果表明,直接覆盖义县组底砾岩的义县旋回第一亚旋回第一小旋回玄武岩的K-Ar年龄为(133.3±2.6)Ma、(133.6±2.6)Ma,激光微区40Ar/39Ar法给出的相关性很好的Ar-Ar等时线年龄为(132.9±4.5)Ma,第三、第四小旋回玄武岩样品40Ar/39Ar阶段升温获得平坦的年龄谱线,坪年龄分别为(130.6±0.5)Ma、(127.7±0.2)Ma;第二亚旋回玄武岩和流纹质凝灰岩样品Ar-Ar等时线年龄为(126.1±1.7)Ma、(127.4±1.3)Ma,第三亚旋回火山岩全岩K-Ar年龄为(124.4±2.4)~(124.9±2.4)Ma。义县火山旋回发生的时间大致介于120~135Ma之间,义县组的时代应为早白垩世。 Mesozoic volcanic rocks are widely d istributed in western Liaoning Prov ince,China.The geological age of Yixian Formation is appointed to d ifferent epochs of Mesozoic Era,such as Late Jurassic,Early Cretaceous or Late Jurassic-Early Cretaceous.Ev en the isotopic ages are also very different.Yixian Formation is continental facies volcanic-sediment layer.From early to late,Yixian Formation may be div ided into four members,correspondi ngly,Yixian volcanic cycle may be divided into four subcycles through detaile d geological survey in Beipiao-Yixian area.The lake sediment layer containing p recious fossils was formed in the period of the second subcycle.K-Ar dating,laser 40 Ar / 39 Ar dating and 40 Ar / 39 Ar stepwise heating dating have been used to dating the Yixian Formation v olcanic rocks systemically.The results ind icate that the basalt collected from the first small cycle which covers th e basal conglomerate of Yixian Formation di rectly yields a K-Ar age of(133.3±2.6)Ma,(133.6±2.6)Ma;its laser 40 Ar / 39 Ar age is(132.9±4.5)Ma.The 40 Ar / 39 Ar stepwise heating experiment performed on the basalt collected from the third and fourth small cycle s yields a remarkably simple pattern,and gives a plateau age of(130.6±0.5)Ma and(127.7±0.2)Ma.The 40 Ar / 36 Ar vs. 39 Ar / 36 Ar isochron age of the basalt and rhyolite tuff formed in the period of the second subcycle is(126.1±1.7)Ma and(127.4±1.3)Ma.The bulk-rock sample of the third subcycle yields a K-Ar apparent age o f(124.2±2.4)~(124.9±2.4)Ma.The K-Ar age of the andesite colle cted from the top bed of the fourth member i s(120.1±2.0)Ma.Yixian volcanic cycle took place during 120~135Ma,the rare fossils-bearing sedime nt was formed during 125~127Ma.On th e basis of the latest available abundant information from field geo logical work,isotopic ages and a lot of magnetostratigraphic data,the t ime of Yixian Formation should belong to Ea rly Cretaceous,and the Jurassic-Cr etaceous boundary in western Liaoni ng is most likely to be located between Tuchengzi and Yixin formations.
出处 《地球化学》 CAS CSCD 北大核心 2003年第5期427-435,共9页 Geochimica
基金 国土资源部科技专项(200010406) 中国地质调查局地质调查项目(200213000041)
关键词 义县组 火山岩 早白垩世 辽宁 K-AR法 40Ar/^39Ar法 Yixian Formation volcanic rocks K -Ar method 40 Ar / 39 Ar dating Early Cretaceous Liaoni ng Province
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