大兴安岭红山子盆地火山岩系岩石地层对比

摘要

针对大兴安岭南部中生代火山岩系岩石地层单位存在的时间跨度大、不同岩石地层单位时代重叠的问题，选择红山子盆地火山岩进行SHRIMP锆石U-Pb测年，并结合其它地区已有的锆石U-Pb年龄数据和岩石组合特征对比火山岩系岩石地层。红山子盆地2个碱性流纹岩样品（HS505和HS102）和1个高钾钙碱性流纹岩样品（HS601）所含锆石均具有明显的振荡环带，Th/U比值高，属典型的岩浆成因锆石。SHRIMP锆石U-Pb测年结果表明，样品HS601的10个分析点的206Pb/238U年龄变化范围为150~160 Ma，加权平均值为（156.5±1.6）Ma，MSWD=1.11；样品HS102的11个分析点的206Pb/238U年龄范围为153~159 Ma，加权平均值为（154.7±1.7）Ma，MSWD=0.77；样品HS505的14个分析点的206Pb/238U年龄变化范围为151~160 Ma，加权平均值为（156.5±1.4）Ma，MSWD=1.16。可见，红山子盆地火山岩的年龄范围为157~155 Ma，属晚侏罗世早期。红山子盆地火山岩以高钾钙碱性流纹岩-碱性流纹岩组合为特征，与新民组的岩石组合特征基本一致，且层位相当，应归入新民组。大兴安岭南部地区原划归满克头鄂博组和玛尼吐组、但地质时代属晚侏罗世的长英质火山岩组合应改归新民组，修正后的新民组与冀北-辽西髫髻山组或蓝旗组和大兴安岭北部塔木兰沟组铁镁质火山岩组合的地质时代一致，显示出中国东北部晚侏罗世火山岩组合具有南北分带性。%Because of the large time span and the age overlap of the lithostratigraphic units of Mesozoic volcanic rocks in southern Great Hingan Range, we have chosen volcanic rocks from Hongshanzi Basin to measure the SHRIMP zircon U-Pb age, together with the zircon U-Pb age of the volcanic rocks from adjacent area and the characteristics of rock associations to correlate the volcanic rock series . The zircon in two alkaline rhyolite samples (sample numbers HS505, HS102) and one high-k calc-alkaline rhyolite samples (sample numbers HS601) from Hongshanzi Basin has obvious oscillatory ring, high Th/U ratio, and they belong to typical magma genesis. The results of zircon U-Pb dating indicate that the 206Pb/238U age range of 10 analysis points of sample HS601 is 150~160 Ma with the weighted average of 156.5±1.6 Ma and MSWD of 1.11. Eleven analysis points of sample HS102 is 153~159 Ma with the weighted average of 154.7±1.7 Ma and MSWD of 0.77. Fourteen analysis points of samples HS505 is 151~160 Ma with the weighted average of 156.5±1.4 Ma and MSWD of 1.16. The age range of the volcanic rocks from Hongshanzi Basin is 157~155 Ma, which belongs to the early Late Jurassic. The volcanic rocks in Hongshanzi Basin show characteristics of high-k calc-alkaline rhyolite-alkaline rhyolite associations, which are similar to those of the Xinmin Formation. The volcanic rocks are also stratigraphically correlatable. Therefore, the volcanic rocks should belong to the Xinmin Formation. The Late Jurassic felsic volcanic rocks in southern Great Hingan Range, which was previously assigned to Manketouerbo Formation and Manitu Formation, should belong to the Xinmin Formation, and the age of the revised Xinmin Formation is similar to that of mafic volcanic rocks of Tiaojishan Formation or Lanqi Formation in northern Hebei-western Liaoning and Tamulan Formation in northern Great Hingan Range, showing two zones, northerly and southerly, of rock association of the Late Jurassic volcanic rock in Northeast China.