伊勒呼里山中生代火山岩:锆石U-Pb年代学及其对岩浆事件的制约

伊勒呼里山地区中生代火山岩由安山岩、粗面英安岩、流纹岩、流纹质凝灰岩和流纹质玻屑凝灰岩等组成。中生代火山岩中的锆石多呈半自形-自形晶，振荡环带发育，Th/U值略高（0.30~2.56），为岩浆成因。锆石U-Pb同位素年代学研究表明：塔木兰沟组安山岩年龄为（161.0±1.0）Ma（n=22），形成于中侏罗世；满克头鄂博组流纹岩年龄为（157.8±2.3）Ma（n=24），形成时代属于晚侏罗世；玛尼吐组火山岩2个样品的年龄分别为（154.0±2.0）Ma（n=23）和（151.7±1.4）Ma（n=25），形成时代属于晚侏罗世；白音高老组火山岩2个样品的年龄分别为（124.1±1.1）Ma（n=25）和（125.1±0.7）Ma（n=23），形成时代为早白垩世。捕获锆石的定年结果显示，本区存在前寒武纪岩浆事件（774 Ma）、加里东期岩浆事件（472 Ma）、印支期岩浆事件（214、210 Ma），这与周边基底岩石中锆石U-Pb的定年结果相吻合。

Mesozoic Volcanic Rocks in Yilehuli Area: Zircon U-Pb Ages and Their Constraints on the Magmatic Events

The Mesozoic volcanic rocks in Yilehuli area consist of andesites, trachy-dacite, rhyolites, fine ash tuff rhyolitic volcanos and rhyolitic vitric tuffs.Zircons from these Mesozoic volcanic rocks has obvious oscillatory zoning, are of euhedral-subhedral shapes and high Th/U ratios (0.30-2.56), implying their magmatic origin.The mean U-Pb age of zircons in volcanic rock from the Tamulangou Formation is (161.0±1.0)Ma(n=22), suggesting the volcanic rock was formed in the Middle Jurassic; mean U-Pb ages of zircon from the volcanic rock in the Manketouebo Formation is (157.8±2.3)Ma(n=24), suggesting these volcanic rock in the Manketouebo Formation was formed in the Late Jurassic; U-Pb age of zircon grains from two volcanic rock samples in the Manitu Formation are (154.0±2.0)Ma(n=23) and (151.7±1.4)Ma(n=25) respectively, suggesting the volcanic rock in Manitu Formation was also formed in the Late Jurassic;mean U-Pb ages of zircon grains from volcanic rocks in the Baiyingaolao Formation are (124.1±1.1)Ma(n=25) and (125.1±0.7)Ma(n=23) respectively, suggesting those volcanic rocks in the Baiyingaolao Formation formed in the Early Carboniferou. The dating results of captured zircons show that the Precambrian (D4554.10:774 Ma), Caledonian (PM₀₀₈TC42.17:472 Ma), Indosinian (D0350.15:214 Ma, D0350.16:210 Ma) magmatic events had taken place in the area, which is consistent with the zircon U-Pb dating results from the surrounding rocks in basement.