鄂尔多斯盆地西北缘奥陶纪凝灰岩锆石U-Pb年龄、Hf同位素特征及地质意义

发布时间：2018-06-28 09:41

本文选题：鄂尔多斯盆地 + 火山凝灰岩　；参考：《地质论评》2017年05期

【摘要】：鄂尔多斯盆地西缘北段奥陶纪剖面中出露有火山凝灰岩夹层,它们是火山喷发的凝灰物质沉积的产物,其研究对于鄂尔多斯盆地奥陶纪年代地层格架的厘定和构造背景的确定有重要意义。本文报道了鄂尔多斯盆地西缘北段乌海地区哈图克沟剖面乌拉力克组顶部火山凝灰岩的锆石U-Pb年龄和Hf同位素特征。锆石LA-ICPMS U-Pb年龄为454.9±3.4Ma,SHRIMP U-Pb年龄为456.4±4.2Ma,结合古生物地层学,将乌拉力克组的沉积时代厘定为中奥陶世达瑞威尔阶晚期—晚奥陶世桑比阶。锆石原位微区Hf同位素εHf(t)=+4.02~+10.98,n(176Hf)/n(177Hf)值变化范围为0.282 619~0.282 963之间,二阶段模式年龄变化范围为729~1178Ma。根据凝灰岩与研究区周缘造山带的锆石U-Pb年龄及Hf同位素特征对比判断火山凝灰岩物质应主要来自于其西南方向的北祁连造山带和/或北秦岭造山带。鄂尔多斯盆地西缘和南缘广泛分布的火山凝灰岩具有一致的就位时间和物源,表明盆地西缘和南缘都受到了中—晚奥陶世北祁连和/或北秦岭洋壳俯冲引起的火山弧喷发的影响。
[Abstract]:Volcanic tuff intercalation appeared in the Ordovician section of the northern section of the western margin of the Ordos Basin. The study is of great significance for the determination of the Ordovician chronostratigraphic framework and the determination of the tectonic background in the Ordos Basin. The zircon U-Pb age and HF isotopic characteristics of volcanic tuff at the top of the Ulalik formation in the northern section of the western margin of the Ordos Basin are reported in this paper. The U-Pb age of zircon LA-ICPMS U-Pb is 454.9 卤3.4 Ma-SHRIMP U-Pb age of 456.4 卤4.2 Ma. combined with paleostratigraphy, the sedimentary age of the Ulalik formation is determined to be the late stage of the Ordovician stage and the late Ordovician stage to the late Ordovician stage. The zircon in-situ HF isotope 蔚 HF (t) = 4.02 ~ 10.98 Hf (176HF) / n (177Hf) varies from 0.282 to 0.282,963, and the two-stage model age range is 72991178 Ma.The zircon in-situ microregion 蔚 HF (t) = 4.02 ~ 10.98 Hf (176HF) / n (177Hf) varies from 0.282 to 0.282,963. According to the zircon U-Pb age and HF isotopic characteristics of the tuff and the marginal orogenic belt of the study area, it is concluded that the volcanic tuff material is mainly from the North Qilian orogenic belt and / or the North Qinling orogenic belt in the southwest direction of the tuff. The volcanic tuff widely distributed in the western and southern margin of the Ordos Basin has a consistent emplacement time and provenance. It is shown that both the western margin and the southern margin of the basin are affected by the volcanic arc eruption caused by the subduction of the North Qilian and / or the North Qinling oceanic crust in the Middle and late Ordovician.
【作者单位】：中国地质科学院矿产资源研究所国土资源部盐湖资源与环境重点实验室;
【基金】：国家重大基础研究计划(973)项目(编号:2011CB403001) 中国地质调查局地调工作项目(编号:1212011085516)的成果~~
【分类号】：P534.42;P597

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