兴蒙造山带南缘早—中二叠世砂岩碎屑锆石U-Pb年龄、Hf同位素组成及其构造意义

发布时间：2019-03-05 09:01

【摘要】：利用LA-MC-ICP-MS分析技术,对兴蒙造山带南缘下二叠统三面井组和中二叠统额里图组砂岩中的碎屑锆石进行了U-Pb年龄和Hf同位素研究。结果显示,三面井组砂岩记录了3组碎屑锆石年龄:280~369Ma(4颗)、1800~2271Ma(43颗,峰值1877Ma)和2507~2711Ma(9颗)。额里图组砂岩碎屑锆石年龄集中分布在271~371Ma(9颗)、1258~1395Ma(18颗,峰值1326Ma)和1695~2454Ma(34颗,峰值1864Ma)3个年龄区间。对比研究发现,样品中的元古宙和太古宙碎屑锆石是华北克拉通古老基底的反映;晚古生代锆石具有较低的ε_(Hf)(t)值(-5.3~-23.7)和较老的Hf模式年龄(1124~3039Ma),与华北克拉通北缘晚古生代岩浆岩具有一致性,而明显区别于兴蒙造山带内岩浆岩Hf同位素特征,说明前者是其物源供给区。结合区域资料认为,华北克拉通北缘在早中二叠世期间不存在类似安第斯型的俯冲大陆边缘,三面井组和额里图组砂岩是在伸展背景下沉积形成的。
[Abstract]:The U-Pb ages and Hf isotopes of clastic zircons in the sandstone of the Lower Permian Trifacial well formation and the Middle Permian Ziritu formation in the southern margin of the Xingmong orogenic belt have been studied by means of LA-MC-ICP-MS analysis technique. The results show that three sets of clastic zircon ages have been recorded in the sandstones of the three well formations: 280~369Ma (4), 1800~2271Ma (43, peak 1877Ma) and 2507~2711Ma (9). The ages of sandstone clastic zircon in the Elitu formation are mainly distributed in three age ranges: 271~371Ma (9), 1258~1395Ma (18, peak 1326Ma) and 1695~2454Ma (34, peak 1864Ma). It is found that the Proterozoic and Archean clastic zircons in the samples are the reflection of the ancient basement of the North China Craton. The late Paleozoic zircon has lower 蔚 _ (Hf) (t) value (- 5.3 / 23.7) and older Hf model age (1124~3039Ma), which is consistent with the late Paleozoic magmatic rocks in the northern margin of North China craton. The Hf isotopic characteristics of magmatic rocks in the Xingmong orogenic belt are obviously different from those in the Xingmeng orogenic belt, indicating that the former is the source and supply area of the magmatic rocks. Combined with regional data, it is concluded that there was no subduction continental margin similar to that of Andean type in the northern margin of North China craton during the Middle Permian, and that the sandstones of Trifacial well formation and Erlitu formation were formed in extensional setting.
【作者单位】：中国地质科学院地质研究所;
【基金】：中国地质调查局项目《中国及邻区海陆大地构造研究》(编号:DD20160343(121201102000150009))
【分类号】：P597.3;P534.46

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