贺根山蛇绿岩就位时代：古生代沉积盖层碎屑锆石U-Pb年代学的制约

发布时间：2018-04-30 19:31

本文选题：贺根山蛇绿岩 + U-Pb数据　；参考：《吉林大学》2017年硕士论文

【摘要】：贺根山蛇绿岩作为中亚造山带出露区典型的蛇绿岩带,对限定中亚造山带古生代构造演化具有重要的意义。目前有关贺根山蛇绿岩的就位时代和形成构造背景仍然存在着巨大的争议。本文通过对不整合界面之上古生代沉积盖层的研究为贺根山蛇绿岩的就位时代提供了直接的制约。贺根山蛇绿岩在乌斯尼黑地区被古生界葛根敖包组碎屑岩不整合覆盖,葛根敖包组碎屑锆石U-Pb年代学研究结果表明,全部锆石的年龄分布在298~363Ma之间,可以划分为两个年龄组(1)298-320Ma,峰值年龄为308Ma。(2)320-360Ma,峰值年龄为330Ma。较年轻的年龄组298-320Ma限定了该沉积岩的沉积下限年龄,并与晚古生代格根敖包组火山岩年龄一致;320-360Ma年龄组的锆石U-Pb年龄则与贺根山蛇绿岩中铁镁质-超铁镁质岩石原岩年龄一致,表明贺根山蛇绿岩曾作为古生界主要沉积物源之一。有鉴于该古生代沉积盖层直接不整合覆盖于贺根山蛇绿岩之上,因此贺根山蛇绿岩的就位时代应早于格根敖包组的沉积时代,极大可能在308-330Ma之间,而不是前人认为的志留纪、泥盆纪或者中生代。
[Abstract]:As a typical ophiolite belt in the exposed area of the Central Asian orogenic belt, the Helgenshan ophiolite plays an important role in defining the Paleozoic tectonic evolution of the Central Asian orogenic belt. At present, there are still great controversies about the age and tectonic background of the ophiolite in Hegen Mountain. The study of Paleozoic sedimentary caprocks on the unconformity interface provides direct constraints for the age of ophiolite emplacement in Hegenshan. The Hergenshan ophiolite was unconformably covered by the clastic rocks of the Gegenaobo formation in the Wushnihei area. The U-Pb chronological study of the detrital zircons of the Gegen Obao formation shows that all the zircons are distributed between 298~363Ma ages. It can be divided into two age groups, the peak age is 308Ma, the peak age is 320-360 Ma, and the peak age is 330Ma. The lower sedimentary age of the sedimentary rocks is defined by the younger age group 298-320Ma, and the zircon U-Pb age is the same as that of the volcanic rocks of the Gegenaobo formation in the late Paleozoic age group (320-360 Ma), and the age of the ferromagnesian-ultraferromagnesitic rocks in the Hegensan ophiolite is the same as that of the original rocks of the igneous rocks in the Hegenshan ophiolite. The results indicate that the ophiolite was one of the main sediments of Paleozoic. In view of the direct unconformity of the Paleozoic sedimentary caprock over the Helgenshan ophiolite, the age of the Hegenshan ophiolite should be earlier than the sedimentary age of the Gegenaobo formation, which is most likely between 308-330Ma and not the Silurian period as previously thought. Devonian or Mesozoic.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P534.4

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