| 内蒙古克什克腾旗哲斯组沉积学和年代学研究及其古地理意义 |
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| 引用本文： | 栗进,徐备,田英杰,姚仲伟.内蒙古克什克腾旗哲斯组沉积学和年代学研究及其古地理意义[J].岩石学报,2018,34(10):3034-3050. |
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| 作者姓名： | 栗进 徐备 田英杰 姚仲伟 |
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| 作者单位： | 北京大学地球与空间科学学院, 北京 100871,河北地质大学资源学院, 石家庄 050031,河北地质大学资源学院, 石家庄 050031,内蒙古矿业科技研究院有限公司, 呼和浩特 010050 |
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| 基金项目： | 本文受国家自然科学基金项目（41672214）、科技部国家重点研发计划（2017YFC0601302）和内蒙古自治区科技厅项目（兴蒙造山带构造演化、成矿信息与成矿作用）联合资助. |
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| 摘 要： | 为了重建西拉木伦河北部晚古生代沉积古地理格局并探讨古亚洲洋的闭合过程,本研究对克什克腾旗西部的哲斯组地层进行了详细的沉积环境与沉积相分析、锆石U-Pb年代学研究。来自哲斯组的凝灰质砂岩与安山岩样品的最年轻锆石组的谐和年龄为262±1Ma和258±17Ma,限定研究区内地层沉积下限为中晚二叠世。前人认为哲斯组地层为深海环境下的浊流沉积,本文研究表明哲斯组以近源快速堆积、快速沉降为特征,沉积环境为三角洲前缘相与前三角洲相的多次交替,同时受到火山活动的影响。通过详细的沉积岩野外剖面观察,区内地层并没有发现以单调的递变层理为特征的连续鲍马序列层序,而是出现从砂岩到粉砂岩或泥岩的不规则截然互层层序,并与巨厚层的滑塌堆积交替发育,表明研究区中二叠世古地理格局并不具备深海浊积扇的发育条件,也暗示中二叠世不存在向南发育的广阔大陆边缘;另一方面,结合古流向恢复和物源分析,哲斯组的沉积物应主要来自于南部的华北克拉通以及南造山带陆缘弧,说明研究区在中二叠世已与华北板块连通,并没有类似大洋俯冲带的阻隔作用。因此,研究区中二叠世古地理格局并不具备深海远源浊积扇的发育条件,而是处于近源快速堆积的伸展环境,中二叠世既不存在向南发育的广阔大陆边缘,也不存在代表板块边界的俯冲带。
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| 关 键 词： | 古地理格局 沉积环境 哲斯组 克什克腾旗 |
| 收稿时间： | 2018/3/20 0:00:00 |
| 修稿时间： | 2018/7/31 0:00:00 |
Sedimentary and geochronology study on the Zhesi Formation from Hexigten Banner, Inner Mongolia and paleogeographic significances |
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| LI Jin,XU Bei,TIAN YinJie and YAO ZhongWei.Sedimentary and geochronology study on the Zhesi Formation from Hexigten Banner, Inner Mongolia and paleogeographic significances[J].Acta Petrologica Sinica,2018,34(10):3034-3050. |
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| Authors: | LI Jin XU Bei TIAN YinJie and YAO ZhongWei |
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| Institution: | School of Earth and Space Science, Peking University, Beijing 100871, China,School of Resource, Hebei GEO University, Shijiazhuang 050031, China,School of Resource, Hebei GEO University, Shijiazhuang 050031, China and Mining Science and Technology Institute Limited Company, Hohhot, 010050, China |
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| Abstract: | There is still in great controversial about the formation process of the Xing''an-Mongolian Orogenic Belt, which involves where the suture position is and when the final closure of the Paleo-Asian Ocean happens. In order to reconstruct the sedimentary paleogeography in the northern margin of Xar Moron River, detailed sedimentary environment and sedimentary facies analyses together with zircon U-Pb geochronological studies on the Zhesi Formation in Hexigten Banner have been carried out. Sample 170917-07 and 170915-05 are collected from the tuffaceous sandstone and andesite of this formation, respectively, to study their zircon ages. Based on the zircon CL images and U-Pb concordia diagrams, the zircons in sample 170917-07 can be divided into four groups:247~309Ma (N=25) with a peak age of 263Ma, 401~475Ma (N=26) with a peak age of 440Ma, 581~1424Ma (N=10), and 1731~2446Ma (N=7); while the 21 zircons in sample 170915-05 analyzed are concordant, and show four groups:group A (258~261Ma, N=2), group B (281~298Ma, N=5) with a concordant age of 285±2Ma, group C (315~485Ma, N=8), and group D (1033~2180Ma, N=8). The youngest concordant age groups of the samples analyzed are 262±1Ma and 258±17Ma, respectively, which constrains that the maximum depositional time of the Zhesi Formation is mid-late Permian. With regard to the Permian tectonic pattern in study area, some researchers believe that the lithology across the Xar Moron River near Hexigten is dominated by broadly northeast trending Permian volcanoclastic turbiditic successions. However, this study shows that the Zhesi Formation is characterized by near-source rapid accumulation and fast subsidence. Accompanied by active volcanic activities, the sedimentary environment of this formation belongs to multiple alternations of delta front and prodelta facies. Detailed observations of field sections suggest that the Zhesi Formation, alternatively developed with thick layered olistostrome, is not characterized by a continuous Bouma Sequence which consists of monotonous graded bedding, but rather than an irregular interfacial sequence from sandstone to siltstone or mudstone. As a result, the Permian paleogeographic frame in the study area doesn''t have conditions for the development of deep-sea turbidite fans, which implied that there was no extensive continental margin to the south during the Middle Permian. On the other hand, according to paleocurrent recovery and provenance analysis, the main sources of the Zhesi Formation are composed of the volcanic activities in the same period, the North China Craton and the Early Paleozoic continental margin arc in the south of the study area, which suggests that the studied area has been connected with the North China plate in Middle Permian, and there is no such barrier effects as an oceanic subduction zone. To sum up, the paleogeographic frame in Middle Permian doesn''t possess the developmental conditions of deep-sea turbidite fan, but the extensional environment of rapid accumulation in a near source environment. Furthermore, the broad southward continental margin and the subduction zone representing the plate boundary don''t exist in Middle Permian. |
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| Keywords: | Sedimentary paleogeography Sedimentary environment Zhesi Formation Hexigten Banner |
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