中祁连中段丹德尔岩体岩石地球化学特征、形成时代及大地构造意义
发布时间：2018-07-22 15:56
【摘要】：研究区位于青海省祁连县丹德尔地区,属于中国西部秦祁昆巨型构造-岩浆岩带的一部分,具有十分独特的地质意义。本文通过对丹德尔岩体的主量元素的分析,得出岩体属于碱性、过铝质型的花岗岩类。对稀土和微量元素研究可知,微量元素蛛网图上显示出富集大离子亲石元素Rb、Th、Ba、K等和亏损高场强元素Sr、Ti、P、Nb、Ta等的特征,可推测其熔融的残留相可能存在角闪石和斜长石(张旗等,2009)。综合研究源岩具有高钾钙碱性特征属于S型花岗岩一个特征,结合其他七个特征判定岩体属于S型花岗岩。本文岩体锆石U-Pb测年所采用的方法是LA-MC-ICPMS,所测年龄分布为1个主峰期和2个次峰期,结合研究区大地构造演化史最终确定岩体成岩年龄为438Ma,属于晚奥陶世晚期,其余两个年龄均为捕获锆石的年龄。岩体物质来源主要根据4种判别图分析得到:在Si O2-Zn图解中,显示的特征为分异结晶花岗岩类,与长英质火成岩的趋势一致(Lentz D.R.,1998)。在Rb/Y-Nb/Y图解上,显示俯冲带富集或地壳混染的趋势。依据Th/Yb-Ta/Yb图解,同样显示分离结晶的演化趋势。在Th/Y-Nb/Y图解中,说明丹德尔岩体起源于壳源物质。结合Sr和Yb的含量,综上认为,花岗岩的源区熔融后的残留相由斜长石+石榴子石组成。按照Sr-Yb含量范围,将岩体归为浙闽型和南岭型过渡类型,这种类型反映了形成时压力较低,地壳厚度为减薄地壳。因此推测成岩时研究区处于水平运动引发的一种向下的垂直运动,同时岩体与钨锡矿产有一定关系。通过对前人所研究38个具有典型特征岩体的统计,初步了解北祁连洋在早古生代经历了先向南俯冲后转为向北俯冲的过程,丹德尔岩体形成于后碰撞造山期。在此基础上,利用Pearce J A花岗岩判别图解、Brown G C花岗岩判别图解和R1-R2构造环境判别图解,较全面地论证了岩体形成于伸展体制背景下,具有后碰撞造山特点,因此岩体的成岩年龄即为祁连洋向北俯冲后碰撞造山结束的标志。
[Abstract]:The study area is located in the Dandell area of Qilian County, Qinghai Province. It is a part of the giant tectonic-magmatic rock belt in Qinqicun, western China, and has a very unique geological significance. Based on the analysis of the principal elements of the Dandel rock mass, it is concluded that the rock mass belongs to alkaline, peraluminous type granites. Studies on rare earth elements and trace elements show that the trace element cobwebs show the characteristics of enrichment of large ion lipophilic element RbTH, Bak, and depleted high field strength element SrnTiTiPNbNbTa-Ta, which suggest that there may be amphibole and plagioclase in the molten residual phase (Zhangqi et al. 2009). The source rocks are characterized by high potassium calc-alkalinity, which belong to S-type granite. Combined with the other seven characteristics, the source rocks belong to S-type granite. The zircon U-Pb dating method used in this paper is LA-MC-ICPMS.The age distribution of the zircon U-Pb dating is one main peak period and two sub-peak periods. Combined with the geotectonic evolution history of the studied area, the diagenetic age of the rock mass is finally determined to be 438 Ma, which belongs to the late Ordovician. The other two ages are the ages of zircon capture. The material source of the rock mass is mainly based on the analysis of four discriminant diagrams: in the Sio _ 2-Zn diagram, the characteristic is the differentiated crystalline granite, which is consistent with the trend of felsic igneous rocks (Lentz D. R. 1998). The Rb / Y-Nb / Y diagram shows a tendency of enrichment or crustal mixing in the subduction zone. According to the diagram of Thr / Yb-Tap-Yb, the evolution trend of separation crystallization is also shown. In the diagram of Th/ Y-Nb / Y, it is shown that the Dandel rock body originated from the crust material. Combined with the contents of Sr and Yb, it is concluded that the residual phases in the source region of the granite are composed of plagioclase garnet. According to the range of Sr-Yb content, the rock mass is classified as Zhejiang Fujian type and Nanling type transition type. This type reflects the low pressure and the thin crust thickness at the time of formation. Therefore, it is inferred that the study area is a downward vertical movement caused by horizontal movement during diagenesis, and that the rock mass is related to tungsten and tin minerals to some extent. Based on the statistics of 38 rock masses with typical characteristics studied by previous authors, it is preliminarily understood that the North Qilian Ocean experienced the process of subduction from south to north in the early Paleozoic, and the Dendell rock body was formed in the post-collision orogenic period. On this basis, using Pearce J A granite discriminant diagram, Brown G C granite discriminant diagram and R1-R2 tectonic environment discriminant diagram, it is proved that the rock body was formed in the extensional system background and has the characteristics of post-collision orogeny. Therefore, the diagenetic age of the rock mass is the sign of the end of collision orogeny after the northward subduction of Qilian Ocean.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588;P548
[Abstract]:The study area is located in the Dandell area of Qilian County, Qinghai Province. It is a part of the giant tectonic-magmatic rock belt in Qinqicun, western China, and has a very unique geological significance. Based on the analysis of the principal elements of the Dandel rock mass, it is concluded that the rock mass belongs to alkaline, peraluminous type granites. Studies on rare earth elements and trace elements show that the trace element cobwebs show the characteristics of enrichment of large ion lipophilic element RbTH, Bak, and depleted high field strength element SrnTiTiPNbNbTa-Ta, which suggest that there may be amphibole and plagioclase in the molten residual phase (Zhangqi et al. 2009). The source rocks are characterized by high potassium calc-alkalinity, which belong to S-type granite. Combined with the other seven characteristics, the source rocks belong to S-type granite. The zircon U-Pb dating method used in this paper is LA-MC-ICPMS.The age distribution of the zircon U-Pb dating is one main peak period and two sub-peak periods. Combined with the geotectonic evolution history of the studied area, the diagenetic age of the rock mass is finally determined to be 438 Ma, which belongs to the late Ordovician. The other two ages are the ages of zircon capture. The material source of the rock mass is mainly based on the analysis of four discriminant diagrams: in the Sio _ 2-Zn diagram, the characteristic is the differentiated crystalline granite, which is consistent with the trend of felsic igneous rocks (Lentz D. R. 1998). The Rb / Y-Nb / Y diagram shows a tendency of enrichment or crustal mixing in the subduction zone. According to the diagram of Thr / Yb-Tap-Yb, the evolution trend of separation crystallization is also shown. In the diagram of Th/ Y-Nb / Y, it is shown that the Dandel rock body originated from the crust material. Combined with the contents of Sr and Yb, it is concluded that the residual phases in the source region of the granite are composed of plagioclase garnet. According to the range of Sr-Yb content, the rock mass is classified as Zhejiang Fujian type and Nanling type transition type. This type reflects the low pressure and the thin crust thickness at the time of formation. Therefore, it is inferred that the study area is a downward vertical movement caused by horizontal movement during diagenesis, and that the rock mass is related to tungsten and tin minerals to some extent. Based on the statistics of 38 rock masses with typical characteristics studied by previous authors, it is preliminarily understood that the North Qilian Ocean experienced the process of subduction from south to north in the early Paleozoic, and the Dendell rock body was formed in the post-collision orogenic period. On this basis, using Pearce J A granite discriminant diagram, Brown G C granite discriminant diagram and R1-R2 tectonic environment discriminant diagram, it is proved that the rock body was formed in the extensional system background and has the characteristics of post-collision orogeny. Therefore, the diagenetic age of the rock mass is the sign of the end of collision orogeny after the northward subduction of Qilian Ocean.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588;P548
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