青海祁漫塔格地区古生代基性—超基性岩浆作用

发布时间：2018-03-18 13:36

本文选题：祁漫塔格　切入点：基性-超基性岩　出处：《中国地质大学(北京)》2017年硕士论文　论文类型：学位论文

【摘要】：祁漫塔格地区是我国近些年来矿产勘查进展最大的地区之一,同时,基性-超基性岩中蕴藏着丰富的矿产资源,因此,基性-超基性岩浆作用的研究对于找矿有非常重要的意义。本文通过详细的野外观察与室内工作,对青海祁漫塔格地区古生代基性-超基性岩进行了矿物学、岩石学、地球化学等方面的研究,探讨了祁漫塔格地区基性-超基性岩浆的形成时代、物质来源及区域构造演化背景。本次在祁漫塔格山主脊南野牛沟所采集的基性-超基性岩样品有蛇纹石化辉石橄长岩和蚀变角闪辉长岩,根据锆石U-Pb年龄数据,可知蛇纹石化辉石橄长岩成岩年龄为380.8±5.3Ma,蚀变角闪辉长岩成岩年龄为391.9±4.0 Ma,时代为中-晚泥盆世;通过对样品主量元素进行分析,表明样品属于亚碱性岩的拉斑玄武岩系列;通过LA-ICP-MS锆石U-Pb法对祁漫塔格基性-超基性岩样品进行稀土和微量元素高精度微区分析,LREE/HREE值在3.24~5.30之间,轻重稀土元素分馏中等,稀土配分曲线呈现轻稀土富集的右倾型;δEu在0.87~1.27之间,均值1.02,Eu略亏损或不亏损,部分岩石显示正铕异常;岩石微量元素比值蛛网图中,样品富集大离子亲石元素Rb、U、Pb、Th、Sr,亏损Ba、Nb、Zr、Cr、Ni,其他元素特征不明显;蛇纹石化辉石橄长岩的Rb/Sr值为0.10和0.09,~(143)Nd/~(144)Nd比值为0.512551和0.512681,εNd(t)为0.67和2.87,暗色蚀变闪长岩的Rb/Sr=0.12,87Sr/86Sr=0.708138,εSr(t)=51.6,εNd(t)=-1.34,表示来源于弱亏损的地幔物质,闪长岩在成岩过程中,有地壳物质的参与,有可能是岩浆在上涌过程中,被地壳物质不同程度的混染。本次所采蛇纹石化辉石橄长岩和暗色蚀变闪长岩样品的Rb/Sr值范围在0.09~0.12,反映出岩浆主要为壳幔混合来源;通过对Pb同位素数据分析可知,样品大多位于造山带与地壳接触区域,其中QM107-7显示上地壳特征,说明本区基性-超基性岩可能存在不同源区或在演化中有不同源区物质的混入;同时,中泥盆世基性岩墙可能是原特提斯洋到古特提斯洋转变的早期岩浆反映,可能标志着中泥盆世东昆仑造山带中古特提斯洋的打开;区内晚泥盆世牦牛山组双峰式火山岩与本次发现的中-晚泥盆世基性-超基性岩形成了良好的组合关系,两者结合起来分析,对于判定区内构造环境有重要意义,表明祁漫塔格地区在中-晚泥盆世由碰撞挤压体制转变为造山后拉张环境。通过综合分析认为,祁漫塔格地区于中-晚泥盆世由碰撞挤压体制转变为造山后拉张环境,本区的基性-超基性岩即形成于中-晚泥盆世,陆内伸展的地质背景下。
[Abstract]:Qimantage area is one of the most advanced mineral exploration areas in China in recent years. At the same time, there are abundant mineral resources in basic-ultrabasic rocks. The study of basic-ultrabasic magma is of great significance for ore prospecting. Through detailed field observation and laboratory work, the paleozoic basic-ultrabasic rocks in Qimantage area, Qinghai Province, have been studied in mineralogy and petrology. The formation age of basic-ultrabasic magma in Qimantage area is discussed. Material source and regional tectonic evolution background. The basic-ultrabasic rock samples collected in the southern buniugou of the main ridge of Qimantag Mountain include ophiopyroxenite olivine and altered hornblende gabbro. According to the zircon U-Pb age data, The diagenetic age of serpentine pyroxene is 380.8 卤5.3 Ma.The diagenetic age of altered hornblende gabbro is 391.9 卤4.0 Ma. the age is middle to late Devonian. The LA-ICP-MS zircon U-Pb method was used to analyze the rare earth and trace elements in the samples of Qimantage-ultrabasic rocks with high accuracy. The LREE / hree value was between 3.24 and 5.30, and the fractionation of heavy and heavy rare earth elements was moderate. The REE partition curve shows the right dip pattern of LREE enrichment, 未 EU is between 0.87 and 1.27, the mean value is 1.02U, and some rocks show positive europium anomaly, and the trace element ratio of rocks is cobwebs. The samples are enriched with large ion lipophilic element RbHN, and depleted in Baan NbsrnbZrCr-Cr-Ni.The other element characteristics are not obvious, the Rb/Sr values of ophiopyroxene olivine are 0.10 and 0.09 ~ 143NdP ~ (144N) ND ratios are 0.512551 and 0.512681, 蔚 Ndtt) are 0.67 and 2.87, Rbr / Sr ~ + 0.128786 Sr ~ + -0.708138, 蔚 SRT ~ + 51.6, 蔚 Ndt ~ (-1) -1.34, indicating weak depleted mantle material, for dark altered diorite, the results are as follows: (1) the ratio of the two elements is 0.67 and 2.87, respectively, and that of the ophiopyroxenite is 0.708138, 0.708138, 51.6, and 0.512551 and 0.512681, respectively, and the results are as follows: (1) the results are as follows: 1. In the diagenetic process of diorite, there is the participation of crustal material, and it is possible that the magma is in the upwelling process. The Rb/Sr values of the serpentine pyroxene olivine and dark altered diorite samples are in the range of 0.09 ~ 0.12, which indicates that the magma is mainly from crust-mantle mixed source. The samples are mostly located in the contact region between the orogenic belt and the crust. QM107-7 shows the characteristics of the upper crust, indicating that the basic-ultrabasic rocks in this area may have different sources or have different source materials in the evolution, and at the same time, The basic rock wall of the Middle Devonian may be an early magmatic reflection of the transition from the original Tethys Ocean to the PaleoTethys Ocean, which may indicate the opening of the Middle Paleo-Tethys Ocean in the East Kunlun orogenic belt of the Middle Devonian. The bimodal volcanic rocks of the late Devonian Yaniushan formation in this area have formed a good association relationship with the basic-ultrabasic rocks discovered in this paper. The combination of the two types of volcanic rocks is of great significance in judging the tectonic environment in the area. The results show that the collisional compression system changed from collisional compression system to post-orogenic extensional environment in the Middle-Late Devonian of Qimantag area, and it is considered by comprehensive analysis that the collisional compression system changed into post-orogenic extensional environment in the Middle-Late Devonian of Qimantag area. The basic-ultrabasic rocks in this area were formed in the geological setting of mid-late Devonian and intracontinental extension.
【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】：2017
【分类号】：P588.1

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