吉林永吉地区镁铁—超镁铁岩锆石U-Pb年代学及地球化学特征

发布时间：2019-03-16 08:45

【摘要】：本文以吉林永吉地区镁铁—超镁铁岩为研究对象,依据锆石LA-ICP-MS U-Pb定年,确定其形成时代;通过对镁铁—超镁铁岩的主、微量元素特征研究,探讨其岩浆源区及形成时的构造背景。锆石CL图像显示,本文样品中的锆石多数呈半自形,少部分为断柱状,内部结构清晰,岩浆振荡生长环带发育,绝大多数锆石Th/U比大于0.1,暗示为岩浆成因锆石。结合岩石镜下特征和锆石LA-ICP-MS U-Pb定年结果分析表明,头道沟变闪长岩的形成年龄为474.4±2.9Ma,小城子变辉绿岩的形成年龄为469.4士5.4 Ma,头道沟和黑石咀地区超镁铁杂岩的形成时代可能为中奥陶世,表明本文研究区镁铁—超镁铁岩的形成时代为早—中奥陶世,表明吉林中部地区存在早—中奥陶世岩浆事件。.本文变质火成岩具有相对富集大离子亲石元素,如Rb、Th、U、K、Pb等,亏损Nb、Ta、Ti等高场强元素,以及弱的Eu异常的地球化学特征。超镁铁杂岩具有相对富集大离子亲石元素,如Th、U、Pb等,亏损Sr、K、P、Ti等高场强元素,以及弱的Eu异常的地球化学特征。通过对镁铁—超镁铁杂岩岩石地球化学特征分析,结合各种构造环境和岩浆源区图解,头道沟变闪长岩和变辉绿岩应为俯冲板片形成的熔体交代地幔楔部分熔融的产物,并存在—定的地壳混染;超镁铁杂岩的源区可能为亏损地幔。结合构造环境分析,镁铁—超镁铁杂岩形成于活动大陆边缘的弧后盆地环境。研究区早古生代处于古亚洲洋的俯冲之下,具有活动大陆边缘的特点。
[Abstract]:In this paper, the magnesite-ultramafic rocks in Yongji area, Jilin Province, are taken as the object of study, and the age of their formation is determined according to the zircon LA-ICP-MS U-Pb dating. By studying the main and trace elements characteristics of mafic-ultramafic rocks, the magmatic source area and tectonic background of the magmatic-ultramafic rocks were discussed. The CL images of zircon show that most of the zircon in this paper are semi-autogenous, a few of them are broken columns, the internal structure is clear, the magmatic oscillatory growth ring is developed, and the Th/U ratio of most zircon is greater than 0.1, suggesting magmatic zircon. Combined with petroscopic characteristics and zircon LA-ICP-MS U-Pb dating results, it is shown that the age of formation of Toutaogou metamorphic diorite is 474.4 卤2.9 Ma, and that of Xiaochengzi diabase is 469.4 卤5.4 Ma,. The age of the ultramafic complex in the Toutaogou and Heishizui areas may be middle Ordovician, indicating that the mafic-ultramafic complex in this study area is early-middle Ordovician, indicating that there is an early-middle Ordovician magmatic event in the central part of Jilin Province. Metamorphosed igneous rocks have relatively rich geochemical characteristics of large ion lithophile elements, such as Rb,Th,U,K,Pb et al., depleted Nb,Ta,Ti and other high field strength elements, as well as weak Eu anomalies. The ultramafic complex is characterized by relatively rich large ion lithophile elements, such as Th,U,Pb et al., depleted Sr,K,P,Ti and other high field strength elements, as well as weak Eu anomalies. Based on the analysis of the geochemical characteristics of mafic-ultramafic complex rocks, combined with the diagrams of various tectonic environments and magmatic sources, the Toutaogou metamorphic diorite and diabase should be the product of partial melting of the melt metasomatism mantle wedge formed by subduction plate. And there are-definite crustal contamination; The source region of ultramafic complex may be depleted mantle. Combined with the analysis of tectonic environment, the mafic-ultramafic complex is formed in the back arc basin environment of the active continental margin. The study area was subducted by the Paleo-Asian Ocean in the early Paleozoic and characterized by the active continental margin.
【学位授予单位】：山东科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P597.3;P588.12

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