中祁连地块北缘羊浴池地区岩墙群的地球化学特征、形成时代及地质意义

发布时间：2019-03-14 13:02

【摘要】：侵入岩可以侵位于不同的地壳层次,其侵位机制复杂,常被视作为是大陆板块刚性化及古应力状态最直接的地质标志,同时也是岩石圈(或地壳)地幔伸展的重要标志,以及古板块恢复再造的重要标志。岩墙群作为原生岩浆的代表,充填在火山或侵入体的补给通道中,用于反演源区的物质组成和岩浆喷出的历史;岩墙群充填在某种构造裂隙中,其特殊的空间配置方式可反映当时的构造应力场;同时,岩墙群所充填的裂隙也是成矿流体赖以上升的良好通道,使其成为有效的找矿标志。岩墙群在一个造山旋回可以贯穿始终,对于再造区域地质演化具有十分重要的意义。本文通过野外踏勘及样品采集,查明脉岩群在工作区的空间展布,对于出露较好的地区,进行大比例尺填图,并对构造接触部位进行素描。通过认识脉岩群岩石组合特征、与围岩接触关系、岩石地球化学特征及同位素年代学特征,分析脉岩群形成时代,结合前人对脉岩群的研究资料,综合探讨该区脉岩群形成大地构造环境以及与矿产的关系。得出以下几点认识:①研究区岩墙群广泛发育,大多呈北西向展布,与围岩呈顺层侵入接触关系。区内岩墙群均产出于奥陶系以及奥陶系以前的地质体,并且种类繁多,中-基性、酸性以及超镁铁质岩墙群均有分布。②中基性岩墙群岩石地球化学特征为高钾质的钙碱性拉斑玄武岩系列,酸性墙群具有过铝质、富硅、低镁、低钙、高钾和钠的岩石化学特点,属于钙碱性岩墙群。③研究区岩墙群捕获的锆石大多集中在460Ma和480Ma两个年龄段,其成岩结晶年龄为都集中在430Ma-440Ma之间。捕获锆石的时间段正是区域上岩浆活动的高峰期,能与区域上的两期岩浆活动对应起来。岩墙群的结晶成岩年龄近一致,形成于早志留世,这与宽谱系岩墙群形成时代一致相对应,为该地区岩墙群符合宽谱系岩墙群的特征提供了年代学证据。④岩墙群形成于碰撞后拉伸环境中。结合年代学特征,早志留世时期中祁连板块和北祁连板块俯冲造山作用结束之后,该区域进入相对稳定阶段,然后逐渐进入后碰撞(后造山)阶段,这一时期整个祁连地区正处于由俯冲造山向碰撞造山的转换时期。研究区宽谱系岩墙群的出现标志着俯冲造山作用的结束。
[Abstract]:Intrusive rocks can be located at different crustal levels, and their emplacement mechanism is complex, which is often regarded as the most direct geological symbol of the rigidity and paleo-stress state of continental plate, and also an important symbol of lithosphere (or crust) mantle extension. And the important symbol of the restoration and reconstruction of the palaeo-plate. As the representative of the primary magma, the dikes are filled in the supply channels of volcanoes or intrusions, and are used to reverse the material composition and the history of magma exhalation in the source area. The rock dike group is filled in some kind of structural fracture, and its special spatial configuration can reflect the tectonic stress field at that time, meanwhile, the fissure filled by the rock wall group is also a good way for the ore-forming fluid to rise, which makes it an effective prospecting mark. The dike group can run through a orogenic cycle all the time, which is of great significance to the reconstruction of regional geological evolution. In this paper, through field survey and sample collection, the spatial distribution of dike groups in the working area is found out, and the large-scale mapping of the well exposed areas is carried out, and the structural contact parts are sketched. Based on the understanding of rock assemblage characteristics, contact relationship with surrounding rock, rock geochemical characteristics and isotopic chronological characteristics of vein rock group, the forming age of vein rock group is analyzed, and combined with previous research data of vein rock group, The formation of geotectonic environment and its relationship with mineral resources in the dike-rock groups in this area are discussed in this paper. The conclusions are as follows: (1) the rock dikes in the study area are widely developed, most of which are distributed in the northwest direction, and the relation between the dike groups and the surrounding rock is bedding intrusive contact. All the rock dikes in the area occur in Ordovician and previous Ordovician geological bodies, and there are a variety of medium-to-basic types. The acidic and ultramafic dyke groups are distributed. 2 the basic dyke group is characterized by high potash calc-alkaline tholeiite series, and the acidic wall group is characterized by superaluminous, silicon-rich, low-magnesium and low-calcium, and the other is characterized by high potash calc-alkaline tholeiite series. The petrochemical characteristics of high potassium and sodium belong to calc-alkaline dyke group. 3 most of the zircon captured by the rock wall group in the study area are concentrated in 460Ma and 480Ma ages, and their diagenetic crystallization ages are between 430Ma-440Ma. The time period during which zircon is captured is the peak of magmatic activity in the region, which corresponds to two periods of magmatic activity in the region. The crystalline diagenetic age of the dike group is nearly the same, which was formed in the early Silurian, which corresponds to the forming age of the broad-spectrum dyke group. It provides chronological evidence for the characteristics of the rock dikes in this area in accordance with the broad spectrum rock dikes. 4 the dikes are formed in the post-collision extensional environment. Combined with the chronological characteristics, after the end of the subduction orogeny of the Qilian plate and the North Qilian plate during the early Silurian period, the area entered a relatively stable stage and then gradually entered the post-collision (post-orogenic) stage. During this period, the whole Qilian area is in the transition period from subducted orogenic to collisional orogenic. The appearance of broad spectrum dykes in the study area marks the end of subduction orogeny.
【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】：P588.12

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