东天山喀拉塔格火山岩地球化学特征及其地质意义

发布时间：2018-11-03 19:20

【摘要】：东天山造山带是中亚造山带的重要组成部分,显生宙期间经历了复杂的演化过程,喀拉塔格火山岩出露于东天山哈密以南的大黑山地区,前人工作相对比较薄弱,对其进行系统的岩石学和地球化学研究对恢复东天山构造演化历史有重要意义。本文在系统总结前人研究资料的基础上,以喀拉塔格火山岩为研究对象,通过详细的野外实地考察,系统的岩石学、地球化学、同位素分析,重新厘定了喀拉塔格地区火山岩的岩石组合和地层序列特征,论证了喀拉塔格火山岩的岩石成因和构造属性,揭示了其对古天山洋和天山造山带演化的重要意义,并取得以下成果(1)喀拉塔格火山岩形成的构造环境:喀拉塔格火山岩包括玄武岩、安山岩、英安岩、流纹岩一系列岩石,以中性火山岩为主,总体具有钙碱性系列趋势,稀土元素球粒陨石标准化配分图解显示右倾型和平坦型的特征,微量元素原始地幔标准化图解中显示相对富集大离子亲石元素(Rb,Ba,Th,Pb),相对亏损高场强元素(Nb,Ta,Ti),负的εNd(t)和古老的继承锆石均说明喀拉塔格火山岩形成于陆缘弧环境。(2)喀拉塔格火山岩演化过程和源区特征:东天山喀拉塔格火山是在天山古老基底上形成的陆缘岛弧,地幔楔中尖晶石二辉橄榄岩在受熔体交代下发生部分熔融形成中-基性岩浆,初始岩浆经历结晶分异过程演化形成中-酸性岩浆,岩浆上升就位中受到过一定程度的地壳混染。(3)通过总结前人研究区域地质资料,特别是喀拉塔格年代学资料,将喀拉塔格火山岩形成时代限制在晚古生代石炭世,结合区域内广泛出露早晚石炭世岛弧性质的火山岩和侵入岩,至少古天山洋在早石炭世依然没有闭合,依然处于俯冲环境,可能一直持续至晚石炭世。喀拉塔格火山岩是中天山弧组成部分,为中天山弧的演化提供了陆缘弧火山岩方面的证据,同时为东天山广泛分布的古生代火山岩(特别是石炭系火山岩)的整体演化特征提供了新的地质证据。
[Abstract]:The East Tianshan orogenic belt is an important part of the Central Asian orogenic belt. During the Phanerozoic period, the Karatagh volcanic rocks emerged in Dashan region, south of Hami in the East Tianshan Mountains, and the previous work was relatively weak. The systematic study of petrology and geochemistry is of great significance to the restoration of the history of tectonic evolution of the East Tianshan Mountains. On the basis of summarizing the previous research data systematically, this paper takes Karatag volcanic rock as the research object, through the detailed field investigation, systematic petrology, geochemistry, isotope analysis, The rock assemblages and stratigraphic sequence characteristics of volcanic rocks in Karatagh area are redefined, the petrogenesis and tectonic properties of Karatagic volcanic rocks are demonstrated, and the significance of these characteristics to the evolution of paleoTianshan ocean and Tianshan orogenic belt is revealed. The main results are as follows: (1) the tectonic environment formed by Karatag volcanic rocks includes basalt, andesite, rhyolite and a series of rocks, mainly neutral volcanic rocks, with a general trend of calc-alkaline series. The normalized partition diagram of chondrites of rare earth elements shows the characteristics of right dip and flat type, and the trace element primitive mantle standardization diagram shows relative enrichment of large ion lithophile elements (Rb,Ba,Th,Pb) and relative depletion of high field strength elements (Nb,). (Ta,Ti), Both the negative 蔚 Nd (t) and the ancient inherited zircon indicate that the Karatag volcanic rocks were formed in the continental margin arc environment. (2) the evolution process and source characteristics of the Karatag volcanic rocks: the Karatag Volcano in the East Tianshan Mountains is located in the ancient basement of Tianshan Mountains. The island arc formed on the continental margin, The spinel lherzolite in the mantle wedge is partially melted to form a meso-basic magma under the melt metasomatism, and the initial magma evolves through the crystallization differentiation process to form the intermediate-acid magma. Magmatic uplift and emplacement have been contaminated by crustal mixing to a certain extent. (3) by summarizing the regional geological data of previous studies, especially the Karatag chronology data, the formation of Karatagic volcanic rocks was limited to the late Paleozoic Carboniferous, and the time of formation of Karatagic volcanic rocks was limited to the late Paleozoic Carboniferous. In combination with the volcanic rocks and intrusive rocks which are widely exposed in the early Carboniferous, at least the Paleo-Tianshan Ocean has not been closed in the early Carboniferous, is still in a subduction environment, and may last until the late Carboniferous. The Karatag volcanic rocks are part of the middle Tianshan arc, which provides evidence for the evolution of the middle Tianshan arc in the continental margin. It also provides new geological evidence for the evolution characteristics of Paleozoic volcanic rocks (especially Carboniferous volcanic rocks) widely distributed in the East Tianshan Mountains.
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.14

【参考文献】