大兴安岭中段索伦地区玛尼吐组火山岩年代学、地球化学及其构造背景

发布时间：2018-04-19 02:33

  本文选题：大兴安岭 + 锆石U-Pb年龄　； 参考：《吉林大学》2017年硕士论文

【摘要】：论文选取大兴安岭中段索伦地区广泛发育的玛尼吐组火山岩为研究对象,在结合前人研究成果的基础上,进一步查证了玛尼吐组火山岩的岩石组合特征与分布规律,厘定了火山岩形成的时代,分析了火山岩的地球化学特征,探讨了火山岩的岩浆源区性质、岩石成因以及构造动力学背景,其成果为大兴安岭中段晚侏罗世-早白垩世的火山活动时间及其构造演化历史提供了新的资料。1.火山岩的岩石学特征火山岩以安山岩,粗安岩和英安岩、安山质凝灰熔岩为主,见少量安山质凝灰岩、英安质凝灰岩,其间夹有零星沉凝灰岩。其中安山岩是该组火山岩的主要组成部分。2.玛尼吐组火山岩的年代学特征锆石LA-ICPMS U-Pb测年结果显示,三件安山岩样品形成时代分别为132±2Ma、130±3Ma、130±1Ma,表明研究区内玛尼吐组火山岩主要形成于早白垩世。3.火山岩的地球化学特征SiO_2含量介于52.11-69.63%之间。在TAS图解中,分别落入玄武安山岩、粗面玄武质安山岩、粗安岩、粗面岩区域,为高钾钙碱性弱过铝质岩石。总体表现为富碱,及贫钙、镁的特征。微量元素特征显示富集大离子亲石元素(LILE)K、Rb、Th和轻稀土元素;亏损高场强元素(HFSE)Nb、Ta、P、Ti。同时微量元素具高Sr(多499)和低Yb(最大值为2.833.6)、Y(多29.9)、和高Sr/Y和低Rb/Sr比值。同时参考各构造环境微量元素对比数值,均显示了弧火山岩的特征。4.火山岩的源区性质及岩浆演化特征研究区玛尼吐期火山岩Rb/Sr比值变化于0.01~0.28之间,平均为0.11,高于原始地幔(0.03)、E-MORB(0.033)、OIB(0.047)的Rb/Sr比值,也低于壳源岩浆(0.5);Th/U比值在2.03~4.40之间,平均为3.34,介于壳源岩石(≈6)与原始地幔之间;εHf(t)值为+9.10±1.10,处于更靠近亏损地幔线的位置。玛尼吐期安山质岩石源区主要为岩石圈地幔的部分熔融,且岩浆形成的过程中受到了流体的改造作用。5.玛尼吐组火山岩形成的构造背景玛尼吐组火山岩形成于岛弧构造环境。该岛弧构造背景的产生可能与受古太平洋板块俯冲作用有关。
[Abstract]:In this paper, the widely developed volcanic rocks of Manitu formation in the middle part of the Daxing'anling Mountains are selected as the research objects. On the basis of the previous research results, the rock assemblages and distribution of the volcanic rocks in the Manitu formation are further verified.The forming age of volcanic rocks is determined, the geochemical characteristics of volcanic rocks are analyzed, and the magmatic origin, petrogenesis and tectonic dynamic background of volcanic rocks are discussed.The results provide new data for the late Jurassic-early Cretaceous volcanic activity time and tectonic evolution history of the central Daxing'anling Mountains.The petrological characteristics of volcanic rocks are composed of andesite, trachyandite and dacite, andesite tuff, a small amount of anshanian tuff and dolomite tuff, which are intercalated with sporadic tuff.Andesite is the main component of volcanic rocks in this group.Zircon LA-ICPMS U-Pb dating of volcanic rocks in Manitu formation shows that the age of formation of the three andesite samples is 132 卤2 Ma, 130 卤3 Ma, 130 卤1 Ma, respectively, indicating that the volcanic rocks of the Manitu formation in the study area were mainly formed in the early Cretaceous. 3.The SiO_2 content of volcanic rocks is between 52.11-69.63%.In the TAS diagram, they fall into Black Tortoise andesite, rough Black Tortoise andesite, coarse andesite and rough rock area, which are high potassium calc alkaline weak peraluminous rocks.The general performance is rich in alkali, as well as the characteristics of poor calcium and magnesium.The characteristics of trace elements show that they are enriched in large ion lithophile element LILEN Ku RbN Th and light rare earth elements, and are depleted in high field strength elements such as HFSEE, NbSe, NbSe, Pnb, Th, Th, Th, Th and Th.At the same time, the trace elements have high Sr (more than 499) and low Yb (the maximum value is 2.833.6) (more than 29.9%), and high Sr/Y and low Rb/Sr ratio.At the same time, the characteristics of arc volcanic rocks are shown by referring to the comparative values of trace elements in each tectonic environment.The Rb/Sr ratio of the volcanic rocks in Manitu period varies from 0.01 to 0.28, with an average of 0.11, which is higher than the Rb/Sr ratio of 0.03 and E-MORBN 0.033 OIBN 0.047 in the primitive mantle, and is also lower than that of the crust-derived magma in the range of 2.034.40.The average value is 3.34, which is between crust-derived rocks (鈮，

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