大兴安岭中段索伦地区白音高老组火山岩岩石成因及构造背景

发布时间：2018-10-14 10:26

【摘要】：本文选取大兴安岭主脊中段索伦地区的白音高老组火山岩为研究对象,通过野外实测剖面和路线地质调查,确定了早白垩世白音高老期火山岩的岩石类型和组合特征,厘定了火山岩的形成时代,分析了火山岩的地球化学特征,并结合火山岩锆石Hf同位素特征,研究了火山岩岩石成因及其构造背景,所获认识对于揭示大兴安岭火成岩的构造-岩浆演化过程提供了新的证据。白音高老组火山岩主要岩性多为灰色、灰绿流纹岩、流纹质岩屑晶屑角砾凝灰熔岩、流纹质晶屑凝灰岩、英安质晶屑凝灰熔岩以及小范围的沉凝灰岩,以流纹岩为主。锆石LA-ICPMS U-Pb测年结果显示,四件火山岩样品形成时代分别为126.7±1.5Ma、127.8±2.8Ma、124.6±2.2Ma、123.1±1.1Ma,结果表明白音高老组火山岩形成于128~123Ma之间,时代为早白垩世。火山岩地球化学特征显示,白音高老组火山岩Si O2含量在69.63~79.94%之间,Na2O含量与K2O含量之和为6.42~9.35%,Na2O/K2O的比值为0.12~1.33,相对富钾,里特曼指数小于3。在TAS图解中,样品大都落在了亚碱性系列的流纹岩范围内,在Si O2-K2O图解上,样品全数落入高钾钙碱性系列范围中。A/CNK值为1.02~1.29,为准铝质-过铝质系列。火山岩主量元素总体表现为高硅、富碱,富铝及贫铁、钙、镁的特征,为准铝质-过铝质高钾钙碱性岩石。在球粒陨石标准化稀土元素配分图中分配模式从左到右逐渐降低,全部样品均表现为明显的Eu负异常。ΣREE的值为61×10-6~208×10-6,(La/Yb)N值范围为3.57~13.27,δEu值为0.21~0.75。火山岩微量元素原始地幔标准化蛛网表现出曲线总体右倾特点,显示为该组火山岩大离子亲石元素Rb、Th、U、K等显著富集、高场强元素Nb、Ta、Ti等强烈亏损,与大兴安岭地区低Ba-Sr流纹岩的特性大体相同,是壳源岩浆的典型特征。通过Hf同位素研究表明,正值εHf(t)与TMD2(828~439Ma)揭示火山岩岩浆来源于新元古代-显生宙期间从亏损地幔新增生的年轻地壳物质的部分熔融。研究区内白音高老组火山岩形成于古太平洋板块俯冲作用引起的岩石圈拆沉减薄有关的伸展构造体制。
[Abstract]:In this paper, the types and assemblages of the early Cretaceous volcanic rocks in the early Cretaceous are determined by taking the volcanic rocks of the Baiyingao formation in the middle part of the main ridge of the Daxing'an Mountains as the research objects. The forming age of volcanic rocks is determined, the geochemical characteristics of volcanic rocks are analyzed, and the genesis and tectonic setting of volcanic rocks are studied in combination with the Hf isotopic characteristics of volcanic zircon. The results provide new evidence for revealing the tectonic-magmatic evolution of igneous rocks in the Daxinganling Mountains. The volcanic rocks of the Baiyingao Lao formation are mainly gray, grey-green rhyolite, fluid-grained crushed-breccia tuff lava, fluid-grain tuff, dolomite chrysotile tuff lava and a small range of sedimentary tuff, mainly rhyolite. The results of zircon LA-ICPMS U-Pb dating show that the age of formation of the four volcanic samples is 126.7 卤1.5 Ma, 127.8 卤2.8 Ma, 124.6 卤2.2 Ma, 123.1 卤1.1 Ma, respectively. The results show that the volcanic rocks of the old formation formed between 128~123Ma and the age is early Cretaceous. The geochemical characteristics of volcanic rocks show that the content of Si O 2 is between 69.63 and 79.94%, and the sum of Na2O content and K 2O content is 6.42 ~ 9.35%. The ratio of Na _ 2O / K _ 2O is 0.12 ~ 1.33, relatively rich in potassium, and the Ritman index is less than 3. In the TAS diagram, the samples mostly fall within the rhyolite range of sub-alkaline series, and on the Si O2-K2O diagram, all samples fall into the range of high-potassium calc-alkaline series. The A/CNK value is 1.02 ~ 1.29, quasi-aluminite-peraluminous series. The main elements of volcanic rocks are characterized by high silicon, high alkali, rich aluminum and poor iron, calcium and magnesium, which are quasi-aluminum-peraluminous and high-potassium calc-alkaline rocks. The distribution pattern of chondrites decreased from left to right, and all samples showed obvious negative Eu anomalies. 危 REE was 61 脳 10 ~ (-6) N = 208 脳 10 ~ (-6), (La/Yb) N = 3.57 ~ (13. 27), 未 Eu = 0.21 ~ (0.75). The trace elements of volcanic rocks show the characteristics of overall right-dip curve, showing that the volcanic rocks are enriched in large ion lithophile elements, such as Rb,Th,U,K, and the high field strength elements such as Nb,Ta,Ti are severely depleted. The characteristics of low Ba-Sr rhyolite are similar to those of Daxinganling area and are typical characteristics of crust-derived magma. Hf isotopic studies show that the positive 蔚 Hf (t) and TMD2 (828~439Ma) reveal partial melting of the volcanic magma from the young crustal material newly accreted from the depleted mantle during the Neoproterozoic to Phanerozoic period. The volcanic rocks of the Baiyinggaolao formation in the study area were formed in the extensional tectonics related to the lithospheric delamination and thinning caused by the subduction of the paleo-Pacific plate.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.14

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