黑龙江省同江—抚远地区晚白垩世花岗质岩的成因及构造意义

发布时间：2018-03-29 05:11

本文选题：黑龙江省同江—抚远地区　切入点：花岗质岩石　出处：《吉林大学》2015年硕士论文

【摘要】：本文以黑龙江省东北部同江—抚远地区的“晚印支期”花岗质岩石作为研究对象，在详细的野外地质调查和室内岩相学研究的基础上，通过锆石LA-ICP-MSU-Pb定年、全岩地球化学分析和锆石Hf同位素测试结果，结合区域地质资料对这些花岗质岩石的形成时代、岩浆源区性质及其构造意义进行了讨论。同江—抚远地区的花岗质岩石主要出露在街津口、勤得利和抚远三个地区，在矿物组成上这些花岗质岩石极为相近，主要岩石类型为含黑云母和/或角闪石的花岗闪长岩和花岗闪长斑岩，角闪石的普遍出现表明它们属于I型花岗岩的成因类型。在所选择的8件锆石LA-ICP-MS U-Pb定年样品中，锆石多呈自形-半自形晶，普遍发育振荡环带，Th/U比值较高（主要为0.31~0.83），指示其为岩浆成因，定年结果代表了岩石的形成时代。从定年结果来看，它们的形成时代基本一致，均为晚白垩世（89.5~94.8Ma）。在主量元素特征上，研究区花岗质岩石均属于准过铝-弱过铝质的高钾-中钾钙碱性系列，总体显示出富SiO2, K2O和贫TFe2O3, MgO, CaO以及过渡族元素的地球化学特征。暗示其原始岩浆应起源于陆壳基性-中基性火成岩的部分熔融。不同样品中的主要氧化物与SiO2含量存在相同的变化趋势，暗示它们具有同源岩浆特征。从稀土元素的组成以及稀土配分模式上看，研究区花岗质岩石的总体特征相似，表现为富含轻稀土元素、亏损重稀土元素、铕异常较弱，重稀土分馏中等且相对含量较高。从微量元素组成与原始地幔标准化蛛网图上来看，，这些花岗质岩石均表现为Nb、Ta以及Ti的亏损，其Th/U比值为4.22~9.53，平均为6.10，显示出明显的壳源特征。结合锆石Hf同位素特征（Hf（t）=+4.45~+9.01、二阶段Hf模式年龄（TDM2）＝583~875Ma），认为研究区花岗质岩石的源区岩石应为基性-中基性火成岩，原始岩浆起源于深部陆壳新增生的基性-中基性火成岩的部分熔融。根据区域上存在的晚白垩世火成岩的组合特征及其分布规律，结合区域构造演化历史对研究区花岗质岩石形成的构造背景进行了讨论。认为同江—抚远地区晚白垩世花岗质岩石形成于大陆边缘的构造背景，其动力学机制与古太平洋板块向东亚大陆之下的正向俯冲作用有关。
[Abstract]:In this paper, the granitic rocks of the late Indosinian period in Tongjiang-Fuyuan area, northeast of Heilongjiang Province, are taken as the research objects. On the basis of detailed field geological surveys and laboratory petrographic studies, zircon LA-ICP-MSU-Pb dating is used to determine the age of the granitic rocks. The geochemistry analysis and zircon HF isotopic measurements are combined with regional geological data to discuss the formation age, magmatic origin and tectonic significance of these granitic rocks. The granitic rocks in Tongjiang-Fuyuan area are mainly exposed in the three areas of Jiejinkou, Guanli and Fuyuan. The mineral composition of these granitic rocks is very similar. The main rock types are granodiorite with biotite and / or hornblende and granodiorite porphyry. The common occurrence of amphibole indicates that they belong to the genetic type of I-type granite. Among the 8 selected zircon LA-ICP-MS U-Pb dating samples, the zircons are mostly automorphic and semi-automorphic, and there is a high ratio of Th / U (mainly 0.31 ~ 0.83) in the oscillating ring zone, indicating that the zircon is of magmatic origin. The dating results represent the age of formation of rocks, and the age of their formation is basically the same as that of the late Cretaceous. The granitic rocks in the study area belong to the high and medium potassium calc-alkaline series of quasi-peraluminum-weak peraluminous elements. The geochemical characteristics of Sio _ 2, K _ 2O and poor TFE _ 2O _ 3, MgO, CaO and transition group elements are shown. It is suggested that the primitive magma originated from the partial melting of continental basic-mesogenic igneous rocks. The main oxides in different samples and SiO2 contents. There is the same trend of change in quantity, From the composition of rare earth elements and the REE distribution pattern, the general characteristics of granitic rocks in the study area are similar, showing that they are rich in light rare earth elements, depleted in heavy rare earth elements, and very weak in europium. The heavy rare earth fractionation is medium and the relative content is high. From the composition of trace elements and the standard spider web diagram of the primitive mantle, these granitic rocks are characterized by the depletion of NB, Ta and Ti. The Th/U ratio is 4.22 ~ 9.53, with an average of 6.10, which shows obvious crustal characteristics. Combined with zircon HF isotopic characteristics (HF) = 4.45 ~ 9.01, the two-stage HF model age of TDM _ 2N _ (583) (875 Ma) shows that the source rocks of the granitic rocks in the study area should be basic-mesogenic igneous rocks, and the source rocks of the granitic rocks in the study area should be basic-mesogenic igneous rocks. The primitive magma originated from the partial melting of the basic-mesogenic igneous rocks newly proliferated in the deep continental crust. According to the assemblage characteristics and distribution of late Cretaceous igneous rocks in the region, Based on the history of regional tectonic evolution, the tectonic background of granitic rock formation in the study area is discussed. It is considered that the late Cretaceous granitic rocks formed in the tectonic setting of continental margin in Tongjiang-Fuyuan area. Its dynamic mechanism is related to the forward subduction of the paleo-Pacific plate beneath the East Asian continent.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121

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