大兴安岭东北部红花尔基地区古生代花岗岩年代学、元素、Hf同位素地球化学特征

发布时间：2018-05-23 12:41

  本文选题：年代学 + Hf同位素　； 参考：《吉林大学》2016年硕士论文

【摘要】：研究区在地理位置上位于大兴安岭北段东坡,在大地构造位置上位于兴蒙造山带东段的兴安地块内。本文通过对红花尔基地区古生代花岗质岩石的锆石U Pb年代学、元素地球学及锆石Hf同位素特征的研究,确定了古生代花岗岩的形成时代,分析了古生代花岗岩的岩石学和地球化学特征,探讨了古生代花岗岩的岩浆源区性质、岩石成因以及形成时的构造背景,其成果对于揭示大兴安岭地区大地构造演化具有一定意义。笔者从研究区古生代花岗岩中选取了2个样品,对其进行了LA-ICP-MS锆石U-Pb同位素年龄的测定,样品中的锆石具有振荡生长环带和较高的Th/U比值,揭示其岩浆成因,可以反映岩石的形成时代。通过分析测试可将红花尔基地区古生代花岗岩划分为早石炭世碱长花岗岩(348.9±2.1 Ma)与晚石炭世二长花岗岩(310.5±1.3 Ma)两期。早石炭世碱长花岗岩主量元素具有高SiO2,富K2O,TFeO值高,贫Al2O3,贫MgO,贫CaO的特征;稀土配分呈现具强烈负铕异常的“海鸥型”分布型式;微量元素蛛网图上呈现富集Rb、Th、U、K和强烈亏损Ba、Sr、P、Ti的特点;锆石饱和温度高,在花岗岩成因判别图解中落入A型花岗岩区域,具有A型花岗岩的特征。晚石炭世二长花岗岩具有高SiO2,高Na2O,低P2O5的特征,且其P2O5含量随着SiO2含量的升高而下降;除两个样品的铝饱和指数ACNK略大于1.1外,其余样品的铝饱和指数均小于1.1,锆石饱和温度低于典型A型花岗岩的形成温度(850℃),在花岗岩成因判别图解中落入分异的I型花岗岩区域,具有I型花岗岩的特征。结合正的εHf(t)值和二阶段模式年龄判断研究区古生代花岗岩来源于中新元古代从亏损地幔中新增生来的地壳物质的部分熔融。结合构造判别图解、同时代大兴安岭地区花岗岩特征及区域构造背景可判断红花尔基地区古生代花岗岩形成于兴安地块与松嫩地块碰撞伸展的转换过程中。
[Abstract]:The study area is located in the eastern slope of the northern Daxing'an Mountains and in the Xingan block in the eastern part of the Xingmeng orogenic belt. Based on the study of U-Pb zircon dating, elemental geology and zircon HF isotopic characteristics of Paleozoic granitic rocks in the Honghuaerji area, the formation age of Paleozoic granites has been determined in this paper. The petrological and geochemical characteristics of Paleozoic granites are analyzed, and the magmatic origin, petrogenesis and tectonic setting of Paleozoic granites are discussed. The results are of significance for revealing the tectonic evolution in the Daxinganling area. Two samples were selected from Paleozoic granites in the study area and their LA-ICP-MS zircon U-Pb isotopic ages were determined. The zircon in the sample has oscillating growth ring and high Th/U ratio, which reveals the magmatic origin. It can reflect the age of rock formation. The Paleozoic granites in the Honghuaerji area can be divided into two periods: early Carboniferous alkali feldspar granite (348.9 卤2.1 Ma) and late Carboniferous monzogranite (310.5 卤1.3 Ma). The main elements of the early Carboniferous alkali feldspar granite are characterized by high SiO2, high K _ 2O-rich TFeO value, poor Al _ 2O _ 3, poor MgO and poor CaO, and the rare earth distribution shows a "seagull type" distribution pattern with strong negative europium anomaly. The trace element cobwebs show the characteristics of enrichment of RbSH-UUK and strong depletion of Bao-Sr-Pa-Ti, and the high saturation temperature of zircon, which falls into A-type granite area in the diagenetic diagram of granite genesis, and has the characteristics of A-type granite. The late Carboniferous monzogranite has the characteristics of high Sio _ 2, high Na _ 2O and low P2O5, and its P2O5 content decreases with the increase of SiO2 content, except for two samples, the Al saturation index (ACNK) is slightly greater than 1.1. The aluminum saturation index of the other samples is less than 1.1, and the zircon saturation temperature is lower than the formation temperature of typical A-type granite at 850 鈩，

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