大兴安岭中段五岔沟地区早白垩世花岗质岩石的地球化学特征及其成因

发布时间：2018-04-15 01:03

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

【摘要】：大兴安岭位于中亚造山带东段,以大面积的中生代火成岩分布为主要特征。近年来随着LA-ICPMS、LA-MC-ICPMS等先进实验测试技术的应用,前人对大兴安岭一带花岗质岩石进行了较为细致的研究,取得了大量的成果,但大兴安岭地区中段晚中生代花岗质岩石的研究程度较低,限制了对大兴安岭地区中段晚中生代花岗质岩石的形成时代和成因的认识。本文将大兴安岭中段五岔沟地区晚中生代花岗质岩石作为研究对象,在区域地质调查为基础上,对大兴安岭中段五岔沟地区晚中生代花岗质岩石进行了锆石U-Pb年代学、Lu-Hf同位素和全岩地球化学研究,从而厘定了花岗质岩石的形成时代,讨论了大兴安岭中段五岔沟地区晚中生代花岗质岩石岩石成因以及相关的地球动力学背景。本文对五岔沟地区7件花岗质岩石样品进行LA-ICP-MS锆石U-Pb同位素分析,测试分析结果显示,锆石多为自形-半自形,呈粒状或短柱状,发育清晰的振荡生长环带,具有较高的Th/U比值(0.63~1.84),暗示其岩浆成因。样品的206Pb/238U加权平均年龄分别为133±1Ma、134±1Ma、127±1Ma、131±2Ma、132±1Ma、129±1Ma、129±2Ma,表明大兴安岭中段五岔沟地区花岗质岩石的形成时代为早白垩世。岩石地球化学结果显示,大兴安岭中段五岔沟地区花岗质岩石普遍具有高硅(SiO2=65.21%~78.43%,平均71.82%),富碱(K2O+Na2O=6.77%~9.66%,平均8.22%),相对低CaO(0.10%~2.55%),MgO(0.07%~1.30%),P2O5(0.01%~0.20%)的特征,A/CNK值介于0.94~1.51,主体为准铝质-弱过铝质岩石;微量元素表现出轻稀土富集的“右倾”配分模式,以及不同程度的负Eu异常,富集Rb、Th、U、K等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素,显示大兴安岭中段五岔沟地区花岗质岩石为I型花岗岩;锆石原位Hf同位素分析表明,大兴安岭中段五岔沟地区花岗质岩石的176Hf/177Hf比值分布于0.282833~0.282930,εHf(t)值介于4.9~8.4,锆石Hf二阶段模式年龄(654~874Ma)。通过年代学、地球化学以及Hf同位素研究,并结合区域地质资料及同时期火成岩物质的时空展布规律,认为大兴安岭中段五岔沟地区花岗质岩石的源区为新元古代期间新增生的地壳物质的部分熔融,其形成与古太平洋板块俯冲作用背景下的伸展环境有关。
[Abstract]:The Daxingan Mountains are located in the eastern part of the Central Asian orogenic belt and are characterized by large area distribution of Mesozoic igneous rocks.In recent years, with the application of LA-ICPMS-LA-MC-ICPMS and other advanced experimental and testing techniques, the granitic rocks in the Daxing'anling area have been studied in detail and a great deal of achievements have been made.However, the study of late Mesozoic granitic rocks in the middle part of Daxinganling area is relatively low, which limits the understanding of the formation age and genesis of late Mesozoic granitic rocks in the middle part of Daxinganling area.In this paper, the late Mesozoic granitic rocks in Wuchaigou area, central Daxing'anling Mountains, are taken as the research objects, and based on the regional geological survey,The late Mesozoic granitic rocks in the Wuchaigou area of the central Daxinganling Mountains have been studied by zircon U-Pb geochronology, Lu-Hf isotopic and whole-rock geochemistry, and the formation age of the granitic rocks has been determined.The genesis of late Mesozoic granitic rocks and the related geodynamic background in Wuchagou area of Daxing'anling Mountains are discussed.In this paper, LA-ICP-MS zircon U-Pb isotopic analysis of 7 granitic rock samples in Wuchagou area is carried out. The results show that the zircon is mostly self-semiautomorphic, granular or short columnar, and has a clear oscillatory growth ring.It has a high Th/U ratio of 0.63 ~ 1.84, indicating its magmatic origin.The 206Pb/238U weighted mean age of the samples is 133 卤1 Ma, 134 卤1 Ma, 127 卤1 Ma, 131 卤2 Ma, 132 卤1 Ma, 129 卤1 Ma, 129 卤2 Ma, indicating that the age of granitic rocks in Wuchagou area, Daxing'an Mountains, is early Cretaceous.The petrogeochemical results show that the granitic rocks in the Wuchagou area of the middle part of the Daxing'anling Mountains are generally characterized by high SiO2SiO2 (65.21), with an average of 71.82%, and alkali-rich K2O Na2O6.777.77 with 9.66, with an average of 8.2220, and a relatively low CaO0.102.55MgO0.07 (1.30P2O5 / 0.01 0.20K). The ACNK value of the main body is between 0.941.551 and 0.941.51and the main body is aluminum-weakly peraluminous rock, which is characterized by the relative low CaO0.102.55MgO0.07mg _ 2O _ (0.07) mg _ 2O _ (0.07) and the relative low CaO0.102.55mg _ 2O _ (0.07) mg _ 2O _ (0.07)).The trace elements show a "right-dip" distribution pattern of LREE enrichment, and negative EU anomalies to varying degrees, enriched in large ion lithophile elements, such as Rbtr, Th, U, K, and depleted high field strength elements, such as NbTa-Ta-Ti-P, etc.The results show that the granitic rocks in Wuchagou area are I-type granites and zircon in-situ HF isotopic analysis shows that the 176Hf/177Hf ratio of granitic rocks in Wuchagou area is 0.282833 0.282930 with 蔚 Hftand between 4.9 and 8.4, and the zircon HF two-stage model age is 6540.874MaHU.By means of geochronology, geochemistry and HF isotope studies, combined with regional geological data and temporal and spatial distribution of igneous materials in the same period,It is considered that the source region of granitic rocks in Wuchagou area of Daxing'anling Mountains is the partial melting of newly accretionary crustal materials during the Neoproterozoic, which is related to the extensional environment in the background of paleo-Pacific plate subduction.
【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】：P588.1

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