[论文解读] The Minerageny of Two Groups of Zircons from Plagioclase- Amphibolite of Mayuan Group in Northern Fujian

Xuezhao Bao, Xiaochun Gan|ArXiv.org|Jul 23, 2007

Geological and Geochemical Analysis参考文献 3被引用 4

一句话总结

本研究通过整合锆石形态、U-Th-Pb年代学、化学带状结构及微区拉曼光谱技术，识别并区分了闽北斜长石角闪岩中岩浆成因与变质成因锆石。关键发现表明，岩浆成因锆石因荧光杂质及反带状结构，其拉曼光谱背景呈高倾斜趋势，且峰值强度由核至边呈反向变化；而变质成因锆石则表现出低水平的平坦背景及相反的趋势，从而实现可靠的成因判别。

ABSTRACT

Zircons can crystallize in a wide range of physical and chemical conditions. At the same time, they have high stability and durability. Therefore zircons can grow and survive in a variety of geological processes. In addition, the diffusivity of chemical compositions in their crystals is very low. Consequently,we can trace back the evolution history of the planetary materials containing zircon with zircon U-Th-Pb geochronology and geochemistry studies. However, this depends on our ability to decipher its genesis, namely magmatic or metamorphic origins. In this paper, magmatic and metamorphic zircons were found from plagioclase-amphibolite samples. Their geneses have been determined by zircon morphology, chemical composition zonations and geological field setting combined with their zircon U-Th-Pb ages. We have found obvious differences in micro-scale Raman spectra between these magmatic and metamorphic zircons. The magmatic zircons exhibit a high sloping background in their Raman spectra, but the metamorphic zircons exhibit a low horizontal background in their Raman spectra, which suggest that the magmatic zircons may contain a much higher concentration of fluorescent impurities than the metamorphic zircons. Moreover, reverse variation trends in Raman spectrum peak intensities from core to rim of a crystal between the magmatic and metamorphic zircons have been found. We think that this can be attributed to their reverse chemical composition zonations. These differences can be used to distinguish magmatic and metamorphic zircons.

研究动机与目标

• 确定闽北麻源组斜长石角闪岩中两类锆石的成因（岩浆成因或变质成因）。
• 通过厘清复杂变质地质环境中锆石的成因，评估锆石U-Th-Pb年代学的可靠性。
• 探讨拉曼光谱作为基于光谱特征区分锆石成因的工具的潜力。
• 将锆石形态、化学带状结构与拉曼光谱特征与地质背景及年龄数据相关联。

提出的方法

• 对锆石颗粒开展U-Th-Pb年代学分析，以确定结晶年龄。
• 利用阴极发光（CL）成像与电子探针技术，分析锆石形态及内部带状结构。
• 对锆石核部与边部分别进行微区拉曼光谱分析，以评估其振动光谱特征。
• 对比岩浆成因与变质成因锆石的拉曼光谱，重点关注背景强度与峰值强度由核至边的变化趋势。
• 结合地质野外观察与矿物组合，约束其构造地层背景。
• 利用反向化学带状结构作为诊断性特征，解释光谱差异。

实验结果

研究问题

• RQ1 麻源组角闪岩中锆石的形态与化学带状结构有何显著特征？
• RQ2 岩浆成因与变质成因锆石在微区拉曼光谱上存在何种差异？
• RQ3 拉曼光谱背景强度与峰值强度由核至边的变化趋势是否能可靠地区分锆石成因？
• RQ4 锆石化学带状结构与拉曼光谱特征之间存在何种关系？
• RQ5 U-Th-Pb年龄与地质背景如何支持对两类锆石成因（岩浆或变质）的判断？

主要发现

• 岩浆成因锆石在拉曼光谱中表现出高倾斜背景，表明其荧光杂质含量高于变质成因锆石。
• 变质成因锆石显示低水平、平坦的拉曼光谱背景，暗示其杂质含量较低。
• 岩浆成因锆石在由核至边的光谱中观察到峰值强度呈反向变化趋势，与反向化学带状结构相关。
• 相比之下，变质成因锆石表现出一致或相反的强度趋势，与正常带状或无带状结构一致。
• 拉曼光谱特征与反向带状结构的结合提供了一种可靠方法，用于区分岩浆成因与变质成因锆石。
• 本研究证实，通过形态、地球化学与拉曼光谱的综合分析，可可靠地确定锆石成因。