Electron paramagnetic resonance signature of rock-forming blue quartz from the Albești (Romania) granite

IF 1.4 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Alexandra C. Joita, Daniela Ghica, Mariana Stefan, Stefan Bulat, Adrian I. Pantia
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引用次数: 0

Abstract

The ca. 480 Ma Albești granite (Southern Carpathians, Romania) is characterized by the presence of color zoned blue quartz grains, and is part of the rather extensive European Cambro-Ordovician blue quartz landscape. The color is heat sensitive, fading at temperatures as low as 300℃, inconsistent with the thermally stable, light scattering, nanometric rutile/ilmenite inclusions cited in literature. Extensive X- and Q-band electron paramagnetic resonance (EPR) investigations were carried out, searching for distinctive features of the Albești quartz that are directly or indirectly involved in the generation of the blue coloration. The analyzed quartz grains were extracted from three granite samples of varying coloration and anisotropy, and the quartz from each rock sample was further separated into colored and colorless fractions. The paramagnetic E’ and [AlO4]0 centers, as well as Mn2+ ions localized in traces of amorphous associated minerals at grain boundaries or fissure planes, were observed in all quartz samples. Broad EPR lines associated with the presence of magnetic clusters were observed in the spectra of the white quartz sample and the corresponding colorless one. Isochronal annealing up to 500℃ induced the correlated recombination of the E’ and [AlO4]0 centers, the strong decrease of the Mn2+ spectrum and the formation of a minority iron oxide phase at the grain boundaries and/or fissure planes. The EPR signature was similar for the colored and the corresponding colorless quartz samples, before and after annealing, showing that the heat sensitive coloration of the Albești quartz does not directly involve the presence of paramagnetic defects and/or minority magnetic phases.

Abstract Image

阿尔贝蒂(罗马尼亚)花岗岩成岩蓝石英的电子顺磁共振特征
约 480 Ma 的阿尔贝希蒂花岗岩(罗马尼亚喀尔巴阡山脉南部)的特点是存在彩色分带的蓝色石英颗粒,它是相当广泛的欧洲寒武-奥陶纪蓝色石英景观的一部分。Albești 花岗岩(罗马尼亚喀尔巴阡山脉南部)的特征是存在彩色带状蓝色石英颗粒,是相当广泛的欧洲寒武-奥陶纪蓝色石英景观的一部分。这种颜色对热敏感,在低至 300℃ 的温度下就会褪色,与文献中提到的热稳定、光散射、纳米金红石/钛铁矿包裹体不符。我们进行了广泛的 X 波段和 Q 波段电子顺磁共振(EPR)研究,寻找阿尔贝蒂石英中直接或间接参与产生蓝色的独特特征。被分析的石英颗粒是从三个不同颜色和各向异性的花岗岩样本中提取的,每个岩石样本中的石英都被进一步分离成有色和无色部分。在所有石英样品中都观察到了顺磁性的 E'和 [AlO4]0 中心,以及在晶粒边界或裂隙面的无定形伴生矿物痕迹中定位的 Mn2+ 离子。在白色石英样品和相应的无色石英样品的光谱中观察到了与磁团存在相关的宽 EPR 线。高达 500℃ 的异步退火会导致 E'和[AlO4]0 中心的相关重组、Mn2+ 光谱的强烈减弱以及在晶界和/或裂隙面形成少数氧化铁相。有色和相应的无色石英样品在退火前后的 EPR 特征相似,这表明 Albești 石英的热敏着色并不直接涉及顺磁缺陷和/或少数磁性相的存在。
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来源期刊
Mineralogy and Petrology
Mineralogy and Petrology 地学-地球化学与地球物理
CiteScore
2.60
自引率
0.00%
发文量
0
审稿时长
1 months
期刊介绍: Mineralogy and Petrology welcomes manuscripts from the classical fields of mineralogy, igneous and metamorphic petrology, geochemistry, crystallography, as well as their applications in academic experimentation and research, materials science and engineering, for technology, industry, environment, or society. The journal strongly promotes cross-fertilization among Earth-scientific and applied materials-oriented disciplines. Purely descriptive manuscripts on regional topics will not be considered. Mineralogy and Petrology was founded in 1872 by Gustav Tschermak as "Mineralogische und Petrographische Mittheilungen". It is one of Europe''s oldest geoscience journals. Former editors include outstanding names such as Gustav Tschermak, Friedrich Becke, Felix Machatschki, Josef Zemann, and Eugen F. Stumpfl.
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