波西米亚微金刚石的形态和拉曼光谱参数:对弹性地温计的影响

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
P. Jakubová, J. Kotková, R. Wirth, R. Škoda, J. Haifler
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引用次数: 2

摘要

在这项工作中,我们将西北波希米亚微金刚石的形态和内部结构与其拉曼光谱参数相结合,来描述和理解它们之间的关系。我们根据弹性理论评估了我们的数据,并讨论了石榴石中金刚石包裹体的弹性地热测量的意义。我们得出的结论是,蓝晶石、石榴石和锆石中包裹的微金刚石在形态和内部结构上不同,这取决于寄主岩石的类型和寄主相。酸性片麻岩中蓝晶石中的单晶金刚石八面体主要表现出向较高波数(升频)的拉曼位移,而中间石榴石-斜辉石岩石中的石榴石和锆石中包裹的单晶和多晶金刚石产生更可变的拉曼移动,包括向较低波数(降频)的位移。这与使用FIB-TEM观察到的金刚石和蓝晶石之间的闭合边界一致,而金刚石和石榴石或锆石之间的界面通常是开放的。此外,由石榴石或锆石主持的金刚石中拉曼位移的较高可变性可能是由复杂的内部结构和其他相的存在引起的。同时,蓝晶石中的金刚石由于热收缩的各向异性而具有相对较高的半峰全宽(FWHM),这反映在T≥1000°C时位错滑移介导的金刚石塑性变形上。使用弹性地质压力计计算了石榴石中金刚石的包埋压力(P陷阱),以测试其与传统热压力计估计的现有峰值压力的兼容性。使用文献中的未应变参考金刚石和自己的测量结果,“降频”金刚石在1100°C的截留温度下分别表现出4.8±0.14和4.99±0.14 GPa的截留压力。这与早期的估计和弹性理论一致,并且不需要任何建议的弹性重置来解释石榴石的升档。我们的数据表明,以石榴石为主体的金刚石的升档与其他金刚石晶粒的接近有关。我们得出的结论是,在弹性气压测量中使用金刚石包裹体应通过仔细评估其内部结构和相关相来支持,并限制为不按该方法的要求出现在团簇中的等距单晶金刚石晶粒。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Morphology and Raman spectral parameters of Bohemian microdiamonds: implications to elastic geothermobarometry
In this work, we combine the morphology and internal structure of northwestern Bohemian microdiamonds with their Raman spectral parameters to describe and understand their relationship. We evaluate our data according to the theory of elasticity and discuss implications for elastic geothermobarometry of diamond inclusions in garnet. We conclude that microdiamonds enclosed in kyanite, garnet and zircon differ in morphology and internal structure depending on the type of the host rock and host phase. Single crystal diamond octahedra in kyanite in the acidic gneiss show predominantly Raman shift towards higher wavenumbers (upshift), while single and polycrystalline diamonds enclosed in garnet and zircon in the intermediate garnet–clinopyroxene rock yield more variable Raman shift including a shift towards lower wavenumbers (downshift). This is consistent with closed boundaries between diamond and kyanite observed using FIB-TEM, while interfaces between diamond and garnet or zircon are commonly open. Moreover, higher variability in the Raman shift in diamond hosted by garnet or zircon may be caused by complex internal structure and the presence of other phases. At the same time, a diamond in kyanite features relatively high full-width-at-half-maximum ( FWHM ) due to the anisotropy of thermal contraction, which is reflected by the plastic deformation of diamond mediated by dislocation glide at T ≥ 1000 °C. The entrapment pressure ( P trap ) for diamonds in garnet was calculated using elastic geobarometry to test its compatibility with the existing peak pressure estimated by conventional thermobarometry. The “downshifted” diamonds exhibit entrapment pressures of 4.8 ± 0.14 and 4.99 ± 0.14 GPa at an entrapment temperature of 1100 °C, using unstrained reference diamond from the literature and own measurements, respectively. This is consistent with the earlier estimates and the elastic theory and does not require any elastic resetting suggested to account for the reported upshift in garnet. Our data suggest that the upshift in diamond hosted by garnet is related to the proximity of other diamond grains. We conclude that the use of diamond inclusions in elastic barometry should be backed by careful evaluation of its internal structure and associated phases and restricted to isometric monocrystalline diamond grains not occurring in clusters as required by the method.
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来源期刊
Journal of Geosciences
Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-MINERALOGY
CiteScore
2.30
自引率
7.10%
发文量
15
审稿时长
>12 weeks
期刊介绍: The Journal of Geosciences is an international peer-reviewed journal published by the Czech Geological Society with support from the Czech Geological Survey. It accepts high-quality original research or review papers dealing with all aspects of the nature and origin of igneous and metamorphic rocks. The Journal focuses, mainly but not exclusively, on: -Process-oriented regional studies of igneous and metamorphic complexes- Research in structural geology and tectonics- Igneous and metamorphic petrology- Mineral chemistry and mineralogy- Major- and trace-element geochemistry, isotope geochemistry- Dating igneous activity and metamorphic events- Experimental petrology and mineralogy- Theoretical models of igneous and metamorphic processes- Mineralizing processes and mineral deposits. All the papers are written in English, even though they may be accompanied by an additional Czech abstract. Each contribution is a subject to peer review by at least two independent reviewers, typically at least one from abroad. The Journal appears 2 to 4 times a year. Formally it is divided in annual volumes, each of them including 4 issues.
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