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Cation order in omphacitic clinopyroxenes: implications for Raman elastic geothermobarometry
No full textOmphacite is a common mineral found in many geological settings, thus its widespread occurrence makes it a valuable candidate for Raman elastic geothermobarometry. This approach uses the deformation recorded by mineral inclusions to determine the pressure and temperature conditions under which they were entrapped [1]. Raman scattering, highly sensitive to structural deformations, provides crucial insights into crystal structure variations that occur due to heating or compression. While many host-inclusion systems have been studied, clinopyroxene inclusions remain relatively unexplored. Therefore, accurate calibration of Raman-peak positions against hydrostatic pressure is essential for applying Raman elastic geobarometry to omphacites in different mineral hosts.
Natural omphacite crystals exhibit cationic ordering associated with crystallization temperature, which affects their elastic properties. To investigate these aspects, in situ high-pressure Raman spectroscopy measurements were performed on natural ordered and experimentally disordered omphacites from Münchberg Massif (Germany). By examining omphacite crystals with varying degrees of order achieved through isothermal annealing experiments, it was observed that increasing cationic disorder leads to peak broadening, while pressure variations influence Raman peak positions. However, the peak position is also affected by the chemical composition. Therefore, Fe3+-rich crystals from Lugros and Camarate (SE Spain), and Voltri massif eclogites (Italy), already characterized by single crystal X-ray diffraction [2], along with synthetic Fe-free omphacites [3], were analyzed, as an initial step towards the chemical calibration of omphacites using Raman spectroscopy.
By considering the influence of chemical composition and cationic ordering, we have expanded our understanding of the elastic behavior of omphacite obtained through Raman spectroscopy and its potential use for geobarometric calculations, important for determining the pressure and temperature conditions involved in geological processes where omphacite growths.
References:
[1] Angel R J et al. (2019) Z Kristallogr Cryst Mater 234(2):129-140
[2] Cámara F (1995) PhD thesis, University of Granada, 504 pp.
[3] Pandolfo F et al. (2015) Phys Chem Minerals 42:1-1
Raman and FTIR spectroscopy of synthetic amphiboles: I. The OH librational bands and the determination of the OH-F content of richterites via Raman spectroscopy
No full textRaman spectroscopic study of omphacite at variable pressures
Get PDFOmphacitic clinopyroxenes ((Ca,Na)(Mg,Al)Si2O6) made up of a solid solution of jadeite, augite and aegirine are among the principal constituents of eclogites and can be found in blueschist facies or ultra-high-pressure rocks. They can be also recovered in the Earth’s upper mantle and in the subducted oceanic crust. Natural omphacites have two distinct polymorphs, a low-temperature phase with a space group P2/n, which shows splitting of the octahedral sites and the relative cation ordering, and a high-temperature chemically disordered phase with space group C2/c.
Raman scattering of a mineral is very sensitive to structural deformations developed while heating or under external stresses, a phenomenon that is the basis of Raman elastic geobarometry. This novel method is based on the contrast in elastic properties between the host and the inclusion, and allows estimating pressure and temperature of entrapment of an inclusion, to the condition of knowing the elastic properties of both the host and the inclusion and the residual strain of the latter, allowing estimating the conditions attained during metamorphic processes (Angel et al., 2018). Therefore, the application of this methodology to omphacites requires an accurate knowledge of their elastic behaviour, for which several data are available (for example Pandolfo et al., 2012) and its response to stresses accounted through Raman spectroscopy, which has never been systematically applied for studying omphacites under variable pressure conditions. This technique has already been used to investigate the order-disorder phenomenon in the octahedral sites of omphacites (Katerinopoulou et al., 2008) and it has been shown how the position and width of some Raman peaks depends on the ordering state. Therefore, this study would permit to calculate the entrapment pressure of omphacite inclusions and would potentially allow calibrating which Raman peaks are insensitive to changes in cation ordering.
Here we report the results from in situ high-pressure Raman spectroscopy on omphacites crystals from Münchberg Massif (Bavaria, Germany) formed at metamorphic-peak conditions of 2.5 GPa/600-700°C (O’Brien, 1993)
Elastic geobarometry using omphacite in eclogites: a Raman spectroscopy approach
Get PDFRaman scattering is very sensitive to structural deformations in crystal structures developed upon heating or compression. Raman elastic geobarometry uses deformation recorded by a mineral inclusion trapped in its host to retrieve the pressure and temperature conditions at which the inclusion has been entrapped [1]. Several host-inclusion systems have been studied, but clinopyroxenes have not yet been investigated. Because of their widespread occurrence in several geological settings and rock-types (e.g. high pressure eclogites, mantle xenoliths etc..), omphacitic clinopyroxenes (solid solution of jadeite, augite and aegirine, with chemical formula (Ca,Na)(Mg,Al)Si2O6) should be exploited for application of elastic geothermobarometry. However, the application of this methodology to omphacites requires the accurate knowledge of their elastic behaviour and at least a detailed Raman spectroscopy calibration as a function of external compression.
For this purpose, we have studied ordered and disordered omphacite crystals (belonging to Münchberg Massif, Bavaria, Germany [2]) by in situ high-pressure Raman spectroscopy and the results have been compared against calculated Raman spectra obtained by performing ab initio simulations on a completely ordered omphacite. Ab initio simulations have been carried out at variable pressures by means of ab initio hybrid HF (Hartree-Fock)/DFT (Density functional theory) simulations using the CRYSTAL17 software [3] following the protocol developed by [4]. The calculations resulted to be in good agreement with the experimental data. The full set of 60 Raman active modes and their intensities have been calculated at variable pressures and the main Raman peaks have been assigned to specific atomic motions.
Our results readily enabled us to calculate the entrapment pressure of omphacite inclusions still trapped in their host rocks by determining the changes in the Raman shift of the main peaks.
[1] Angel, R. J., Murri, M., Mihailova, B., Alvaro, M. (2018). Stress, strain and Raman shifts. Crystalline Materials, 234, 2, 129-140.
[2] O’Brien, P. J. (1993). Partially retrograded eclogites of the Münchberg Massif, Germany: records of a multi-stage Variscan uplift history in the Bohemian Massif. Journal of Metamorphic Geology 11, 241-260.
[3] Dovesi, R., Erba, A., Orlando, R., Zicovich-Wilson, C. M., Civalleri, B., Maschio, L., R ́erat, M., Casassa, S., Baima, J., Salustro, S., Kirtman, B. (2018). Quantum-Mechanical Condensed Matter Simulations with CRYSTAL. WIREs Comput. Mol. Sci., e1360.
[4] Prencipe, M. (2019) Quantum mechanics in Earth sciences: a one‐century‐old story. Rendiconti Lincei. Scienze Fisiche e Naturali, Vol. 30, pp.239–259
Raman spectroscopic study of omphacites at variable pressures: implications for elastic geobarometry
Get PDFThe widespread occurrence of omphacitic clinopyroxenes (a solid solution of jadeite, augite and aegirine, with the general chemical formula (Ca,Na)(Mg,Fe2+,Al,Fe3+)Si2O6) in several geological settings and rock-types (e.g. high pressure eclogites, mantle xenoliths etc..), make them ideal candidates to be exploited for Raman elastic geothermobarometry applications. Raman elastic geobarometry uses the deformation recorded by a mineral inclusion trapped in its host to retrieve the pressure and temperature conditions at which the inclusion has been entrapped (Angel et al., 2019), because Raman scattering is very sensitive to structural deformations in crystal structures developed upon heating or compression. Several host-inclusion systems have been studied so far, but clinopyroxene inclusions have not been thoroughly investigated yet. Therefore, the application of Raman elastic geobarometry to omphacites in various mineral hosts requires an accurate calibration of the Raman-peak positions against hydrostatic pressure.
However, the Raman-peak positions and their pressure evolution depend also on the chemical composition. Besides, natural omphacite crystals can show a significant degree of cationic ordering related to the crystallization temperature, which can also affect the elastic behaviour of omphacite. Therefore, we have started with the study of natural ordered (P2/n) and experimentally disordered (C2/c) crystals of omphacite coming from Münchberg Massif, Bavaria, Germany (peak conditions P > 2 GPa, T = 600-650 °C; O’Brien, 1997). On these samples, we carried out in situ high-pressure Raman spectroscopy measurements using a diamond anvil cell. As expected, the modes frequencies increase as pressure increases.
Since the study included omphacite crystals with different degrees of order, obtained with isothermal annealing experiments at different times, we were able to observe that progressive cationic disorder causes essentially a broadening of the peaks, whereas the changes in the Raman peak positions and FWHM are mostly due to pressure variations.
To better understand the elastic behaviour of the modes best suitable for elastic geobarometry, the Raman spectrum of a completely ordered omphacite of composition Jd50Di50, has been simulated at variable pressures with ab initio Hartree-Fock / Density Functional Theory simulations and compared with experimental spectra. The calculated data resulted to be in a good agreement with experiments and allowed us to understand changes in the pressure dependence of some modes.
Our results readily enabled us to calculate the entrapment pressure of omphacite inclusions still trapped in their host rocks by determining the Raman shifts of the main peaks along with changes in the cation order.
Angel R.J., Murri M., Mihailova B., Alvaro M. (2019) - Stress, strain and Raman shifts. Z Kristallogr Cryst Mater, 234(2), 129-140, https://doi.org/10.1515/zkri-2018-2112.
O’Brien P.J. (1997) - Garnet zoning and reaction textures in overprinted eclogites, Bohemian Massif, European Variscides: A record of their thermal history during exhumation. Lithos, 41, 119-133, https://doi.org/10.1016/S0024-4937(97)82008-7
Elastic geobarometry applied to omphacite: a Raman spectroscopy approach
Get PDFThe widespread occurrence of omphacitic clinopyroxenes (a solid solution of jadeite, augite and aegirine, with the general chemical formula (Ca,Na)(Mg,Fe2+,Al,Fe3+)Si2O6 in several geological settings and rock-types (e.g. high pressure eclogites, mantle xenoliths etc.), make them attractive to be exploited for Raman elastic geothermobarometry applications. Raman elastic geobarometry uses the deformation recorded by a mineral inclusion trapped in its host to retrieve the pressure and temperature conditions at which the inclusion has been entrapped [1], because Raman scattering is very sensitive to structural deformations in crystal structures developed upon heating or compression. Several host-inclusion systems have been studied so far, but clinopyroxene inclusions have not been thoroughly investigated yet. Therefore, the application of Raman elastic geobarometry to omphacites in various mineral hosts requires an accurate calibration of the Raman-peak positions against hydrostatic pressure. However, the Raman-peak positions and their pressure evolution depend also on the chemical composition. Besides, natural omphacite crystals can show a significant degree of cationic order related to the crystallization temperature, which can also affect the elastic behavior of omphacite.
To give an insight into the relation between the chemical order and pressure dependence of atomic dynamics, we have studied by in situ high-pressure Raman spectroscopy a series of crystals of omphacite from Münchberg Massif, Bavaria, Germany (peak conditions P > 2 GPa, T = 600-650 °C; [2]). The samples were free of iron, with compositions ranging between Jd45Di55 and Jd52Di48 and various degrees of cationic order achieved via isothermal annealing at different temperatures and for different times. We show that the pressure dependence of the wavenumber of the strongest Raman peak near 680 cm-1 is insensitive to the degree of chemical order, whereas the width of the same peak increases with cationic disorder and thus is indirectly related to closure temperature. To better understand the elastic behavior of the modes best suitable for elastic geobarometry, the Raman spectrum of a completely ordered omphacite of composition Jd50Di50, has been simulated at variable pressures with ab initio Hartree-Fock/Density Functional Theory simulations and compared with experimental spectra. The calculated data resulted to be in a good agreement with experiments and allowed us to understand changes in the pressure dependence of some modes. The experimentally obtained wavenumber-against-pressure trends can be potentially used to estimate the entrapment pressure of omphacite inclusions, assuming that they have the same chemical composition as the samples studied here. The dependence of Raman shifts on composition is planned as future work.
Acknowledgments: Financial support to the Italian Ministry of University and Research (LB), the University of Milan, project “Dipartimenti di Eccellenza 2023–2027” (LB, FC), to the Humboldt foundation (MM) as well as to the European Research Council, grant n.714936 (ERC-STG TRUE DEPTHS), PRIN-MUR project “THALES” Prot.2020WPMFE9_003 and the Fondi Regione Lombardia DGR 3776 (MA) is gratefully acknowledged.
[1] R.J. Angel, M.Murri, B. Mihailova, M. Alvaro Z Kristallogr Cryst Mater. 2019, 234(2), 129-140.
[2] P.J. O’Brien Lithos. 1997, 41, 119-133
Raman elastic geobarometry: investigating cation order in omphacitic clinopyroxenes
No full textOmphacitic clinopyroxenes exhibit widespread occurrence in various geological settings and rock types, making them promising candidates for Raman elastic geothermobarometry applications. Raman elastic geobarometry uses the deformation recorded by mineral inclusions to determine the pressure and temperature conditions under which they were entrapped. Raman scattering, which is highly sensitive to structural deformations, provides valuable insights into the variations in crystal structure that occur due to heating or compression. While several host-inclusion systems have been investigated, clinopyroxene inclusions have not been extensively studied. Therefore, the application of Raman elastic geobarometry to omphacites in different mineral hosts necessitates an accurate calibration of Raman-peak positions against hydrostatic pressure.
Natural omphacite crystals can exhibit cationic ordering associated with crystallization temperature, which affects their elastic behaviour. To address these aspects, we conducted a study on natural ordered (P2/n) and experimentally disordered (C2/c) omphacite crystals from Münchberg Massif (Germany). In situ high-pressure Raman spectroscopy measurements were performed using a diamond anvil cell. As expected, the frequencies of the modes increased with increasing pressure. By examining omphacite crystals with varying degrees of order obtained through isothermal annealing experiments, we observed that progressive cationic disorder primarily led to peak broadening, while changes in Raman peak positions were predominantly influenced by pressure variations.
Additionally, the chemical composition of omphacites influences the Raman-peak positions and their pressure evolution. Therefore, we analysed Fe3+-rich omphacites from Lugros and Camarate (Bétic Cordilleras, SE Spain), and Voltri (Italy) along with synthetic iron-free omphacites. This analysis is an initial step towards the chemical calibration of omphacites using Raman spectroscopy.
To gain a deeper understanding of the elastic behaviour of modes suitable for elastic geobarometry, we simulated the Raman spectrum of a fully ordered omphacite (Jd50Di50 composition) at different pressures using ab initio Hartree-Fock/Density Functional Theory simulations. The simulated data exhibited excellent agreement with experimental spectra, enabling us to comprehend the pressure dependence of specific modes. Leveraging these findings, we can calculate the entrapment pressure of omphacite inclusions still confined within their host rocks by determining Raman shifts of the main peaks alongside changes in cation order.
Our results provide valuable insights into the calibration and application of Raman elastic geobarometry for omphacitic clinopyroxenes. By considering the influence of chemical composition and cationic ordering, we have enhanced our understanding of the elastic behaviour of omphacite and its potential for geobarometric calculations. These findings offer a valuable tool for determining the pressure and temperature conditions of geological processes involving omphacitic clinopyroxenes
Raman and FTIR spectroscopy of synthetic amphiboles: II. Divalent (Mg-Co) substitutions at the octahedral sites
No full textCharacterisation of flow behaviour and velocity induced by ultrasound using particle image velocimetry (PIV): Effect of fluid rheology, acoustic intensity and transducer tip size
No full textAcoustic streaming phenomena of ultrasound propagation through liquid media was investigated experimentally employing particle image velocimetry (PIV). Parameters associated with the ultrasonic processor of ultrasonic amplitude (i.e., acoustic power) and transducer tip diameter (i.e., surface area), as well as, fluid rheology (i.e., water, glycerol solution and CMC solution), were studied for their effects on overall flow behaviour and fluid velocity. PIV yielded velocity gradient maps, demonstrating the acoustic streaming phenomena of ultrasound and its associated flow behaviour as a function of ultrasonic amplitude and fluid rheology, whereby increasing amplitude allowed for greater penetration of the acoustic-beam through the bulk of the fluid, and increasing fluid rheology yielded the converse effect. Moreover, upon impingement of the acoustic-beam with the base of vessel, vortex formation occurred, yielding a recirculation pattern. The maximum observed fluid velocities for water, glycerol solution and CMC solution were 0.329 m s−1, 0.423 m s−1, and 0.304 m s−1, respectively (large diameter sonotrode tip for an ultrasonic amplitude of 80%). Furthermore, shear rates were attained (maximum values of 24.25 s−1), and Reynolds numbers were determined in order to assess the degree of turbulence as a function of investigated parameters
Kinetics of hydrogen diffusion in riebeckite, Na2Fe3+2Fe2+3Si8O22(OH)2: an HT-FTIR study
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