Comparison of the raman microprobe spectra of (Mg, Fe)2SiO4 and Mg2GeO4 with olivine and spinel structures

Guyot, F.; Boyer, H.; Madon, M.; Velde, B.; Poirier, Jean‐Paul

doi:10.1007/bf00311898

“…3 displays the Raman spectra obtained from a lamella in porphyroclastic grain of lamellae-bearing olivine inside the shock veins. Raman spectrum of the lamella contains two strong bands at 798 and 844 cm Ϫ1 and a weak band at 298 cm Ϫ1 , and all three bands unambiguously can be assigned to ringwoodite (20,21), whereas the spectrum of olivine matrix of this grain displays two characteristic strong bands at 822 and 852 cm Ϫ1 . The weak bands at 714 and 918 cm Ϫ1 in the spectrum of lamella indicate the existence of traces of wadsleyite (21).…”

Section: Resultsmentioning

confidence: 97%

“…The other bands at 600, 822, 852, and 955 cm Ϫ1 appearing in the spectrum of lamella emerge from olivine (20,21). The spectrum of olivine neighboring the The BES image shows two sets of high-density ringwoodite lamellae at the rim of a porphyroclastic olivine from a and Ͼ95% by volume of olivine being transformed into ringwoodite lamellae.…”

Section: Resultsmentioning

confidence: 99%

Ringwoodite lamellae in olivine: Clues to olivine–ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs

Chen

¹

,

Goresy

²

,

Gillet

³

2004

Proc. Natl. Acad. Sci. U.S.A.

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The first natural occurrence of ringwoodite lamellae was found in the olivine grains inside and in areas adjacent to the shock veins of a chondritic meteorite, and these lamellae show distinct growth mechanism. Inside the veins where pressure and temperature were higher than elsewhere, ringwoodite lamellae formed parallel to the {101} planes of olivine, whereas outside they lie parallel to the (100) plane of olivine. The lamellae replaced the host olivine from a few percent to complete. Formation of these lamellae relates to a diffusion-controlled growth of ringwoodite along shear-induced planar defects in olivine. The planar defects and ringwoodite lamellae parallel to the {101} planes of olivine should have been produced in higher shear stress and temperature region than that parallel to the (100) plane of olivine. This study suggests that the time duration of high pressure and temperature for the growth of ringwoodite lamellae might have lasted at least for several seconds, and that an intracrystalline transformation mechanism of ringwoodite in olivine could favorably operate in the subducting lithospheric slabs in the deep Earth. N atural ringwoodite had been found in many shocked chondritic meteorites, in which the ringwoodite occurs as finegrained polycrystalline aggregates formed through a phase transition of olivine during exogenous dynamic events on the parent asteroids (1-4). It was also suggested that the olivineringwoodite transformation could take place in cold subducting slabs at the deep transition zone, where pressure oversteps the ringwoodite stability field (5-9). An experiment-produced texture characteristic of this phase transition in the slabs is the formation of ringwoodite lamellae within individual olivine crystals (6,7,(10)(11)(12). A number of laboratory experiments on compositions like Mg 2 GeO 4 , Fe 2 SiO 4 , and (Mg,Fe) 2 SiO 4 showed that the spinel-structured lamellae lie parallel to the (100) planes of olivine (6,(10)(11)(12)(13)(14)(15)(16)(17)(18). These ringwoodite lamellae form platelets from several unit cells to 100 nm in thickness (6,(10)(11)(12)(14)(15)(16)(17)(18). The formation of ringwoodite lamellae in olivine was attributed either to a martensitic transformation mechanism (6,13,(15)(16)(17)(18)(19) or an intracrystalline nucleation and growth mechanism by which coherent nucleation of ringwoodite occurs on the stacking faults of olivine (10-12). However, no natural occurrence of ringwoodite lamellae had been found so far either in the shocked meteorites or exhumed subducted slabs.Sixiangkou meteorite is a heavily shock-metamorphosed L6-chondrite with a number of shock-produced veins up to 10 mm in thickness. The shock veins contain abundant high-pressure minerals including ringwoodite, majorite, garnet, and magnesiowüstite, for which the shock-produced pressure and temperature of Ϸ20 GPa and 2,000°C were inferred (4). Polycrystalline aggregates of ringwoodite and majorite up to 100 m in size and porphyroclastic grains of olivine and pyroxene up to 1.5 mm in size distr...

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“…The frequencies depend on the masses of the vibrating atoms, as may be deduced qualitatively using a simple harmonic oscillator model, which relates the frequency, m, to the reduced mass of the oscillator, l, and its force constant k as m = (1/2p)(k/l) 1/2 . In spite of the simple frequency-composition behavior, Guyot et al (1986) showed that the interpretation of the substitutional effect of magnesium by iron on Si-O band shifts is not straightforward and that it involves a three-body effect, such as Fe-O-Si rather than a two-body effect, such as Fe-O. Instead of attempting to relate vibrational frequencies to atomic masses and the nature of the atomic interactions we follow an empirical approach to describe the phonon frequencies as function of composition.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…According to Huang et al (2000) and Mernagh and Hoatson (1997) a similar trend is present in pyroxenes and according to Hofmeister and Mao (2001) in silicates with the spinel structure. Guyot et al (1986) have shown that a quantitative theoretical interpretation of the substitutional effect of magnesium by iron is not straightforward. We follow an empirical approach to describe the phonon frequencies as function of composition.…”

Section: Introductionmentioning

confidence: 99%

“…13, solid curves are not significantly different from a linear behavior (dashed curves). Experimental data for olivine are from Guyot et al (1986), circle, Besson et al (1982), triangle. Data for pyroxene are from Huang et al (2000): synthetic crystals: circle, natural specimens, triangle, Chopelas (1999), square have become available for a number of minerals, such as forsterite, perovskite and akimotoite through the work of Gillet et al (1991), Gillet et al (2000) and Reynard and Rubie (1996), respectively.…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic mixing properties of olivine derived from lattice vibrations

Jong

¹

2009

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We use a lattice vibrational technique to derive thermophysical and thermochemical properties of fayalite, Fe 2 SiO 4 . This semi-empirical technique is based on an extension of Kieffer's model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity and electronic effects based on crystal field theory. We extend it to predict thermodynamic mixing properties of olivine (Mg,Fe) 2 SiO 4 solid solutions by using results of our previous work on the system MgO-SiO 2 . Achieving this requires a relation between phonon frequency and composition and a composition relation for the energy of the static lattice. Directed by experimental Raman spectroscopic data for specific optic modes in magnesium-iron solid solutions of olivine and pyroxene we use an empirical relation for the composition dependence for phonon frequencies. We show that lattice vibrations have a large effect on the excess entropy and that the static lattice contribution and lattice vibrations have a large impact on excess enthalpy and excess Gibbs energy. Our model indicates that compositional effects in electronic and magnetic properties are negligible. The compositional variation the Néel temperature has a large impact on excess heat capacity for temperatures below 100 K.

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Applications of Vibrational Spectroscopy to Geology

Gillet

¹

2001

Handbook of Vibrational Spectroscopy

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The sections in this article are Introduction Vibrational Spectra of Minerals, Glasses and Fluids: Basic Aspects Minerals: The Example of Carbonates Glasses: The Example of Si O 2 Fluids Micro‐ R aman and Micro‐Infrared Spectroscopy Micro‐ R aman Spectroscopy Micro‐Infrared Spectroscopy Vibrational Spectroscopy of Minerals at High Pressure and Temperature The Diamond Anvil Cell Vibrational Spectroscopy at Elevated Temperatures Some Examples in the Si O 2 System From Vibrational Spectra of Minerals to Thermodynamic Properties Spectroscopic Data for Some Representative Mineral Groups Simple Minerals: Diamond, Graphite, Alkali Halides, Mg O , Ti O 2 and Simple Hydrous Phases Si O 2 Polymorphs and Glass Orthosilicates Feldspars, Feldspathic Glasses and Other Framework Aluminosilicates Chain Silicates: Pyroxenes and Amphiboles Sheet Silicates: Micas, Clays and Serpentines Pyrosilicates Ring Silicates Corundum and Ilmenite Perovskites Spinels Carbonates Phosphates Sulfates and Sulfides Conclusion Acknowledgments

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Comparison of the raman microprobe spectra of (Mg, Fe)2SiO4 and Mg2GeO4 with olivine and spinel structures

Cited by 78 publications

References 14 publications

Ringwoodite lamellae in olivine: Clues to olivine–ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs

Ringwoodite lamellae in olivine: Clues to olivine–ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs

Thermodynamic mixing properties of olivine derived from lattice vibrations

Applications of Vibrational Spectroscopy to Geology

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