1. Raman spectroscopy study of shocked olivine in Hungarian
L-chondrite, Mócs
J. Fürj ( ) (1), I. Gyollai (1), Sz. Bérczi (1), A. Gucsik (2), Sz. Nagy (1), M. Veres (3).
(1) Eötvös University, Faculty of Science, Institute of Physics, Dept. Material Physics, H-1117 Budapest, Pázmány P. s. 1/a, Hungary. (2) Max Planck Institute for Chemistry, Dept. of Geochemistry, Joh.-J. Becherweg 27, D-55128, Mainz, Germany. (3) Institute for Solid State Physics and Optics H-1121 Budapest Konkoly-Thege M. street 29-33
Introduction.
The Mócs meteorite is L5-type chondrite, wich was falling in 1882, Kolozs county. The meteorite major modal composition are: olivine, pyroxene, plagioclase feldspars, and opaque minerals. The meteorite is highly cracked, and in some places we can observe shock induced veins too. The cracks are filled by iron rich material. The sample contains shock-metamorphic effects, such as weakly-moderately olivine mosaicism, very low interference color in plagioclase, planar fractures (PF’s) in olivine grains, and in some regional places planar deformation features (PDF’s) in olivine (Fig. 1), and reduce interference color in pyroxene. We have investigated a PDF’s rich olivine grain by Raman spectroscopy, and looking for evidence for the shock-metamorphic effects in the lattice vibrational changes. In this grain we has occured raman peaks which are characteristics of -(Mg, Fe)2 SiO4 olivine phase (wadsleyite).
Fig 3: Map of Carpathian Basin : and the locality of Mócs, where the samples of the L6 chondrite fall in 1883
Mócs
Fig 1: Macroscopic photo of Mocs chondrite (5)
Fig 4: Micro-Raman Spectroscope
at the Central research Institute of Physics,
Where we carried out the measurements
Samples and Experimental Procedure
The mineral assemblages and textures were characterized with a Renishaw-1000 Raman spectrometer, the used laser wave lenght was 785 nm, the focused energy 8 mW. The maximal focus was driven to 1m diameter spot. The thin section was mounted in epoxy material, and the sample thickness is 30 m.
Fig. 2.:Raman energy levels (6)
Fig. 5 Reflexion microscopy photo about PDF’s lamellae in olivine from Mócs meteorite sample. (Two red dots represent the Raman measurement points).
Fig 6 Shocked olivine in Mocs sample /polarized microscopy photo, crossed nicols
Fig 7 Phase diagramm of olivin phases depending of pressure and temperature.. The wadsleyte, that was measured by Micro-Raman spectrroscopy, is modified spinel structure.
Fig. 8 Raman spectra of shocked olivine from Mócs meteorite sample. The pure wadsleyite Si2O7 stretching vibrational mode is signed by red arrow and number.
Trudy’s mine, Arizona, USA
Mócs II.
Mócs I.
vibrational oscillations type belonging to the top positions -
421(s)
Olivine SiO4 tetrahedrals defectioning and symmetrical deformation vibration
430(m)
543(m)
Olivine SiO4 tetrahedrals asymmetrical deformation vibration
577(m)
588(m)
630(s)
642(w)
706(m)
Wadsleyite Si2O7 symmetrical stretching vibration (Kleppe et al. 2006)
722(vw)
751(w)
Si-O-Si dimer kötandek (Durben et al. 1993; Gillet et al. 2005)
823(vs)
822(vs)
Olivine SiO4simmetric (60%), and asimmetric (40%) stretching vibration
852(vs)
Olivine SiO4 symmetrical (60%), and asymmetrical (40%) stretching vibration
854(vs)
Olivine SiO4 symmetrical (40%), and asymmetrical (60%) stretching vibration
883(vs)
920(m)
Olivine SiO4 asymmetrical stretching vibration
960(s)
958(w)
987(m)
Results and Discussion
The Mócs I. spektrum was measured on the PDF’s lamellae, but the Mócs II. spektrum was between two
PDF’s lamellae. The Mócs I. spektrum characteristic peaks are: 630(s), 706(m), 722(vw), 751(w), 852(vs), 883(vs), 987(s). The Mócs II. spektrum contains the following peaks: 421(s), 577(m), 642(w), 822(vs), 854(vs), 920(m), 958(m). We used to reference material from the Trudy’s mine olivine to comparison the vibrational changes between three spectra (Fig. 2). The spektrum was derived from CALTECH Raman database.
The most characteristic changes are in the Mócs I. spektrum. The olivine doublet peak position shift to higher wavenumbers, that might be means the olivine structure starting disorder. The doublet can shift according to the chemical composition changes, but it’s rate must be between for the 850 cm-1 peak, and for 820 cm-1 peak. In this case, the changes too high just from the chemical composition changes. Moreover, the Mócs II. spectrum direction is less than 5 m from Mócs I. measurement point! The doublet shifting was observed in experimentally shocked olivine (crystalline forsterite) between 0-50 GPa [1]. We assume, that doublet shifting might be in connection with shock mechanism.
The second important change in the Mócs I. spektrum is in the middle wavenumber region. The olivine structure vibrations are forbidden in this region. The 751 cm-1 peak appears, that corresponding to the presence of Si-O-Si bridges characteristic of wadsleyite [1,2]. It might be represents highly deformed olivine [2]. The 722 cm-1 peak appears too, that corresponding to the wadsleyite Si2O7 symmetric stretching vibrational mode [3,4]. However the 918 cm-1 peak that corresponding to the wadsleyit SiO3 symmetric stretching vibrational mode is not identify because of the doublet peak position.
Table 1: Raman peaks and their vibration types of PDF-rich olivine grain in Mócs chondrite. The intensity of peaks: (vw) very weak, (w) veak, (m) middle, (s) strong, (vs) very strong
Conclusion
The results suggested for us, that in amorphous PDF’s lamellae contains modified spinel structure wadsleyite crystallite, in a highly deformed olivine grains, that is evidence for the localised high stage shock-metamorphism in Mócs (L5) Hungarian meteorite.
References
[1] Durben et al., (1993) American Mineralogist, Volume 78, pp
[2] Gillet et al., (2005) Meteoritcs & Planetary Science 40, pp
[3] Kleppe et al., (2006) American Mineralogist, Volume 91, pp
[4] Kleppe et al., (2002) Physics and Chemistry of Minerals, 29,
(5)
madaras-big.jpg
(6)ttp://en.wikipedia.org/wiki/File:Raman_energy_levels.jpg
Acknowledgments:
We are grateful for Professor I. Kubovics and Z. Ditrói-Puskás for valuable discussions, and for KFKI (Central Physical Research Institution) and LRG (Eötvös University) for instrumental background