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Shock heterogeneity and shock history of the recently found ordinary Csátalja chondrite in Hungary

Kereszturi A., Fintor K, Gyollai I., Kereszty Z., Szabo M., Szalai Z., Walter H.

Geological Quarterly

2018

Vol. 62, No. 2

433--446

Shock impact-produced mineral alterations in two thin sections of the recently found Csátalja H4 ordinary chondrite meteorite are compared. Peak positions of Raman and infrared spectra of mineral clasts show peaks shifted in wavenumber relative to unshocked reference minerals, and both peak shifts and FWHM values seem to correlate to each other. In the less shocked thin section (Csátalja-1) a more monomineralic and homogeneous composition indicate shock pressures of <15 GPa, while the more shocked Csátalja-2 indicates shock pressure in the 15–17 GPa range. The highest identified infrared peak position shifts range between –48 and +28 cm–1 with peak broadening between 60–84 cm–1 in the case of the feldspars, which, together with sulphide globules, were produced by the shock itself. Feldspar spectra could be detected only by FTIR spectroscopy, but in most cases (above the S3 shock level) the mixed type of the pyroxene-feldspar spectra (both peaks in the same spectra) is in agreement with the shock-produced secondary feldspars. These grains are located around crystalline borders, and probably formed by selective melting, due to shock annealing. In reconstruction of the shock history, an early fragmentation by a lower shock effect and a later increased shock level-related vein and melt pocket formation occurred, with subsequent shock annealing; temporal reconstruction of the shock event is possible only in part. The joint usage of Raman and infrared spectroscopy provided useful insights into the shock-produced changes and their spatial inhomogeneity, while shocked feldspar could be better detected by infrared than by the Raman method.

A new classification of Nyirábrany, an ordinary chondrite from Hungary

Mészáros M., Kereszturi A., Ditrói-Puskás Z.

Meteorites

2014

Vol. 3, No. 1-2

19--32

The Nyirábrany meteorite is an ordinary chondrite from Hungary that fell in 1914 and, to date, has been studied very little. The aim of this work was to carry out a more detailed examination of this meteorite (using optical polarization microscope, energy dispersive X-ray spectroscopy and Raman micro spectroscopy) and re-investigate its previous classification as an LL5 type ordinary chondrite, moreover to complete its classification with a shock stage and a weathering grade. Our new results indicate that Nyirábrany could be a transition type between the L and LL chondrites. The main mineral phases of Nyirábrany are olivine, pyroxene and opaque minerals (e.g. Fe-Ni metal, troilite, chromite), minor constituents are plagioclase, Cl-apatite, cristobalite and glass. The Fe-Ni metal content (1.32 vol%) of Nyirábrany is typical of the LL group, the Fa content of olivines (26.71 mol%) is between the range of the L and LL types, while the Fs-content of the low-Ca pyroxenes (20.51 mol%) is typical of the L-chondrites. Chondrules appear in different sizes, mineral compositions and textures. The textural and mineralogical features (e.g. mostly homogeneous silicate minerals, dominance of clinopyroxenes, recrystallized matrix, well-defined chondrules) indicate petrological type 4-5 for Nyírábrány. The shock stage and the weathering grade of this meteorite were examined for the first time. On the basis of the observed optical and textural features of the olivine grains (e. g. sharp optical extinction, irregular and planar fractures) Nyirábrany has an S2 shock stage. About 30–40% of the opaque phases are affected by oxidation, which shows a W2 weathering grade.