MICRO RAMAN SPECTROSCOPY OF AMPHIBOLES AND Al-Ti-RICH PYROXENES IN THE MARTIAN METEORITES ZAGAMI AND LEW88516. T. Mikouchi

Introduction: Amphibole has been reported from a few groups of Martian meteorites (basaltic, lherzolitic and dunitic groups) [1-4]. They are always present within a magmatic inclusion trapped in pyroxene and olivine in spite of the large difference of the host petrology. Their mineral compositions are almost identical to one another and are kaersutitic. So far, only observations by optical microscopy and analyses by electron and ion microprobes have been performed on these interesting and important phases [1-4]. In this abstract, we present the results of micro Raman spectroscopy on amphiboles in Martian meteorites (Zagami and LEW88516) in order to obtain their crystal structural information. We could successfully detect the Raman peaks for Martian amphiboles that were identical to those from a terrestrial kaersutite. Samples and methods: We studied amphiboles in the thin sections of Zagami (PTS #1, Mineral. Inst.) and LEW88516 (LEW88516,24). First, we looked for an amphibole-like phase by optical microscopy and analyzed it by electron microprobe. Then, Raman spectra were measured by a JASCO micro Raman spectrometer with a method similar to [5]. Terrestrial amphiboles (kaersutite from Oki, Japan and actinolite from Iratsu, Japan) were analyzed for comparison. Because Al-Ti-rich pyroxene in the magmatic inclusion of Martian meteorites has a broadly similar composition to amphiboles in Zagami and LEW88516 [e.g., 6], we also analyzed these pyroxenes to see the difference between kaersutitic amphibole and Al-Tirich pyroxene in Raman spectra. Fassaitic pyroxene (4 wt% TiO2 and 7 wt% Al2O3) in Asuka-881371 angrite was also analyzed for comparison. Host pyroxene (pigeonite) of Zagami was analyzed for the standard of typical pyroxene. Results: We could find one amphibole grain in each Martian meteorite that was large enough for the analyses (Fig. 1). They are up to a few tens of μm across and show pleochroism from brownish orange to bright brown as reported by [1-4]. Microprobe analysis of amphiboles gave chemical compositions enriched in Al and Ti, nearly identical to the reported values [1-4] and they were close to the kaersutite (Table 1). Al-Tirich pyroxenes were included in many magmatic inclusions within olivine of LEW88516 and have high Al2O3 contents of 8-15 wt%. However, they are distinct from amphibole especially in Si and Ti (45 wt% SiO2 and up to 4 wt% TiO2) contents. Table 1. Composition of amphiboles in Zagami and LEW88516