EPSC Abstracts Vol. 6, EPSC-DPS2011-792, 2011 EPSC-DPS Joint Meeting 2011 c Author(s) 2011

Transformation of pyroxene to akimotoite (MgSiO 3- ilmenite) in NWA 5011 L6 chondrite

Sz. Nagy (1), I. Gyollai (1), S. Józsa (1), Sz. Bérczi (1), A. Gucsik (2), M. Veres (3) (1) Eötvös University, Budapest, Hungary; (2) Tohoku University, Sendai, Japan; KFKI-SZFKI, Budapest, Hungary

1. Introduction growth solid state transformation. The observed akimotoite aggregates clearly distinguishable from The NWA 5011 L6 type chondrite is a heavily the pyroxene grains. The akimotoite has grayish shocked meteorite. It contains up to 6mm wide shock colour in our sample (Fig. 1). At higher melt veins (SMV). The akimotoite was firstly magnification the akimotoite aggregates show discovered in Tenham chondrite [1]. These shock granular texture. veins attribute high pressure and high temperature to phase transformation its inside and near by its boundary. We found MgSiO 3 ilmenite which clearly distinguish from the pyroxene. This high pressure phase is connecting with ringwoodite and maskelynite environment in the chondritic portion very close to boundary of the shock vein.

2. Sample and Method The NWA 5011 meteorite has unknown fall date. It contains more than 3000 pieces. The major mineralogical components are as follows: olivine, orthoenstatite, plagioclase (mainly presence as maskelynite or lingunite), troilite. The most important accessory is the chromite. The optical Fig. 1. Akimotoite aggregates (ak) in the chondritic observation was done with a Nikon LV100POL portion of NWA 5011. (OM-image, pp-light) microscope, and the structural identification was using Renishaw RM2000 raman spectrometer. The The micro-raman investigation revealed that this lenght of detection time was 120 sec. grayish colour phase has ilmenite structure with pyroxene glass (Fig. 2). The observed peaks for 3. Results akimotoite are: 797, 480, 286 cm -1, and the pyroxene glass represents by 664 cm -1 and centered at about The NWA 5011 meteorite has a complex network of 930 cm -1[2]. shock melt veins, which cross-cutting the whole sample. The shock veins have two major textural 4. Summary and Conclusion units: The first unit is the recrystallized matrix material which is mainly pyroxene transformation The presence of akimotoite represents that in local product (majorite-pyrope ss ), and glass with different environment the pressure was between 18-23 Gpa in chemical composition. The other is a clastic unit, NWA 5011 depending on chemical composition of which preserved the original texture. In this latter the host pyroxene [3]. unit the melting effect is minor. The main phase transformation mechanism is the nucleation and Fig. 2. Raman spectrum of akimotoite in the NWA 5011 meteorite. The spectrum was collected from the Fig. 1 area.

5. References

[1] Tomioka, N., and Fujino, K. (1999) American Mineralogist, vol.84, p. 267-271

[2] Ferroir et al. (2008) EPSL, vol. 275, p. 26-31

[3] Gasparik, T. (1990) Journal of Geophysical Research, vol. 95, p. 15751-15769