Transformation of (Mg,Fe)2SiO4 olivine under excimer laser irradiation

Olivine alpha-(Mg,Fe)(2)SiO4 is the most abundant mineral of the Earth's upper mantle but is also the main mineralogical constituent of meteorites (mainly constituted of silicates and metals) which are mostly believed to be primitive materials. The origin of the accretion of the primitive dust and chunks in the solar system might be due to electrostatic and gravitational forces but this origin is conjectured though, given the abundance of solar UV radiation in space which might be thought to interfere in the procedure. In order to better understand the effect of UV irradiation on olivine, we carried out series of different irradiation regimes using a Kr-F excimer laser source on olivine single crystals. Optical and scanning electron microscope investigations show that in some area the samples are mostly molten/resolidified while in others they are mostly ablated thus revealing the underlying olivine single crystal. The defect microstructures of this later evidenced by transmission electron microscope are typical defects found in olivine shocked either naturally in our solar system or experimentally using high explosives or light gas guns. Excimer laser would thus provides a convenient new tool to study the formation mechanisms of these shock defects and would allow to better understand the role of time in impact processes. Furthermore, it is shown that olivine irradiated under excimer laser is able to bond chemically with a metal when samples are immersed in an autocatalytic bath thus suggesting that UV irradiation might have played a role in the accretion of the primitive dusts in the solar system. (C) 2002 Elsevier Science B.V. All rights reserved.