The Plagioclase-maskelynite Transition in an External Heated Diamond Anvil Cell

Introduction: In heavily shocked stony meteorites, plagio-clase in the host rock has transformed into glass (maskelynite) in a solid-state reaction. So far, the formation pressure of maske-lynite has been estimated only based on dynamic high-pressure experiments [1]. However, duration of pressure in laboratory shock experiments is significantly smaller (10-6 sec) than that in meteorite parent bodies (10 0 sec) estimated by the mineralogy of shock veins [2-3]. Therefore, there is a possibility that shock pressures of heavily shocked meteorites are overestimated due to kinetic effect on the plagioclase amorphization. In this study, amorphization pressure of plagioclase was investigated based on static high-pressure and-temperature experiments that can produce longer pressure duration (10 3-4 sec) than dynamic compression. Experimental Methods: Fine-grained powders (~5-30 mi-cron) of natural Ab 99 plagioclase were compressed by an external heated diamond anvil cell in pressure ranges of 20-39, 21-41 and 24-32 GPa at room temperature, 170 and 270 °C, respectively. The samples were kept at elevated pressures and temperatures for ~30 minutes and then decompressed after cooling. Recovered samples were examined by laser-Raman spectroscopy and transmission electron microscopy.