Plagioclase under compression: A path to diaplectic glass and maskelynite.

Abstract

Diaplectic glass and maskelynite in shocked plagioclase serve as key diagnostic features for high level of shock metamorphism in impact craters and meteorites. However, their formation mechanisms remain unclear and have long been argued, mainly due to the lack of phase diagram for plagioclase with extended pressure-temperature conditions. We report the stabilities of labradorite and anorthite at pressure up to 65 gigapascals and temperature up to 4000 kelvin. Our experimental results reveal the pressure-temperature conditions for amorphization, decomposition, and melting of labradorite and anorthite. The boundary between amorphous plagioclase and crystalline high-pressure phases in our phase diagram indicate diaplectic glass can form at 1300 to 1500 kelvin, and the melting line suggests that maskelynite can be generated above 3000 kelvin at high pressures. Formation conditions of diaplectic glass and maskelynite in plagioclase-bearing rocks are also suggested by the combination of phase diagram and shock Hugoniot data. These findings will advance our understanding of the bombardment history on rocky planetary surfaces.