Experimental investigation of OH/H2O in H+-irradiated plagioclase: Implications for the thermal stability of water on the lunar surface

Abstract

Determining the characteristics and thermal stability of solar wind-produced OH/H2O is critical to understanding the formation and migration of water on the lunar surface. In this study, terrestrial plagioclase (An50−53) was used as a lunar analogue and was irradiated with 5 keV H+ at a fluence of ∼1×1017 H+/cm2. The irradiated plagioclase was characterized via Fourier transform infrared spectroscopy, nanoscale secondary ion mass spectrometry, Raman spectroscopy, and transmission electron microscopy. The thermal stability of OH/H2O in the irradiated plagioclase was investigated via heating experiments. Our results reveal (1) a ∼100–200 ppm increase in the water content of the irradiated plagioclase; (2) structural hydrous species formation in the plagioclase through H+ implantation, including Type I H2O (∼2.75 μm) and Type II H2O (∼2.90 μm); and (3) the escape of much of the OH/H2O formed by H+ implantation at a temperature equivalent to the highest temperature on the lunar surface. The results of this study can improve our understanding of OH/H2O thermal stability on the lunar surface and provide a baseline for the interpretation of remote sensing observations.