Maskelynite- as seen in shocked Lonar target basalt, India, and martian and lunar meteorites

Abstract

In this study, we investigate the mineralogical and petrochemical characteristics of maskelynite occurring in a shocked basalt boulder from a terrestrial impact crater on a basaltic target - the Lonar impact crater in India, and the martian and lunar meteorites. The majority of Lonar maskelynite experienced solid-state transformation and maintained almost a uniform chemical composition, consistent with the unshocked feldspar. The locally flow-like texture and marginal vesiculation in feldspathic glass are needed in interaction with the impact-melt. The vesiculated melt occasionally occurring at the margins of maskelynite is characterised by Na-loss due to the shock-induced volatility. A shock pressure of <= 42 GPa and at a temperature of <= 1000 degrees C appear consistent for the formation of Lonar vesiculated melt/feldspathic glass. Under the impact-induced shock metamorphism, maskelynite samples from the moon retain both the crystalline and amorphous domains with a distinct chemical heterogeneity attributed to different shock metamorphism effects of the plagioclase. In contrast, the martian maskelynites exhibit a smooth, homogeneous composition. The estimated shock pressure is relatively higher at similar to 42-45 GPa based on experiments and models. The difference in Si/Al ratio in lunar (1-1.3) and martian maskelynite (1.5-1.9) suggests its inherent difference in composition of the crust, whereas the Lonar maskelynite shows overlapping composition with the martian maskelynite contending Lonar basalt as a potential terrestrial analogue to the martian crust.