Apatite Microstructures and its Volatile Composition in Eucrites

Apatiteis a common phosphate mineral in planetary materials known to contain appreciable amounts of volatiles (F, Cl, OH) [e.g. 1-4]. As such, apatite has recently been of significant interest in assessing the volatile evolution of various bodies within the Solar System via in-situ analysis (e.g. [5-7]). Whilst these works account for the textural context of the apatite grain and the surrounding mineralogy, less attention has been given to understanding as to how the structure of grains may be influenced by metamorphism and shock deformation. Electron Backscatter Diffraction (EBSD) analyses provide structural information at the μmand sub-μmlength scales. In extraterrestrial samples, it is largely used to interpret larger-scale plastic deformation [8] and shock deformation in geochronometers such as zircon and baddeleyite [e.g. 9-11]. Importantly, these studies highlight the importance of understanding deformation at the μm-scale when interpreting complex U-Pbdata and the mobility of Pb, a moderately volatile element. As yet, there have been no studies of how deformation-induced microstructures may influence the abundance and isotopic composition of volatiles in apatite in eucrites. In this study we investigate the microstructure of apatite grains in eucritesfor which H and Cl isotopic composition have been previously reported [12, 13], in order to explore the relationship between crystallographic features of apatite and its volatile content and isotopic composition in eucritesof different shock grades