The compositional and physical properties of localized lunar pyroclastic deposits

Abstract

Lunar localized pyroclastic deposits are low albedo deposits with areas <2500km2. These deposits were difficult to study before the turn of the millennium because of the lack of available high spatial-resolution data. With the launch of the Lunar Reconnaissance Orbiter, Kaguya, and Chaandrayan-1, new sets of diverse high spatial-resolution data are now available. Using several of these data sets, we conducted a study of 34 localized pyroclastic deposits globally. For each localized pyroclastic deposit, we examined topography to estimate pyroclastic volume and juvenile proportions, S-band radar backscatter, thermal-infrared-derived measures of surficial rock abundance and regolith density, and mineral abundances. Our goals are to (1) quantitatively characterize the physical and mineralogical properties of each localized pyroclastic deposit, (2) investigate the physical and mineralogical variations among localized pyroclastic deposits, (3) compare these properties of localized (<2500km2) to regional pyroclastic deposits (>2500km2), and (4) provide useful parameters for future volcanological modeling. From this study, we find that: (1) localized pyroclastic deposits exhibit low relief structures, (2) the surface rock abundance and circular polarization ratio of localized pyroclastic deposits display a wide range of values (0.2–0.5% and 0.3–0.6, respectively), (3) the glass abundance of localized pyroclastic deposits vary between ∼0 and ∼80wt.%, (4) there are four types of localized pyroclastic deposits based upon the surface rock abundance and glass abundance parameters, (5) pyroclastic deposits within the same floor-fractured crater tend to have similar properties, and (6) localized pyroclastic deposits are diverse with respect to regional pyroclastic deposits, but a subset of localized pyroclastic deposits have similar physical and mineralogical properties to regional pyroclastic deposits.