High-Ti Melts From the Taurus-Littrow Valley (TLV). A Product of Volcanism or Impact? An ANGSA Investigation Using the Station 3 Double Drive Tube 73001/73002

The ANGSA initiative examined an unopened Apollo 17 double drive tube that penetrated a “light mantle” surface feature that represents a landslide deposit originating from the South Massif in the Taurus Littrow Valley. Within this double drive tube are several lunar lithologies not identified in the Apollo, Luna, Chang'e 5 or lunar meteorite collections. One such lithology is lithic fragment 73002, 27G. It consists of a fine-grained, high-Ti melt lithology which hosts lithic clasts and mineral fragments derived from a variety of high-Ti basalts. This lithology represents either a quickly cooled mare basalt with xenocrysts produced by thermal erosion of older crystalline high-Ti basalts, or a high-Ti impact melt with remnants of the target lithologies. Both types of lithologies are rare to non-existent, so this new sample has the potential to shed light on either the dynamical near-surface interactions between erupting magmas and previously erupted flows, or impact processes involving high-Ti mare basalt targets. Although not entirely unambiguous, numerous lines of evidence support an impact origin for this rock type. Based on crystal size distribution, the interclast melt experienced rapid cooling, exceeding rates documented in most high-Ti mare basalts. Mineral and bulk chemistry and preferred orientations of matrix grains indicate that the rapidly cooled portion of this lithology contains remnants of a variety of mare basalts. It seems unlikely that basalt flow would contain such a variety of xenoliths at its chilled surface. Although the interclast melt falls on an appropriate liquid-line-of-descent, its composition has characteristics distinct from other high-Ti basalts.