Investigations of the Optical Maturity of Lobate Scarps: Implications for Our Understanding of Lunar Surface Materials

Abstract:

Lunar lobate scarps are long, curvilinear structures resulting from tectonic events (e.g. thrust faults.) They may be associated with late-stage global contraction of the Moon; crater counting techniques imply young ages (<400Ma) [1-5]. Remote sensing data suggest they are not all equally optically mature [2,6]. The optical maturity parameter (OMAT) can be used to estimate the maturity of surface materials and exposure to space weathering [7]. High OMAT values are common on steep slopes or sharp surface features where weathering either shatters or exposes fresh, immature materials [8]. We examined OMAT values derived from high spatial resolution Kaguya Multiband Imager data (~20 m/px) using the algorithm of [9] and LROC NAC imagery for several scarps and wrinkle ridges. Those with OMAT above background include Mandel’shtam scarp cluster (lobate), Henderson scarp (lobate), and near Plato crater (wrinkle). Those lacking higher OMAT include Lee-Lincoln, Feoktistov, and Gemma Firsuis C lobate scarps. Extended areas of scarps expressing complicated relationships with OMAT include Slipher/dAlembert and Vitello. Lack of a consistent OMAT signature for scarps may imply (1) the slope profile is too shallow for rapid erosion and ‘refreshing’ or (2) the shaking that may also erase craters could mix mature/immature soils [2]. This may be akin to acoustic fluidization as seen on asteroids [10], where particles flow further and faster than expected. Our ongoing work will create: detailed OMAT maps of scarp/wrinkle clusters; correlate apparent ages of scarps with OMAT; and generate models of scarp profiles. Continued comparison of OMAT with photometric and other data will provide insight into implications for lunar materials and exploration [11]. Supported by NASA SSERVI; TREX (NNH16ZDA001N) and VORTICES (NNA14AB02A). [1] Watters T.R., Johnson C.L. (2010) Planetary Tectonics, Cambridge Univ. Press. [2] Binder A.B. (1982) Earth, Moon, and Planets, 26. [3] Schultz P.H. (1976) Univ. Texas Press. [4] van der Bogert C.H. et al. (2018) Icarus, 306. [5] Clark J.D. et al. (2015) LPSC XLVI, #1730. [6] Banks M.E. et al. (2019) LPSC L, #2577. [7] Lucey, P.G., et al. (2000) JGR 105, E8.. [8] Grier, J.A. et al. JGR 2001. [9] Lemelin, M., et al. PSS 2019. [10] Richardson, E.R. et al. (2020) Icarus, 347. [11] Banks, M.D. et al. (2020) LPSC, #2903.