Evolutionary History of the Large-Scale Scarp in Jules Verne Crater, Moon

Evolutionary History of the Large-Scale Scarp in Jules Verne Crater, Moon . Congzhe Wu1, 2, Jianzhong Liu2, Gregory Michael2, Harald Hiesinger4, Carolyn H. van der Bogert4, Wajiha Iqbal4, Kai Zhu2 and Jingwen Liu2, 1 College of Earth Sciences, Jilin University, Changchun 130012, China; wu[email protected].cn, 2 Center for Lunar and Planetary Science, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China; liujianzho[email protected].cn;[email protected].cn; [email protected].ac.cn; [email protected]. Institut für Planetologie, Universität Münster, 48149 Münster, Germany; [email protected]; [email protected]; [email protected] Introduction: Lobate scarps are among the youngest geologic-tectonic features on the Moon [1– 5]. Lobate scarps typically appear as linear or curved features with an asymmetric shape—a steep front and a gentle back slope [1,2]. They are generally less than 10 km long and tens of meters high [2,6,7]. Most of them are found in the lunar highlands and are thought to be surface expressions of thrust faults [2,7,9]. Lobate scarps appear young because of their sharp shape and the small craters (<50 m) that either cut across or lie on them. Later studies refined these results using crater counting methods, confirming their youth. Some scarps also show evidence of boulder falls, suggesting recent geological activity [4]. In the southern polar region, many scarp segments are younger than 50 million years, with some around 10 million years [10]. Other studies suggest scarp activity has continued over the past 400 million years, with recent events as young as 24 million years [5]. Jules Verne crater, on the Moon’s far side, is about 145 km wide and located at 34.9°S, 147.3°E. Its floor is filled with basalt, and its rim has been heavily eroded. It is considered pre-Nectarian [11] or Nectarian [12] in age. A large linear structure inside the crater was once thought to be a graben [11] but may actually be the Moon’s largest isolated lobate scarp [8]. Previous studies mostly focused on small scarps. However, large isolated scarps may reflect more complex geological histories. This study aims to date the largest isolated lobate scarp in Watters’ Scarp Database and analyze its tectonic evolution. Data: This study uses LROC NAC images (0.5– 2 m/pixel) and Kaguya TC mosaics (~7 m/pixel) for detailed analysis of the lobate scarp in Jules Verne crater and for mapping dating craters. NAC images were processed using ISIS 7.2.0 and categorized by solar azimuth (eastward/westward) and incidence angle (low to very high), resulting in eight groups to capture surface features under different lighting. Terrain slope was analyzed using Kaguya TC stereoderived DTM (10 m/pixel, ~3–4 m vertical accuracy). Additional geochemical data, including TiO₂ (from LRO WAC UV/VIS at ~400 m/pixel) and FeO, Al₂O₃, CaO (from Kaguya MI at ~60 m/pixel), supported the study. Method: To determine the absolute model age (AMA) of a lobate scarp, a suitable crater counting area must be selected. This area should have gentle slopes, be free of secondary craters, and belong to a single geological unit based on morphology and composition, as steep slopes and crater clusters can distort age estimates [13,14]. In regions affected by resurfacing event, crater size–frequency distributions (CSFDs) often display a “kink” in differential plots, marking the erasure of smaller craters and a reset of the surface age [15]. CSFD segments that follow the production function can be used to determine absolute model ages (AMAs), which may indicate the timing of fault activity when other resurfacing sources are absent [3]. To reduce the influence of secondary cratering, we applied randomness analyses using mean 2ndclosest neighbor distance (M2CND) and standard deviation of adjacent area (SDAA) measurements, comparing observed spatial distributions to Monte Carlo simulations. High iteration counts (e.g., 3,000) improved statistical precision. This integrated approach enhances age determination accuracy and distinguishes primary crater accumulation from resurfacing effects, particularly in complex terrains where Poisson timing analysis provides the only robust solution. Figure 1.Count area of all dating units on Kaguya TC mosaic Result and discussion: Based on the geological features and topography of the region, we have delineated the following dating areas to analyze the geological evolution of the region (Figure 1): north lineament unit (Ln), south scarp unit (Ss), northeast mare unit (Mne), west mare unit (Mw), crater filled unit (CF), linear depression filled unit (LDF), lobate scarp south dating unit 1 (LSs1), and lobate scarp south dating unit 2 (LSs2). The dating results are shown in Figure 2. Figure 2. Dating results of all units. The letters above the chart indicate different lunar geological periods: C stands for the Copernican period, E for the Eratosthenian period, I for the Imbrian period, N for the Nectarian period, and A for the Aitken period — a subdivision of the early Pre-Nectarian era, associated with the formation of the South Pole–Aitken basin. Our elevation-based reclassification of the Mw unit into three sub-regions (Mw-a, Mw-b, Mw-c) revealed that lower-elevation areas tend to be younger. AMA results show Mw-a has an age of 3.28 Ga, consistent with previous findings, while Mw-b and Mw-c are closer to 2.86 Ga, similar to the Mne unit. This age trend may be due to gravitational subsidence. Elevated areas on the crater floor, distinct from central peaks, suggest uplifted remnants of early crater-floor fractures. Cooling-related subsidence along concentric fractures may have transformed these features into faults or scarps. Figure 3. (a) Count area and measured craters of Mw-a unit on Kaguya TC Mosaic; (b) count area and measured craters of Mw-b unit on Kaguya TC Mosaic; (c) count area and measured craters of Mw-c unit on Kaguya TC Mosaic; AMAs derived for the (d) Mwa, (e) Mw-b, and (f) Mw-c units. Conclusions: Our results suggest that the CF unit formed earlier (~3.5 Ga), followed by major basaltic eruptions at ~3.4 Ga and ~2.6 Ga, which created the Mw and Mne units. Gravitational subsidence from denser mare basalts likely caused younger stratigraphic levels in lower-elevation regions. Crater-floor fractures were interpreted to predate mare volcanism and likely evolved into lobate scarps due to subsequent tectonic activity. The most recent tectonic resurfacing event occurred ~1.4 Ga, potentially linked to moonquakes, which reset the crater record in parts of the scarp area. Our findings support a complex geological evolution involving early magmatic intrusion, multiple basalt flows, structural deformation, and resurfacing. This abstract is derived from a full-length manuscript recently accepted for publication in Remote Sensing. References: [1] Binder, A.B and Gunga, H.-C. (1985) Icarus, 63, 421–441. [2] Watters, T.R. et al. (2010) Science, 329, 936–940. [3] van der Bogert, C.H. et al. (2018) Icarus, 306, 225–242. [4] Kumar, P.S.et al. (2016) J. Geophys. Res. Planets, 121, 147–179. [5] Clark, J.D. et al. (2024) Earth Planet. Sci. Lett., 633, 118636. [6] Banks, M.E.et al. (2012) J. Geophys. Res., 117, E00H11. [7] Watters, T.R. (2003) J. Geophys. Res., 108(E6). [8] Watters, T.R. et al. (2019) Nat. Geosci., 12, 411– 417. [9] Binder, A.B. (1982) Earth Moon Planets, 26, 117–133. [10] Mishra, A. and Kumar, P.S. (2022) Geophys. Res. Lett., 49, e2022GL098505. [11] Fortezzo, C.M. et al. (2020) LPSC LI, Abstract #2760 [12] Stuart-Alexander, D.E. (1978). U.S. Geological Survey, Map I–1047. [13] Basilevskii, A.T. (1976) LPSC VII, 1005–1020. [14] Meyer, H.M. et al. (2016) LPSC XLVII, Abstract #1242. [15] Michael, G. et al. (2012). Icarus, 218, 169–177.