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Figure Descriptions
Figure 1. Schematic model of the signs of recent tectonic activity of surface features. A small crisp wrinkle ridge segment in Mare Tranquillitatis served as a template for the topographic profile. The signs of recent tectonic activity apply, however, both for lobate scarps and wrinkle ridges. These signs include crisp morphology, deformed craters, cross-cut craters, small graben and troughs, lower crater density, and boulder fields/patches. In this study, the boulder abundance was not used to determine the degradational stage of a wrinkle ridge or lobate scarp. Shallow moonquakes detected by the Apollo missions have been previously correlated to the activity of lobate scarps.
Figure 2. a) Location of Mare Tranquillitatis (white outline; Nelson et al., 2014) near the lunar equator projected onto the global merged WAC mosaic. b) Mare Tranquillitatis (black outline) projected onto the LRO LOLA – SELENE Kaguya DEM (Neumann, 2009; Barker et al., 2016). A color-blindness-friendly version can be accessed in the supplementary materials (Fig. S1). c) The black outline of Mare Tranquillitatis projected onto the GRAIL Free Air Gravity map (Kahan, 2013; harmonic degree and order of 660). The black lines sketch the proposed quasi-rectangular pattern of ancient intrusion (after Andrews-Hanna et al., 2012).
Figure 3. Tectonic map of Mare Tranquillitatis projected on the merged LRO LOLA – SELENE Kaguya DEM (Barker et al., 2016). A color-blindness-friendly version can be accessed in the supplementary materials (Fig. S2). Parts of the lobate scarp cluster in the northern mare cross the highland boundary and continue into Mare Serenitatis near the Taurus-Littrow valley. Unidentified features are linear positive topographic features with a possible but unproven tectonic origin (other possible origins are, e.g., dikes, lava flows, surface expressions of buried structures, or ejecta remnants).
Figure 4. Tectonic feature map with all degradational classified segments colorized according to their respective class and projected onto the WAC global mosaic (Robinson et al., 2012). This map includes wrinkle ridge, lobate scarp, and unidentified features. Tectonic features in the western part are mostly comprised of advanced and heavily degraded features. Crisp and moderately degraded features occur scattered in clusters throughout the mare.
Figure 5. NAC images of crisp features. White arrows show representative graben. a) Wrinkle ridge north of Ross Crater with a crisp morphology and small graben (M1184668142RE; 11.82°N, 24.27°E). b) Image of the same wrinkle ridge further west. Visible are several sets of small graben and a small boulder patch (black arrow; M1184668142RE; 11.90°N, 24.17°E). c) Small and faint lobate scarp in the vicinity of Taurus-Littrow valley. The image shows some faint graben-like features and deformed craters with ~100 to ~50 m in diameter (black arrows; M1154023134RE; 19.11°N, 29.93°E). d) Set of graben in close vicinity of a crisp lobate scarp cluster near Taurus-Littrow (M1157549836RE; 18.52°N, 30.55°E).
Figure 6. NAC images of moderately degraded features with relatively sharp contacts (white arrows) in Mare Tranquillitatis. a) A moderately degraded wrinkle ridge in the eastern mare deforming and cross-cutting several craters (black arrows; M1245756057LE/RE; 12.29°N, 39.82°E) and b) a small moderately degraded lobate scarp in the northwestern mare which also deforms a ~100 m diameter crater (black arrows; M1279976340LE; 14.60°N, 20.04°E).
Figure 7. Kaguya Terrain Camera images of a representative advanced degraded wrinkle ridges. The advanced degraded wrinkle ridge (7.54°N, 22.75°E) has a well-developed wrinkle ridge morphology consisting of a broad arch and a superimposed ridge (white arrows). In addition, it exhibits several dominant boulder fields, which are visible as bright spots along the ridge (black arrows). b) Close up NAC image (M1234102538LE) of the ridge shown in 7a, featuring boulder fields (black arrow) and the “elephant-hide” texture (white arrows).
Figure 8. Kaguya Terrain Camera images of representative heavily degraded wrinkle ridges (white arrows). Both wrinkle ridges (a), 1.31°N, 22.56°E; b), 8.10°N, 22.20°E) have gentle slopes and less well-developed wrinkle ridge morphologies than seen in figure 7. The ~1 km sized crater in the center of image a) resembles a rare case, which shows the possible deformation of a crater by a heavily degraded ridge. Survival times of ~1 km sized craters are still estimated to be several billion years (Fassett & Thomson, 2014).
Figure 9. Bouguer anomaly map of Tranquillitatis superposed on the WAC global mosaic. The map has the same spatial extent as the map in Fig. 4, and shows the tectonic feature map of Fig. 4. The outline of Mare Tranquillitatis is shown as a fine white line. Yellowish colors indicate positive gravitational anomalies, which implies a thin crust and mantle upwelling, as well as a thick abundance of basalt. Mascon basins like Mare Serenitatis in the northwestern part of the map are represented in yellow colors, whereas non-mascon basins like Mare Tranquillitatis appear in more heterogenous and mainly blue and green colors. The western part of Mare Tranquillitatis has more pronounced positive gravitational anomalies than the eastern part. Concentric wrinkle ridges occur at the positive Lamont anomaly in southwestern Tranquillitatis. Crisp and moderately degraded features are not correlated with gravitational anomalies.
Figure 10. Grail bouguer gravity gradients map of Mare Tranquillitatis (supplement material from Andrews-Hanna et al., 2018) in units of Eötvös (1 E = 10–9 s–2) and our tectonic map of Fig. 3. Gravity gradient maps are used to identify buried deep-seated structures, like large igneous intrusions and ring-faults in impact basins (e.g., Andrews-Hanna et al., 2013, 2014, 2018; Valantinas & Schultz, 2020). Eastern Tranquillitatis does not exhibit clearly detectable anomalies known from deep faults.
Figure 11. Rose diagram of the orientations of crisp features within Mare Tranquillitatis, including lobate scarps and wrinkle ridges. Crips features share a western to northwestern orientation.
Figure 12. Evidence for recent activity by ancient wrinkle ridges in Mare Tranquillitatis. (a) Shows the topographic map of the region southeast of the Lamont anomaly. The stars mark the locations of (b) and (c). (b) Shows NAC image (M1108125194LE; 3.43°N, 23.97°E) showing a part of a concentric wrinkle ridge at the southeastern Lamont anomaly. It crosscuts craters with ~100 m in diameter (white arrow) and exhibits several boulder fields (black arrows). (c) NAC image (M162134363LE) of faint graben-like features on the hanging wall of a wrinkle ridge (0.45°S, 26.47°E). A color-blindness-friendly version can be accessed in the supplementary materials (Fig. S3).