Intrusions Below Volcanically Buried Craters in Mare Fecunditatis Indicated by Extrusive Features Associ-

Introduction: Mare ridge ring structures (MRRSs) are deformed surface features and have long been studied on the floors of the maria since the early exploration of the Moon [1, 2, 3]. They are ridge segments having the form of rings (circular, elliptical or irregular in shape) with the size varing from 1-2 km to over 80 km in diameter [1]. The analogical structures were also found in the northern plains of Mercury [8-10] and in the ridged plains volcanic units throughout Mars [1113]. Several mechnisms have been proposed to explain the formation of MRRSs on the Moon, including: (i) volcanic in nature and occur in association with mare wrinkle ridges [1, 14]; (ii) the interaction of (impact) craters with molten lavas [4, 5, 15], as well as those similar analogs found on Mercury and Mars [8-13]; and (iii) more than one processes (volcanism and tectonism), including modification by endogenic processes [3]. However, the direct evidence which requires more confidence in linking subsurface magmatism to MRRSs is still lacked. In this work, we highlight a category of mare ridge ring structures in Mare Fecunditatis that was not reported before and use the topographical and geometrical features to gain insight into the subsurface geology of Mare Fecunditatis. Data and method: The overall characteristics and detailed small geologic features associated with MRRSs are investigated from the high-resolution images derived from LRO [16] and Kaguya [17]. Small surface feature which was not covered by LROC NAC image will be studied by using Kaguya Terrain Camera (TC) data [18]. At 10 m/pixel globally, the Kaguya TC data effectively bridges the gap of the resolution between the WAC (100 m/pixel) and the NAC (~1 m/pixel) data of LROC and thus provide an invaluable contextual information. A Moon Mineralogy Mapper (M) mosaic of Mare Fecunditatis has been created at a resolution of 280 m/pixel by using 10 orbits of data from Optical Period 2C (OP2C) [19]. The level 2 reflectance M data products that were derived from the level 1B reflectance data products with spectral resolutions of 20 and 40 nm, total 85 bands in global mode. Because the coverage of the Fecunditatis region is incomplete or absent from other observation period, the 280 m/pixel OP2C data are used to detect spectral properties of the volcanic features, though its resolution is two times lower than OP2A and OP1B. The detailed information of the calibration of M can be found in previous studies [19, 20]. We obtained M IBD color composite using the method adopted by the M science team [21-23]. The color shown on the composite depends on relative ferrous band strengths and/or band centers that result from differences in mineralogy and optical maturity [21]. Thus, the composite can reveal useful information of geologic units with different composition. Results: In this study, more than 50 MRRSs in the Fecunditatis basin were identified. Here, we present several typical examples from Fecunditatis MRRSs, which were not reported before. These MRRSs retain a series of volcanic landforms along their circular rings indicating extrusive features resulted from post-craterformation magmatism. These structures are circled ridge segments with the diameter varied from ~12 to 30 km, ranked into the mid-size complex impact structures (e.g., ~15-30 km).