Near Surface Expression of Linear Gravity Anomalies (LGAs): Potential Clues and Implications for Emplacement

Introduction: Gravity Recovery and Interior Laboratory (GRAIL) mission has recently revealed evidence for large scale occurrence of magmatic intrusions in the form of linear gravity anomalies or LGAs [1]. The largest of these intrusions span several hundred kilometers in length and extend for several kilometers in width. We report here potential near surface expressions of some of these geophysical anomalies which have direct implications for understanding the emplacement of these massive and spatially pervasive features. Data and Methods: We have utilized coordinated imaging and spectral datasets from recent missions in conjunction with the reported gravity anomalies to evaluate spatial correlations. Imaging data from Wide Angle Camera (WAC) at 100 meter per pixel and Narrow Angle Camera (NAC) at 0.5-1 m per pixel from Lunar Reconnaissance Orbiter (LRO) mission and Terrain Camera (TC) at 10 meter per pixel from Selenological and Engineering Explorer (SELENE) mission have been utilized to study the geomorphological character of the region around LGAs. Hyperspectral data from Moon Mineralogy Mapper (M) on Chandrayaan1 mission has been utilized to further evaluate the mineralogical signatures of geomorphologically interesting locations in the proximity of LGAs. New Findings: We report the occurrence of floor fractured craters (FFCs) in proximity to some of the LGA segments. FFCs are known to have formed by the modification of impact craters by subsequent intrusive magmatic activity [e.g. 2, 3]. We describe here four such occurrences which seem to be linked to the nearby LGA segments and could therefore provide additional information about the associated LGA: a) Crater Karpinskiy (91 km dia.): It is located in close proximity to the largest LGA in the northern high latitudes (Figure 1). The crater is separated from the LGA by ~50 km. Recent work by [4] reported the crater to have a feldspathic mineralogy along with strong hydration signatures. Karpinskiy is flanked by many large craters, similar to its size but none show evidence of any floor fractures. b) Crater Montgolfier P (36 km dia.) and Unnamed Crater (31.2 km dia.): These two craters are located at mid-latitudes in the northern hemisphere, at the far southern end of the largest LGA (same as the one associated with Karpinskiy). Their spatial relations indicate that any association with LGA would be with a subsegment rather than the main segment. Interestingly, both craters exhibit a circular exposure of mafic material on the floor (Figure 2). With the surrounding region being largely feldspathic, the mafic