Buried impact structures found in MarsCrust-3 crustal thickness model: Identification, classification, & significance

The addition of buried impact structures to the known database of surface structures is key to a complete understanding of the geologic history of Mars because it allows for a more precise calculation of crustal age. Also, because these buried structures record an impact event and a resurfacing event they can be used to clearly define crustal versus surface ages. This study used topographic data and a crustal thickness model to identify buried and visible impact structures. This process was repeated twice and then correlated to create a global database of impact structures greater than 200 km. During the study confidence factor protocol was developed based on [1] ratio of crater diameter to relief and [2] percentage of rim present. This criteria was applied to each visible and buried structure. The comparison of visible and buried impact structures provides constraints on the timing of resurfacing events. Cumulative and N(300) values were calculated to derive the relative crustal ages in major geologic provinces. It was found that [1] the Martian lowlands and highlands have similar crustal ages when combining the visible and buried impact structures, [2] Tharsis is younger than these two regions, [3] the lowlands appear to have been thinned before or during the Late Heavy Bombardment (LBH), and [4] the resurfacing of the lowlands must have happened at the same time or shortly after the rise of the Tharsis bulge.