Evidence of ring-faults in Orientale from gravity

摘要

The Orientale basin on the Moon is a well-preserved multi-ring impact basin that spans 900 km in diameter at its outermost ring. It consists of three concentric ring structures known as the Inner Rook, Outer Rook, and Cordillera . Orientale has been the focus of attempts to understand ring formation mechanisms because of its well-defined structure. Based on inwardly dipping faces consistent with the morphology of fault scarps, the Cordillera ring has been interpreted as forming through listric normal faulting from the inward collapse of the interior basin. A similar mechanism may have been responsible for the formation of the Outer Rook, though it has also been interpreted as the rim corresponding to the collapsed excavation cavity. This study uses gravity and topography data to examine the internal crustal structure of Orientale using a Monte Carlo Markov Chain approach to find the best-fit fault dip and displacement, as well as the depth to an intracrustal density interface and the density contrast across that interface. The best-fit solution for the case of both a Cordillera fault and Outer Rook fault has an intracrustal interface depth of 10.8 km, a vertical component of fault displacement fault displacement of 7.8 km, a fault dip of 28°, and a density contrast of 350 kg/m 3 between the upper and lower crust giving a lower crustal density of 3050 kg/m3. However, models with faults only at the Cordillera or with faults that do not cross the Moho also provide adequate fits to the data. This analysis presents quantitative evidence for the existence of faults beneath the rings of Orientale. Such analyses can be extended to future higher resolution gravity data sets such as GRAIL to more tightly constrain the subsurface structure of Orientale and other similar basins.