Normal faulting origin for the Cordillera and Outer Rook Rings of Orientale Basin, the Moon

Abstract

Orientale Basin is the youngest and best‐preserved large impact basin on the Moon with at least four topographic rings contained within the topographic rim marked by the Cordillera Ring (diameter = 930 km). Its well‐exposed interior makes this basin a prime location to study basin formation processes. Forward mechanical modeling of basin ring topography shows that the outermost rings, the Cordillera Ring (CR) and Outer Rook Ring (ORR) are large‐scale normal faults with displacements (D) of 0.8 to 5.2 km, fault dip angles (δ) of 54° to 80°, and vertical depth of faulting (T) between 19 and 37 km with most faults having T = 30 ± 5 km. These faults and the distribution of maria inside the basin suggest that the transient crater, important for determining many impact‐related characteristics such as projectile size, was contained entirely within the ORR and likely had a diameter between 500 and 550 km. The difference in crustal thickness between the western and eastern sides of the basin is not a result of the basin‐forming event, which indicates the formation of the hemispheric crustal thickness asymmetry was likely before the formation of Orientale Basin 3.68 to 3.85 Ga.