Timing and Origin of Compressional Tectonism in Mare Tranquillitatis

The lithosphere of the Moon has been deformed by tectonic processes for at least 4 billion years, resulting in a variety of tectonic surface features. Extensional large lunar graben formed during an early phase of net thermal expansion before 3.6 Ga. With the emplacement of mare basalts at similar to 3.9-4.0 Ga, faulting and folding of the mare basalts initiated, and wrinkle ridges formed. Lunar wrinkle ridges exclusively occur within the lunar Maria and are thought to be the result of superisostatic loading by dense mare basalts. Since 3.6 Ga, the Moon is in a thermal state of net contraction, which led to the global formation of small lobate thrust faults called lobate scarps. Hence, lunar tectonism recorded changes in the global and regional stress fields and is therefore an important archive for the thermal evolution of the Moon. Here, we mapped tectonic features in the non-mascon basin Mare Tranquillitatis and classified these features according to their respective erosional states. This classification aims to provide new insights into the timing of lunar tectonism and the associated stress fields. We found a wide time range of tectonic activity, ranging from ancient to recent (3.8 Ga to <50 Ma). Early wrinkle ridge formation seems to be closely related to subsidence and flexure. For the recent and ongoing growth of wrinkle ridges and lobate scarps, global contraction with a combination of recession stresses and diurnal tidal stresses, as well as with a combination of South Pole-Aitken ejecta loading and true polar wander are likely.

Automated summary

The Moon's lithosphere has undergone deformation due to tectonic processes for over 4 billion years, resulting in various surface features. Large lunar graben were formed during an early thermal expansion phase before 3.6 billion years ago. Subsequent faulting and folding of mare basalts led to the formation of wrinkle ridges, which are exclusive to lunar Maria and caused by loading from dense mare basalts. Since 3.6 billion years ago, the Moon has been in a thermal state of net contraction, resulting in the global formation of lobate scarps. Lunar tectonism is an important record of the Moon's thermal evolution.