Summary

Tectonic landforms on the Moon predominantly occur on the nearside, associated directly with the lunar maria. Basin-localized lunar tectonics is expressed by two landforms: wrinkle ridges, and linear and arcuate rilles or troughs. Wrinkle ridges are complex morphologic landforms found in mare basalts, interpreted to be contractional tectonic landforms formed by thrust faulting and folding. Linear and arcuate rilles are long, narrow troughs, interpreted to be graben formed by extension, deforming both mare basalts at basin margins and the highlands adjacent to the basins. In contrast to basin-localized tectonics, landforms of the nearside are the more broadly distributed lobate scarps. Lobate scarps on the Moon are relatively small-scale asymmetric landforms that are often segmented with lobate margins. These landforms are the surface expression of thrust faults and are the dominant tectonic feature on the lunar farside. Crater density ages indicate that crustal extension associated with lunar maria ceased at ~3.6 Ga. Crustal shortening in the maria, however, continued to as recently as ~1.2 Ga. The cessation of extension may have resulted from the superposition of compressional stresses from global contraction on flexural extensional stress due to loading from the mare basalts. The lobate scarps formed less than 1 Ga and appear to be among the youngest endogenic features on the Moon. The presence of young lobate scarp thrust faults supports late-stage compression of the lunar crust.