Amazonian Tectonic Evolution of Ceraunius and Tractus Fossae, Mars, and Implications for Local Magmatic Sources.

The heavily faulted Martian terrains of Ceraunius Fossae and Tractus Fossae, south of the Alba Mons volcano, have previously only been considered as parts of larger tectonic studies of Alba Mons, and consequently the complexity of the faulting remains unclear. As these terrains are in the midst of the large Tharsis volcanoes, the study of their surface deformation has the potential to help unravel the volcano‐tectonic deformation associated with the growth of Tharsis as well as to decipher details of the magma‐tectonic processes responsible for graben formation. Here, we distinguish between faults and collapse structures based on image and topographic evidence. We mapped ∼12,000 faults, which we grouped into three distinct fault groups based on orientation, morphology, and relative ages. These show a temporal evolution in the mapped fault orientations from NE to N‐S to NW with associated changes in stress orientations. We also mapped collapse features and categorized them into four different groups: pit‐crater chains, catenae, u‐shaped troughs and chasmata. Examining the four collapse structure groups reveals that they are likely four progressive stages in the erosional evolution of pit‐crater chains. Together, this revealed a structural history heavily influenced by lateral diking from both local (radial to Alba Mons, Pavonis Mons and Ascraeus Mons) and regional (radial to Tharsis) sources, and vertical diking from a proposed Ceraunius Fossae centered magma source. This, along with an updated crater size‐frequency distribution analysis of the unit ages, reveals a highly active tectonic and magmatic environment south of Alba Mons in the Middle Amazonian. Plain Language Summary: The large‐scale faults surrounding the dome of the Alba Mons volcano on Mars have been studied intensely, while the faulted area south of Alba Mons has received relatively little attention. Closer inspection of these southern terrains, namely Ceraunius Fossae and Tractus Fossae, reveals that this area is far more complex in structure and more recent in activity than previously thought. In this study, we mapped and measured all the faults in the study areas. In addition to the faults, the surface of the study area is covered in "collapse structures." These are circular to trough‐like features created when the surface material has fallen into a subsurface cavity. We mapped and characterized these faults and collapse structures, in order to determine the history of events and which geological process created them. We found three distinct extensional faulting events, and examples of four types of collapse structures. These events all took place within 2.4–1.4 billion years ago during the Amazonian period. Together, these results show that magmatic activity drove structure deformation, both from the surrounding Alba Mons, Ascraeus Mons and Pavonis Mons volcanoes, and also from a local large magmatic source situated directly underneath Ceraunius Fossae. Key Points: Three fault populations and four types of collapse features are mapped and analyzed in Ceraunius Fossae and Tractus FossaeWe present a four‐stage structural evolution of the area, with dike‐induced deformation being the prevalent processThe stages of activity in the study area all occurred during the Amazonian, with activity from a local magmatic source beneath Ceraunius Fossae [ABSTRACT FROM AUTHOR]