Search

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]

Ulysses Fossae is a faulted region surrounded by lava flows that sits between the major volcanoes of the Tharsis Rise volcanic province on Mars. This area is unique, as it is the only exposure of extensional faulting which can be related to the Olympus Mons volcano and one of the only a few faulted areas relating to the Tharsis Montes. In order to determine the area's structural evolution through time, we mapped all identifiable faults, divided them into 10 fault groups determined by their orientation and morphology, and performed detailed crater size‐frequency analysis of the geological units. We divide the fault groups into two overall types based on their genesis: local diking and regional extension. The complex structural evolution recorded in the extensional faults in Ulysses Fossae is dominated by local dike‐related activity (8/10 fault groups), along with deformation from large, regional scale extensional processes related to the development of the Tharsis province as a whole (2/10 fault groups). Strain values measured across the 1 fault groups vary between 0.4%–2.2%, with the grabens related to regional extension accommodating larger extensional strains than the local dike‐related grabens. The crater size‐frequency distribution analysis of three distinct areas in Ulysses Fossae (UF Dome, UF North, and UF South) revealed that the majority of the faulting in Ulysses Fossae was active during the Early Amazonian. Plain Language Summary: The volcanoes in the Tharsis province on Mars are normally associated with deformation of the surface near them and with the growth and development of the volcano. However, in Tharsis, due to its significant coverage of lava, we only find volcanically associated surface deformation for some of the Tharsis volcanoes in an area called Ulysses Fossae. In this study, we map and characterize the surface structures in Ulysses Fossae, which are then used to define the structural history of the area. Our work reveals that there are 10 distinct episodes of deformation in Ulysses Fossae, where most of the activity responsible for the surface structures are associated with subsurface activity from nearby volcanoes. Two of the episodes also show signs of movement associated with the development of the Tharsis region as a whole. Additionally, we determined the ages of this deformation and found that most of the activity takes place during the Amazonian period (∼3 billion years ago) in Mars' geologic history. This shows that the volcanic systems surrounding Ulysses Fossae were active for longer than previously determined and together with the mapped structures and provides a detailed history of the different stages of activity in the area. Key Points: We map and characterize 10 fault groups in Ulysses Fossae; the majority of the fault groups are interpreted to be initiated by radial dikingWe present an overview of the volcano‐tectonic history of the area constraining relative and absolute ages using crater frequency analysisThe majority of the faulting takes place during the Early Amazonian and reflects an active diking system in Tharsis during this period [ABSTRACT FROM AUTHOR]

Jezero crater is a ~45‐km impact crater on the margin of Isidis basin on Mars. Jezero is the landing site for NASA's Mars 2020 rover mission. The crater hosts a paleolake, and fluvio‐lacustrine deposits formed in this lake remain accessible to exploration. A dark‐toned deposit on the crater floor overlies light‐toned carbonate‐bearing deposits and has been interpreted as a lava flow. We determined the average thickness of this deposit at the margins to be ~13.0 ± 0.8 m. We analyzed the statistics of impact craters superposed on this deposit and estimated its model age as 2.6 ± 0.5 Ga in the Hartmann system, placing it most likely in the Early Amazonian. The error estimate here includes an estimate of the uncertainty associated with the crater counts. Acquisition, caching, and eventual return of a sample from this unit could provide an important calibration point for Mars crater chronology. Plain Language Summary: Jezero crater is a large impact crater on Mars with a diameter of about 45 km. In the Martian deep past this crater hosted a long‐lived lake. On 19 November NASA announced that Jezero crater will be the landing site for the coming Mars 2020 mission. On top of sediments on the central crater floor is a distinctive deposit of dark rocks that possibly originated as a lava flow after the lake had dried out. We studied the statistics of small impact craters on this dark deposit. Such impact crater statistic is widely used as a tool for dating Martian terrains. We report a derived "model age" of 2.6 ± 0.2 Ga for these rocks. One central goal of the Mars 2020 mission is to select and store a cache of rock samples that will be returned to Earth by a later mission for study in terrestrial laboratories. If this dark deposit is indeed lava, a sample could be dated in terrestrial laboratories. Together with our crater statistics reported here, this could provide a crucial tie‐point for recalibration of the crater count dating system for Mars, which now relies on extrapolation from samples collected on the Moon. Key Points: Based on craters 177‐500 m we estimated the model age of the dark‐toned floor unit as 2.6 ± 0.2 Ga in the Hartmann systemWith 25% as an estimate of the uncertainty associated with identifying and measuring diameters, we find a model age range of 2.6 ± 0.5 GaThe average thickness of the unit at the margins is determined to be ~13.0 ± 0.8 m [ABSTRACT FROM AUTHOR]