Deciphering the Structural History of Ulysses Fossae, Mars, Using Fault Pattern Analysis

• Published in: Journal of geophysical research. Planets 2023-05, Vol.128 (5), p.n/a
• Main Authors: Shahrzad, Stephanie, Bramham, Emma K., Thomas, Mark, Piazolo, Sandra, Byrne, Paul K., Mortimer, Estelle
• Format: Article
• Language: English
• Subjects: Chronology; Deformation; Evolution; Fault detection; Fault lines; fault mapping; Frequency analysis; Frequency distribution; Geological history; Graben; Lava; Lava flows; Mars; Mars surface; Mars volcanoes; Pattern analysis; Planetary geology; Regional development; structural history; Ulysses Fossae; Volcanic activity; Volcanoes
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2022JE007633

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 volca