An Investigation of the First-Order Mechanics of Polygonal Fault Networks of Utopia Planitia, Mars

• Main Author: Islam, Fariha
• Format: Others
• Published: ScholarWorks@UMass Amherst 2009
• Subjects: Utopia Planitia; polygonal terrain; buried topography; North Sea sedimentary basins; BEM models; Mars; Geology
• Online Access: https://scholarworks.umass.edu/theses/225; https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1316&context=theses

This study investigates the first-order mechanics of polygonal fault networks in Utopia Planitia, Mars and whether terrestrial sedimentary basin polygonal terrains are an analog for giant Martian polygons since there is an overlap in scale between the 3 km terrestrial polygons and the 1-40 km giant polygons of Mars. Volumetric contraction accommodates the extensional faulting observed in both cases. Boundary Element Method numerical models are used to simulate the first-order-mechanics of the faulting process. Models use material properties for wet, fine sediment, and apply an extensional strain to produce volumetric contraction. Fracture seeds that simulate the buried topography beneath the basin are placed at the base of the model. MOLA tracks from the Highlands are used to create the uneven topography beneath the basin since the underlying topography of the Northern Lowlands is thought to be similar to the topography of the older, Southern Highlands. The model investigates whether 1 & 2 km layer of wet, fine sediments will produce the fracture spacing observed within the polygonal terrains in Utopia (~5 – 6.5 km). A fracture network that is similar to the scale of the polygonal terrain in the Utopia Basin is established within the model at low strain, supporting the idea that buried topography could be the primary scaling factor for the polygon grabens. The results do not constrain an upper limit for strain; the observed trough widths in Utopia suggest that further strain was expressed by the widening of the troughs. Material properties for wet, fine sediments, analogous to the terrestrial counterpart, are appropriate for the model to match what is observed in Utopia. The power-law scale of Highlands topography controls the scale of the surface fracture spacing in the models. Measurements of running average of trough spacing along radial transects with respect to the center of the basin did not yield a monotonic decrease in trough spacing as would be expected for a smooth basement with no buried topography. Study results support the case for buried topography controlling the scale of the giant polygons of Utopia Planitia.