HR: 0830h
AN: P41A-0394    [PDF]
TI: Structural Origins of Martian Pit Chains
AU: * Wyrick, D
EM: dwyrick@swri.org
AF: CNWRA, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
AU: Ferrill, D A
EM: dferrill@swri.org
AF: CNWRA, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
AU: Morris, A P
EM: amorris@utsa.edu
AF: Department of Earth and Environmental Science, University of Texas at San Antonio, 6900 N. Loop 1604 West, San Antonio, TX 78249 United States
AU: Colton, S L
EM: scolton@swri.org
AF: CNWRA, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
AU: Sims, D W
EM: dsims@swri.org
AF: CNWRA, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
AB: Pit craters are circular to elliptical depressions found in alignments (chains), which in many cases coalesce into linear troughs, and are common on the surface of Mars. Pit craters lack an elevated rim, ejecta deposits, or lava flows that are associated with impact craters or calderas. It is generally agreed that these features are formed by collapse into a subsurface cavity. Hypotheses regarding the formation of pit crater chains require development of a substantial subsurface void to accommodate collapse of the overlying sediments. Suggested mechanisms of formation include: collapsed lava tubes, dike swarms, collapsed magma chamber, karst dissolution, fissuring beneath loose material, and dilational faulting. The research described here is intended to constrain current interpretations of pit crater chain formation by analyzing their distribution and morphology. The western hemisphere of Mars was systematically mapped using Mars Orbiter Camera (MOC) images to generate ArcView Geographic Information System (GIS) coverages. All visible pit crater chains were mapped, including their orientations and associations with other structures. We found that pit chains commonly occur in areas that show regional extension or local fissuring. There is a strong correlation between pit chains and fault-bounded grabens. Frequently, there are transitions along strike from (i) visible faulting to (ii) faults and pits to (iii) pits alone. We performed a detailed quantitative analysis of pit crater morphology using MOC narrow angle images, Thermal Emission Imaging System (THEMIS) visual images and Mars Orbiter Laser Altimeter (MOLA) data. This allowed us to interpret a pattern of pit chain evolution and calculate pit depth, slope, and volume. The information collected in the study was then compared with non-Martian examples of pit chains and physical analog models. We evaluated the various mechanisms for pit chain development based on the data collected and conclude that dilational normal faulting and sub-vertical fissuring provide the simplest and most comprehensive mechanisms to explain the regional associations, detailed geometry, and progression of pit chain development.
DE: 5460 Physical properties of materials
DE: 5475 Tectonics (8149)
DE: 6225 Mars
DE: 8010 Fractures and faults
DE: 8040 Remote sensing
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting