HR: 1340h
AN: P13D-1552    [Abstracts]
TI: Was there a period of global contraction on Mars?
AU: * Nahm, A L
EM: nahma@mines.unr.edu
AF: University of Nevada, Reno, Department of Geological Sciences and Engineering MS 172, Reno, NV 89557, United States
AU: Schultz, R A
EM: schultz@mines.unr.edu
AF: University of Nevada, Reno, Department of Geological Sciences and Engineering MS 172, Reno, NV 89557, United States
AB: It has been suggested that a period of global contraction occurred on Mars during the Late Noachian-Early Hesperian in association with basaltic resurfacing and wrinkle ridge formation around Tharsis. To evaluate this hypothesis, we calculated the horizontal strain for all faults, both thrust and normal, using the comprehensive MOLA-derived Knapmeyer database and Kostrov's formula. Strains for the faults were then used to calculate the global radius change, assuming the source of stress was global contraction alone as has been done for Mercury, but also including the globally averaged contribution of normal fault strain. These calculations were done for both the proposed Late Noachian-Early Hesperian pulse of global contraction and the entire span of Martian history. Compressional faults were assumed to be either all thrust faults (with larger offsets and cutting the Martian surface, corresponding to an upper bound on the strain) or wrinkle ridges (with superjacent folding, smaller offsets, and no intersection with the surface, for a lower bound). Four scenarios were evaluated: wrinkle ridges for the entirety of Mars history, wrinkle ridges during the Late Noachian-Early Hesperian, thrust faults for the entirety of Mars history, and thrust faults during the Late Noachian-Early Hesperian. Surface strains are -0.023% for the wrinkle ridges only during the Late Noachian-Early Hesperian, -0.028% for wrinkle ridges only over the history of Mars, -0.145% for thrust faults during the hypothesized global contraction pulse, -0.181% for all thrust faults, 0.045% for normal faults during the Late Noachian-Early Hesperian, and 0.087% for normal faults only over the entire history. The only decreases in radius, ~1.6 km, were obtained for both the Late Noachian-Early Hesperian pulse and over Mars' history with all compressional structures assumed to be thrust faults, in conflict with the observations of Tharsis-related structures being wrinkle ridges rather than deep-seated thrust faults. Our results show that extensional strains associated with normal faults and other sources of stress such as Tharsis may have masked any signature of global contraction.
DE: 5455 Origin and evolution
DE: 5475 Tectonics (8149)
DE: 5494 Instruments and techniques
DE: 8010 Fractures and faults
DE: 8149 Planetary tectonics (5475)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting