Accommodation of lithospheric shortening on Mercury from altimetric profiles of ridges and lobate scarps measured during MESSENGER flybys 1 and 2 |
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Authors: | Maria T Zuber Laurent GJ Montési Steven A Hauck II Roger J Phillips David E Smith James W Head III Thomas R Watters |
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Institution: | a Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139-4307, United States b Department of Geology, University of Maryland, College Park, MD 20742, United States c Department of Geological Sciences, Case Western Reserve University, Cleveland, OH 44106, United States d Planetary Science Directorate, Southwest Research Institute, Boulder, CO 80302, United States e Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, United States f Department of Geological Sciences, Brown University, Providence, RI 02912, United States g Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States h Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, United States i Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 |
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Abstract: | The Mercury Laser Altimeter on the NASA MESSENGER mission has ranged to several ridges and lobate scarps during two equatorial flybys of the planet Mercury. The tectonic features sampled, like others documented by spacecraft imaging and Earth-based radar, are spatially isolated and have vertical relief in excess of 1 km. The profiles also indicate that the faulting associated with their formation penetrated to tens of kilometers depth into the lithosphere and accommodated substantial shortening. To gain insight into the mechanism(s) of strain accommodation across these structures, we perform analytical and numerical modeling of representative dynamic localization mechanisms. We find that ductile localization due to shear heating is not favored, given our current understanding of thermal gradients and shallow thermal structure of Mercury at the time of ridge and scarp formation, and is likely to be of secondary importance at best. Brittle localization, associated with loss of resistance during fault development or with velocity weakening during sliding on mature faults, is weakly localizing but permits slip to accumulate over geological time scales. The range of shallow thermal gradients that produce isolated faults rather than distributed fault sets under the assumption of modest fault weakening is consistent with previous models for Mercury’s early global thermal history. To be consistent with strain rates predicted from thermal history models and the amount of shortening required to account for the underlying large-offset faults, ridges and scarps on Mercury likely developed over geologically substantial time spans. |
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Keywords: | Mercury Terrestrial planets Tectonics Thermal histories |
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