P41F-06
Amount, Timing, and Rate of Global Contraction on Mercury
Thursday, 17 December 2015: 09:15
2007 (Moscone West)
Christian Klimczak1,2, Paul K Byrne3,4, Maria E Banks5,6 and Sean C Solomon1,7, (1)Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC, United States, (2)University of Georgia, Department of Geology, Athens, GA, United States, (3)North Carolina State University Raleigh, Marine, Earth, and Atmospheric Sciences, Raleigh, NC, United States, (4)Carnegie Inst Washington, Department of Terrestrial Magnetism, Washington, DC, United States, (5)Smithsonian Institution, National Air and Space Museum, Center for Earth and Planetary Studies, Washington, DC, United States, (6)Planetary Science Institute Tucson, Tucson, AZ, United States, (7)Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, United States
Abstract:
Mercury’s surface hosts a large number of thrust-fault-related landforms that primarily accommodated global contraction driven by interior cooling. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft returned a wealth of data that allow for a detailed characterization of the amount and timing of that contraction. In particular, mapping of thrust-fault-related landforms shows that the planet experienced a radius decrease of 5.1±2 km since the end of heavy bombardment. Cross-cutting relationships of thrust faults with impact craters of different degradation stages indicate that global contraction operated throughout much of Mercury’s past, with the earliest evidence for faulting dating from near the time of cessation of widespread plains volcanism. An assessment of the brittle strength of Mercury’s lithosphere indicates that 0.4±0.1 to 2.1±0.4 km of radius change is necessary for stresses to be sufficiently large to overcome the frictional resistance to sliding on pre-existing fractures and faults. These values not only increase estimates for the overall amount of global contraction but also imply that this process was initiated before any evidence of shortening in the geologic record was manifest as brittle deformation. Together, these observations and results have implications for the rate at which global contraction operated through Mercury’s geologic history. Higher initial strain rates are required if the radial contraction prior to the initiation of thrust faulting was ~2.1 km, and are possible but not required if the radial contraction accommodated prior to the onset of thrust faulting was ~0.4 km. These findings incorporate an aspect of global contraction not previously considered, as well as a contribution to radius change beyond that inferable from mapping. This approach is applicable to inferences on global contraction from tectonic mapping, and constraints on thermal histories, for any world dominated by secular cooling.
