P51D-02
Understanding the Interior Evolution of Mercury from Its Tectonic History
Friday, 18 December 2015: 08:15
2007 (Moscone West)
Paul K Byrne1,2, Christian Klimczak1,3, A M Celal Sengor4, Steven A. Hauck II5 and Sean C Solomon1,6, (1)Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC, United States, (2)North Carolina State University Raleigh, Marine, Earth, and Atmospheric Sciences, Raleigh, NC, United States, (3)University of Georgia, Department of Geology, Athens, GA, United States, (4)Istanbul Technical Univ, Istanbul, Turkey, (5)Case Western Reserve University, Cleveland, OH, United States, (6)Lamont-Doherty Earth Observatory, Palisades, NY, United States
Abstract:
The surface of Mercury provides compelling insight into the planet’s interior. Excluding impact craters and basins, the most prominent landforms on Mercury are tectonic; these features are distributed globally and crosscut all major surface units. More than seven years of flyby and orbital observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft show that tectonism on Mercury is overwhelmingly shortening in nature; extensional structures occur only within volcanically flooded impact craters and basins, in part the result of thermal contraction of thick plains units. Shortening structures show no coherent, planet-wide pattern, although many have an approximately north–south orientation, and some form fold-and-thrust belts thousands of kilometers long. Even so, their widespread distribution points to a global source of stress, primarily from global contraction in response to secular interior cooling. Some of the largest such landforms are 2–3 km in relief and hundreds of kilometers long, their underlying thrust faults penetrating 30–40 km into the lithosphere. Shortening landforms as small as hundreds of meters in length have been identified during MESSENGER’s low-altitude campaign; the crisp morphology of these features indicates that thrust faulting, and thus global contraction, continued until the geologically recent. Displacement–length scaling analysis shows that Mercury’s shortening landforms have accommodated a reduction in planetary radius of up to 7 km since the end of the late heavy bombardment. Such a magnitude of contraction is more consistent with models of global contraction from interior cooling and partial core crystallization than pre-MESSENGER estimates of tectonic shortening. Notably, the emplacement of major volcanic plains deposits on Mercury ended globally by 3.6 Ga, consistent with the onset of a state of net horizontal lithospheric compression that served to inhibit the vertical ascent and eruption of magma.
