Dr. Klimczak and Dr. Loveless have a new publication in AGU Advances

AGU – Advances: "Several Kilometers of Global Contraction on Mercury: A Sample-Size Independent Assessment of Fault Strain"

Authors: 

Dr. Stephan R. Loveless ¹ and  Dr. Christian Klimczak ¹

^{1 Center for Planetary Tectonics at UGA, Department of Geology, University of Georgia, Athens, GA, USA,} 

Abstract

Mercury underwent global contraction due to the sustained cooling of the planet. Positive-relief landforms, found widespread across Mercury, are thought to be the surface expressions of thrust faults accommodating the contraction. Disagreement exists in the literature on the amount of contraction, with estimates of radius change ranging from ∼1 to 7 km. These differences solely arise from the method used to estimate the fault population strain, which relies on the number of structures. Here, we adapt a previous framework by which the continuum approximation to shortening strains can be determined from fault length and displacement statistics for an incompletely sampled fault population. We apply this method to three data sets that sample different numbers of faults. Our results show that even for conservative fault parameters, 2 to 3.5 km of radial contraction are returned, irrespective of the data set used, and thus resolve the debate on the amount of global contraction on Mercury.

Key Points

• We implement a method to estimate contractional fault strain independent of the number of faults considered
• We resolve the long-standing disagreement of the amount of Mercury's global contraction
• Our results indicate Mercury radially contracted by multiple kilometers for a wide range of fault geometries and depths

Plain Language Summary

The planet Mercury has shrunk due to the long, sustained cooling of its interior. This process has led to the development of faults to accommodate the shrinking in the cold uppermost rocky parts of the planet. Multiple studies use the uplifted topography that overlie these faults to estimate the amount Mercury has shrunk. However, these studies are in disagreement with one another due to the number of landforms that each study attributes to global contraction. Here, we use an alternate approach of calculating the change in volume caused by a population of faults by statistically scaling the change from the largest fault to the entire fault population. From the literature, we use three fault data sets with noticeably different numbers of structures that previously showed the disagreement. The method in this study produces results that are comparable to one another, resolving the long-standing disagreement in the literature. Our results find that at least three kilometers of change in Mercury's radius occurred for a conservative set of fault-geometric parameters. Therefore, this newly applied method should replace the previous approach to estimate the amount by which Mercury has shrunk.

This publication has also been featured as an EOS spotlight:

How Much Has Mercury Shrunk?