We propose a global investigation of mercury s tectonic shortening structures to better characterize the planet s history of contraction. The tectonic scarps and ridges of mercury occur globally and…

This is a $210,219.05 grant awarded by the National Aeronautics and Space Administration (NASA) to Arizona State University for a research project to investigate the tectonic shortening structures on the planet Mercury. The goal is to better characterize the history of contraction on the planet using data from the MESSENGER spacecraft. The research will involve mapping and analyzing global tectonic features to determine the timing and rate of contraction throughout Mercury's history. No set-aside designation was used for this award. Arizona State University will be the prime contractor conducting this research, which supports NASA's broader efforts to understand the geology and evolution of the solar system.

We propose a global investigation of mercury s tectonic shortening structures to better characterize the planet s history of contraction. The tectonic scarps and ridges of mercury occur globally and were found to result mostly from contraction driven by secular cooling. This process lasted throughout most of mercury s history and resulted in a radius decrease of up to 7 KM. However, even after messenger revolutionized our understanding of the planet, IT is still not known when global contraction started, in part because the surface record of tectonic deformation may not date further back than the end of the late heavy bombardment. Furthermore, the rate of contraction and the associated strain rates have only been roughly constrained. While mercury s contraction should persist through the present day and small scarps have been found, IT remains unknown whether the resulting stresses are still sufficient to overcome the lithospheric frictional strength. In order to improve our understanding of mercury s shrinking, its change over time, and the associated implications for the planet s thermal evolution and geology, we will use messenger data to assemble the most complete inventory of shortening structures possible with current datasets. We will use the final, best resolution mdis mosaic, the derived global DTM, as well as novel stereo-DTM quadrangles with three times the resolution of the global one. Further, we will employ byrne ET AL. S (2014) map as vantage point to locate scarps, but then use the refined, small-scale technique crane and klimczak (2019) applied to the northern smooth plains to remap all structures on the remainder (~80%) of the planet s surface. Using the latest mosaics and shaded relief maps, we expect to significantly increase the number of cratered plains structures compared to those mapped by byrne ET AL. (2014). The refined technique will allow US to more reliably measure the widths of scarps, taking into account potentially associated back faults. Based on forward modelling, the average width-depth of faulting ratio for mercury s fault scarps is ~2.3 to 1, based on which we will also offer depth estimates for each structure. Furthermore, we will measure the displacement-length (d/l) value of sufficiently large scarps, which has been interpreted as a result of rheological parameters, e.g., the rock strength. In total, the geographic distribution of 12 measured and derived values (e.g., width, length, height, depth of faulting, lobateness, segmentation, spatial density, d/l) will be displayed as heat maps among others. This spatial database will then be complemented with temporal data by assigning an age constraint to all those mapped structures that clearly intersect at least one impact crater. The structures thereby lend themselves to a stratigraphic classification via the degradation state of the superposing/ superposed crater(s) ([pre-]tolstojan, calorian, mansurian, kuiperian), a technique that was developed for the moon by trask (1971) and moore ET AL. (1981) and applied to mercury by crane and klimczak (2017), albeit on preliminary, lower resolution data. For about 100 suitable scarps that intersect sufficiently large craters, we will further narrow down the stratigraphy-based age brackets with absolute model ages derived via crater-size-frequency distribution measurements on the floors and/or ejecta blankets of such craters. Our database will enable US to discern any spatial as well as temporal trends within any of our gathered values.