Large-scale lobate scarps in the southern hemisphere of Mercury

Utilizing Mariner 10 images of Mercury, we derived a digital elevation model to examine the topography of the large-scale lobate scarps Adventure Rupes, Resolution Rupes, and Discovery Rupes. The thrust faults that formed these landforms occur along a rough arc that extends for over 1000 km. The new topography shows that vertical uplift occurred on the same side of the three structures suggesting that the fault-planes all dip to the concave side of the arc. These data also show that Adventure and Resolution Rupes are topographically continuous, suggesting the two features were formed by a single thrust fault on Mercury. If this is the case, the Adventure-Resolution Rupes thrust fault is comparable in scale to the Discovery Rupes thrust fault. It is generally believed that Mercurian lobate scarps were formed by compressional stresses induced in the crust as the planet's interior cooled and shrank. Global contraction models predict that stresses at the planetary surface are horizontally isotropic (horizontal principal stresses being equal) resulting in randomly distributed thrust faults with no perferred orientations. The location, orientation, and geometry of the Discovery and Adventure-Resolution Rupes thrust faults, may not be randomly distributed. Analysis of the inferred stresses that formed these faults suggests that they were influenced by regional stresses or by mechanical discontinuities in the crust possibly caused by buried impact basins. The new topographic data reveal a broad, roughly circular topographic low interpreted to be an ancient impact basin centered near Schubert crater (43°S, 54°W), not far from an inferred stress center (48°S, 58°W). Thus the Discovery and Adventure-Resolution Rupes thrust faults may have been influenced by mechanical discontinuities in the Mercurian crust introduced by ancient buried impact basins.