Structure
Morphologically diverse scarps, ridges, troughs, and other structural lineaments are relatively common in the Discovery quadrangle. Dzurisin documented a well-developed pattern of linear lithospheric fractures in the quadrangle that predate the period of heavy bombardment. A dominant structural trend is recognized at N. 50° –45° W., and subsidiary trends occur at N. 50° –70° E. and roughly due north. Joint-controlled mass movements were most likely responsible for the fact that many craters of all ages have polygonal outlines, and some linear joints may have provided surface access for lavas that formed the intercrater plains. Evidence of the latter may be recorded by several linear ridges that may have been formed by lava accretion along linear volcanic vents (for example, Mirni Rupes at latitude 37° S., longitude 40° W., FDS 27420).
Planimetrically arcuate escarpments in the Discovery quadrangle cut intercrater plains and crater materials as young as c4. These scarps are typically 100 to 400 km long and 0.5 to 1.0 km high, and they have convex-upward slopes in cross section that steepen from brink to base. More trend closer to north-south than to east-west. Discovery (lat 55° S., long 38° W.), Vostok (lat 38° S., long 20° W.), Adventure (lat 64° S., long 63° W.), and Resolution (lat 63° S., long 52° W.) Rupes are the most prominent examples in the quadrangle. Vostok transects and foreshortens the crater Guido d'Arezzo, which suggests that arcuate scarps are compressional tectonic features (thrust or high-angle reverse faults). Melosh and Dzurisin have speculated that both arcuate scarps and the global mercurian lineament pattern may have formed as a result of simultaneous despinning and thermal contraction of Mercury.
Planimetrically irregular scarps on the floors of many plains-filled craters and basins are the youngest recognized structural features in the quadrangle, as they cut both the smooth plains and intermediate plains materials. Their occurrence inside only smooth-floored craters and basins suggests that the stresses responsible for their formation were local in extent, perhaps induced by magma intrusion or withdrawal beneath volcanically flooded craters.
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