July 5, 2013
A Tongue & a Bench
image by Gari Arrillaga, Cambrils, Spain, and map from Taylor, Martel and Spudis (2010)
Yesterday's LPOD proposed that the Archimedes Mountains (AM) and nearby lower terrain were emplaced by giant landslides off the Apennine Mountains. Longtime LPOD participant Howard Eskildsen questioned how that could happen. It would be a long landslide displacement - over 200 km horizontally - from a mountain range only 5 km high. Furthermore, with so much material transferred away from the Apennines wouldn't there be a large indent in the Apennines where the AM were removed? I am delighted by this question because it is geologically reasonable and is based on observations. By chance Gari send an image that gives us a wider perspective on this area and problem. And a map from a paper from a few years ago provides more understanding. The non-mare region around Archimedes crater has been mapped as two different kinds of terrains by lunar scientists. The AM are part of the white material in the map that is generally understood as mountainous material, at least some of which slumped off the Apennines; this image shows near bottom center masses of rocks lower than the Apennines but quite likely stuff that previously was part of them. The Apennine front is in fact sightly indented here. The two curved arcs of the Archimedes Mountains themselves have also been considered by some as part of an inner Imbrium Basin ring, and therefore material uplifted from depth at that location. Geologist are most interested in the second material, the one shown in blue. This Apennine Bench Formation is most commonly interpreted as a type of unique volcanism that occurred on the floor of the Imbrium Basin before the mare lavas erupted. So there are likely a range of origins for the material here. Some mountains close to the Apennines are quite likely to be slump blocks, the AM might be too, or perhaps isolated pieces of an inner basin ring. And the smoother stuff surrounding the hills and mountain is iron and titanium-poor lavas, and hence not dark like the later mare lavas.
29-06-2013, 02:44 UT. C11 - ZWOptical ASI 120 MM.
21st Century Atlas charts 18 & B6.
Yesterday's LPOD: Tongues And Bumps
Tomorrow's LPOD: Manufacturing Dreams