May 28, 2012

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Anorthosite Rays

image by Mario Weigand, Offenbach am Main / Germany

Once again the LPOD Photo Gallery has provided an image for LPOD. In this case it is Mario's excellent view of bright Anaxagoras overlapping shallow Goldschmidt to the right, with the even brighter simple crater Epigenes A to the bottom right. The pudgy central mountains of Anaxagoras are pure anorthosite - plagioclase feldspar - a mineral that is thought to have formed the calcium-rich crust above the magma ocean. Continuous ejecta and rays from the crater that drape across Goldschmidt are also anorthositic. Mario's image shows better than I've noticed elsewhere two broad zones of material on the western wall and continued beyond the rim crest down the exterior wall. Although the distribution of rays and impact melt imply that Anaxagoras formed by oblique impact with the projectile coming from the west, it seems most likely that the wall zones are bright (hence anorthosite) material ejected during formation of the crater.

Chuck Wood

Related Links
Rükl plate 4
Mario's website

Yesterday's LPOD: Droppings From a Passing Mountain?

Tomorrow's LPOD: Smaller Frac - Again


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