Lunar thin section 14305
This is an impact breccia that incorporates fragments from several different lithologies. It consists of a very fine-grained crystalline matrix and fragments ranging from highlands anorthosite to mare basalt. Many of the fragments are themselves breccias. This sample was collected by the Apollo 14 mission to the Fra Mauro crater, on the northeastern margin of Mare Nubium. The material represents part of the Mare Imbrium ejecta blanket. Rocks of this type from the Apollo 14 site have been dated at ~3.82 Ga.
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This low-magnification view shows a dark matrix in which are set a variety of crystal and lithic fragments, including breccias. The large light-colored fragment on the right is shocked anorthosite. The large grain to the left of center is a breccia clast, as is the smaller fragment closer to the lower left corner. The fragmental nature of the breccia clasts is more obvious in cross-polarized light. The two clasts on the left are quite feldspathic. Field width is 8 mm.
Views in plane- and cross-polarized light.
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Basalt fragment. Notice how the edges are not sharp. The heating event that melted and permitted crystallization of the matrix also permitted partial assimilation of some of the clasts, making their margins fuzzy. The two grains at the very top of this basalt clast are colorless and have high birefringence, and are probably olivine. Field width is 4 mm.
Views in plane- and cross-polarized light.
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This is a small fragment, of probably a gabbro. It may contain fragments of only a few plagioclase and pyroxene crystals in the original coarse-grained rock. In cross-polarized light the fragmental nature of this fragment is obvious. Field width is 1.6 mm.
Views in plane- and cross-polarized light.
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This is an unusual plagioclase fragment that appears to have undergone considerable shock deformation. The unusual texture is indicative to me of shock-induced deformation twinning. Maybe. Field width is 1.6 mm.
Views in plane- and cross-polarized light.
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Quenched glass fragment with lath-shaped dark-gray plagioclase, lighter gray pyroxene, bright white specks of iron, and tiny light brown crystals of ilmenite. Much of the matrix of this whole breccia looks like the finer-grained matrix of this fragment. Field width is 0.8 mm. |
