Lunar thin section 78235
This rock is a norite that was strongly affected by shock metamorphism. The sample was collected by the Apollo 17 mission from the Taurus-Littrow Valley area, in a range of mountains between Mare Serenetatis and Mare Tranquillitatis. This rock has been dated at ~4.3 Ga.
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This is a sample of coarse-grained norite, probably a cumulate, of the highland plutonic suite. It has undergone strong shock metamorphism that resulted in several shock features: impact melt veins quenched to glass, polygonized orthopyroxene, and plagioclase that has been partially converted to maskelynite and, in some places, flow-deformed. In plane-polarized light you can see the highly fractured orthopyroxene, and plagioclase that seems to have cores containing abundant exsolved oxide dust. In cross polarized light much of the plagioclase is isotropic where it has been transformed to a glassy state by intense shock. The plagioclase did not melt, but the crystal lattice was destroyed. Notice how the maskelynite occurs mostly in a network of fractures. Field width is 4 mm. Views in plane and cross-polarized light. |
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An irregular fracture filled with impact melt. Bubbles occur in the glass, so presumably the glass was still liquid at low pressure after the shock wave passed. The glass in the vein is very dark, though it is also isotropic. The maskelynite is particularly abundant near the orthopyroxene grains around the margin. Field width is 8 mm. Views in plane and cross-polarized light. |
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Another view of highly fractured orthopyroxene, plagioclase containing exsolved oxide dust, and an impact melt vein. The polygonized orthopyroxene (shattered with different domains rotated in different directions) are clearly visible. The plagioclase has undergone flow deformation, especially visible in the region from the lower left to the top center. Elongate smears of plagioclase are bent around orthopyroxene and around one another. Field width is 4 mm. Views in plane and cross-polarized light. |
