Structure and Petrology of a Cumulus Norite Boulder Sampled by Apollo 17 in Taurus-Littrow Valley, the Moon

A glass-coated half-meter-size boulder was sampled by the Apollo 17 crew at station 8 near the foot of the Sculptured Hills. The rock proved to be a coarse-grained (0.5-cm) plagioclase-orthopyroxene cumulate, and the samples are the only true norites returned from the lunar surface. Photographs of the boulder showed it to contain at least nine structural surfaces and four glass veins. Orientation and inspection of three of the returned samples resulted in the identification of six surfaces and one vein. One of the structural surfaces visible in the boulder was identified as primary cumulus planar lamination, which was folded through an angle of at least 35° between two oriented samples, whereas fracture sets representing the other surfaces were coincident. The boulder is believed to be a sample of the deeper highlands or submare lunar crust, derived from a depth of 8 to 30 km and somewhat shock-metamorphosed during at least two excavation events. The chemical composition of the norites, when determined, should be of special interest in view of the large amount of literature concerning glass, cataclasite, hornfels, and “basalt” of noritic composition returned by other Apollo missions. However, the cumulus texture of the boulder precludes its being representative of any magmatic liquid composition, suggests that the lunar crust is heterogeneously layered, and that plagioclase sank, not floated, in magmatic liquids that formed the lunar crust.