The geological investigation of the Taurus-Littrow Valley: Apollo 17 landing site

Abstract

Astronauts Cernan and Schmitt, of Apollo 17, landed in the Taurus-Littrow valley of the Moon on December 11,1972. Their major objectives were (1) to sample very ancient lunar material such as might be found in pre-Imbrian highlands as distant as possible from the Imbrium basin and (2) to sample pyroclastic materials that had been interpreted as significantly younger than the mare basalts returned from previous Apollo landing sites. The crew worked approximately 22 hours on the lunar surface; they traversed about 30 km, collected nearly 120 kg of samples, took more than 2,200 photographs, and recorded many direct geologic observations. The lunar surface data, sample results, and geologic interpretation from orbital photographs are the bases for this geologic synthesis. The Taurus-Littrow massifs are interpreted as the upper part of the thick, faulted ejects deposited on the rim of the transient cavity of the large southern Serenitatis basin, which was formed about 3.9 to 4.0 b.y. ago by the impact of a planetesimal. The target rocks, predominantly of the dunite-anorthosite-norite-troctolite suite or its metamorphosed equivalents, were fractured, sheared, crushed, and melted by the impact. The resulting mixture of crushed rock and melt was transported up and out of the transient cavity and deposited on and beyond its rim. Hot fragmental to partly molten ejecta and relatively cool cataclasite and relict target rocks were intermixed in a melange of lenses, pods, and veins. Crystallization of melts and thermal metamorphism of fine-,grained fragmental debris produced breccia composed of rock and mineral fragments in a fine-grained, coherent, crystalline matrix. Such breccia dominates the massif samples. High-angle faults that bound the massifs were activated during formation of the basin, so that structural relief of several kilometers was imposed on the ejecta almost as soon as it was deposited. Massive slumping that produced thick wedges of colluvium on the lower massif slopes probably occurred nearly contemporaneously with the faulting. Material of the Sculptured Hills, perhaps largely cataclasite excavated from the southern Serenitatis basin by the same impact, was then deposited on and around the massifs. Basalt, estimated to be about 1,400 m thick in the landing site, flooded the Taurus-Littrow graben before approximately 3.7 b.y. ago. The basalt (subfloor basalt) is part of a more extensive unit that was broadly warped and cut by extensional faults before the accumulation in Mare Serenitatis of younger, less deformed basalts that overlap it. A thin volcanic ash unit, probably about 3.5 b.y. old, mantled the subfloor basalt and the nearby highlands. It, too, was subsequently overlapped by the younger basalt of Mare Serenitatis. In the time since deposition of the volcanic ash, continued bombardment by primary and secondary projectiles has produced regolith, which is a mechanical mixture of debris derived mainly from the subfloor basalt, the volcanic ash, and the rocks of the nearby massifs and Sculptured Hills. T...

Osmium isotope and highly siderophile element systematics of lunar impact melt breccias: Implications for the late accretion history of the Moon and Earth

“…However, there is no consensus concerning the origin of the aphanites. Some authors have proposed that they are a different facies of Serenitatis melt (Dence et al, 1976;James et al, 1978;Wolfe et al, 1981), but others attribute these rocks to a different, or several different, impacts (Dalrymple and Ryder, 1996). Radiometric age data for the two types overlap within uncertainties and can not resolve separate events (Dalrymple and Ryder, 1996).…”

Complex magmatic and impact history prior to 4.1Ga recorded in zircon from Apollo 17 South Massif aphanitic breccia 73235

“…Wood (e.g., Marvin, 1975;Wood, 1975;Ryder et al, 1975). It consists of two main parts (see summary in Wolfe et al (1981)): a light-gray friable feldspar-rich matrix (e.g., sample 72275) and a dark-gray competent microbreccia (72215 and 72275, and clast within 72275). The dark gray part is interpreted as an older impact breccia incorporated into the light gray matrix (Wolfe et al, 1981).…”

“…The Taurus-Littrow Valley, located between two highland massifs called the South and North massifs (Wolfe et al, 1981) was selected as the Apollo 17 landing site because it lies just outside the transient cavity of the Serenitatis impact basin (Head, 1979;Ryder et al, 1997) and is interpreted to overlie the upper part of thick ejecta from this impact (e.g., Wolfe et al, 1981). This is consistent with the composition of boulders at the base of the South Massif which consist of texturally heterogeneous breccias (Simonds, 1975).…”

“…(ii) The abundance of clasts and clast populations: poikilitic breccias contain a relatively small proportion of clasts derived mostly from relatively deep-seated Mgsuite rocks (Ryder et al, 1975;Spudis and Ryder, 1981;Wolfe et al, 1981;Ryder, 1993), while aphanitic samples show a larger proportion and diversity of clasts, including some higher level rocks such as granulite and felsic clasts (e.g., Simonds, 1975;Spudis and Ryder, 1981;Jolliff et al, 1996). (iii) Major and trace element concentrations of the matrices: aphanitic breccias show a larger range of chemical variations and are especially distinguished from the poikilitic melts by their lower Ti and higher Al content (Spudis and Ryder, 1981), as well as lower Na 2 O, Sr and Eu concentrations (Jolliff et al, 1996).…”

40Ar/39Ar and cosmic ray exposure ages of plagioclase-rich lithic fragments from Apollo 17 regolith, 78461

“…Apollo 17 astronauts sampled the regolith at the base of the Sculptured Hills during their last surface traverse at station 8 (latitude 20.278°N, longitude 30.848°S; Robinson and Jolliff 2002). They dug a 25-cm-deep trench (Wolfe et al 1981) that revealed the best preserved lunar regolith stratigraphy collected during the Apollo missions (Mitchell et al 1973; Fig. 1).…”