Geology and petrology of the Apollo 15 landing site - Past, present, and future understanding

The main objectives of the Apollo 15 lunar mission were to investigate and sample materials from the Apennine Front (expected to be Imbrium ejecta and pre-Imbrian materials), the Hadley Rille, and the mare lavas of Palus Putredinis. The Hadley Rille was found to be a collapsed lava tube or channel, and from it, many mare basalt samples were collected which form two main chemical groups of the same age (3.3 b.y.), isotopic characteristics, and rate-earth element patterns. One group, olivine-normative, contains many vescular specimens and shows an olivine fraction trend. The other group, quartz-normative, is pigeonite-phyric and contains both vitrophyric and coarse-grained samples but exhibits little fractionation. The Apennine Front samples include such highland materials as ferroan anorthosites, spinel-bearing troctolites, norites, impact melts and metamorphosed breccias. A conspicuous component of the regolith breccias is volcanic green glass. The Apennine Front is characterized by a low-KREEP composition, a composition which has never been found as a pristine igneous rock type. Another unexpected discovey was the common occurrence of 3.5 b.y. old volcanic KREEP basalts. It is concluded that all major lunar processes can be profitably studied from the samples and observations at this single location.