American Mineralogist, Volume 91, pages 15211535, 2006 0003-004X/06/00101521$05.00/DOI: 10.2138/am.2006.2147 1521 INTRODUCTION The Apollo 14 mission landed in the Fra Mauro region of Oceanus Procellarum (Fig. 1) in February, 1971 and returned 42 kg of lunar samples that consisted of predominantly impact- generated breccias. Some of these breccias contained a wealth of basaltic clasts and these have proven to be signicant because they are, at present, the only samples that record pre-4 Ga vol- canism on the Moon (Taylor et al. 1983; Dasch et al. 1987). On the basis of current data, the basaltic clasts from the Fra Mauro region represent mare volcanic events that that occurred over a period of ~400 Myr from ~3.9 to ~4.3 Ga (Papanastassiou and Wasserburg 1971; Compston et al. 1971, 1972; Taylor et al. 1983; Dasch et al. 1987; Shih and Nyquist 1989a, 1989b). This age range pre-dates the main mare magmatism recorded at other sample return sites (e.g., Nyquist and Shih 1992; Snyder et al. 2000) and may represent the end of the effusive cryptomare eruptions (Head and Wilson 1992). In addition, the major-ele- ment geochemistry of the basalts is distinct relative to the great majority of mare basalts from other sample return sites. The Fra Mauro basalts are relatively enriched in Al 2 O 3 (1116 wt%) and hence, in a lunar reference, are termed high-Al (e.g., Ridley 1975). Samples returned by Luna 16 from Mare Fecunditatis are also high-Al, containing from 11 to ~19 wt% Al 2 O 3 (e.g., Albee et al. 1972; Grieve et al. 1972; Helmke and Haskin 1972; Kurat et al. 1976; Ma et al. 1979), but are signicantly younger (~3.4 Ga; Papanastassiou and Wasserburg 1972). The high-Al nature of both the Apollo 14 and Luna 16 basalts is manifest in the fact that they contain proportionally greater modal plagioclase rela- tive to mare basalts from other sample return sites (e.g., Albee et al. 1972; Papike et al. 1974; Papike and Vaniman 1978; Neal and Taylor 1992). The Fra Mauro region is generally accepted as being made up of ejecta deposits from the Imbrium impact (Wilhelms 1987). The Apollo 14 high-Al basalts, therefore, probably are not indigenous to that region. The surface ows from which the clasts were de- rived probably originated from the Imbrium region prior to basin formation. These units now either are covered by younger mare ows, have been effectively obliterated by subsequent impacts, and/or are masked by impact ejecta. Although they show relatively small to moderate variations in major-element chemistry, the Apollo 14 high-Al basalts do exhibit a large range in trace-element abundances. Though using different nomenclature, both Shervais et al. (1985) and Dickinson et al. (1985) divided these basalts into groups on the basis of incompatible-trace-element (ITE) abundances (Fig. 2a). They noted a general increase in FeO and MgO as ITE abundances decrease, leading Dickinson et al. (1985) to conclude their more * E-mail: neal.1@nd.edu The petrogenesis of the Apollo 14 high-Al mare basalts CLIVE R. NEAL* AND GEORGIANA Y. KRAMER Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A. ABSTRACT In this paper, we report analysis of various basaltic lunar samples including 14053 and 14072, KREEP basalt 15386, thirty basalt clasts from Apollo 14 breccia 14321, as well as impact-generated samples (matrix from breccia 14168, olivine vitrophyres 14321,1180 and 14321,1539, and impact melt 14310) using a combination of solution and laser ablation inductively coupled plasma mass spectrometry (ICP-MS). The basalt clast samples were previously analyzed by instrumental neutron activation. On plots of incompatible trace elements (ITEs) vs. compatible trace elements, the Apollo 14 high-Al basalts form three approximately subparallel trends that, on the basis of current data, are also separated by age. Plots of ITE ratios (i.e., Nb/Ce vs. Zr/Y) can be used to indicate source com- position, and also divide the basalts into three groups: Group A (~4.3 Ga); Group B (~4.1 Ga); and Group C (~3.9 Ga). New data for 14072 suggest the sample does not t with any of the three groups dened here, and may indicate the presence of a fourth group of high-Al basalts in the proximity of the Apollo 14 site. The Apollo 14 high-Al basalts are compositionally distinct from known Apollo 14 impact melts and impact-generated lithologies. The three groups cannot be related by varying degrees of partial melting of a single, KREEP-contaminated source and, therefore, require three separate source regions. The new data indicate that Group A basalts evolved through closed-system crystal fractionation. However, the new data from basalts forming Groups B and C require open-system evolution that involves combined assimilation and fractional crystallization (AFC). Unlike previous AFC modeling of the Apollo 14 high-Al basalts, an assimilant composed of KREEP is not sufcient to generate the compositional ranges of each basalt group. The modeling of both groups requires a mixture of KREEP and granite as the assimilant, which supports the notion of a genetic relationship between these two lunar components. Keywords: Moon, assimilation, basalt petrogenesis, Apollo 14 high-Al basalts, mare basalts, fractional crystallization, KREEP, granite