PROCEEDINGS OF THE FIFTEENTH LUNAR AND PLANETARY SCIENCE CONFERENCE, PART 1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 89, SUPPLEMENT, PAGES C41-C49, NOVEMBER 15, 1984 Magnesian Anorthosites and Associated Troctolites and Dunitc in Apollo 14 Breccias MARILYN M. LINDSTROM Department of Earth and PlanetarySciences and McDonnell Center for the Space Sciences, Washington University STEVEN A. KNAPP, JOHN W. SHERVAIS, AND LAWRENCE A. TAYLOR Departmentof Geological Sciences, University of Tennessee Magnesiananorthosite,a new type of pristine lunar highlands rock, has been found in Apollo 14 breccias. It has primitive (high Ca and Mg) silicatemineral compositions, and high and variable REE concentrations. Variations in REE contents can be accounted for by variations in modal abundance of REE-rich apatite. Magnesian anorthosites are associated with troctolitesand a dunire with very similar mineral compositions and it is suggested that all crystallized from a differentiated troctolitic intrusion. The origin of the REE-rich apatite is enigmatic.It is unlikely to have crystallized from an igneous liquid in equilibrium with the major minerals in the anorthosite. Possible origins are assimilation of urKREEP or metasomatism by REE-rich fluids. REE-rich alkali anorthosites and gabbronorites are also found and are likely to be related to KREEP basaltmagmas. Lunar compositional associations are distributed in a regional rather than global manner. INTRODUCTION SAMPLING AND ANALYSIS Apollo 14 breccias are compleximpactbreccias dominated by KREEP and high-A1 mare basalt components. Recent studies [ Warren and Wasson, 1980; Warren et al. , 1981, 1983a, b; Hunter and Taylor, 1983; Shervais et al., 1983] have shown that they also contain a diverseand fascinating suite of pristine highland clasts.Theseincludetroctolites,gabbros, granites, and both alkali and ferroananorthosites. The present study describes magnesian anorthosites, a new and unusual rock type, and discusses the relationshipof this rock and associated mafic rocksto other highlands rock types. Breccia 14321 is a large and complex rock under study by a consortium headedby L. A. Taylor. All the lithologies of 14321 are being studied in order to evaluate the source regions of the Imbrium breccias. A previous consortium focused its attention on the dominant impact breccia and basalt components[Duncan et al., 1975]. In order to learn more about the pre-Imbrium highlands crust,we havealso studied pristine highlands clasts. A companion paper[Shervais et al., 1984c] describes the high-A1mare basaltclasts. The KREEPy polymictbreccias are the subject of further study. Of the 38 samplesof 14321 clast and matrix analyzed by INAA, 10 appearto be pristine highland rocks.An additional nine pristine clastswere studiedonly in thin section.The 10 analyzed pristine clasts include four troctolites, three anorthosites,and one each of dunitc, gabbro, and granite. Troctolites are the most common pristineclast type in 14321 and other Apollo 14 breccias [Shervais et al., 1983]. Anorthosites have been foundpreviously in Apollo 14 breccias, but they are commonly alkali anorthosites [Warren et al., 1983a]. The anorthosites of the present study are a newvariety, magnesian anorthosites, which have primitive mineral compositions and evolved traceelement characterics. Copyright 1984by the American Geophysical Union. Paper Number 4B5833. 0148-0227/84/004B-5833505.00 Following detailed mapping of all rock surfaces and preparation of the brecciaguidebook[Shervais et al., 1984a], clasts wereselected for analysis and extracted by the curatorial staff. Most clasts weresplit for simultaneous petrographic and geochemical studies. A few very smallclasts werestudied only in thin section. Geochemical analyses of up to 27 major and trace elements were done by INAA. Procedures are described by Lindstrom [1984] with data reduction based on the TEABAGS program of Lindstrom and Korotev [1982]. Analytical uncertaintiesbased on counting statistics are: 1- 2%, A1203, FeO, Na20, Sc, Cr, Mn, Co, La, Sm, Eu; 3-5%, CaO, Ce, Tb, Yb, Lu, Hf, Ta, Th; 5-15%, TiO2, MgO, Sr, Ba, Nd, U; 15-25%, K:O, V, Ni, Zr. Ir and Au determinations were attempted but peaks were not observedfor any clast discussed here, indicating concentrations below the limits of detection of 1-2 ppb. Such low concentrations suggest but do not prove pristinity of the clasts. Mineralogical analyses were done on a MAC 400-S electron microprobe. Analytical conditions and correction procedures are described in Shervais et al. [1984b]. PETROGRAPHIC AND COMPOSITIONAL CHARACTERISTICS Magnesian Anorthosites Two clasts(three samples)of magnesian anorthosite were separated from 14321. One (1211/1273) is an apatite-rich anorthosite with areas of relict igneous texture. The other (1205/1269) is maskelynite with no relict primary texture. Magnesian anorthosite 1211 (PM1273) consists of 98% plagioclase (An94)and 1% REE-rich fluorapatite, with minor olivine (Fo83.8) and diopside (Wo46En50). Plagioclaseoccurs in two habits: (1) a granoblastic-polygonal mosaic of untwinned,strain-free neoblasts (0.1-0.6 mm) with 120 ø triple junctions, indicatinga period of static recrystallization, and (2) relict unrecrystallized grains (up to 2 mm) with blocky, prismatic shapes, abundant twin lamellae, and subparallel C41