ALBERT

Description: The Kerguelen Plateau and Broken Ridge in the southern Indian Ocean together represent one of the most voluminous large igneous provinces (LIPs) ever emplaced on Earth. A scientific objective of Ocean Drilling Program (ODP) Leg 183 was to constrain the post-melting magma evolution of Kerguelen Plateau magmas. In an effort to better understand this evolution, isotopic and trace element analysis of individual plagioclase crystals hosted within two Kerguelen Plateau basalts recovered from Elan Bank were undertaken. Previous whole-rock studies established that the two host basalts investigated in this study are samples of crustally contaminated (lower group) and relatively uncontaminated (upper group) basalt. Plagioclase phenocrysts from the uncontaminated basalt are dominantly normal zoned and exhibit a 87Sr/86SrI range of 0.704845-0.704985, which overlaps uncontaminated group whole-rock values previously reported. Plagioclase crystals from the contaminated basalt are dominantly reverse zoned and exhibit a 87Sr/86SrI range of 0.705510-0.705735, which all lie within contaminated group whole-rock values previously reported. There are no systematic within crystal core to rim variations in 87Sr/86SrI from either group, with the exception that contaminated group crystal rims have overall less radiogenic 87Sr/86SrI than other zones. These observations indicate that crustal assimilation occurred before the formation of Unit 10 plagioclase phenocrysts, which is supported by parent magma trace element abundance data inverted using carefully calculated partition coefficients. Trace element diffusion modeling indicates that the upper group basalt (Unit 4) experienced a more vigorous eruptive flux than the lower group basalt (Unit 10). We suggest that plagioclase phenocrysts in both the upper and lower group basalts originated from the shallowest section of what was likely a complex magma chamber system. We contend that the magmatic system contained regions of extensive plagioclase-dominated crystal mush. Crustal assimilation was not a significant ongoing process in this portion of the Elan Bank magmatic system. Both basalts exhibit compelling evidence for remobilization and partial resorption of crystalline debris (e.g., reverse zoned crystals, glomerocrysts). We suggest Unit 4 and 10 magmas ascended different sections of the Elan Bank magma system, where the Unit 10 magmas ascended a section of the magma system that penetrated a stranded fragment of continental crust.

Description: The criteria and clues for identifying meteorite contamination are outlined to aid in the quest for more knowledge regarding the evolution of the Moon and the early Earth. The Warren and Wasson seven criteria for establishing the pristine nature of highland rocks are presented. Other topics covered include iron/nickel metals, monomict nature, and lunar glasses. The major conclusion is that pristinity should not be the primary consideration in the study of lunar rocks. The most important criterion to establish is whether or not the lunar sample contains more than one lunar rock type. Even if a sample is non-pristine, as long as only one lunar rock type is present, petrogenetic interpretation can still be carried out.

Description: The Apollo 17 high-Ti mare basalts are derived from source regions containing plagioclase that was not retained in the residue. Ilmenite appears to remain as a residual phase, but plagioclase is exhausted. The open-system behavior of the type B2 basalts results in slightly higher Yb/Hf and La/Sm ratios. The nature of the added component is not clear, but may be a KREEP derivative or residue. The recognition of plagioclase in the source(s) of these basalts suggests that the location of the source region(s) would be more likely to be less than 150 km (i.e., closer to the plagioclase-rich crust), which would allow incorporation of plagioclase into the source through incomplete separation of crustal feldspar.

Description: As we are all aware, the Apollo 17 mission marked the final manned lunar landing of the Apollo program. The lunar module (LM) landed approximately 0.7 km due east of Camelot Crater in the Taurus-Littrow region on the southwestern edge of Mare Serenitatis. Three extravehicular activities (EVA's) were performed, the first concentrating around the LM and including station 1 approximately 1.1 km south-southeast of the LM at the northwestern edge of Steno Crater. The second traversed approximately 8 km west of the LM to include stations 2, 3, 4, and 5, and the third EVA traversed approximately 4.5 km to the northwest of the LM to include stations 6, 7, 8, and 9. This final manned mission returned the largest quantity of lunar rock samples, 110.5 kg/243.7 lb, and included soils, breccias, highland samples, and mare basalts. This abstract concentrates upon the Apollo 17 mare basalt samples.

Description: The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modeling, and proportions of fractionating phases were determined using the MAGFOX prograqm of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts-produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an 'r' value of 0.3). (2) Ilmenite basalts-produced by variable degrees of partial melting (4-8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts-produced by variable degrees of partial melting (5-10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and late-stage Lunar Magma Ocean (LMO) cumulates, requiring an overturn of the cumulate pile.

Description: New data are reported from five previously unanalyzed Apollo 12 mare basalts that are incorporated into an evaluation of previous petrogenetic models and classification schemes for these basalts. This paper proposes a classification for Apollo 12 mare basalts on the basis of whole-rock Mg# (molar 100*(Mg/(Mg+Fe))) and Rb/Sr ratio (analyzed by isotope dilution), whereby the ilmenite, olivine, and pigeonite basalt groups are readily distinguished from each other. Scrutiny of the Apollo 12 feldspathic 'suite' demonstrates that two of the three basalts previously assigned to this group (12031, 12038, 12072) can be reclassified: 12031 is a plagioclase-rich pigeonite basalt; and 12072 is an olivine basalt. Only basalt 12038 stands out as a unique sample to the Apollo 12 site, but whether this represents a single sample from another flow at the Apollo 12 site or is exotic to this site is equivocal. The question of whether the olivine and pigeonite basalt suites are co-magmatic is addressed by incompatible trace-element chemistry: the trends defined by these two suites when Co/Sm and Sm/Eu ratios are plotted against Rb/Sr ratio demonstrate that these two basaltic types cannot be co-magmatic. Crystal fractionation/accumulation paths have been calculated and show that neither the pigeonite, olivine, or ilmenite basalts are related by this process. Each suite requires a distinct and separate source region. This study also examines sample heterogeneity and the degree to which whole-rock analyses are representative, which is critical when petrogenetic interpretation is undertaken. Sample heterogeneity has been investigated petrographically (inhomogeneous mineral distribution) with consideration of duplicate analyses, and whether a specific sample (using average data) plots consistently upon a fractionation trend when a number of different compostional parameters are considered. Using these criteria, four basalts have been identified where reported analyses are not representative of the whole-rock composition: 12005, an ilmenite basalt; 12006 and 12036, olivine basalts; and 12031 previously classified as a feldspathic basalt, but reclassified as part of the pigeonite suite.

Description: To determine the chemical characteristics of the MAC88104/5 meteorite six thin sections and three bulk samples were analyzed by electron microprobe and instrumental neutron activation. It is concluded that this meteorite is dominated by lithologies of the ferroan anorthosite suite and contains abundant granulitized highland clasts, devitrified glass beads of impact origin, and two small clasts of basaltic origin. It is suggested that one of these basaltic clasts, clast E, is mesostasis material, and clast G is similar to the very low-Ti or low-Ti/high-alumina mare basalts. Impact melt clasts MAC88105, 69, and 72 have major and trace element compositions similar to the bulk meteorite.

Description: The origin of whitlockite, a REE-rich mineral present in lunar highlands, is investigated using available experimental results of elemental partitioning between whitlockite and melt and between two immiscible liquids. A comparison with occurrences in mare basalt mesostasis assemblages demonstrated that whitlockite in the lunar highlands has not resulted from crystallization from the residual interstitial melt, and the nature of REE partition coefficients for whitlockite showed that they cannot have crystallized from KREEP melts. The only lunar melt which contains REE abundances compatible with whitlockite composition is the basic immiscible melt derived from a KREEPy liquid. It is suggested that whitlockite found in the lunar highlands is a post-cumulus metasomatic phase that precipitated from a melt formed when the urKREEP underwent silicate liquid immiscibility.

Description: The 'urKREEP' hypothesis of Warren and Wasson (1979) is extended by defining KREEP in terms of specific (i.e., constrained) lunar components. It is shown that, the presilicate liquid immiscibility (pre-SLI) composition can be obtained by recombining experimental data on KREEP basalt components, or by calculating from liquid-liquid Kd's. Both calculated urKREEP compositions were lower in MgO and Al2O3 and higher in FeO and P2O5 than reported low- and high-K KREEP compositions. The calculated REE abundances were higher and the REE profiles were slightly more LREE-enriched than the previously reported KREEP compositions.

Description: The classification, sources, and overall petrogenesis of mare basalts are reviewed. All mare basalt analyses are used to define a sixfold classification scheme using TiO2 contents as the primary division. A secondary division is made using Al2O3 contents, and a tertiary division is defined using K contents. Such divisions and subdivisions yield a classification containing 12 categories, of which six are accounted for by the existing Apollo and Luna collections. A variety of postmagma-generation such as fractional crystallization, either alone or combined with wallrock assimilation, are invoked to explain the compositional ranges of the various mare basalt suites. High-Ti mare basalts are found at Apollo 1 and Apollo 17 sites; the A-11 basalts contain lower TiO2 abundances, a considerably larger range in trace-element contents, and the only occurrence of high-Ti/high-K mare basalts. The low-Ti basalts exhibit a wide range of major-and trace-element compositions and require source heterogeneity, fractional crystallization, and some assimilation.