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Shergottite meteorites are ultramafic to mafic igneous rocks derived from partial melting of distinct regions of the martian mantle. As such, they trace magmatic processes, including fractional crystallization and mixing processes in Mars. New chalcophile (Cu, Se, Zn, Pb), siderophile (Ni, Co, W), and highly siderophile element (HSE: Au, Re, Pd, Rh, Pt, Ru, Ir, Os) abundance data are reported for sulfide assemblages in a suite of thirteen incompatible trace-element depleted, intermediate and enriched shergottites, along with new whole-rock HSE abundance and 187Os/188Os data for seven shergottites. Sulfide grains in depleted and intermediate shergottites typically have the highest absolute abundances of HSE, with broadly flat CI-chondrite normalized patterns. Enriched shergottite sulfide grains typically have highly variable Au, elevated Pd and Rh and are relatively depleted in Zn, Ir and Os. The new HSE whole-rock data for enriched (Northwest Africa [NWA] 7397, NWA 7755, NWA 11043), and intermediate shergottites (NWA 10961, NWA 11065, NWA 12241, and NWA 12536) are generally consistent with existing 187Os/188Os and HSE abundance data for these geochemical groupings. Enriched shergottites with >1 ppb bulk rock Os have measured 187Os/188Os ranging between 0.1296 and 0.1471, with variable Pd and Pt contents. Intermediate shergottites with >1 ppb bulk rock Os have chondrite-relative proportions of the HSE at ∼0.01 to 0.001 × CI chondrites and 187Os/188Os from 0.1284 and 0.1295. Sulfides are the major host of the HSE, and they control the behavior of the HSE during petrogenetic processes in shergottite magmas, enabling the determination of HSE compatibility for martian magmatism in the order: Os > Ir ≥ Ru ≥≥ Rh ≥ Pd ≥ Re ≥ Pt ≥ Au. Fractionation models of removal of an olivine-dominated cumulate recreate HSE patterns for the whole-rock shergottites. Enriched shergottites are best reproduced by 25 to 30% of fractionation from a degassed parent melt (250 ± 50 ppm of S), whereas depleted and intermediate shergottites can be explained by slightly lower fractionation (10 to 15%) from higher S content parent melts (350 ± 100 ppm of S). Sulfur contents in the melt that are ∼50% higher than these estimates yield earlier S-saturation during fractional crystallization, leading to an abrupt decrease of the more compatible HSE (Ru, Ir, Os), which is not observed. These results indicate that the martian mantle and partial melts derived from it, are probably not anomalously enriched in S, and instead are similar to slightly higher than those of the terrestrial mantle and its partial melts.

We report partition coefficients for Sr, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, and Th for plagioclase, pigeonite, and olivine experimentally grown from a lunar basaltic liquid at 1 bar and two different oxygen fugacities (fO2; fayalite-magnetite-quartz (FMQ) and the iron-wustite (IW) oxygen buffers) at temperatures (Ts) of 1100–1125 °C. These results expand the partitioning database for plagioclase-silicate melt partitioning at lunar relevant conditions and compositions. Variations of partition coefficients for rare earth elements (REEs) are highly systematic with respect to ionic radii, in agreement with lattice strain theory. We use the lattice strain model to evaluate partition coefficients for highly incompatible elements such as the light (or in the case of plagioclase, heavy) REEs, for which direct determinations are experimentally and analytically difficult. Our experiments suggest that within analytical and experimental uncertainty, over the range of explored fO2 (FMQ to IW), T (1100–1125 °C) and An# conditions (An# >94.5, where An#=Ca/(Ca + Na) × 100, in moles), fO2 exerts an important but secondary control on Eu partitioning in anorthitic plagioclase. In contrast, the global plagioclase-melt partitioning dataset highlights the first-order role of fO2 in determining plagioclase-melt Eu partition coefficients over a wide range of An#s. Using experimental results and predictive models for divalent and trivalent element plagioclase-melt partitioning in the plagioclase ring site, we parameterized an fO2-dependent plagioclase-melt Eu partitioning model. Within a factor of two, the model reproduces measured Eu partition coefficients for a wide range of experimental conditions (750–1400 °C) and compositional systems (basalts to dacites) over > 15 orders of magnitude variation in fO2. When equilibrium partitioning of Eu between plagioclase and melt can be established, the model may be applied as a plagioclase-melt oxybarometer. Preliminary application to plagioclase-hosted melt inclusions in mid-ocean ridge basalts suggests they equilibrated near the FMQ buffer. We used the new Eu partitioning model to evaluate the petrogenesis of a lunar anorthositic impactite that hosts plagioclase with both positive and negative Eu anomalies. Our investigation suggests the distribution of REEs and Eu in this sample is consistent with subsolidus reequilibration after impact-induced heating.

We conducted a thorough analysis of the feldspathic breccia meteorite Dhofar 1428 with the aim of better understanding the composition and evolution of lunar crust. This sample comprises a heterogeneous array of lithic fragments including magnesian and ferroan anorthositic granulites, mafic granulites/granulitic breccia, basalts, and different kinds of impact melt rocks. In which, a high-Ti basalt clast comprising large zoned pyroxene was observed. Based on equilibrium melt calculations of mineral zonations from this basalt, Mg-pyroxene cores were interpreted to be formed from a light rare earth element (LREE) enriched liquid, whereas the Fe-pyroxene rims grew from an LREE-depleted magma. We propose that LREE-depleted signature of Fe-pyroxene results from co-crystallization with apatite. The Mg-pyroxenes suggest that enriched liquids with higher REE contents and different REE patterns relative to KREEP existed within lunar interior. Oscillating Ti/Al ratios across pyroxene in this basalt may indicate several magma recharge events or crystal movement within a zoned magma chamber. This feature illustrates that magmas were derived from a variety of sources around the time of formation of this basalt. In situ U-Pb dating was conducted on apatite grains within this basalt, the excellent consistence between the U-Pb Concordia age (3941 ± 24 Ma, 2σ) and 207Pb/206Pb isochron age (3934 ± 24 Ma, 2σ) indicates the most likely crystallization age of this high-Ti basalt at ∼3940 Myr, making it one of the oldest high-Ti basalts formed on the Moon. Magnesian anorthositic granulites are mineralogically and geochemically similar to those trace element-poor magnesian anorthositic granulites in many lunar meteorites. These magnesian granulites cannot form from simple mixing of pristine Ferroan Anorthosite and lithologies from the Mg-Suite, and do not have any affinities with KREEP or the Procellarum KREEP Terrane, and they could be important components of farside highlands.

Very high potassium or VHK basalts have been described from the Apollo 14 landing site at Fra Mauro on the lunar near side. Many of the known samples are clasts in polymict breccias with a few as New work completed on fourteen VHK basalts include Crystal Size Distributions (CSDs) and in-situ chemical analyses and element maps collected by electron probe microanalysis (EPMA). CSDs completed on three VHK basalt samples indicate that these basalts are not impact melts and represent endogenous melts of the lunar interior. Potassium Kα element maps reveal the spatial relationship between the K-rich material and the basalt clasts with attached breccia matrix if present. In-situ EPMA analyses have identified two distinct types of K-rich material: K-feldspar and K-rich glass. With these new data, an additional mechanism for an exogenic petrogenesis of VHK basalts is proposed that involves the impact process. VHK basalts can be divided into two groups based on density and viscosity. VHK-1 basalts formed when a hot impact ejecta covered the granite/felsite-rich matrix material containing high-Al basalt clasts. Heat from the impact ejecta partially melted and possibly evaporated nearby K-bearing materials, which then infiltrated and contaminated the high-Al clasts. VHK-2 basalts are consistent with the hypothesis of granite assimilation by a high-Al magma, as seen in the higher abundances of network-forming elements.

The Joint Workshop on Induced Special Regions convened scientists and planetary protection experts to assess the potential of inducing special regions through lander or rover activity. An Induced Special Region is defined as a place where the presence of the spacecraft could induce water activity and temperature to be sufficiently high and persist for long enough to plausibly harbor life. The questions the workshop participants addressed were: (1) What is a safe stand-off distance, or formula to derive a safe distance, to a purported special region? (2) Questions about RTGs (Radioisotope Thermoelectric Generator), other heat sources, and their ability to induce special regions. (3) Is it possible to have an infected area on Mars that does not contaminate the rest of Mars? The workshop participants reached a general consensus addressing the posed questions, in summary: (1) While a spacecraft on the surface of Mars may not be able to explore a special region during the prime mission, the safe stand-off distance would decrease with time because the sterilizing environment, that is the martian surface would progressively clean the exposed surfaces. However, the analysis supporting such an exploration should ensure that the risk to exposing interior portions of the spacecraft (i.e., essentially unsterilized) to the martian surface is minimized. (2) An RTG at the surface of Mars would not create a Special Region but the short-term result depends on kinetics of melting, freezing, deliquescence, and desiccation. While a buried RTG could induce a Special Region, it would not pose a long-term contamination threat to Mars, with the possible exception of a migrating RTG in an icy deposit. (3) Induced Special Regions can allow microbial replication to occur (by definition), but such replication at the surface is unlikely to globally contaminate Mars. An induced subsurface Special Region would be isolated and microbial transport away from subsurface site is highly improbable.

It is widely accepted that the Apollo 17 orange glass beads are of volcanic origin. The degree of degassing of the glass beads depends on their cooling rates, so the estimation of volatile contents in the parental magmas of these lunar pyroclastic glasses also depends on the cooling rates. The cooling rate can be estimated using the calorimetric properties of the glass across the glass transition. In this study, a series of heat capacity measurements were carried out on hand-picked lunar volcanic orange glass beads during several cycles of heating to temperatures above their glass transition using a differential scanning calorimeter. The cooling rate of orange glass beads (sample 74220,867) was calculated to be 101 K/min using the correlation between glass cooling rates and fictive temperatures estimated from their heat capacity–temperature paths. This cooling rate is close to the lower end of the range that best fits the diffusion profiles of several volatile species in the glass beads, and at the upper end of the cooling-rate range recorded in glasses quenched subaerially on Earth. The cooling rate is likely to be controlled by the cooling environment (cooling medium) such that the lunar volcanic glass beads could have been cooled in a gaseous medium released from volcanic eruptions on the Moon, but not during “free flight” in vacuum. The existence of a gas medium suggests, in turn, that there may have been at least a short-lived or episodic atmosphere on the early Moon at around 3.5 Ga.

Knowing the amount and timing of water incorporation into the Moon has fundamental implications for our understanding of how the Earth–Moon system formed. Water has been detected in lunar samples but its abundance, distribution and origin are debated. To address these issues, we report water concentrations and hydrogen isotope ratios obtained by secondary ion mass spectrometry (SIMS) of plagioclase from ferroan anorthosites (FANs), the only available lithology thought to have crystallized directly from the lunar magma ocean (LMO). The measured water contents are consistent with previous results by Fourier transform infrared spectroscopy (FTIR). Combined with literature data, δD values of lunar igneous materials least-degassed at the time of their crystallization range from −280 to +310‰, the latter value being that of FAN 60015 corrected for cosmic ray exposure. We interpret these results as hydrogen isotopes being fractionated during degassing of molecular hydrogen (H_2) in the LMO, starting with the magmatic δD value of primordial water at the beginning of LMO being about −280‰, evolving to about +310‰ at the time of anorthite crystallization, i.e. during the formation of the primary lunar crust. The degassing of hydrogen in the LMO is consistent with those of other volatile elements. The wide range of δD values observed in lunar igneous rocks could be due to either various degrees of mixing of the different mantle end members, or from a range of mantle sources that were degassed to different degrees during magma evolution. Degassing of the LMO is a viable mechanism that resulted in a heterogeneous lunar interior for hydrogen isotopes.

The lunar magma ocean (LMO) model was proposed after the discovery of anorthosite in Apollo 11 samples. However, the chemical and isotopic compositions of lunar anorthosites are not fully consistent with its LMO origin. We have analyzed major and trace elements in anorthositic clasts from ten lunar feldspathic meteorites, which are related to the solidification of the LMO. The plagioclase rare earth element (REE) abundances and patterns are not correlated with the Mg# of coexisting mafic minerals in anorthosites, implying that mafic minerals and plagioclase may not be in chemical equilibrium, consistent with their textural differences. The REE abundances in plagioclase range approximately fortyfold, which cannot be produced by fractional crystallization of a single magma. Combining plagioclase trace element data from Apollo and meteoritic anorthosites, we propose that plagioclases derived from the LMO floated to the surface to form the primordial crust, which then may have been metasomatized by incompatible-element-rich KREEP (potassium, rare earth element, phosphorus) melts and mantle-derived partial melts. The lunar anorthosites may represent this metasomatized crust rather than solely a derivative from the LMO. Furthermore, silicate melts similar to the metasomatic agents may also have melted the crust to form the Mg-suite rocks. This hypothesis is consistent with overlapping ranges of age and initial eNd between lunar anorthosites and Mg-suite rocks. These events are consistent with an overturn event of the cumulate mantle very early after primordial crust formation to produce the partial melts that metasomatized the crust.

Quantitative textural analysis is a powerful tool in the investigation of basalt crystallization. We present the first comprehensive crystal size distribution analysis of Apollo 17 high-titanium lunar basalts, with a focus on ilmenite. Crystal size distributions of ilmenite, pyroxene, plagioclase, olivine and armalcolite were determined for 18 high-Ti mare basalt samples from the Apollo 17 mission. A subset of the ilmenite size distribution (size bins of

The development of the Global Exploration Roadmap (GER) by 12 space agencies participating in the International Space Exploration Coordination Group broadly outlines a pathway to send humans beyond low Earth orbit for the first time since Apollo. Three themes have emerged: Exploration of a Near-Earth Asteroid, Extended Duration Crew Missions, and Humans to the Lunar Surface. The lack of detail within each of these themes could mean that realizing the goals of the GER would be significantly delayed. The purpose of this paper is to demonstrate that many of the details needed to fully define and evaluate these themes in terms of scientific rationale, economic viability, and technical feasibility already exist and need to be mapped to the GER. Here, we use the Humans to the Lunar Surface theme as an example to illustrate how this process could work. By mapping documents from a variety of international stakeholders, this process can be used to cement buy-in from the current partners and attract new ones to this effort.

Aside 2 from Earth, the inner solar system is like a vast desert where water and other volatiles are scarce. An old saying is, “In the desert, gold is useless and water is priceless.” While water is common on Earth, it is of very high value in space. Science missions to the Moon have provided direct evidence that regions near the lunar poles, which are permanently in shadow, contain substantial concentrations of water ice. On the lunar surface, water itself is critical for human consumption and radiation shielding, but water can also be decomposed into hydrogen and oxygen via electrolysis. The oxygen thus produced can be used for life support, and hydrogen and oxygen can be combusted for rocket propulsion. Due to the Moon’s shallow gravity well, its water-derived products can be exported to fuel entirely new economic opportunities in space. This paper is the result of an examination by industry, government, and academic experts of the approach, challenges, and payoffs of a private business that harvests and processes lunar ice as the foundation of a lunar, cislunar (between the Earth and the Moon), and Earth-orbiting economy. A key assumption of this analysis is that all work—construction, operation, transport, maintenance and repair—is done by robotic systems. No human presence is required. Obtaining more data on conditions within the shadowed regions is vital to the design of a lunar ice processing plant. How much water is actually present, and at what percentage in the lunar regolith? How firm or soft are the crater bottoms, and how will that affect surface transportation? How deep is the ice resource, and in what state is it deposited amongst the regolith? These and other questions must be answered by precursor prospecting and science missions. A wide range of potential customers for the hydrogen and oxygen products has been identified. They can be used to fuel reusable landers going back and forth between the lunar surface and lunar orbit. They can make travel to Mars less expensive if the interplanetary vehicle can be refueled in cislunar space prior to departure. Operations closer to Earth can also benefit from this new, inexpensive source of propellant. Refueling in Low Earth Orbit can greatly improve the size, type, and cost of missions to Geosynchronous Earth Orbit and beyond. This study has identified a near term annual demand of 450 metric tons of lunar derived propellant equating to 2450 metric tons of processed lunar water generating $2.4 billion of revenue annually. Unlike terrestrial mining operations that utilize heavy machinery to move resources, the mass constraints of a lunar polar water mine are highly restrictive because of delivery cost. A revolutionary concept has been introduced that solves this issue. It has been discovered that instead of excavating, hauling, and processing, lightweight tents and/or heating augers can be used to extract the water resource directly out of the regolith in place. Water will be extracted from the regolith by sublimation—heating ice to convert it into water vapor without going through the liquid phase. This water vapor can then be collected on a cold surface for transport to a processing plant where electrolysis will decompose the water into its constituent parts (hydrogen and oxygen). To achieve production demand with this method, 2.8 megawatts of power is required (2 megawatts electrical and 0.8 megawatts thermal). The majority of the electrical power will be needed in the processing plant, where water is broken down into hydrogen and oxygen. This substantial amount of power can come from solar panels, sunlight reflected directly to the extraction site, or nuclear power. Because the bottoms of the polar craters are permanently shadowed, captured solar energy must be transported from locations of sunlight (crater rim) via power beaming or power cables. Unlike solar power sources, nuclear reactors can operate at any location; however, they generate heat that must be utilized or rejected that may be simplified if located in the cold, permanently shadowed craters. New or exotic technologies have been excluded from this study but may be incorporated into future architectures as they become available. Instead, the equipment described in this lunar propellant operation will be built from existing technologies that have been modified for the specific needs on the Moon. Surprisingly little new science is required to build this plant. Extensive testing on Earth will precede deployment to the Moon, to ensure that the robotics, extraction, chemical processing and storage all work together efficiently. The contributors to this study are those who are currently developing or have already developed the equipment required to enable this capability. From a technological perspective, a lunar propellant production plant is highly feasible. Now is the time to establish the collaborations, partnerships, and leadership that can make this new commercial enterprise a reality. Currently, no one company has all of the capabilities necessary to build the lunar plant, but the capabilities all exist within United States aerospace industry and others (such as the chemical industry). It is necessary that new or existing competing companies establish the leadership needed to coordinate the variety of technologies required for a fully integrated Commercial Lunar Propellant Architecture. Free market competition among these companies will aid in driving down costs, promoting innovation, and expanding the market. To justify such action, a secure customer base, solid business case, and high fidelity economic model is required. This too will help secure the investment required for development and implementation. The initial investment for this operation has been estimated at $4 billion, about the cost of a luxury hotel in Las Vegas. With this investment however, a scalable market can be accessed. As refueling decreases in-space transportation costs, entirely new business and exploration opportunities will emerge with potential to vastly benefit the economies of Earth. Even with the early customers identified within this study, it has been determined that this could be a profitable investment with excellent growth opportunities. The United States Government has critical roles to play in the development of this commercial capability as well. Government science/prospecting and communications missions to the Moon can be very helpful in both the development and operational phases of the business. Government laboratories can contribute some of their technologies and help facilitate integrated systems tests of a terrestrial pilot plant. Government must also work to fill the gaps in international law regarding property rights on celestial bodies such as the Moon. In addition, between Earth orbit, Moon, and Mars missions, government could be an important anchor customer for the resource, stimulating the private sector into action with proposed demands and price points while improving its mission costs and capabilities. This study demonstrates both the technical and economic feasibility of establishing a commercial lunar propellant production capability. It provides recommendations to interested government and private organizations and defines a path to implementation; and explains that by doing so the United States will fuel a new age of economic expansion, sustained space exploration, settlement, and American leadership in space.

Apollo 14 (A-14) impact melt olivine vitrophyres (OVs), composed of olivine phenocrysts in an opaque glass matrix with minor amounts of pyroxene and plagioclase, are petrographically similar to pristine quenched A-14 high-alumina (high-Al) and Apollo 12 (A-12) basalts. Textural and chemical analyses have been conducted on olivines within impact melt and pristine mare basalt clasts from A-14 breccia 14321 as well as various olivine-phyric Apollo 12 and 17 basalts to be able to distinguish between the petrographically similar samples. The A-14 high-Al basalts examined here represent samples from each of the three chemical groups (A, B, C). Examples from the three A-12 basalt suites (Ilmenite, Olivine, Pigeonite) and olivine-rich Apollo 17 (A-17) Type C basalt, 74275, have also been analyzed. As a complement to the chemical analyses, crystal size distributions (CSDs) were determined for approximately half of the samples investigated here (due to a small number of olivine crystals that did not produce statistically meaningful CSDs on half of the samples), and confirm that although similar, the basalts and impact melts are texturally distinct. Olivines from A-14 impact melts have the highest average forsterite contents (average Fo ∼0.82) and generally the lowest average Co (37 ppm) and Mn (1544 ppm) abundances, thus chemically distinguishing them from the pristine basalts. In addition, chemical compositions obtained for olivine from 14321,1486 are most likely representative of an impact melt and thus contradict its previous classification as a high-Al basalt ( Neal et al., 1988 ); olivine from, 1486 have similar average forsterite (average Fo ∼0.82) and Ti/V-ratio to the OVs. Furthermore, on the basis of their chemical compositions, olivines have been identified within the impact melts that are likely inherited from basalts; these olivines are chemically distinct from the rest of the impact melt olivine population with lower forsterite (0.67–0.80) and low Ti/V (∼10), which are similar to olivine compositions from the A-14 high-Al basalts. In addition to distinguishing between sample types from A-14, olivine compositions can also be used to distinguish between pristine mare basalts from various missions. Olivine within the selected samples from the individual A-12 basalt suites can also be distinguished chemically from one another using the Ti/V ratio, where Olivine suite basalts have Ti/V 3.5. The results indicate that combined use of CSDs and chemical analyses of olivine can be used to reliably distinguish between (1) impact melts and pristine Apollo 14 basalts, (2) basalts from different landing sites, and (3) individual basalt suites from a single site.

Coupled 187Os/188Os compositions and highly-siderophile-element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for eight angrite achondrite meteorites that include quenched- and slowly-cooled textural types. These data are combined with new major- and trace-element concentrations determined for bulk-rock powder fractions and constituent mineral phases, to assess angrite petrogenesis. Angrite meteorites span a wide-range of HSE abundances from 100 ppb Os (NWA 4931). Chondritic to supra-chondritic 187Os/188Os (0.1201–0.2127) measured for Angra dos Reis and quenched-angrites correspond to inter- and intra-sample heterogeneities in Re/Os and HSE abundances. Quenched-angrites have chondritic-relative rare-earth-element (REE) abundances at 10–15×CI-chondrite, and their Os-isotope and HSE abundance variations represent mixtures of pristine uncontaminated crustal materials that experienced addition (

In response to the growing importance of space exploration in future planning, the Committee on Space Research (COSPAR) Panel on Exploration (PEX) was chartered to provide independent scientific advice to support the development of exploration programs and to safeguard the potential scientific assets of solar system objects. In this report, PEX elaborates a stepwise approach to achieve a new level of space cooperation that can help develop world-wide capabilities in space science and exploration and support a transition that will lead to a global space exploration program. The proposed stepping stones are intended to transcend cross-cultural barriers, leading to the development of technical interfaces and shared legal frameworks and fostering coordination and cooperation on a broad front. Input for this report was drawn from expertise provided by COSPAR Associates within the international community and via the contacts they maintain in various scientific entities. The report provides a summary and synthesis of science roadmaps and recommendations for planetary exploration produced by many national and international working groups, aiming to encourage and exploit synergies among similar programs. While science and technology represent the core and, often, the drivers for space exploration, several other disciplines and their stakeholders (Earth science, space law, and others) should be more robustly interlinked and involved than they have been to date. The report argues that a shared vision is crucial to this linkage, and to providing a direction that enables new countries and stakeholders to join and engage in the overall space exploration effort. Building a basic space technology capacity within a wider range of countries, ensuring new actors in space act responsibly, and increasing public awareness and engagement are concrete steps that can provide a broader interest in space exploration, worldwide, and build a solid basis for program sustainability. By engaging developing countries and emerging space nations in an international space exploration program, it will be possible to create a critical bottom-up support structure to support program continuity in the development and execution of future global space exploration frameworks. With a focus on stepping stones, COSPAR can support a global space exploration program that stimulates scientists in current and emerging spacefaring nations, and that will invite those in developing countries to participate—pursuing research aimed at answering outstanding questions about the origins and evolution of our solar system and life on Earth (and possibly elsewhere). COSPAR, in cooperation with national and international science foundations and space-related organizations, will advocate this stepping stone approach to enhance future cooperative space exploration efforts.

The petrogenesis of Apollo 14 high-Al basaltic melts was studied using crystal stratigraphy, which involves textural (crystal size distributions — CSDs) and chemical analyses (electron microprobe and laser ablation inductively coupled plasma mass spectrometry). The samples studied here include pristine basalt 14072 and basaltic clasts from breccia 14321, and impact-generated crystalline samples 14073, 14276 and 14310. Plagioclase was the focus of this study because of its relatively high modal abundances and because it was on the liquidus for much of the melt cooling histories. Plagioclase crystals were analyzed (core-to-rim compositions where possible) to test and refine petrogenetic models based upon whole-rock compositions (Groups A, B, and C designations) and to investigate basalt 14072 and impact-melt crystallization. Textural studies have shown that each basalt group has distinctive plagioclase CSDs, which are in turn distinctive from those of the impact melts. Evolution of the individual basaltic melts was studied by comparing the equilibrium-melt compositions (calculated from plagioclase compositions using relevant partition coefficients) to fractional crystallization (FC) and assimilation and fractional crystallization (AFC) models. Petrogenetic modeling of trace elements in Group A basalts revealed that petrogenesis continued beyond 40% total crystallization required to model whole-rock compositions, and that there were open-system processes that affected the magma during plagioclase crystallization. Petrogenetic modeling of pristine high-Al basalts (14072 and Groups A, B and C) using trace elements shows that the equilibrium-melt compositions do not fall on a single AFC or FC trajectory. This is consistent with fluctuating degrees of assimilation (i.e., variable r-values) and/or variable assimilant compositions during petrogenesis. Petrogenetic modeling reveals that the impact melts experienced only closed-system fractional crystallization. This work demonstrates the importance of crystal stratigraphy in revealing the intricacies of lunar basalt petrogenesis.

Previous investigations of pipe-like intrusions of alnoite within northern Malaita (Solomon Islands) have detailed the chemical and isotopic nature of the alnoite and entrained megacrysts/xenoliths. Alnoite emplacement is poorly constrained since available ages include an Ar–Ar date of 34 Ma (phlogopite) from a mantle xenolith, and a 206Pb/238U date of 33.9 Ma for a zircon megacryst. Hence, we report chemical data, in-situ U–Pb age determinations and Hf isotope compositions for megacrystic zircons recovered from alnoite-derived, ilmenite-rich gravels in the Auluta, Kwainale, and Faufaumela rivers of Malaita. The Zr/Hf ratio (39 to 50) is variable for zircons from Auluta and Faufaumela, whereas it is relatively uniform (40 to 42) in most zircons from Kwainale. Chemical imaging reveals the homogeneous nature for all of the 16 grains analyzed. Trace element compositions obtained by LA-ICP-MS indicate parallel chondrite-normalized REE patterns at variable levels of enrichment; these patterns combined with their low abundances (

The recently recovered paired Antarctic achondrites Graves Nunatak 06128 and 06129 (GRA) are meteorites that represent unique high-temperature asteroidal processes that are identified in only a few other meteorites. The GRA meteorites contain high abundances of sodic plagioclase, relatively Fe-rich pyroxenes and olivine, abundant phosphates, and low temperature alteration. They represent products of very early planetesimal melting (4565.9 +/- 0.3 Ma) of an unsampled geochemical reservoir from an asteroid that has characteristics similar to the brachinite parent body. The magmatism represented by these meteorites is contrary to the commonly held belief that the earliest stages of melting on all planetary bodies during the first 2-30 Ma of solar system history were fundamentally basaltic in nature. These sodic plagioclase-rich rocks represent a series of early asteroidal high-temperature processes: (stage 1) melting and partial extraction of a low-temperature Fe-Ni-S melt, (stage 2) small degrees of disequilibrium partial melting of a sodium- or alkali-rich chondritic parent body with additional incorporation of Fe-Ni-S melt that was not fully extracted during stage 1, (stage 3) volatile-enhanced rapid extraction and emplacement of the Na-rich, high-normative plagioclase melt, (stage 4) final emplacement and accumulation of plagioclase and phosphates, (stage 5) subsolidus reequilibration of lithology between 962 and 600 degrees C at an fO(2) Of IW to IW + 1.1, and (stage 6) replacement of merrillite and pyroxene by Cl-apatite resulting from the interaction between magmatic minerals and a Cl-rich fluid/residuum melt. The subsolidus events started as early as 4561.1 Ma and may have continued for upwards of 144 million years. The existence of assemblages similar to GRA on several other planetary bodies with different geochemical characteristics (ureilite, winonaites, IAB irons) implies that this type of early asteroidal melting was not rare. Whereas, eucrites and angrites represent extensive melting of a parent body with low concentrations of moderately-volatile elements, GRA represents low-degrees of melting of a parent body with chondritic abundances of moderately volatile elements. The interpretation of the low-temperature mineral assemblage is somewhat ambiguous. Textural features suggest multiple episodes of alteration. The earliest stage follows the interaction of magmatic assemblages with a Cl-rich fluid. The last episode of alteration appears to cross-cut the fusion crust and earlier stages or alteration. Stable isotopic measurements of the alteration can be interpreted as indicating that an extraterrestrial volatile component was preserved in GRA. (C) 2009 Elsevier Ltd. All rights reserved.

The Moon likely accreted from melt and vapor ejected during a cataclysmic collision between Proto-Earth and a Mars-sized impactor very early in solar system history. The identical W, O, K, and Cr isotope compositions between materials from the Earth and Moon require that the material from the two bodies were well-homogenized during the collision process. As such, the ancient isotopic signatures preserved in lunar samples provide constraints on the bulk composition of the Earth. Two recent studies to obtain high-precision 142Nd/144Nd ratios of lunar mare basalts yielded contrasting results. In one study, after correction of neutron fluence effects imparted to the Nd isotope compositions of the samples, the coupled 142Nd–143Nd systematics were interpreted to be consistent with a bulk Moon having a chondritic Sm/Nd ratio [Rankenburg K., Brandon A. D. and Neal C. R. (2006) Neodymium isotope evidence for a chondritic composition of the Moon. Science 312, 1369–1372]. The other study found that their data on the same and similar lunar mare basalts were consistent with a bulk Moon having a superchondritic Sm/Nd ratio [Boyet M. and Carlson R. W. (2007) A highly depleted Moon or a non-magma origin for the lunar crust? Earth Planet. Sci. Lett. 262, 505–516]. Delineating between these two potential scenarios has key ramifications for a comprehensive understanding of the formation and early evolution of the Moon and for constraining the types of materials available for accretion into large terrestrial planets such as Earth. To further examine this issue, the same six lunar mare basalt samples measured in Rankenburg et al. [Rankenburg K., Brandon A. D. and Neal C. R. (2006) Neodymium isotope evidence for a chondritic composition of the Moon. Science 312, 1369–1372] were re-measured for high-precision Nd isotopes using a multidynamic routine with reproducible internal and external precisions to better than ±3 ppm (2σ) for 142Nd/144Nd ratios. The measurements were repeated in a distinct second analytical campaign to further test their reproducibility. Evaluation of accuracy and neutron fluence corrections indicates that the multidynamic Nd isotope measurements in this study and the 3 in Boyet and Carlson [Boyet M. and Carlson R. W. (2007) A highly depleted Moon or a non-magma origin for the lunar crust? Earth Planet. Sci. Lett. 262, 505–516] are reproducible, while static measurements in the previous two studies show analytical artifacts and cannot be used at the resolution of 10 ppm to determine a bulk Moon with either chondritic or superchondritic Sm/Nd ratios. The multidynamic data are best explained by a bulk Moon with a superchondritic Sm/Nd ratio that is similar to the present-day average for depleted MORB. Hafnium isotope data were collected on the same aliquots measured for their 142Nd/144Nd isotope ratios in order to assess if the correlation line for 142Nd–143Nd systematics reflect mixing processes or times at which lunar mantle sources formed. Based on the combined 142Nd–143Nd–176Hf obtained we conclude that the 142Nd–143Nd correlation line measured in this study is best interpreted as an isochron with an age of 229+24−20Ma after the onset of nebular condensation. The uncertainties in the data permit the sources of these samples to have formed over a 44 Ma time interval. These new results for lunar mare basalts are thus consistent with a later Sm–Nd isotope closure time of their source regions than some recent studies have postulated, and a superchondritic bulk Sm/Nd ratio of the Moon and Earth. The superchondritic Sm/Nd signature was inherited from the materials that accreted to make up the Earth–Moon system. Although collisional erosion of crust from planetesimals is favored here to remove subchondritic Sm/Nd portions and drive the bulk of these bodies to superchondritic in composition, removal of explosive basalt material via gravitational escape from such bodies, or chondrule sorting in the inner solar system, may also explain the compositional features that deviate from average chondrites that make up the Earth–Moon system. This inferred superchondritic nature for the Earth similar to the modern convecting mantle means that there is no reason to invoke a missing, subchondritic reservoir to mass balance the Earth back to chondritic for Sm/Nd ratios. However, to account for the subchondritic Sm/Nd ratios of continental crust, a second superchondritic Sm/Nd mantle reservoir is required.

With the cancellation of the Apollo program after Apollo 17 returned from the Moon in 1972, the focus of NASA switched to other areas of the Solar System. Study of the Moon did continue through analysis of the returned samples and remotely sensed data sets (both orbital and surface), as well as through Earth-based telescopic studies. In the 1990s, new orbital data were obtained from several missions (fly-by and orbital), the first being Galileo that allowed the lunar farside to be mapped, followed by global mapping by the Clementine and Lunar Prospector missions. Interest in the Moon started to increase at the beginning of the 21st century as other nations focused their space exploration programs on the Moon. The speech by President Bush in January 2004 put the Moon back into the critical exploration path for NASA, paving the way for humans to return to the lunar surface by 2020. This return will be critical for developing technologies and protocols for the eventual human exploration of other parts of the solar system. At the time of writing (June 2008), the SELENE/Kaguya mission (Japan and Chang’e-1 (China) are orbiting the Moon, with Chandrayaan-1 (India) and Lunar Reconnaissance Orbiter (USA) being scheduled to launch later in 2008. The past (and present) exploration of the Moon begs the question ‘‘what’s left to be done?’’ With the renewed focus on the Moon, now that it is on the pathway for the exploration of Mars (and beyond) a similar question has been raised – what should the astronauts do on the Moon? The publication of the New Views of the Moon book [Jolliff et al., 2006. New Views of the Moon, Reviews in Mineralogy, vol. 60. American Mineralogical Society, 721pp] highlighted a number of important scientific questions that remain unanswered as well as posing many more on the basis of the currently available data. These questions resonated in three Lunar Exploration Analysis Group (LEAG) reports pertinent to this discussion, which were also published (on line) during 2006 (http://www.lpi.usra.edu/leag), and in the National Research Council of the National Academies [2007. The Scientific Context for Exploration of the Moon. National Academies Press, Washington, DC, 112pp] report entitled ‘‘The Scientific Context for Exploration of the Moon’’. This paper synthesizes these recent studies, along with those from the 1980s and 1990s, to emphasize the lunar science questions that remain unanswered. In addition, it summarizes the missions already flown to the Moon along with those that are planned in order to give the reader an idea of exactly what lunar science has been and will be conducted in the hope that it will inspire proposals for missions to address the outstanding science questions. r 2008 Elsevier GmbH. All rights reserved.

In the context of sample evidence alone, the high-alumina (HA) basalts appear to be an unique, and rare variety of mare basalt. In addition to their distinct chemistry, radiometric dating reveals these basalts to be among the oldest sampled mare basalts. Yet, HA basalts were sampled by four missions spanning a lateral range of ∼2400 km, with ages demonstrating that aluminous volcanism lasted at least 1 billion years. This evidence suggests that HA basalts may be a widespread phenomenon on the Moon. Knowing the distribution of HA mare basalts on the lunar surface has significance for models of the origin and the evolution of the Lunar Magma Ocean. Surface exposures of HA basalts can be detected with compositional remote sensing data from Lunar Prospector Gamma Ray Spectrometer and Clementine. We searched the lunar surface for regions of interest (ROIs) that correspond to the intersection of three compositional constraints taken from values of sampled HA basalts: 12–18 wt% FeO, 1.5–5 wt% TiO2, and 0–4 ppm Th. We then determined the “true” (unobscured by regolith) composition of basalt units by analyzing the rims and proximal ejecta of small impacts (0.4–4 km in diameter) into the mare surface of these ROIs. This paper focuses on two ROIs that are the best candidates for sources of sampled HA basalts: Mare Fecunditatis, the landing site of Luna 16; and northern Mare Imbrium, hypothesized origin of the Apollo 14 HA basalts. We demonstrate our technique's ability for delineating discrete basalt units and determining which is the best compositional match to the HA basalts sampled by each mission. We identified two units in Mare Fecunditatis that spectrally resemble HA basalts, although only one unit (Iltm) is consistent with the compositional and relative age of the Luna 16 HA samples. Northern Mare Imbrium also reveals two units that are within the compositional constraints of HA basalts, with one (Iltm) best matching the composition of the basalts sampled by Apollo 14.

The effect of natural organic matter (NOM) on arsenic adsorption by a commercial available TiO2 (Degussa P25) in various simulated As(III)-contaminated raw waters was examined. Five types of NOM that represent different environmental origins were tested. Batch adsorption experiments were conducted under anaerobic conditions and in the absence of light. Either with or without the presence of NOM, the arsenic adsorption reached steady-state within 1 h. The presence of 8 mg/L NOM as C in the simulated raw water, however, significantly reduced the amount of arsenic adsorbed at the steady-state. Without NOM, the arsenic adsorption increased with increasing solution pH within the pH range of 4.0–9.4. With four of the NOMs tested, the arsenic adsorption firstly increased with increasing pH and then decreased after the adsorption reached the maximum at pH 7.4–8.7. An appreciable amount of arsenate (As(V)) was detected in the filtrate after the TiO2 adsorption in the simulated raw waters that contained NOM. The absolute amount of As(V) in the filtrate after TiO2 adsorption was pH dependent: more As(V) was presented at pH > 7 than that at pH 7 . The arsenic adsorption in the simulated raw waters with and without NOM were modelled by both Langmuir and Frendlich adsorption equations, with Frendlich adsorption equation giving a better fit for the water without NOM and Langmuir adsorption equation giving a better fit for the waters with NOM. The modelling implies that NOM can occupy some available binding sites for arsenic adsorption on TiO2 surface. This study suggests that in an As(III)-contaminated raw water, NOM can hinder the uptake of arsenic by TiO2, but can facilitate the As(III) oxidation to As(V) at TiO2 surface under alkaline conditions and in the absence of O2 and light. TiO2 thus can be used in situ to convert As(III) to the less toxic As(V) in NOM-rich groundwaters.

ICP-MS; ICP-OES; Africa; Benin; Regional characterization Summary Groundwater samples were collected at over 100 locations in Benin, West Africa, for the purpose of characterizing region-wide spatial variation in groundwater quality as indicated by concentrations of a number of elements measured within the samples. Analytic techniques ranged from field measures of conductivity and pH, to characterization of major and trace element concentrations using ICP-MS and ICP-OES. Five methods of data analysis were applied to the resulting data set: indicator variables, parameter plots, cluster analysis, variogram analysis, and principal component analysis (PCA). A number of observations are developed from these analyses including regional trends in concentrations and variation of concentration of major and trace elements in specific geologic settings. Perhaps most significant is the identification of a region in the southern portion of the study area where the element chemistry shows high spatial variability. This region had not been identified in prior studies of the regional geochemistry. The mechanisms leading to this variability remain under study. The results presented provide significant insight into the regional variation in groundwater elemental chemistry for Benin. Further, they provide further illustration of the utility of applying multiple data analysis techniques to assessment of regional water quality data sets. a 2007 Elsevier B.V. All rights reserved.

Petrologic studies of igneous rocks often rely on whole-rock analyses alone to deduce source and melting histories. Whole-rock compositions represent a mixture of the processes responsible for the final texture and composition of the rock, but do not emphasize the evolutionary processes that the rock may have experienced. We examine the major, minor, and trace element compositions of plagioclase phenocrysts and plagioclase-rich cumulate xenoliths from a sequence of Kwaimbaita pillow basalt and massive flows recovered from Ocean Drilling Program (ODP) Site 1183 on the expansive ∼ 122 Ma Ontong Java Plateau (OJP) and from subaerial outcrops on the island of Malaita, Solomon Islands. These data are used to reconstruct equilibrium liquid compositions to understand magma dynamics, magma evolution, and the distribution basalt types across the OJP. Results reveal that crystals frequently are out of equilibrium with their host basalt. Two distinct compositional zones are present in plagioclase phenocrysts and xenolith crystals — An80–86 and An65–79. Equilibrium magma compositions derived from each of these zones are distinct. In relative terms, the following distinctions are made: An80–86: Sr, Y, and Eu richer, Ba and LREE depleted, higher Sr / Ti, lower Ba/Sr and La / Y; An65–79: Sr, Y, and Eu poorer, Ba and LREE enriched, lower Sr / Ti, higher Ba/Sr and La / Y. We observed several An65–79 parent magmas with higher La / Y, lower Sr, and higher LREE than the majority of An65–79 zones, which suggests that they grew from highly fractionated magmas. The An80–86 zones of both xenolith crystals and phenocrysts appear to have crystallized relatively early and are attributed to growth in magmas more primitive than parent magmas of An65–79 zones or the host magma. Using MELTS modeling we demonstrate a significant role for H2O is not necessary to form An-rich crystals from known OJP magma types. These types of zones can instead form when relatively primitive OJP magmas ascend and partially crystallize at low pressures. Crystal mush layers are rheological elements of multiply saturated solidification fronts, and conditions for extreme fractionation are met deep with thermally and mechanically insulated mush-solidification fronts. Conditions in a homogenous magma body alone cannot generate the range of magma compositions and textures recorded in OJP plagioclase crystals. We suggest that the OJP magma chamber system consisted of crystal mush dominated regions and liquid dominated regions in a laterally and vertically extensive system of interconnected dikes and sills. Solidification front disruption was common during magma recharge and transport, which freed debris to mix with OJP magmas. The volume of crystalline debris from disrupted solidification fronts was small relative to the overall magma volume, which leads to little change of bulk magma chemistry. This can explain the dominance of the Kwaimbaita basalt type across the OJP. Evidence of solidification front disruption is best preserved as allochthonous crystals both more and less primitive than bulk magma chemistry, both of which were observed in OJP basalts. Coincident with a zone of neutral buoyancy, the shallow OJP magma chamber system existed at a depth of 0–7 km. The OJP magma chamber system was thinner near the plateau margins, which provided less density filtration of magmas. This allowed more diverse magma types to reach the surface along the margins. It is envisaged that as the OJP formed, the zone of neutral buoyancy slowly migrated upward leading to slow yet pervasive assimilation of overlying seawater-altered basalt at the base of the lava pile.

LaPaz Icefield 02205 (LAP 02205) is a new low-Ti mare-basalt meteorite that was discovered in the LaPaz Ice Field in Antarctica. This is the first crystalline lunar basalt in the US Antarctic collection and the only 5th unbrecciated mare-basalt meteorite to be discov- ered to date. The rock has a typical basaltic texture with tabular and elongated pyroxene and plagioclase crystals, and minor olivine grains commonly rimmed by pyroxenes. Core- to rim- zoning in terms of Fe and Mg is present in almost all pyroxene grains. Accessory minerals include ilmenite, chromite, ulvospinel, troilite, and FeNi metal. This rock is highly enriched in late-stage mesostasis. Free silica is also abundant. In terms of texture and mineralogy, LAP 02205 displays features of low-Ti mare basalts, with similarities to some low- Ti Apollo 12 and Apollo 15 basalts. Whole-rock major- and trace-element compositions confirm the highly fractionated nature of this basalt. The whole-rock REE contents of the meteorite are the highest among all known low-Ti mare basalts. The platinum group element (PGE) contents in LAP are also enriched suggesting the possibility of endogenously enriched source regions or the PGEs generally behaved as incompatible elements during crystal fractionation under low fO2 conditions. Trace-element contents of mineral grains in LAP 02205 display wide variations, suggesting extensive non-equilibrium crystallization. The REE concentrations in the earliest-formed minerals provide constraints on the composition of the parental liquid, which is similar to the measured whole-rock composition. Crys- tallization modeling of the LAP 02205 bulk composition yields a reasonable fit between predicted and observed mineral phases and com- positions, except for the high-Mg olivine cores, which are observed in the rock but not predicted by the modeling. An isochron age of 2929 ± 150 Ma for phosphate minerals makes this rock one of the youngest lunar basalts known to date. The young age and specific geochemical characteristics of LAP distinguish it from those of most other low-Ti mare basalts. However, the low-Ti mare basalt mete- orite, NWA 032, has a similar young age, and the two meteorites also appear to be closely related from some geochemical perspectives and might have originated from similar source regions on the Moon.

Seventeen basalts from Ocean Drilling Program (ODP) Leg 183 to the Kerguelen Plateau (KP) were analyzed for the platinum-group elements (PGEs: Ir, Ru, Rh, Pt, and Pd), and 15 were analyzed for trace elements. Relative concentrations of the PGEs ranged from 0.1 (Ir, Ru) to 5 (Pt) times primitive mantle. These relatively high PGE abundances and fractionated patterns are not accounted for by the presence of sulfide minerals; there are only trace sulfides present in thin-section. Sulfur saturation models applied to the KP basalts suggest that the parental magmas may have never reached sulfide saturation, despite large degrees of partial melting (30%) and fractional crystallization (45%). First order approximations of the fractionation required to produce the KP basalts from an 30% partial melt of a spinel peridotite were determined using the PELE program. The model was adapted to better fit the physical and chemical observations from the KP basalts, and requires an initial crystal fractionation stage of at least 30% olivine plus Cr-spinel (49:1), followed by magma replenishment and fractional crystallization (RFC) that included clinopyroxene, plagioclase, and titanomagnetite (15:9:1). The low Pd values ((Pd/Pt)pm 1.7) for these samples are not predicted by currently available Kd values. These Pd values are lowest in samples with relatively higher degrees of alteration as indicated by petrographic observations. Positive anomalies are a function of the behavior of the PGEs; they can be reproduced by Cr-spinel, and titanomag- netite crystallization, followed by titanomagnetite resorption during the final stages of crystallization. Our modeling shows that it is difficult to reproduce the PGE abundances by either depleted upper or even primitive mantle sources. Crustal contamination, while indicated at certain sites by the isotopic compositions of the basalts, appears to have had a minimal affect on the PGEs. The PGE abundances measured in the Kerguelen Plateau basalts are best modeled by melting a primitive mantle source to which was added up to 1% of outer core material, followed by fractional crystallization of the melt produced. This reproduces both the abundances and patterns of the PGEs in the Kerguelen Plateau basalts. An alternative model for outer core PGE abundances requires only 0.3% of outer core material to be mixed into the primitive mantle source. While our results are clearly model dependent, they indicate that an outer core component may be present in the Kerguelen plume source. Copyright © 2005 Elsevier Ltd

Lunar meteorite EET 96008 is a fragmental breccia that predominantly consists of basaltic mineral clasts (0.5–2 mm), along with minor lithic fragments and breccia clasts. The matrix consists mainly of smaller mineral fragments ( The molar Fe/Mn ratio in olivines and pyroxenes and the age of the meteorite are evidence for a lunar origin. The mineralogy of EET 96008 shows close affinity to a mare-basalt source, albeit with possible minor highland/non-mare components. The bulk-rock, major-, trace- and rare-earth-element (REE) contents are similar to that of very low-titanium (VLT) basalts, which have experienced extreme fractional crystallization to the point of silicate liquid immiscibility. Mineralogical and textural features of this sample suggest that at least some of the breccia components were derived from a slow-cooled magma. The mineralogy and petrology of EET 96008 is strikingly similar to the lunar meteorite EET 87521, and we support the conclusion that EET 96008 and EET 87521 should be paired. Isochron ages of 3530 ± 270 Ma for apatite and 3519 ± 100 Ma for whitlockite of this rock are consistent with derivation from a mare-basalt precursor. These ages are within error of the low-Ti basalts, dated from the Apollo 12 and 15 sites. The whole-rock, platinum-group-element (PGE) contents of EET 96008 overlap with pristine low-Ti mare basalts, suggesting the presence of only a minimal extraterrestrial component.

Fractionated basalts (4.5–8.9 wt.% MgO) from the islands of Malaita and Makira (San Cristobal) in the Solomon Islands represent outpourings of magma that formed the Ontong Java Plateau (OJP), SW Pacific. The origin of the OJP is explored by examining platinum-group element (PGE: Ru, Rh, Pd, Ir, Pt) abundances in these basalts. On Makira, mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) are occasionally intercalated within the stratigraphic sequence of the OJP—the OIBtype basalts could be representative of the plume tail sequence and the MORB-type flows may be an indication of heterogeneity within the OJP source. Partial melting models indicate that the MORB-type basalts were generated from a source dominated by upper mantle material. However, they suggest that the OJP basalts and the OIB-type basalts were not generated from an exclusively upper mantle source. Our illustrative modeling shows the range of PGE compositions in these plume-generated basalts are best generated from a hybrid source that incorporates 0–0.5 wt.% of outer core material, 50% depleted upper mantle and 50–49.5% lower (primitive) mantle. D 2002 Elsevier Science B.V. All rights reserved.

We have evaluated the highly siderophile element (HSE) signatures of the martian (SNC) meteorites using new and literature data. These Ir and Os concentrations correlate with the Mg# [molar Mg/(Mg+Fe)], Cr and Ni, suggesting that olivine or chromite acts as a host for compatible siderophiles. Our analysis agrees with others who have suggested that the martian mantle has chondritic relative abundances of siderophiles. We also agree that, unlike the Sr and Nd isotopic systems, there is no evidence from Os isotopes for crustal assimilation. Comparisons of the siderophile element ratios of ALH 84001 to younger SNCs give no indication of a change in the martian siderophile element pattern over time. D 2002 Published by Elsevier Science B.V.

A method for analyzing low abundances of the platinum group elements (PGEs) and gold has been developed using cation exchange chromatography and ultrasonic nebulization inductively coupled plasma mass spectrometry (USN-ICP-MS). Ultrasonic nebulization increases sensitivity over regular pneumatic nebulization so that resolvable signals above background are possible in the fg/g range. Small sample sizes (≤250 mg) and low volumes of reagents produce procedural blank levels below the detection limit for Ru, Pd and Ir, in the fg/g range for Rh and in the low pg/g range for Pt and Au. Heterogeneous PGE and Au distributions in geological samples are avoided by a rigorous homogenization/rehomogenization procedure. The reference material UMT-1, which contains rock concentrations of the PGEs and Au at the low ng/g levels, monitored recoverability. Interferences of HfO+ and TaO+ on Ir, Pt and Au were not seen in the analyses of UMT-1 because Hf and Ta have low abundances in this reference material. However, these interferences are acute for silicate rocks, even after cation exchange chromatography. Isotope dilution cannot be adapted to this method for Ir and Pt because two interference-free isotopes are not available. An external calibration method has been developed for the accurate and precise determination of the PGEs and Au in rocks with low abundances of Hf and Ta (

The Solomon Islands are a complex collage of crustal units or terrains (herein termed the ‘Solomon block’) which have formed and accreted within an intra-oceanic environment since Cretaceous times. Predominantly Cretaceous basaltic basement sequences are divided into: (1) a plume-related Ontong Java Plateau terrain (OJPT) which includes Malaita, Ulawa, and northern Santa Isabel; (2) a ‘normal’ ocean ridge related South Solomon MORB terrain (SSMT) which includes Choiseul and Guadalcanal; and (3) a hybrid ‘Makira terrain’ which has both MORB and plume=plateau affinities. The OJPT formed as an integral part of the massive Ontong Java Plateau (OJP), at c. 122 Ma and 90 Ma, respectively, was subsequently affected by Eocene‐Oligocene alkaline and alnoitic magmatism, and was unaffected by subsequent arc development. The SSMT initially formed within a ‘normal’ ocean ridge environment which produced a MORB-like basaltic basement through which two stages of arc crustal growth subsequently developed from the Eocene onwards. The Makira terrain records the intermingling of basalts with plume=plateau and MORB affinities from c. 90 Ma to c. 30 Ma, and a contribution from Late Miocene‐present-day arc growth. Two distinct stages of arc growth occurred within the Solomon block from the Eocene to the Early Miocene (stage 1) and from the Late Miocene to the present day (stage 2). Stage 1 arc growth created the basement of the central part of the Solomon block (the Central Solomon terrain, CST), which includes the Shortland, Florida and south Isabel islands. Stage 2 arc growth led to crustal growth in the west and south (the New Georgia terrain or NGT) which includes Savo, and the New Georgia and Russell islands. Both stages of arc growth also added new material to pre-existing crustal units within other terrains. The Solomon block terrane collage records the collision between the Alaska sized OJP and the Solomon arc. Initial contact possibly first occurred some 25‐20 Ma but it is only since around 4 Ma that the OJP has more forcefully collided with the Solomon arc, and has been actively accreting since that time, continuing to the present day. We present a number of tectonic models in an attempt to understand the mechanism of plateau accretion. One model depicts the OJP as splitting in two with the upper 4‐10 km forming an imbricate stack verging to the northeast, over which the Solomon arc is overthrust, whilst deeper portions of the OJP (beneath a critical detachment surface) are subducted. The subduction of young (

The island of Malaita, Solomon Islands, represents the obducted southern margin of the Ontong Java Plateau (OJP). The basement of Malaita formed during the first and possibly largest plateau-building magmatic event at ∼122 ± 3 Ma. It subsequently drifted passively northwards amassing a 1–2 km thickness of pelagic sediment overburden. A major change in OJP tectonics occurred during the Eocene, possibly initiated by the OJP passing over the Samoan or Raratongan hotspot. Extension facilitated increased sedimentation and basin formation (e.g., the Faufaumela basin) and provided readily available deep-crustal pathways for alkali basalt and subsequent Oligocene alnoite magmas, with related hydrothermal activity producing limited Ag + Pb mineralisation. Eocene to Mid-Miocene sediments record the input of arc-derived turbiditic volcaniclastic sediment indicating the relative closeness of the OJP to the Solomon arc. The initial collision of the OJP and Solomon arc at 25-20 Ma was of a ‘soft docking’ variety and did not result in major compressive deformation on Malaita. South-directed subduction of the Pacific Plate briefly ceased at this time but resumed intermittently on a local scale from ∼15 Ma. Subduction of the Australian Plate beneath the Solomon arc commenced at ∼8-7 Ma. Increased coupling between the Solomon arc and the OJP led to the gradual emergence of the OJP at 6-5 through to 4 Ma. The most intense period of compressive to transpressive deformation recorded on Malaita is stratigraphically bracketed at between 4 and 2 Ma, resulting in estimated crustal shortening of between 24 and 46%, and the inclusion of between 1 and 4 km of basement OJP basalts within the larger anticlines. Basement and cover sequences are deformed together in a coherent geometry and there are no major decollement surfaces; the large asymmetrical fold structures of Malaita are likely to be the tip regions of blind thrusts with detachment surfaces between 1 and 4 km beneath the cover sequence. Mid-Pliocene deformation records the detachment of the upper parts of the OJP, with initial material movement direction towards the northeast and later obduction of an upper allochthonous block of the OJP southwestwards over the Solomon arc. A model is presented whereby an upper 5–10-km-thick flake of the OJP is obducted over the Solomon arc to form the Malaita

In an effort to elucidate the processes of lunar mantle melting, and the magma evolution of mare basalts within Oceanus Procellarum on the western lunar near-side, we have analyzed seven fine-grained to vitrophyric Apollo 12 basalts for trace-elements; five of these also have been analyzed for Nd and Sr isotopic compositions. These samples represent all three main groups identified among the Apollo 12 mare basalts and have been proposed as parental melts to their respective groups, i.e., olivine-, pigeonite-, and ilmenite-basalts. The sources for these low-Ti mare basalts are postulated to have formed from crystallization of a global magma ocean. LiBe systematics, combined with REE data, indicate that the specific sources for the Apollo 12 low-Ti mare basalts were generated after 82–94% crystallization of this lunar magma ocean. In fact, it seems that all mare basalts analyzed from the Apollo collections were generated from cumulates precipitated in the last 20% of the magma ocean. Chemical compositions of fine-grained pigeonite and olivine basalts are consistent with 7–9% nonmodal (in proportions not defined by experimental petrology and phase equilibria) melting of a source consisting of 48% olivine, 30% calcic clinopyroxene, and 22% pigeonite (as per Neal et al., 1994b). SmNd and RbSr abundance data also suggest that the pigeonite- and olivine-basalt source contained from 0.3 to 0.5% trapped residual liquid from the magma ocean. The compositions of the two fine-grained ilmenite basalts are consistent with 5–7% partial melting of a source with subequal proportions of olivine (45.5%) and pigeonite (42.5%) and lesser amounts of clinopyroxene (11.5%) and entrained plagioclase (0.5%). Furthermore, the ilmenite source was nearly devoid of trapped liquid ( Isotopic systematics of the Apollo 12, fine-grained, parental basalts are consistent with their derivation from two distinct mantle source regions. Both of these sources were LREE depleted for extended periods of time: up to 600 million years for the ilmenite-basalt source and up to 900 million years for the pigeonite- and olivine-basalt source. Due in part to the relatively small proportion of low Sm Nd , trapped, residual magma-ocean liquid in the source ( By integrating this information on parental, low-Ti, Apollo 12 basalts with mare basalt and picritic glass data from other landing sites, as well as telescopic and remote-sensing data, we propose a model for melting of the lunar interior. The upper 400–500 km of the lunar mantle is a consequence of incipient melting of the Moon and formation of a global magma ocean. This magma ocean became progressively enriched in incompatible elements as it precipitated the cumulate upper mantle. This incompatible-earliest, extensive mare magmas (high-Ti mare basalts) were generated at shallow depths in the mantle from cumulate source-regions that had trapped relatively large proportions of this incompatible-element enriched, residual, magma ocean liquid. These source regions also contained the late-crystallizing phase ilmenite and, thus, generated high-Ti magmas. The trapped liquid component contained elevated abundances of heat-producing elements (K, U, and Th), increasing the fertility of associated source-regions. With time, melting moved progressively deeper in the mantle to source-regions with less of the residual, heat-producing, magma ocean liquid. Due to density contrasts, the ilmenite-bearing upper portions of the lunar mantle sank into the cumulate pile, possibly carrying more fertile material with it and allowing melting of more Mg-enriched source regions (to form the high-Ti picritic glass beads). Thus, the major controlling factors in the melting of the lunar interior could be the proportion of trapped, magma-ocean liquid in the cumulate source and the sinking of more fertile, ilmenite-bearing material into the lower mantle.

A chemical model for simulating the sources of the lunar mare basalts was developed by considering a modified mafic cumulate source formed during the combined equilibrium and fractional crystallization of a lunar magma ocean (LMO). The parameters which influence the initial LMO and its subsequent crystallization are examined, and both trace and major elements are modeled. It is shown that major elements tightly constrain the composition of mare basalt sources and the pathways to their creation. The ability of this LMO model to generate viable mare basalt source regions was tested through a case study involving the high-Ti basalts.

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.

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.

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.

The geochronological and compositional differences between previously identified magma types (A, B1, B2, and C) were investigated using high-precision Rb-Sr and Sm-Nd isotopic data for a set of Apollo 17 high-Ti mare basalt samples chosen to span the range of each of the magma types. These data, combined with previously reported geochemical ages, suggest that Apollo 17 volcanism was initially dominated by an eruption of Type B basalts. Data obtained from new whole-rock Sr and Nd isotopic analyses exhibited distinct differences in initial Sr and Nd isotopic compositions between Types A, B1, B2, and C basalts and were found to be consistent with existing petrogenetic models.

The Sr, Nd, and O isotopic compositions of garnet and clinopyroxene mineral separates from nine eclogite xenoliths from the Bellsbank kimberlite (erupted at 120 Ma) define three groups. Group A eclogites, considered to be mantle cumulates, are characterized by 6180, and 87Sr/Srsr values typical of mantle-derived materials (+5.1 to +5.6%o and 0.7042-0.7046, respectively), and very low Sm/Nd ratios, (apparent) Rb/Sr ratios and ~NaLlZ01 values (0.057-0.078, 0.00005-0.00136 and - 14 to - 16 respectively). The REE and isotopic data for these eclogites can be modelled in terms of crystallization from a Group II kimberlite magma at - 1-1.5 Ga. Group B and C eclogites, believed to be the metamorphosed products of ancient subducted oceanic crust, are characterized by low 3180 (+2.9 to +4.7), extremely high ~Nd[a20] (-- +40 to +219), and radiogenic 87Sr/S6Sr ratios (0.708-0.710). The Sm/Nd ratios of the Group B eclogites are very high (up to 1.6). The data for Group B and C eclogites define a linear correlation on Sm/Nd and 1/Nd vs. ~Nal~201 diagrams. These relationships are consistent with mixing of the Bellsbank kimberlite (CNO [1201 = --10; Sm/Nd = 0.10) with a depleted eclogite end-member (eNd[120 ] + 219; Sm/Nd = 1.6) during a cryptic metasomatic event. The Sr isotopic variations in Group B and C eclogites cannot be generated by simple two-component mixing. The St, Nd, and O isotope data for Group B and C eclogites probably reflect a complex sequence of depletion and enrichment events, in both crust and mantle settings. Enrichments which possibly affected the Group B and C eclogites include seawater-alteration of a MORB-like protolith, which lowered the 6180 and raised the SVSr/86Sr ratio, but left the Nd isotopic compositions unchanged, and cryptic metasomatism by the magmatism that produced the Bellsbank kimberlite. The high Sm/Nd ratio of the depleted eclogite end-member cannot be generated by extraction of a melt from a modern MORB composition. Rather, it is argued that such high Sm/Nd ratios are produced as a result of partitioning during the recrystallization of a MORB-like component to eclogite during subduction. Nd model ages suggest that this process occurred - 2.3-2.4 Ga.

Whole-rock and mineral analyses of 26 'new' type A and B Apollo 17 basalts are reported. The petrography and mineral chemistry of these basalts are similar to previously reported Apollo 17 basalts. However, these 'new' whole-rock data extend the compositional ranges of previously reported type A and B basalts and require the division of the type B basalts into type B1 and B2 varieties. These three types display similar trends when both major and trace elements are plotted against a fractionation index of Cr/La ratio. Major element compositions of basalts from all three types fall on olivine + Ti oxide control lines. This study demonstrates that Apollo 17 type A, B1, and B2 basalts have a relatively simple petrogenesis, with the only postmagma-generation process being fractional crystallization.

The Ma&tan alnijite contains a rich and varied megacryst suite of unprecedented compositional range. We have undertaken trace element and isotope modeling in order to formulate a petrogenetic scheme which links the host alniiite to its entrained megacrysts. This requires that a proto-alntiite magma is the product of zone refining initiated by diapiric upwelling (where the initial melt passes through 200 times its volume of mantle). Isotopic evidence indicates the source of the proto-alniiite contains a time- integrated LREE-depleted signature (143Nd/'44Nd = 0.51274). Impingement upon the rigid lithosphere halts or dramatically slows the upward progress of the mantle diapir. At this point, the magma cools and megacryst fractionation begins with augites crystallizingjirst, followed by subcalcic diopsides and finally phlogopites. Garnet probably crystallizes over the entire range of clinopyroxene fractionation. Estimated proportions of fractionating phases are 30% augite, 24.5% subcalcic diopside, 27% garnet, 12.9% phlogopite, 5% bronzite, 0.5% ilmenite, and 0.1% zircon. As this proto-alnoite magma crystallizes, it assimilates a subducted component of seawater-altered basalt which underplates the Ontong Java Plateau. This is witnessed in the isotopic composition of the megacrysts and alnoite.

The presence of negative cerium anomalies in island arc lavas has been considered enigmatic. Such negative Ce anomalies must be inherent in the source region and can be produced by subducting pelagic sediments + seawateraltered basalts (SWAB) into the mantle. A mantle peridotite from the Malaitan alnoite also contains a negative Ce anomaly, which can be produced by sediment recycling into the upper mantle. However, in spite of the poorly defined effects of cryptic metasomatism and associated ƒO 2 conditions, such a process also seems plausible for the generation of negative Ce anomalies. In order to define the petrogenesis of this peridotite within the constraints of the present experimental data, we have attempted various mixing models with the end-members: mantle peridotite, Pacific sediment and seawater-altered basalt. In our model, it was assumed that negative Ce anomalies cannot be produced by magmatic or metasomatic processes. Best results were obtained from mixing a maximum of 3 to 5% seawater-altered basalt and 2 to 3% pelagic sediment, with a LREE-enriched mantle precursor. Our model stresses the importance of the contribution that recycled crustal materials can have on the composition of the upper mantle, in particular the recognition of a crustal signature in a mantle regime.

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.