L. A. Taylor

Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1

Lunar Water The Moon has been thought to be primarily anhydrous, although there has been some evidence for accumulated ice in permanently shadowed craters near its poles (see the Perspective by Lucey, published online 24 September). By analyzing recent infrared mapping by Chandrayaan-1 and Deep Impact, and reexamining Cassini data obtained during its early flyby of the Moon, Pieters et al. (p. 568, published online 24 September), Sunshine et al. (p. 565, published online 24 September), and Clark et al. (p. 562, published online 24 September) reveal a noticeable absorption signal for H2O and OH across much of the surface. Some variability in water abundance is seen over the course of the lunar day. The data imply that solar wind is depositing and/or somehow forming water and OH in minerals near the lunar surface, and that this trapped water is dynamic. Space-based spectroscopic measurements provide evidence for water or hydroxyl (OH) on the surface of the Moon The search for water on the surface of the anhydrous Moon had remained an unfulfilled quest for 40 years. However, the Moon Mineralogy Mapper (M3) on Chandrayaan-1 has recently detected absorption features near 2.8 to 3.0 micrometers on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M3 data with neutron spectrometer hydrogen abundance data suggests that the formation and retention of hydroxyl and water are ongoing surficial processes. Hydroxyl/water production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.

A chemical model for generating the sources of mare basalts - Combined equilibrium and fractional crystallization of the lunar magmasphere

Abstract It is generally considered that mare basalts were generated by the melting of a cumulate mantle formed in an early Moon-wide magma ocean or magmasphere. However, the nature and chemistry of this cumulate mantle and the logistics of its origin have remained elusive. Extensive studies of terrestrial layered mafic intrusions over the past sixty years have emphasized the imperfection of fractional crystallization and attendant crystal-crystal and crystal-liquid separation in a convecting magma chamber. Crystal-liquid and crystal-crystal separations were similarly inefficient during evolution of the lunar magma ocean (LMO), allowing for the trapping of interstitial liquid and entrainment of a small proportion of less-dense plagioclase into the denser mafic cumulate mush. Indeed, petrography of lunar highlands samples demonstrates this for anorthosites (with 1–10% olivine). The residual liquid after 80–90% crystallization was very evolved (in fact KREEPy) and, even in small proportions (1–5%), would have a noticeable effect on the trace-element chemistry of melts generated from these cumulates. This trapped residual liquid would elevate total REE abundances in the cumulate pile, while synchronously deepening the already negative Eu anomaly. Essentially, this trapped liquid will make the cumulate more fertile for melting to generate both KREEP basalt and mare basalt magmas. Plagioclase entrained in the mafic cumulate pile adds an essential Al component to the high-Ti basalt source and will moderate the requisite negative Eu anomaly in the cumulate. Early in the evolution of the lunar mantle, when the LMO still was largely liquid, it is likely that vigorous convection was an important factor in crystallization. Such convection would allow crystals to remain suspended and in equilibrium with the LMO liquid for relatively long periods of time. This extended period of equilibrium crystallization would then have been followed by fractional crystallization once plagioclase became a liquidus phase and began to float to form the lunar highlands crust. Previous authors have proposed a three-component model for the evolution of high-Ti mare basalt source regions. This model includes KREEP, early (olivine-rich, high Mg#) cumulates, and late (ilmeniterich, low Mg#) cumulates in various proportions. However, we propose a model for high-Ti basalt parent magmas which is in accord with studies of terrestrial layered intrusions. This model for the high-Ti source includes trapped instantaneous residual liquid (TIRL; 1–3%) and entrainment of a small (2–5%) proportion of plagioclase into the late-stage cumulate pile in order to account for both the observed Al compositions and trace-element characteristics of high-Ti mare basalts. Melting of this relatively shallow, ilmenite- and clinopyroxene-bearing, late-stage cumulate can generate high-Ti mare basalt magmas. Furthermore, we are in agreement with other workers that only through a process of nonmodal melting will the high Ti values for the parent magmas be realized. Large-scale convective overturn of the cumulate pile and mixing of KREEP with early- and late-stage cumulates is not required. However, localized overturn of the upper tenth of the cumulate pile is likely and, in fact, required to achieve an appropriate major-element balance for the high-Ti mare basalt source region.

Lunar Mare Soils: Space weathering and the major effects of surface‐correlated nanophase Fe

Lunar soils form the “ground truth” for calibration and modeling of reflectance spectra for quantitative remote sensing. The Lunar Soil Characterization Consortium, a group of lunar sample and remote sensing scientists, has undertaken the extensive task of characterization of lunar soils, with respect to their mineralogical and chemical makeup. This endeavor is aimed at deciphering the effects of space weathering of soils from the Moon, and these results should apply to other airless bodies. Modal abundances and chemistries of minerals and glasses in the <45 μm size fractions of nine selected mare soils have been determined, along with the bulk chemistry of each size fraction, and their IS/FeO values. These data can be addressed at http:/web.utk.edu/∼pgi/data.html. As grain size decreases, the bulk composition of each size fraction continuously changes and approaches the composition of the agglutinitic glasses. Past dogma had it that the majority of the nanophase Fe0 resides in the agglutinitic glasses. However, as grain size of a soil decreases, the percentage of the total iron present as nanophase-sized Fe0 increases dramatically, while the agglutinitic glass content rises only slightly. This is evidence for a large contribution to the IS/FeO values from surface-correlated nanophase Fe0, particularly in the <10 μm size fraction. This surficial nanophase Fe0 is present largely as vapor-deposited patinas on the surfaces of almost every particle of the mature soils. It is proposed that these vapor-deposited, nanophase Fe0-bearing patinas may have far greater effects upon reflectance spectra of mare soils than the agglutinitic Fe0.

Lunar apatite with terrestrial volatile abundances

The Moon is thought to be depleted relative to the Earth in volatile elements such as H, Cl and the alkalis. Nevertheless, evidence for lunar explosive volcanism has been used to infer that some lunar magmas exsolved a CO-rich and CO2-rich vapour phase before or during eruption. Although there is also evidence for other volatile species on glass spherules, until recently there had been no unambiguous reports of indigenous H in lunar rocks. Here we report quantitative ion microprobe measurements of late-stage apatite from lunar basalt 14053 that document concentrations of H, Cl and S that are indistinguishable from apatites in common terrestrial igneous rocks. These volatile contents could reflect post-magmatic metamorphic volatile addition or growth from a late-stage, interstitial, sulphide-saturated melt that contained ∼1,600 parts per million H2O and ∼3,500 parts per million Cl. Both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable terrestrial materials. One possible implication is that portions of the lunar mantle or crust are more volatile-rich than previously thought.

Petrogenesis of mare basalts - A record of lunar volcanism

Returned rock and soil samples from our nearest planetary neighbor have provided the basis for much of our understanding of the origin and evolution of the Moon. Of particular importance are the mare basalts, which have revealed considerable information about lunar volcanism and the nature of the mantle, as well as post-magma-generation processes. This paper is a critical review of the petrogenetic models for the generation of mare basalts formulated over the last twenty years. We have used all available mare basalt analyses to define a six-fold classification scheme using TiO2 contents as the primary division (i.e., ∗ 1 wt% = very low-Ti or VLT; 1–6 wt% = low-Ti; > 6 wt% = high-Ti). A secondary division is made using Al2O3 contents (i.e., ∗ 11 wt% = low-Al; > 11 wt% = high-Al), and a tertiary division is defined using K contents (i.e., ∗ 2000 ppm = low-K; > 2000 ppm = high-K). Such divisions and subdivisions yield a classification containing twelve categories, of which six are accounted for by the existing Apollo and Luna collections. Therefore, we present our discussions in the form of six mare basalt rock types: 1. (1) high-Ti/low-Al/low-K (referred to as “high-Ti/low-K”). 2. (2) high-Ti/low-Al/high-K (referred to as “high-Ti/high-K”). 3. (3) low-Ti/low-Al/low-K (referred to as “low-Ti”). 4. (4) low-Ti/high-Al/low-K (referred to as “high-alumina”). 5. (5) low-Ti /high-Al/ high-K (referred to as “VHK”). 6. (6) VLT/low-Al/low-K basalts (referred to as “VLT”). A variety of post-magma-generation processes have been invoked, such as fractional crystallization, either alone or combined with wallrock assimilation, to explain the compositional ranges of the various mare basalt suites. In order to evaluate these proposed petrogenetic processes, this review is by rock type and is non-site specific, but for each rock type, reference to particular lunar sample return missions is brought forth. This permits a comparison of similarities and differences of broadly similar rock types correlated with geography on the Moon, which, in turn, allows a more thorough petrogenetic evaluation. High-Ti mare basalts (i.e., high-Ti/low-Al/low-K) are found at Apollo 11 and Apollo 17 sites; however, 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. Fractional crystallization and source heterogeneity within each site are the keys to understanding the petrogenesis of the high-Ti basalts. Low-Ti basalts (including both low-Al/K and high-Al/K varieties) are found at Apollo 12, 14, and 15, and Luna 16 sites. The low-Ti basalts exhibit a wide range of major- and trace-element compositions and require source heterogeneity, fractional crystallization, and some assimilation. The high-alumina mare basalts (i.e., low-Ti/high-Al/low-K) are found at Apollo 14 and Luna 16 sites and exhibit a wide range of major-and trace-element compositions. However, in these examples, source heterogeneity is not a major factor. Indeed, fractional crystallization coupled with KREEP assimilation, particularly for the Apollo 14 variants, can explain the compositional ranges of these high-alumina basalts. The VHK mare basalts (i.e., low-Ti/high-Al/high-K) have been sampled only at the Apollo 14 locale and are products of a parental highalumina magma assimilating lunar granite. Very low-Ti (VLT) mare basalts (i.e., VLT/low-Al/low-K) are found at Apollo 17 and Luna 24 sites. Fractional crystallization has had a major influence upon the range in VLT compositions, but Luna 24 VLT basalts have been derived from a source slightly different in composition from that for Apollo 17 VLT varieties. For example, the Luna 24 VLT basalts generally exhibit positive Eu anomalies, a unique property for mare basalts, which almost always have negative Eu anomalies. The concept of a lunar magma ocean (LMO) is generally accepted, and source modelling of all basalts invokes a “mafic LMO cumulate source.” This is the only unifying model for mare basalt petrogenesis, but the semantics and logistics of it are and will be debated for many years. For example, major convective overturn of the LMO appears plausible, but whether this occurred on a local- or planet-wide scale to produce source heterogeneity remains to be determined.

Eclogites with Oceanic Crustal and Mantle Signatures from the Bellsbank Kimberlite, South Africa, Part I: Mineralogy, Petrography, and Whole Rock Chemistry

Three groups of eclogite xenoliths have been identified from the DeBruyn and Martin Mine of the Bellsbank kimberlite, South Africa. These eclogites are divided into the three groups on the basis of petrography, clinopyroxene and garnet mineral chemistry, and rare earth element (REE) contents of the whole rocks, clinopyroxenes, and garnets. Abundances of the REE and garnet-clinopyroxene Kds are consistent with a petrogenesis by fractional crystallization for Group A eclogites, but not Groups and We suggest, on the basis of bulk-rock major-element and REE analyses and reconstructed REE patterns, that eclogites from Groups and are the metamorphosed products of ancient subducted oceanic crust. Group eclogites have major element chemistry similar to Archean basalts, and Group eclogites have high

Analysis of terrestrial and martian volcanic compositions using thermal emission spectroscopy: 1. Determination of mineralogy, chemistry, and classification strategies

Al_{2}O_{3}

Pre-4.2 AE mare-basalt volcanism in the lunar highlands

abundances. Metasomatism has affected all groups of eclogites, producing phlogopite, feldspar, amphibole, and a breakdown of primary clinopyroxene. On the basis of large ion lithophile (LIL) elements, this metasomatism can be traced to the host kimberlite. Our study demonstrates that petrogenesis by fractional crystallization cannot account for all eclogite xenolith compositions found in kimberlite.