No abstract

Lunar crustal rocks can be divided into two groups: the terra, or highland, types and the mare basalts. Interpretation of the highland samples is complicated by their derivative nature, which resulted from a series of crystallization, shock, and brecciation events. In contrast, mare basalts appear to be much less complicated and to have been rather uncompromised since their arrival at the lunar surface; thus a synthesis appears possible at this time. Although the mare basalts comprise less than 1% of the lunar crust, they contain much information about the thermal history of the moon and the nature of the lunar interior. It is now known that a complete suite of basalts, sampling all of the chemically and temporally distinct units, was not sampled by the Apollo and Luna missions. The mare basalts that have been studied have ages between 3.15 and 3.96 Gy. However, photogeologic evidence (crater counts and crater degradation studies) indicates that basalts as young as 2.5 Gy exist on the moon and were not sampled. The returned samples can be divided into two broad groups: the older, high‐titanium group (ages, ∼3.55–3.85 Gy; TiO2, 9–14 wt %) and the younger, low‐titanium group (ages, 3.15–3.45 Gy; TiO2, 1–5 wt %). Basalts from Apollo 11 and 17 fall into the older, high‐titanium group; basalts from Apollo 12 and 15 and Luna 16 fall into the younger, low‐titanium group. The two major groups of basalts can be further subdivided on the basis of major‐ and minor‐element chemistry. Within each of these subgroups a variety of grain sizes and textures, which result from different cooling histories, are present. Near‐surface fractionation of these basalts involved mainly olivine in the low‐titanium basalts and olivine plus iron‐titanium oxides in the high‐titanium basalts. The alkali‐depleted mare basalts evolved by rapid cooling at the lunar surface under extremely reducing conditions (∼10−13 atm at 1150°C). This low oxygen fugacity resulted in reduced valence states for Ti (Ti4+ → Ti3+) and Cr (Cr3+ → Cr2+), which in turn affected both the chemistry and the stability of the mare basalt minerals. The most important mineralogical species in these rocks are the silicates (pyroxene, feldspar, and olivine) and the Fe‐Ti oxides (ilmenite, spinel, and armalcolite). Models for the source regions of the mare basalts remain controversial. Three basic models for mare basalt source regions have been advanced. These include the cumulate source model (remelting of cumulates resulting from early lunar differentiation), the primitive source model (melting of deep undifferentiated mantle), and the assimilation model (primary melts are contaminated by assimilation). All of these models have problems. If one assumes that at least some of the lunar basalt samples arrived at the surface with unaltered chemistry, the high‐pressure experimental phase equilibria approach can provide constraints on the nature of the source regions for these rocks. Results of these studies indicate that the low‐ and high‐Ti mare basalt groups were derived from miner...

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or impiy its endorsement, m mmendattion, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. summary Pacific Northwest National Laboratory (PNNL) conducted a Phase I, Resource Conservation and Recovery Act of 1976 (RCRA) groundwater quality assessment for the Richland Field Office of the U.S. Department of Energy (DOE-RL) under the requirements of the Federal Facility Compliance Agreement. The purpose of the investigation was to determine if the Single-Shell Tank Waste Management Areas (WMAs) T and TX-TY have impacted groundwater quality. Waste Management Areas T and TX-TY, located in the northern part of the 200 West Area of the Hanford Site, contain the 241-T, 241-TX, and 241-TY tank farms and ancillary waste systems. These two units are regulated under RCRA interim-status regulations (under 40 CFR 265.93) and were placed in assessment groundwater monitoring because of elevated specific conductance in downgradient wells. Anomalous concentrations of technetium-99, chromium, nitrate, iodine-129, and cobalt-60 also were observed in some d o w m e n t wells. Phase I assessment, allowed under 40 CFR 265, provides the owner-operator of a facility with the opportunity to show that the observed contamination has a source other than the regulated unit. For this Phase I assessment, PNNL evaluated available information on groundwater chemistry and past waste management practices in the vicinity of WMAs T and TX-TY. Background contaminant concentrations in the vicinity of WMAs T and TX-TY are the result of several overlapping contaminant plumes resulting from past-practice waste disposal operations. This background has been used as baseline for determining potential WMA impacts on groundwater. Examination of contaminant patterns in downgradient wells at the two WMAs indicate that: Elevated values of specific conductance in downgradient wells 299-W10-15 (WMA T) and 299-WlO-17 (WMA TX-TI) are a result of elevated concentrations of sodium and nitrate originating outside of the WMAS. Elevated technetium-99 and co-contaminants (e.g., chromium, tritium, and nitrate) observed in well 299-Wll-27, immediately d o w n w e n t to WMA T, are the result of a contaminant source within the WMA. Contaminant chemistry is consistent with a small volume tank waste source and l...

Coarse‐grained lherzolitic peridotites and two‐pyroxene gabbros recovered at Deep Sea Drilling Project site 334 beneath a thin layer of fine‐grained basalt are primary magmatic cumulates similar to the upper cumulate portion of ophiolite complexes. Mineral chemistry indicates that they are the crystallization product of oceanic tholeiite magma. Long cooling and annealing times indicated by exsolution and equilibration in pyroxenes indicate emplacement near the Mid‐Atlantic Ridge and long residence time in oceanic layer 3, prior to tectonic emplacement at shallow crustal levels. Slow depletion of the anorthite component in cumulate plagioclase relative to increase of Fe/Fe + Mg in coexisting mafic phases indicates more efficient fractionation of sodium into residual liquid than implied by fractionation of plagioclase phenocryst found in oceanic magmas. Strong depletion of incompatible minor elements and lack of intercumulate residual phases may indicate the operation of a diffusion mechanism that would allow interaction of pyroxene and magma prior to the crystallization of pyroxene as a liquidus phase.