ALBERT

Description: Many studies exist on magmatic volatiles (H, C, N, F, S, Cl) in and on the Moon, within the last several years, that have cast into question the post-Apollo view of lunar formation, the distribution and sources of volatiles in the Earth-Moon system, and the thermal and magmatic evolution of the Moon. However, these recent observations are not the first data on lunar volatiles. When Apollo samples were first returned, substantial efforts were made to understand volatile elements, and a wealth of data regarding volatile elements exists in this older literature. In this review paper, we approach volatiles in and on the Moon using new and old data derived from lunar samples and remote sensing. From combining these data sets, we identified many points of convergence, although numerous questions remain unanswered. The abundances of volatiles in the bulk silicate Moon (BSM), lunar mantle, and urKREEP [last ~1% of the lunar magma ocean (LMO)] were estimated and placed within the context of the LMO model. The lunar mantle is likely heterogeneous with respect to volatiles, and the relative abundances of F, Cl, and H 2 O in the lunar mantle (H 2 O 〉 F 〉〉 Cl) do not directly reflect those of BSM or urKREEP (Cl 〉 H 2 O F). In fact, the abundances of volatiles in the cumulate lunar mantle were likely controlled by partitioning of volatiles between LMO liquid and nominally anhydrous minerals instead of residual liquid trapped in the cumulate pile. An internally consistent model for lunar volatiles in BSM should reproduce the absolute and relative abundances of volatiles in urKREEP, the anorthositic primary crust, and the lunar mantle within the context of processes that occurred during the thermal and magmatic evolution of the Moon. Using this mass-balance constraint, we conducted LMO crystallization calculations with a specific focus on the distributions and abundances of F, Cl, and H 2 O to determine whether or not estimates of F, Cl, and H 2 O in urKREEP are consistent with those of the lunar mantle, estimated independently from the analysis of volatiles in mare volcanic materials. Our estimate of volatiles in the bulk lunar mantle are 0.54–4.5 ppm F, 0.15–5.3 ppm H 2 O, 0.26–2.9 ppm Cl, 0.014–0.57 ppm C, and 78.9 ppm S. Our estimates of H 2 O are depleted compared to independent estimates of H 2 O in the lunar mantle, which are largely biased toward the "wettest" samples. Although the lunar mantle is depleted in volatiles relative to Earth, unlike the Earth, the mantle is not the primary host for volatiles. The primary host of the Moon’s incompatible lithophile volatiles (F, Cl, H 2 O) is urKREEP, which we estimate to have 660 ppm F, 300–1250 ppm H 2 O, and 1100–1350 ppm Cl. This urKREEP composition implies a BSM with 7.1 ppm F, 3–13 ppm H 2 O, and 11–14 ppm Cl. An upper bound on the abundances of F, Cl, and H 2 O in urKREEP and the BSM, based on F abundances in CI carbonaceous chondrites, are reported to be 5500 ppm F, 0.26–1.09 wt% H 2 O, and 0.98–1.2 wt% Cl and 60 ppm F, 27–114 ppm H 2 O, and 100–123 ppm Cl, respectively. The role of volatiles in many lunar geologic processes was also determined and discussed. Specifically, analyses of volatiles from lunar glass beads as well as the phase assemblages present in coatings on those beads were used to infer that H 2 is likely the primary vapor component responsible for propelling the fire-fountain eruptions that produced the pyroclastic glass beads (as opposed to CO). The textural occurrences of some volatile-bearing minerals are used to identify hydrothermal alteration, which is manifested by sulfide veining and sulfide-replacement textures in silicates. Metasomatic alteration in lunar systems differs substantially from terrestrial alteration due to differences in oxygen fugacity between the two bodies that result in H 2 O as the primary solvent for alteration fluids on Earth and H 2 as the primary solvent for alteration fluids on the Moon (and other reduced planetary bodies). Additionally, volatile abundances in volatile-bearing materials are combined with isotopic data to determine possible secondary processes that have affected the primary magmatic volatile signatures of lunar rocks including degassing, assimilation, and terrestrial contamination; however, these processes prove difficult to untangle within individual data sets. Data from remote sensing and lunar soils are combined to understand the distribution, origin, and abundances of volatiles on the lunar surface, which can be explained largely by solar wind implantation and spallogenic processes, although some of the volatiles in the soils may also be either indigenous to the Moon or terrestrial contamination. We have also provided a complete inventory of volatile-bearing mineral phases indigenous to lunar samples and discuss some of the "unconfirmed" volatile-bearing minerals that have been reported. Finally, a compilation of unanswered questions and future avenues of research on the topic of lunar volatiles are presented, along with a critical analysis of approaches for answering these questions.

Description: Apatite-melt partitioning experiments were conducted in a piston-cylinder press at 1.0–1.2 GPa and 950–1000 °C using an Fe-rich basaltic starting composition and an oxygen fugacity within the range of IW-1 to IW+2. Each experiment had a unique F:Cl:OH ratio to assess the partitioning as a function of the volatile content of apatite and melt. The quenched melt and apatite were analyzed by electron probe microanalysis and secondary ion mass spectrometry techniques. The mineral-melt partition coefficients ( D values) determined in this study are as follows: D F Ap-Melt = 4.4–19, D Cl Ap-Melt = 1.1–5, D OH Ap-Melt = 0.07–0.24. This large range in values indicates that a linear relationship does not exist between the concentrations of F, Cl, or OH in apatite and F, Cl, or OH in melt, respectively. This non-Nernstian behavior is a direct consequence of F, Cl, and OH being essential structural constituents in apatite and minor to trace components in the melt. Therefore mineral-melt D values for F, Cl, and OH in apatite should not be used to directly determine the volatile abundances of coexisting silicate melts. However, the apatite-melt D values for F, Cl, and OH are necessarily interdependent given that F, Cl, and OH all mix on the same crystallographic site in apatite. Consequently, we examined the ratio of D values (exchange coefficients) for each volatile pair (OH-F, Cl-F, and OH-Cl) and observed that they display much less variability: K d Cl-F Ap-Melt = 0.21 ± 0.03, K d OH-F Ap-Melt = 0.014 ± 0.002, and K d OH-Cl Ap-Melt = 0.06 ± 0.02. However, variations with apatite composition, specifically when mole fractions of F in the apatite X-site were low ( X F 〈 0.18), were observed and warrant additional study. To implement the exchange coefficient to determine the H 2 O content of a silicate melt at the time of apatite crystallization (apatite-based melt hygrometry), the H 2 O abundance of the apatite, an apatite-melt exchange K d that includes OH (either OH-F or OH-Cl), and the abundance of F or Cl in the apatite and F or Cl in the melt at the time of apatite crystallization are needed (F if using the OH-F K d and Cl if using the OH-Cl K d ). To determine the H 2 O content of the parental melt, the F or Cl abundance of the parental melt is needed in place of the F or Cl abundance of the melt at the time of apatite crystallization. Importantly, however, exchange coefficients may vary as a function of temperature, pressure, melt composition, apatite composition, and/or oxygen fugacity, so the combined effects of these parameters must be investigated further before exchange coefficients are applied broadly to determine volatile abundances of coexisting melt from apatite volatile abundances.

Description: Petrologic investigations of martian rocks have been accomplished by mineralogical, geochemical, and textural analyses from Mars rovers (with geologic context provided by orbiters), and by laboratory analyses of martian meteorites. Igneous rocks are primarily lavas and volcaniclastic rocks of basaltic composition, and ultramafic cumulates; alkaline rocks are common in ancient terranes and tholeiitic rocks occur in younger terranes, suggesting global magmatic evolution. Relatively uncommon feldspathic rocks represent the ultimate fractionation products, and granitic rocks are unknown. Sedimentary rocks are of both clastic (mudstone, sandstone, conglomerate, all containing significant igneous detritus) and chemical (evaporitic sulfate and less common carbonate) origin. High-silica sediments formed by hydrothermal activity. Sediments on Mars formed from different protoliths and were weathered under different environmental conditions from terrestrial sediments. Metamorphic rocks have only been inferred from orbital remote-sensing measurements. Metabasalt and serpentinite have mineral assemblages consistent with those predicted from low-pressure phase equilibria and likely formed in geothermal systems. Shock effects are common in martian meteorites, and impact breccias are probably widespread in the planet’s crustal rocks. The martian rock cycle during early periods was similar in many respects to that of Earth. However, without plate tectonics Mars did not experience the thermal metamorphism and flux melting associated with subduction, nor deposition in subsided basins and rapid erosion resulting from tectonic uplift. The rock cycle during more recent time has been truncated by desiccation of the planet’s surface and a lower geothermal gradient in its interior. The petrology of Mars is intriguingly different from Earth, but the tried-and-true methods of petrography and geochemistry are clearly translatable to another world.

Description: The distribution and abundances of H 2 O and other volatiles in our Solar System are of fundamental interest because of the important roles volatiles play in geological and biological processes. Apatite, Ca 5 (PO 4 ) 3 (F,Cl,OH), is a ubiquitous accessory mineral and provides a consistent window into volatile abundances and processes across the Solar System and throughout its history. Consequently, the chemical composition of apatite can be used as a tool for exploring such diverse topics as the compositions and roles of the Solar System's earliest fluids on asteroids, the volatile abundances of planetary bodies, and the habitability of past environments (e.g. on Mars) for life as we know it.

Description: In marked contrast to the single, narrow 29 Si MAS NMR resonance for pure forsterite (Mg 2 SiO 4 ), the spectra for synthetic forsterite containing 0.05 to 5% of the Mg 2+ replaced with Ni 2+ , Co 2+ , or Fe 2+ display between 4 and 26 additional, small, paramagnetically shifted peaks that are caused by interactions of the unpaired electron spins on the transition metal cations and the nuclear spins. Analyses of these relative peak areas, their numbers, and comparison of their positions to those in spectra of synthetic monticellites (CaMgSiO 4 ) containing similar levels of transition metals, allows at least partial assignment to the effects of cations in either the M1 octahedral site only or to both M1 and M2 sites. More detailed analyses indicate that in forsterite, Ni 2+ occupies only M1, Fe 2+ occupies M1 and M2 roughly equally, and Co 2+ occupies both M1 and M2 in an approximately 3:1 ratio. These findings for low concentrations agree with expectations from previous studies by other methods (e.g., XRD) of olivines with much higher transition metal cation contents. However, even low concentrations of Mn 2+ (e.g., 0.1%), as well as higher Fe 2+ contents (e.g., in natural San Carlos olivine) can broaden NMR peaks sufficiently to greatly reduce this kind of information content in spectra.

Description: 〈span〉Trace metals are essential for life in the oceans but are present in extremely low concentrations. The availability of trace elements in surface waters frequently regulates the growth of microscopic marine plants called phytoplankton. As phytoplankton are responsible for taking up atmospheric carbon dioxide and exporting this to the deep ocean, trace elements are key components regulating the carbon cycle. New observations of the distribution of trace metals across all ocean basins from the GEOTRACES program have revealed a fascinating story of how the combination of trace metals interact with the ocean to regulate biological activity in new and surprising ways.〈/span〉

Description: The 〉700 km 3 Peach Spring Tuff (PST), erupted at 18.8 Ma from the Silver Creek caldera in the southern Black Mountains volcanic center (SBMVC) of western Arizona, is the only supereruption-scale ignimbrite in the northern Colorado River Extensional Corridor. The SBMVC contains pre- and post-caldera volcanic rocks and caldera-related intrusions (~19–17 Ma) that provide a detailed petrologic record of ignimbrite antecedence and aftermath. Whole-rock Sr-Nd-Pb-Hf isotopic data combined with complementary zircon O and Hf isotopic data from a suite of pre- through post-PST samples provide robust constraints on (1) how the SBMVC evolved with respect to magmatic sources and processes throughout its ~2 Ma history and (2) the petrogenetic relationships between the PST and slightly younger intracaldera plutons. Both pre- and post-PST units have isotopic ranges ( Nd = –8.3 to –11.6, Hf = –8.2 to –14.0, 87 Sr/ 86 Sr i = 0.709–0.712; 206 Pb/ 204 Pb = 18.19–18.49, 207 Pb/ 204 Pb = 15.60–15.62, 208 Pb/ 204 Pb = 38.95–39.29) that fall within the spectrum of Miocene Colorado River Extensional Corridor rocks and are consistent with mixing of substantial fractions of Proterozoic (Mojave) crust and juvenile material derived from regional enriched mantle. Compared to the PST, which has relatively uniform isotopic ratios ( Nd = –11.4 to –11.7, Hf = –13.8 to –14.3, 87 Sr/ 86 Sr i = 0.709–0.712; 206 Pb/ 204 Pb = 18.20–18.29, 207 Pb/ 204 Pb = 15.60–15.62, 208 Pb/ 204 Pb = 39.02–39.33), individual pre- and post-PST units are isotopically more variable and generally more primitive. Consistent with whole-rock isotopes, zircon Hf (–8 to –14) and oxygen 18 O (+4.5 to +7.2) for most pre- and post-PST units also have wider ranges and more mantle-like values than those of the PST (–12 to –15, +6.1 to +7.1). Moreover, zircon isotopic compositions decrease in post-PST samples. A few zircons from post-PST intrusions have 18 O values lower than mantle values (〈+5), suggesting incorporation of hydrothermally altered rock. Whole-rock and zircon elemental and isotopic analyses indicate that (1) most pre- and post-PST units are less evolved and less homogenized than the PST itself; (2) intrusions in the Silver Creek caldera are petrogenetically distinct from the PST and therefore represent discrete magmatic pulses, not unerupted PST mush; (3) enriched mantle input increased in the SBMVC following the paroxysmal PST eruption; (4) post-PST history of the SBMVC was characterized by periodic influx of magmas with varying juvenile fractions into pre-existing mushy or solidified intrusions, resulting in variable and incomplete hybridization; and (5) melting and assimilation of hydrothermally altered crust played a relatively minor role in the generation and evolution of magmas in the SBMVC.

Description: 〈span〉〈div〉Abstract〈/div〉This paper presents a new X-ray absorption spectroscopy (XAS) method for making two-dimensional maps of Fe〈sup〉3+〈/sup〉 in-situ in polished glass samples, which opens the door to study redox changes associated with magmatic processes such as crystallization, assimilation, ascent, and eruption. Multivariate analysis (MVA) allows selection of specific channels in a spectrum to inform predictions of spectral characteristics. Here, the sparse model of the least absolute shrinkage and selection operator (Lasso) is used to select key channels in XAS channels that can be used to predict accurate in-situ Fe〈sup〉3+〈/sup〉 analyses of silicate glasses. By tuning the model to use only six channels, analytical time is decreased enough to allow mapping of Fe〈sup〉3+〈/sup〉 variations in samples by making gridded point analyses at the scale of the XAS beam (1–2 μm). Maps of Fe〈sup〉3+〈/sup〉 concentration can then be constructed using freely available, open source software (〈a href="http://cars.uchicago.edu/xraylarch/"〉http://cars.uchicago.edu/xraylarch/〈/a〉). This result shows the enormous potential of using MVA to select indicative spectral regions for predicting variables of interest across a wide variety of spectroscopic applications. Redox gradients in lunar picritic glass beads first observed with point analyses are confirmed through this XAS mapping and suggest degassing processes during ascent and eruption are responsible for the range of Fe〈sup〉3+〈/sup〉 values measured in these samples.〈/span〉