Apatites in ultramafic xenoliths from Hawaii, Kamchatka, Nunivak Island, Lunar Crater volcanic field and the Navajo volcanic field have variable volatile (F, Cl, OH) compositions that correlate with ...their petrogenesis. Apatites in metasomatized lherzolite/harzburgite xenoliths are relatively Cl-rich whereas apatites in igneous pyroxenite and amphibolite xenoliths are relatively F-rich. Our results support the generalization of O'Reilly and Griffin (2000) that metasomatic apatites tend to be Cl-rich and magmatic apatites tend to be F-rich. Mantle metasomatism may largely be the consequence of devolatilization of Cl-rich fluids from subducted lithosphere. However, the occurrence of metasomatic xenoliths far removed from subduction zones (e.g., Bullenmerri) as well as the geochemistry of Cl in some plume basalts and diamonds indicates that not all metasomatism is subduction-triggered. Thermodynamic modeling of the influence on apatite compositions of variable F, Cl, H2O, and P abundances, as well as temperature, is consistent with the idea that terrestrial mantle fluids are H2O-rich, and that halogen enrichment in terrestrial apatites need not represent large absolute halogen abundances in the fluids. The models indicate that the occurrence of volatile-poor calcium phosphate (merrillite/whitlockite) in the Martian and terrestrial mantles is facilitated by halogen- and phosphorus-rich and water-poor environments — the rarity of this assemblage in the terrestrial mantle compared to Mars is consistent with the relatively wet and halogen- and phosphorus-poor nature of the terrestrial mantle compared to that of Mars.
► New apatite analyses strengthen links between Cl, subduction and mantle metasomatism. ► Thermodynamic modeling suggests that metasomatic fluids are H2O-rich, with Cl>F. ► Thermodynamic modeling suggests that the Martian mantle is relatively Cl- and P-rich and H2O poor.
Apatite was analyzed by electron microprobe in 3 cumulate and 10 basaltic eucrites. Eucritic apatite is fluorine‐rich with minor chlorine and hydroxyl (calculated by difference). We confirmed the ...hydroxyl content by measuring hydroxyl directly in apatites from three representative eucrites using secondary ionization mass spectroscopy. Overall, most eucritic apatites resemble fluorine‐rich lunar mare apatites, but intriguing OH‐ and Cl‐rich apatites suggest a role for water and/or hydrothermal fluids in the Vestan interior or on other related differentiated asteroids. Most late‐stage apatite found in mesostasis has little hydroxyl or chlorine and is thought to have crystallized from a degassed magma; however, several apatites exhibit atypical compositions and/or textural characteristics. For example, the isotopically anomalous basaltic eucrite Pasamonte has apatite in the mesostasis with significant OH. Apatites in Juvinas also have significant OH and occur as veinlets crosscutting silicates. Euhedral apatites in the Moore County cumulate eucrite occur as inclusions in pyroxene and are also hydroxyl‐rich (0.62 wt% OH). The OH was confirmed by SIMS analysis and this apatite clearly points to the presence of water, at least locally, in the Vestan interior. Portions of Elephant Moraine (EET) 90020 have large and abundant apatites, which may be the product of apatite accumulation in a zone of melt‐rock reaction. Relatively chlorine‐rich apatites occur in basaltic eucrite Graves Nunataks (GRA) 98098 (approximately 1 wt% Cl). Particularly striking is the compositional similarity between apatite in GRA 98098 and apatites in lunar KREEP, which may indicate the presence of residual magmas from an asteroid‐wide magma ocean on Vesta.
The behavior of igneous continental crust during subduction is modeled by means of vapor-absent partial melting experiments on a tonalite, containing equal amounts of biotite and hornblende, at ...pressures of 15–32 kbar. The experiments produce leucogranitic melts coexisting with garnet + omphacitic clinopyroxene + K-feldspar + kyanite + quartz/coesite ± phengite ± zoisite. Experimental constraints and geometrical analysis of phase equilibria show that the hydrous phases that control dehydration-melting of tonalites in deep thickened continental crust and in the upper mantle are phengite and zoisite. The negatively sloping amphibole + quartz vapor-absent solidus characteristic of amphibolites is largely suppressed in tonalites, because amphibole is eliminated by water-conserving reactions that also consume K-feldspar and kyanite and produce phengite and zoisite. The temperature at which melt first appears in the experiments varies from <900°C at 15 kbar, to 1000°C at 27 kbar, to <925°C at 32 kbar. Moderate degrees of partial melting (20–30%) yield residual assemblages with mantle-like densities but which can still contain minor amounts of hydrous phases. Partial melting of tonalitic crust during continental subduction can thus generate incompatible element-rich residues that would be able to remain in the mantle indefinitely, acting as long-term sources of metasomatic fluids.
Apatite preserves a record of the halogen and water fugacities that existed during the waning stages of crystallization of planetary magmas, when they became saturated in phosphates. We develop a ...thermodynamic formalism based on apatite–merrillite equilibria that makes it possible to compare the relative values of halogen and water fugacities in Martian, lunar and terrestrial basalts, accounting for possible differences in pressure, temperature and oxygen fugacities among the planets. We show that each of these planetary bodies has distinctive ratios among volatile fugacities at apatite saturation and that these fugacities are in some cases related in a consistent way to volatile fugacities in the mantle magma sources. Our analysis shows that the Martian mantle parental to basaltic SNC meteorites was dry and poor in both fluorine and chlorine compared to the terrestrial mantle. The limited data available from Mars show no secular variation in mantle halogen and water fugacities from ∼4
Ga to ∼180
Ma. The water and halogens found in present-day Martian surface rocks have thus resided in the planet’s surficial systems since at least 4
Ga, and may have been degassed from the planet’s interior during a primordial crust-forming event. In comparison to the Earth and Mars, the Moon, and possibly the eucrite parent body too, appear to be strongly depleted not only in H
2O but also in Cl
2 relative to H
2O. Chlorine depletion is strongest in mare basalts, perhaps reflecting an eruptive process characteristic of large-scale lunar magmatism.
Industrial, technological, and economic developments depend on the availability of metallic raw materials. As a greater fraction of the Earth’s population has become part of developed economies and ...as developed societies have become more affluent, the demand on metallic mineral resources has increased. Yet metallic minerals are non-renewable natural resources, the supply of which, even if unknown and potentially large, is finite. An analysis of historical extraction trends for eighteen metals, going back to the year 1900, demonstrates that demand of metallic raw materials has increased as a result of both increase in world population and increase in per-capita consumption. These eighteen metals can be arranged into four distinct groups, for each of which it is possible to identify a consistent pattern of per-capita demand as a function of time. These patterns can, in turn, be explained in terms of the industrial and technological applications, and in some cases conventional uses as well, of the metals in each group. Under the assumption that these patterns will continue into the future, and that world population will grow by no more than about 50% by the year 2100, one can estimate the amount of metallic raw materials that will be required to sustain the world’s economy throughout the twenty-first century. From the present until the year 2100, the world can be expected to require about one order of magnitude more metal than the total amount of metal that fueled technological and economic growth between the age of steam and the present day. For most of the metals considered here, this corresponds to 5–10 times the amount of metal contained in proven ore reserves. The two chief driving factors of this expected demand are growth in per-capita consumption and present-day absolute population numbers. World population is already so large that additional population growth makes only a small contribution to the expected future demand of metallic raw materials. It is not known whether or not the amount of metal required to sustain the world’s economy throughout this century exists in exploitable mineral resources. In the accompanying paper, I show that it is nevertheless possible to make statistical inferences about the size distribution of the mineral deposits that will need to be discovered and developed in order to satisfy the expected demand. Those results neither prove nor disprove that the needed resources exist but can be used to improve our understanding of the challenges facing future supply of metallic raw materials.
Supplying worldwide demand of metallic raw materials throughout the rest of this century may require 5–10 times the amount of metals contained in known ore deposits. This demand can be met only if ...mineral deposits containing the required masses of metals, in excess of present day ore reserves, exist in the Earth’s crust. It is, by definition, not known whether or not such mineral deposits exist. On the basis of the statistical distribution of metal tonnages contained in known ore deposits, however, it is possible to place constraints on the size distribution of the deposits that must be discovered in order to meet the expected demand. A nondimensional analysis of the distribution of metal tonnages in deposits of 20 metals shows that most of them follow distributions that, although not strictly lognormal, share important characteristics with a lognormal distribution. Chief among these is the observation that frequency falls off symmetrically and geometrically with deposit size, relative to a median deposit size that is approximately equal to the geometric mean deposit size. An immediate consequence of this behavior is that most of the metal endowment is concentrated in deposits that are several orders of magnitude larger than the median deposit size, and that are much rarer than the most common deposits that cluster around the median deposit size. The analysis reveals remarkable similarities among the statistical distributions of most of the metals included in this study, in particular, the fact that distribution of most metals can be fully described with essentially the same value (about 2–3) of the scale parameter,
σ
, which is the only parameter needed to describe the behavior of a normalized lognormal variable. This observation makes it possible to derive the following general conclusions, which are applicable to most metals—both scarce and abundant. First, it is unlikely that undiscovered mineral deposits of sizes comparable to those that contain most of the known metal endowment exist in sufficient quantities to supply the expected worldwide demand throughout the rest of this century. Second, if the expected demand is to be met, one must hope that very large deposits, perhaps up to one order of magnitude larger than the largest known deposits, exist in accessible portions of the Earth’s crust, and that these deposits are discovered.
This textbook provides an intuitive yet mathematically rigorous introduction to the thermodynamics and thermal physics of planetary processes. It demonstrates how the workings of planetary bodies can ...be understood in depth by reducing them to fundamental physics and chemistry. The book is based on two courses taught by the author for many years at the University of Georgia. It includes 'Guided Exercise' boxes; end-of-chapter problems (worked solutions provided online); and software boxes (Maple code provided online). As well as being an ideal textbook on planetary thermodynamics for advanced students in the Earth and planetary sciences, it also provides an innovative and quantitative complement to more traditional courses in geological thermodynamics, petrology, chemical oceanography and planetary science. In addition to its use as a textbook, it is also of great interest to researchers looking for a 'one stop' source of concepts and techniques that they can apply to their research problems.
A loss distribution model is developed and applied to estimate the probabilities of finding enough new mineral deposits to meet demand, throughout the rest of this century, of the ten metals: Au, Ag, ...Cu, Mo, Pb, Zn, Ni, Co, Cr, and platinum-group elements (PGE). The model assumes that the necessary amount of metal exists in undiscovered mineral deposits and looks only at the probabilities of finding the required amount of metal in undiscovered resources. The probability density function that describes aggregate tonnage discovery over a specified period of time is the convolution of a mass density function that describes number of discoveries per unit time with a probability density function that describes deposit size distribution. Two alternatives for the deposit size distribution density function are used: pure lognormal or lognormal with a power-law upper tail, both taken from Patiño Douce (Nat Resour Res 25:365–387,
2016c
). A Pascal (negative binomial) distribution is found to accurately reproduce number of yearly metal discoveries for the period 1950–2007, and is used to estimate future discovery probabilities. The convolution of the two functions is accomplished by means of a simple Monte Carlo method. Numerical experiments consisting of 10
6
iterations are used to estimate the aggregate tonnage most likely to be discovered until the year 2100, as well as the largest deposit most likely to be discovered over the same time period, together with confidence intervals for the two quantities. The results for Au, Ag, Zn, and Cu strongly suggest that serious shortages of these metals are likely to occur before the year 2100. At the other end of the spectrum, the models suggest that supplies of Mo and Co are not likely to become critical over that time frame. Ni and Pb occupy intermediate positions, and the results for Cr and PGE are inconclusive, chiefly owing to the large variability found in their deposit size distributions. Using a pure lognormal distribution versus a lognormal distribution with a power-law upper tail for deposit sizes does not affect these conclusions. The results do not prove nor disprove that the required amount of metal exists in undiscovered resources, but provide concrete actionable intelligence about the intensity of the exploration efforts needed to find the metal, if the deposits exist.
Xenoliths of subducted crustal origin hosted by Miocene ultrapotassic igneous rocks in the southern Pamir provide important new information regarding the geological processes accompanying tectonism ...during the Indo-Eurasian collision. Four types have been studied: sanidine eclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite), felsic granulites (garnet, quartz, sanidine and kyanite), basaltic eclogites (omphacite and garnet), and a glimmerite (biotite, clinopyroxene and sanidine). Apatite, rutile and carbonate are the most abundant minor phases. Hydrous phases (biotite and phengite in felsic granulites and basaltic eclogites, amphiboles in mafic and sanidine eclogites) and plagioclase form minor inclusions in garnet or kyanite. Solid-phase thermobarometry reveals recrystallization at mainly ultrahigh temperatures of 1000–1100°C and near-ultrahigh pressures of 2·5–2·8 GPa. Textures, parageneses and mineral compositions suggest derivation of the xenoliths from subducted basaltic, tonalitic and pelitic crust that experienced high-pressure dehydration melting, K-rich metasomatism, and solid-state re-equilibration. The timing of these processes is constrained by zircon ages from the xenoliths and 40Ar/39Ar ages of the host volcanic rocks to 57–11 Ma. These xenoliths reveal that deeply subducted crust may undergo extensive dehydration-driven partial melting, density-driven differentiation and disaggregation, and sequestration within the mantle. These processes may also contribute to the alkaline volcanism observed in continent-collision zones.
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