Band 101, Heft 12

Experimental observations on the dissolution of elements in minerals and melts and the partitioning between the two materials show that the concentration (or the partition coefficient) of trace elements depends on the properties of elements as well as those of relevant materials (minerals and melts) and the thermochemical conditions. Previous models of element solubility in minerals contain a vague treatment of the role of the stiffness of the element and have a difficulty in explaining some observations including the solubility of the noble gases. A modified theory of element solubility in minerals is presented where the role of elasticity of both matrix mineral and the element is included using the continuum theory of point defects by Eshelby (1951, 1954, 1956). This theory provides a framework to explain the majority of observations and shows a better fit to the published results on the effective elastic constants relevant to element partitioning. However, the concept of “elasticity of the trace element” needs major modification when the site occupied by a trace element has large excess charge. The experimental data of the solubility coefficients of noble gases in melts show strong dependence on the atomic size that invalidates the “zero-charge” model for noble gas partitioning. A simple model of element solubility in melts is proposed based on the hard sphere model of complex liquids that provides a plausible explanation for the difference in the dissolution behavior between noble gases and other charged elements. Several applications of these models are discussed including the nature of noble gas behavior in the deep/early Earth and the water distribution in the lithosphere/asthenosphere system.

Biomaterials are synthetic compounds and composites that replace or assist missing or damaged tissue or organs. This review paper addresses Ca phosphate biomaterials that are used as aids to or substitutes for bones and teeth. The viewpoint taken is that of mineralogists and geochemists interested in (carbonated) hydroxylapatite, its range of compositions, the conditions under which it can be synthesized, and how it is used as a biomaterial either alone or in a composite. Somewhat counter-intuitively, the goal of most medical or materials science researchers in this field is to emulate the properties of bone and tooth, rather than the hierarchically complex materials themselves. The absence of a directive to mimic biological reality has permitted the development of a remarkable range of approaches to apatite synthesis and post-synthesis processing. Multiple means of synthesis are described from low-temperature aqueous precipitation, sol-gel processes, and mechanosynthesis to high-temperature solid-state reactions and sintering up to 1000 °C. The application of multiple analytical techniques to characterize these apatitic, frequently nanocrystalline materials is discussed. An online supplement Deposit item AM-16-125732, Supplemental Appendix. Deposit items are free to all readers and found on the MSA web site, via the specific issue’s Table of Contents (go to http://www.minsocam.org/msa/ammin/toc/2016/Dec2016_data/Dec2016_data.html). details the specific physical and chemical forms in which synthetic apatite and related Ca phosphate phases are used in biomaterials. The implications from this overview are the enhanced recognition of the structurally and chemically accommodating nature of the apatite phase, insight into the effects of synthesis techniques on the specific properties of minerals (specifically apatite), and the importance of surface chemistry of apatite nanocrystals. The wide range of synthesis techniques, types of analytical characterization, and applications to human health associated with apatite are a non-geological demonstration of the power of mineralogy.

A growing body of research supports widespread future reliance on apatite for radioactive waste cleanup. Apatite is a multi-functional radionuclide sorbent that lowers dissolved radionuclide concentrations by surface sorption, ion exchange, surface precipitation, and by providing phosphate to precipitate low-solubility radionuclide-containing minerals. Natural apatites are rich in trace elements, and apatite’s stability in the geologic record suggest that radionuclides incorporated into apatite, whether in a permeable reactive barrier or a waste form, are likely to remain isolated from the biosphere for long periods of time. Here we outline the mineralogic and surface origins of apatite-radionuclide reactivity and show how apatites might be used to environmental advantage in the future.

Mineral replacement reactions are common in the various environments where rocks have undergone re-equilibration with geologic fluids. Replacement reactions commonly take the form of fluid-aided, coupled dissolution-precipitation and often result in pseudomorph formation. One class of environment that frequently shows significant examples of mineral replacements is hydrothermal ore deposit systems. The goal of this study was to test the simultaneous reactivity of fluorapatite and monazite in Na- and Si-rich hydrothermal fluids, which partially mimic the mineralogy and fluid chemistry of the Llallagua tin deposit in Bolivia. A series of experiments were performed at 300 to 600 °C and 100 MPa, utilizing various combinations of monazite, fluorapatite, and H 2 O + Na 2 Si 2 O 5 . Reaction products were evaluated using scanning electron microscopy, electron microprobe analysis, and single-crystal X-ray diffraction. The results of this experimental study show that fluorapatite and monazite are differentially reactive under the conditions studied. The reaction products, pathways, and kinetics have a large temperature dependence. The 300 and 400 °C experiments show variable amounts of monazite replacement and only minor, if any, dissolution or reactivity of fluorapatite. The high-temperature 500 and 600 °C experiments are characterized by massive replacement of monazite by vitusite and britholite. Exclusively at 600 °C, monazite alteration takes the form of symplectite development at the reaction front as vermicular intergrowths of vitusite and britholite. The higher-temperature experiments also show substantially more reactivity by fluorapatite, which is partially pseudomorphically altered into britholite. This is an example of regenerative mineral replacement where both fluorapatite and britholite share the same atomic structure and are crystallographically coherent after the partial replacement. The britholite replacement is characterized by the presence of oriented nanochannels, which facilitate fluid-based mass transfer between the bulk solution and the reaction front. The fluorapatite replacement is enhanced by monazite alteration through a self-perpetuating, positive feedback mechanism between these two reactions, which enhance the REE mobility in alkali-bearing fluids and further drives bulk re-equilibration. These results have potential geochronologic implications and may be significant in the evaluation of monazite and fluorapatite as potential solid nuclear waste forms. They also give us deeper insights into the mechanism of mineral replacement reactions and porosity development.

We have measured high-pressure Raman spectra of both siderite single-crystalline and polycrystalline powder samples in diamond-anvil cell experiments across the pressure-induced high-spin (HS) to lowspin (LS) transition of Fe 2+ . Between 43.3 and 45.5 GPa, we observed a color change from transparent to green, which is associated to the spin transition. Furthermore, we calibrated the position of the Raman active v 1 mode with pressure. In a second diamond-anvil cell experiment, we observed the color change from transparent to green in the form of a transition front passing through the single crystal and collected Raman spectra across the transition front. We were able to constrain the stress variation across this transition front to about 0.2 GPa, well below the resolution of our Raman-based pressure/stress calibration. In contrast to the single crystal, the powder sample shows the spin transition over a pressure range of 5 GPa, which we attribute to intergranular stresses. We conclude that within the resolution of our stress/pressure calibration the spin transition of iron in single-crystalline siderite is sharp.

The dehydration reactions of minerals in subduction zones strongly control geological processes, such as arc volcanism, earthquakes, serpentinization, or geochemical transport of incompatible elements. In aluminum-bearing systems, chlorite is considered the most important hydrous phase at the top of the subducting plate, and significant amount of water is released after its decomposition. However, the dehydration mechanism is not fully understood, and additional hydrates are stabilized by the presence of Al beyond the stability field of chlorite. We applied here a cutting-edge analytical approach to characterize the experimental rocks synthesized at the high pressures and temperatures matching with deep subduction conditions in the upper mantle. Fast electron diffraction tomography and high-resolution synchrotron X-ray diffraction allowed the identification and the successful structure solution of two new hydrous phases formed as dehydration product of chlorite. The 11.5 Å phase, Mg 6 Al(OH) 7 (SiO 4 ) 2 , is a hydrous layer structure. It presents incomplete tetrahedral sheets and face-sharing magnesium and aluminum octahedra. The structure has a higher Mg/Si ratio compared to chlorite, and a significantly higher density (ρ 0 = 2.93 g/cm 3 ) and bulk modulus [ K 0 = 108.3(8) GPa], and it incorporates 13 wt% of water. The HySo phase, Mg 3 Al(OH) 3 (Si 2 O 7 ), is a dense layered sorosilicate, [ρ 0 = 3.13 g/cm 3 and K 0 = 120.6(6) GPa] with an average water content of 8.5 wt%. These phases indicate that water release process is highly complex, and may proceed with multistep dehydration, involving these layer structures whose features well match the high-shear zones present at the slab-mantle wedge interface.

Solid-solid mineral reaction rates are influenced by the microfabrics of reactant phases and concurrent deformation. To investigate this interplay in carbonate systems, we performed annealing and deformation experiments on polycry stalline and single-crystal calcite and magnesite, forming dolomite (Dol) and magnesio-calcite (Mg-Cal). At a fixed temperature of T = 750 °C and confining pressure of P = 400 MPa, samples were either annealed for 29 h, or deformed in triaxial compression or torsion for 18 h using a Paterson-type gas deformation apparatus. At the contact interface of the starting reactants, Dol reaction rims and poly cry stalline Mg-Cal layers were formed. The widths of the layers were in the ranges 4–117 and 30–147 μm, respectively, depending on the microstructure of starting materials and experimental conditions. Annealing experiments with polycrystalline reactants in contact with each other resulted in a ~22-fold increase in Dol rim thickness compared to a contact between two single crystals and a larger Mg-Cal layer width by a factor of 5 (cf. Helpa et al. 2014). This suggests that the micro structure of magnesite controls migration of the reaction front. For polycrystalline starting materials, axial stress accelerated Mg-Cal growth rates but not Dol growth rates. Highly strained torsion samples showed Dol formation along grain boundaries in Mg-Cal as well as in the polycrystalline calcite reactant. A reduction of Dol rim thickness between polycrystalline reactants deformed in torsion is possibly caused by concurrent grain coarsening of polycrystalline magnesite. Dol and Mg-Cal growth kinetics between single crystals were unaffected by the addition of ~0.3 wt% water. The experiments demonstrate that Dol reaction kinetics strongly correlate with magnesite reactant grain sizes, while Mg-Cal growth depends on the calcite reactant grain sizes. The dolomite-forming mineral reaction kinetics are not significantly affected by concurrent deformation. In contrast, deformation enhances Mg-Cal formation, especially at small calcite grain sizes that promote efficient grain boundary diffusion. Therefore, the fastest reactions forming Dol and Mg-Cal in nature are expected to occur in very fine-grained reactants. Concurrent deformation may drastically enhance reaction kinetics if grain size reduction of the reactants occurs by, for example, cataclasis or dynamic recrystallization.

Any poorly crystalline serpentine-type mineral with a lack of recognizable textural or diffraction features for typical serpentine varieties (i.e., chryotile, lizardite, and antigorite) is usually referred to as proto-serpentine. The formation of the so-called proto-serpentine seems ubiquitous in serpentinization reactions. It is related to dissolution-precipitation of strongly reactive particles prior to true serpentine formation (e.g., in veins where both chrysotile and proto-serpentine are described). However, the structural characteristics of proto-serpentine and its relation with serpentine crystalline varieties remain unclear. In this study a model describing the transformation from proto-serpentine to chrysotile is presented based on experimental chrysotile synthesis using thermogravimetric analyses, transmission electron microscopy, and high-energy X-ray diffraction with pair distribution function analyses. The combination of the high-resolution TEM and high-energy X-ray diffraction enables to resolve the local order of neo-formed particles and their structuration processes occurring during pure chrysotile formation (i.e., during the first three hours of reaction). The formation of individual nanotubes is preceded by the formation of small nanocrystals that already show a chrysotile short-range order, forming porous anastomosing features of hydrophilic crystallites mixed with brucite. This is followed by a hierarchical aggregation of particles into a fiber-like structure. These flake-like particles subsequently stack forming concentric layers with the chrysotile structure. Finally, the individualization of chrysotile nanotubes with a homogeneous distribution of diameter and lengths (several hundreds of nanometer in length) is observed. The competitive precipitation of brucite and transient serpentine during incipient serpentinization reaction indicates that both dissolution-precipitation and serpentine-particle aggregation processes operate to form individual chrysotile. This study sheds light into mineralization processes and sets a first milestone toward the identification of the factors controlling polymorph selection mechanisms in this fascinating system.

Experimental silicate glasses are often used as analog and calibration material for terrestrial and planetary materials. Measurements of Fe oxidation state using electron energy loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope (ac-STEM) show that a suite of experimental silicate (e.g., basaltic, andesitic, rhyolitic) glasses have spatially heterogeneous oxidation states at scales of tens of nanometers. Nano-crystals are observed in several of the glasses, indicating nucleation and incipient crystallization not seen at the scale of electron microprobe analysis (EMPA). Glasses prepared in air are uniformly oxidized while glasses prepared at the iron-wustite (IW) or quartz-fayalite-magnetite (QFM) buffers range from reduced to highly oxidized. EELS spectral shapes indicate that oxidized glasses have tetrahedral Fe 3+ . The nanoscale compositional and structural heterogeneities present in the experimental glasses mean that the suitability of such glasses as analogs for natural materials and calibration standards depends strongly on the scale of the measurements being done. The electron beam quickly damages silicate glass, but data showing changes in oxidation state among and within samples can be obtained with careful control of the beam current and dwell time. Determination of oxidation state in silicate glasses via STEM-EELS is very challenging, and accurate and reliable measurements of Fe 3+ /ΣFe require careful sample preparation and control of microscope conditions and benefit from comparison to complementary techniques.

Both prograde and retrograde skarns from the Tengtie iron deposit, South China, contain rounded, euhedral, and anhedral zircon grains. Rounded grains were originally derived from detritus in carbonate rocks and were incorporated into the skarns. Euhedral and anhedral crystals are intergrown with various skarn minerals and are clearly hydrothermal in origin. These hydrothermal grains have low (Sm/La) N ratios and high La contents relative to typical magmatic ones and display fat LREE and subdued fattening of HREE chondrite-normalized patterns, similar to those of zircon crystallized from Zr-saturated fluids. Prograde skarns also contain baddeleyite rimed by zircon, which record a period of low Si activity during prograde skarnization relative to original magmatic-hydrothermal fluids. Hydrothermal zircon grains from Tengtie have variable Eu anomalies and slightly positive Ce anomalies, indicating that they may have crystallized from highly heterogeneous, but generally reducing fluids. They have low δ 18 O values (–5.1 to –2.7 ‰), suggesting the involvement of meteoric fluids. Fluorine-rich fluids played an important role in remobilizing and transporting some high field strength elements (HFSE), including Zr, from the host granites into the skarn system. Reaction between HFSE-bearing fluids and carbonate rocks at the prograde stage decomposed F complexes to deposit HFSE-rich skarn minerals and baddeleyite. At the retrograde stage, alteration of the HFSE-rich skarn minerals released HFSE, including Zr and Sn, consequently producing a mineral assemblage of zircon, cassiterite, and retrograde skarn minerals. Dating results of zircons from the Tengtie skarn system by SIMS indicates roughly less than several million years duration for skarnization. Our study indicates that Zr was not only mobile locally under favorable conditions, but was also readily transported and deposited in different stages of skarnization.

Hematite ( a -Fe 2 O 3 ) and goethite ( a -FeOOH) can incorporate considerable amounts of tungsten (W). Although W concentrations up to several wt% in hematite and goethite have been reported in the literature, none of the proposed models for a structural incorporation has been generally accepted yet. Here, the first combination of X-ray absorption fine structure (XAFS) measurements with X-ray diffraction (XRD), Raman spectroscopy (RS), electron microprobe (EMPA) and total reflection X-ray fluorescence (TXRF) provides a general relation between W content and its structural incorporation into hematite and goethite. Botryoidal specimens of goethite and hematite, obtained from the Schwarzwald ore district, Black Forest, SW Germany, and from the Grantcharitza W deposit, Bulgaria, display W concentrations of up to 5.5 and 2.15 mol% W for goethite and hematite, respectively. In addition to these natural specimens, goethite and hematite were synthesized in the presence of W and incorporate up to 7 and 1.3 mol% W, respectively. X-ray diffraction analysis does not indicate the presence of separate W-phases, supporting the structural incorporation of W into the hematite and goethite. Refined unit-cell parameters indicate no changes with increasing W concentration in hematites but a rising structural disorder within the structure of the synthetic goethites. Raman spectroscopy, however, shows an increasing structural disorder for both synthetics, indicating an increase of Fe vacancies in both hematite and goethite. A deprotonation mechanism for the goethite structure is unlikely according to the Raman results. XAS near-edge spectra indicate a strong distortion of the WO 6 octahedra in both hematite and goethite. Extended XAFS spectra of the natural and synthetic goethites and hematites show striking similarities and suggest that W 6+ resides in all samples on the Fe 3+ position, again without developing separate W phases. Calculations of the Fe-loss related to W incorporation reach mean values of ~2.9 and ~2.8 for goethite and hematite, respectively. The formation of two Fe 3+ vacancies in close proximity to the newly incorporated W 6+ in addition to a protonation of the structures achieves charge balance within the hematite and goethite structure. Hematite and goethite record the presence of W in fluids even in the absence of visible W minerals. After W adsorption to ferrihydrite (the hematite and goethite precursor phase) and after its transformation to either hematite or goethite, only hematite with up to 0.4 wt% W is clearly able to continuously monitor a changing W signature as a record of the fluid history within its oscillatory growth zones. In contrast, goethite is probably not a good monitor of a primary W fluid history. Their combination, however, could be particularly useful, as hematite records the W concentrations in a fluid during ferihydrite precipitation, while goethite records W concentrations during later ferrihydrite maturation. Botryoidal Fe-ores have never been considered for W recovery but could play an important role to fight a potential supply risk of W as a high-technology metal.

The term “ontogeny,” which is commonly used in biology, was introduced into the Earth sciences in 1961 to include the genesis and evolution of single crystals and crystal aggregates. The term encompasses nucleation, growth, alteration , and destruction . We present results of studies concerning the ontogeny of natural corundum (rubies and sapphires), and the chemical and morphological evolution of corundum crystals from deposits in Africa (Kenya, Tanzania, Madagascar) and Southeast Asia (Vietnam). Trace-element compositions indicative for different corundum habits were determined by rim-to-rim LA-ICP-MS and electron microprobe analyses. Raman spectroscopy was applied for Cr 3+ photoluminescence mapping. Results traced the development of corundum crystals and the evolution of their chemistry and morphology, and helped to clarify the geological processes within particular deposits. These variations of corundum morphology are directly correlated with Cr and Fe contents and varying P-T conditions that prevailed during crystal growth. Dipyramidal habits combined with white color in corundum from two deposits in the Mangari area in Kenya have Cr concentrations of ~200–700 μg/g in crystals that grew under high P-T conditions. Prismatic habit of bright red ruby crystals was linked to Cr concentrations of ≥1500 μg/g in samples from Luc Yen (Vietnam) and Mangari (Kenya), formed under lower P-T . Concentrations of Cr between 700–1500 μg/g are associated with pink color and combinations of different habits (dipyramidal, prismatic, or dipyramidal-prismatic) in these samples. Contents of Fe ~700 μg/g and Cr ~1200 μg/g in sapphire crystals from the Morogoro area of Tanzania caused pink color that correlated with dipyramidal habit and elongation along the c axis. Rhombohedral habit and blue-violet color were observed at Cr ~600 μg/g and Fe ≥2000 μg/g in sapphires from Andranondambo in Madagascar, formed during the final stage of contact metamorphism.

Knowledge of potential carbon carriers such as carbonates is critical for our understanding of the deep-carbon cycle and related geological processes within the planet. Here we investigated the high-pressure behavior of (Ca,Mn)CO 3 up to 75 GPa by synchrotron single-crystal X-ray diffraction, laser Raman spectroscopy, and theoretical calculations. MnCO 3 -rich carbonate underwent a structural phase transition from the CaCO 3 -I structure into the CaCO 3 -VI structure at 45–48 GPa, while CaCO 3 -rich carbonate transformed into CaCO 3 -III and CaCO 3 -VI at approximately 2 and 15 GPa, respectively. The equation of state and vibrational properties of MnCO 3 -rich and CaCO 3 -rich carbonates changed dramatically across the phase transition. The CaCO 3 -VI-structured CaCO 3 -rich and MnCO 3 -rich carbonates were stable at room temperature up to at least 53 and 75 GPa, respectively. The addition of smaller cations (e.g., Mn 2+ , Mg 2+ , and Fe 2+ ) can enlarge the stability field of the CaCO 3 -I phase as well as increase the pressure of the structural transition into the CaCO 3 -VI phase.

Dry annealing of Au x Ag 1–x alloys (x = 0.19, 0.35, 0.56 or of fineness 300, 500, 700‰) and pyrite was used to reveal the solubility of Au (Ag) in FeS 2 and study phase equilibria in the FeS 2 -Au x Agi 1–x system at 500 °C. Pyrrhotite, acanthite, and uytenbogaardtite and Au-Ag alloys with increased fineness were established at the contacts of pyrite blocks with Au-Ag plates. The obtained results evidence the absence of solubility between FeS 2 and Au (Ag) at 500 °C. The Ag content in alloys influences the stability of pyrite and contributes to its transformation in pyrrhotite and sulfidation and ennobling of Au-Ag alloys. Au-Ag sulfides and pyrrhotite may be present in the sulfide ores of metamorphogene deposits as annealing products of Au-Ag-pyrite-bearing ores.

Cell parameters and atomic coordinates for the true micas are varied to simulate layer deformation along the [001]* direction by an external force. The resulting (deformed) structures are then used to determine bonding forces and to calculate a maximum force component along the [001]*. Bonding forces are compared to experimental observations of bond lengths of the interlayer, octahedral, and tetrahedral sites. Calculated bonding forces are consistent with experimental observations that locate the cleavage plane along the interlayer. Because many studies have shown that the chemical composition of the cleavage surface often differs from the structure of the bulk, compositional variations were considered in determining cleavage energy. The chemical composition of the cleavage surface may produce a reduction in cleavage energy. This reduction in energy depends on various elements occurring in greater number at the cleavage surface than in the bulk. A reduction in cleavage energy occurs if there is a reduction in the interlayer site size, as measured by the area defined by the first-coordination basal oxygen atoms. In addition, a reduction in lateral cell dimensions and an increase in the bonding force between the basal oxygen atoms and the interlayer cation also results in a reduction in cleavage energy in the direction normal to the layer. Joins considered are phlogopite-annite, tetra-ferriphlogopite-tetra-ferri-annite, polylithionite-siderophyllite, muscovite-celadonite, and muscovite-paragonite. A lack of homogeneity in composition may produce preferential cleavage locations within the family of (001) planes. The cleavage energy appears to be greater for homogeneous synthetic micas compared to natural micas.

Mining accidents are sometimes preceded by high levels of crackling noise, which follow universal rules for the collapse of minerals. The archetypal test cases are sandstone and coal. Their collapse mechanism is almost identical to earthquakes: the crackling noise in large, porous samples follows a power law (Gutenberg-Richter) distribution P ~ E -ɛ with energy exponents ɛ for near critical stresses of ɛ = 1.55 for dry and wet sandstone, and ɛ = 1.32 for coal. The exponents of early stages are slightly increased, 1.7 (sandstone) and 1.5 (coal), and appear to represent the collapse of isolated, uncorrelated cavities. A significant increase of the acoustic emission, AE, activity was observed close to the final failure event, which acts as “warning signal” for the impending major collapse. Waiting times between events also follow power law distributions with exponents 2+ξ between 2 and 2.4. Aftershocks occur with probabilities described by Omori coefficients ρ between 0.84 (sandstone) and 1 (coal). The “Båth’s law” predicts that the ratio between the magnitude of the main event and the largest aftershock is 1.2. Our experimental findings confirm this conjecture. Our results imply that acoustic warning methods are often possible within the context of mining safety measures, although it is not only the increase of crackling noise that can be used as early warning signal but also the change of the energy distribution of the crackling events.

This study investigates magnetite exsolution in ilmenite from Fe-Ti oxide gabbro in the Xinjie intrusion, SW China. Exsolved magnetite lamellae in ilmenite contain nearly pure Fe 3 0 4 with ~l wt% TiO 2 . EBSD-based analyses indicate that the magnetite lamellae have close-packed oxygen planes and directions parallel to those in the host ilmenite with {111}Ma g //(0001) Ilm and <110> Mag //<1 0 10>. The Fe 2+ in the magnetite lamellae is probably derived from adjacent titanomagnetite by sub-solidus inter-oxide cation repartitioning of Fe 2+ + Ti 4+ = 2Fe 3+ during cooling. It is thus suggested that only Fe 3+ cations in the magnetite lamellae should be included into the composition of the Ilm-Hem ss precursor for the Fe-Ti oxide oxy-thermometer. The existence of magnetite exsolution in ilmenite also provides an alternative explanation for unusually strong natural remnant magnetization in natural ilmenite.

The breakup of supercontinents is accompanied by the emplacement of continental flood basalts and dike swarms, the origin of which is often attributed to mantle plumes. However, convection modeling has showed that the formation of supercontinents result in the warming of the sub-continental asthenospheric mantle (SCAM), which could also explain syn-breakup volcanism. Temperature variations during the formation then breakup of supercontinents are therefore fundamental to understand volcanism related to supercontinent cycles. Magmatic minerals record the thermal state of their magmatic sources. Here we present a data mining analysis on the first global compilation of chemical information on magmatic rocks and minerals formed over the past 600 million years: a time period spanning the aggregation and breakup of Pangea, the last supercontinent. We show that following a period of increasingly hotter Mgrich magmatism with dominant tholeiitic affinity during the aggregation of Pangea, lower-temperature minerals crystallized within Mg-poorer magma with a dominant calc-alkaline affinity during Pangea disassembly. These trends reflect temporal changes in global mantle climate and global plate tectonics in response to continental masses assembly and dispersal. We also show that the final amalgamation of Pangea at ~300 Myr led to a long period of lithospheric collapse and cooling until the major step of Pangea disassembly started at ~125 Myr. The geological control on the geosphere magma budget has implications on the oxidation state and temperature of the Earth’s outer envelopes in the Phanerozoic and may have exerted indirect influence on the evolution of climate and life on Earth.

We have refined the clinopyroxene-based hygrometer published by Armienti et al. (2013) for a better quantitative understanding of the role of H 2 O in the differentiation of Etnean magmas. The original calibration data set has been significantly improved by including several experimental clinopyroxene compositions that closely reproduce those found in natural Etnean products. To verify the accuracy of the model, some randomly selected experimental clinopyroxene compositions external to the calibration data set have been used as test data. Through a statistic algorithm based on the Mallows’ C P criterion, we also check that all model parameters do not cause data overfitting, or systematic error. The application of the refined hygrometer to the Mt. Etna 2011–2013 lava fountains indicates that most of the decreases in H 2 O content occur at P < 100 MPa, in agreement with melt inclusion data suggesting abundant H 2 O degassing at shallow crustal levels during magma ascent in the conduit and eruption to the surface.