Experimental Petrology Research Articles

Geochemical insights into the role of metasomatic hornblendite in generating alkali basalts

Experimental petrology suggested the role of hornblendite in generating alkali basalt. This mechanism is confirmed by an integrated study of major-trace elements and radiogenic isotopes for Mesozoic alkali basalts from the Qinling orogen in China. The alkali basalts have high contents of MgO (4.8–11.1 wt %, Mg# = 47–69), Na2O + K2O (2.9–5.4 wt %), TiO2 (2.0–3.1 wt %) but low content of SiO2 (41.4–49.6 wt %), which are generally silica-undersaturated with normative minerals of nepheline and olivine. They exhibit OIB-like trace element distribution patterns, with enrichment of LILE and LREE but no depletion of HFSE relative to the primitive mantle. They also show relatively depleted Sr-Nd-Hf isotope compositions, with low initial 87Sr/86Sr ratios of 0.7028–0.7058, positive εNd(t) values of 4.0–9.8 and εHf(t) values of 8.8–13.5 for whole-rock, and positive εHf(t) values of 5.2–16.4 for zircon. Such element and isotope features indicate their origination from the juvenile subcontinental lithospheric mantle (SCLM) source with involvement of crustal components. The alkali basalts generally have high K2O/Na2O ratios, and high K2O and TiO2 contents, suggesting their derivation from partial melting of hornblendite-rich mantle lithology. They also exhibit variable K/La and Ti/La ratios that are correlated with (La/Yb)N ratios, indicating a geochemical heterogeneity of the SCLM source. Taken together, all the above geochemical features can be accounted for by partial melting of a hornblendite-rich SCLM source. The hornblendite would be generated by reaction of the juvenile SCLM wedge peridotite with hydrous felsic melts derived from subducted Palaeotethyan oceanic crust at the slab-mantle interface in the subduction channel. Therefore, orogenic alkali basalts record recycling of the subducted fossil oceanic crust, and the metasomatic hornblendite is an important lithology in local SCLM domains above fossil subduction channels.

Introduction to the special issue on SFB 574 “Volatiles and fluids in subduction zones: climate feedback and trigger mechanisms for natural disasters”

combine field work on land with marine cruises probing the seafloor. During the course of the SFB 574, many different aspects of subduction zone processes were investigated. Geophysical investigations identified and quantified the input of water through hydration of the bend-faulted subducting plate as far as mantle depths. This process and water release from the subducting slab deeper in the subduction zone was investigated by numerical modeling. These studies highlighted the important role of hydration and dehydration of mantle rocks for the global water cycle. Subducted oceanic fracture zones are another conduit for water transported deep into the subduction zone. Compactional and thermal dehydration of the subducted sediment layer affects the strength of interplate coupling and the depth and lateral extension of the seismogenic zone where disastrous earthquakes are generated. The fluids, largely generated by clay mineral transformation, are expelled through the forearc by splay faults. At the seafloor, the sites of cold seeps, often associated with mud volcanoes, are populated by biota that control the carbon transfer to the ocean. The most prominent manifestations of cold seeps are authigenic carbonates that form from anaerobic oxidation of methane and which serve as archives of forearc processes. The largest cold seep emissions occur at faults generated by the subduction of volcanic seamounts. Petrological analyses of ancient, exhumed subduction zone metamorphic rocks revealed the important role of pervasive, typically channelized fluids in high-pressure metamorphic reactions of dewatering subducted igneous crust and mantle. Slab-derived fluids hydrate the mantle wedge along the slab–wedge interface and form a subduction channel in which mixing of different fluids and fluid–rock interaction causes metasomatic overprinting. The element redistributions associated with the liberation of fluids from Sonderforschungsbereiche (SFBs) are a successful funding model in use by the German Science Foundation (DFG) for over 30 years to strengthen basic research first locally at universities and later also supra-regionally by including academic institutions at different cities and states. Literally translated, SFB means “special research area” that comprises research that complements but does not duplicate research at participating institutions and departments. The English terminology used by the DFG is “Collaborative Research Centre,” which better describes the expected approach by emphasizing collaboration and interdisciplinary efforts in such a way that the overall result is better than the sum of individual results. The SFB 574 had united more than 70 scientists with expertise in structural geology, geophysics, sedimentology, geochemistry, empirical and experimental petrology, volcanology, and biology for 11 years (2001–2012). The overarching theme addressed the role of volatiles in subduction zone tectonic, hydrological, metamorphic and magmatic processes, and resulting hazards. The main areas of research were the subduction zones of Central America and southern Chile. Both extend across shorelines from deepsea trenches to arc-volcano summits and thus required to

Bimodal magmatism produced by progressively inhibited crustal assimilation.

The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.

Fluids and H2O activity at the onset of granulite facies metamorphism

Evidence is accumulating from experimental petrology and thermodynamic calculations based on detailed descriptions of key natural occurrences that H2O activity at the regional amphibolite facies-granulite boundaries in high-grade Precambrian gneiss terranes (coincident with the orthopyroxene isograd) is considerably higher (0.3–0.6) than previously thought (0.15–0.3). This revision provides insight into the significance of fluid inclusions in minerals of the incipient charnockites characteristic of the granulite facies transitions in several Precambrian gneiss terranes. Observations on NaCl-dominated brine inclusions in minerals, including some new data in this paper, in rocks from such places as the Kabbal–Satnur–Halagur area of the Archean Shield of South India have salt concentrations consonant with the stabilization of orthopyroxene relative to calcic amphibole and biotite; closely associated CO2-dominated fluid inclusions can have substantial H2O contents at typical incipient granulite facies conditions (700–750°C and 0.5–0.7GPa) and can thus have been in equilibrium with the associated brines as immiscible metamorphic fluids. Observed densities of the best-preserved CO2-rich fluid inclusions in quartz are consistent with those expected from the equation of state of CO2 at incipient granulite facies pressure-temperature conditions.It seems likely that the role of fluids in granulite facies metamorphism of the deep crust has been considerably underemphasized in discussions, still prevalent, which concentrate on the role of fluid-deficient partial melting as the primary agent, to the exclusion of a possible role of metamorphic fluids and metasomatism.

Experimental Constraints on Dacite Pre-eruptive Magma Storage Conditions beneath Uturuncu Volcano

Cerro Uturuncu is a long-dormant, compositionally monotonous, effusive dacitic volcano in the Altiplano–Puna Volcanic Complex (APVC) of SW Bolivia. The volcano recently gained attention following the discovery of an ∼70 km diameter Interferometric Synthetic Aperture Radar (InSAR) anomaly roughly centred on its edifice. Uturuncu dacites, erupted over the past ∼1 Myr, invariably have a phase assemblage of plagioclase–orthopyroxene–biotite–ilmenite–magnetite–apatite–zircon and rhyolite glass. To better constrain storage conditions of the dacite magmas and to help understand their relationship with the observed deformation, petrological experiments were performed in cold-seal hydrothermal vessels. Volatile-saturated (PH2O = PTOTAL and PH2O + PCO2 = PTOTAL) phase equilibria experiments were run between 50 and 250 MPa and 760 and 900°C at fO2 ∼ Ni–NiO. Two synthetic starting compositions were investigated based on a typical Uturuncu dacite whole-rock and its rhyolitic groundmass glass. Pre-eruptive magma storage conditions have been estimated by comparing results from the experiments with natural phase assemblages, modes, and mineral and glass compositions. H2O-saturated experiments constrain storage pressures to 100 ± 50 MPa, equivalent to 1·9–5·7 km below surface. In the dacite, natural phase assemblages are reproduced at 870°C, 100 MPa with both orthopyroxene and biotite stabilized concurrently. Natural glass chemistries are most closely replicated at 50 MPa at 870°C, reflecting the role of decompression crystallization prior to eruption. In H2O-saturated rhyolite experiments the natural phase assemblage is most closely replicated at 870°C, 50 MPa. Isothermal, mixed volatile dacite experiments at 870°C further constrain storage pressures to 110 ± 10 MPa. Assuming that there has been no dramatic change in the eruptive behaviour of Uturuncu in the last 270 kyr, pre-eruptive storage of dacite magmas at ∼100 MPa precludes their role in producing the large diameter deformation anomaly. If deformation is a result of magmatic intrusion, then intrusion of less evolved magmas into deeper, mid-crustal storage regions is a more probable explanation. Intrusion within the Altiplano–Puna Magma Body (APMB), the extent of which is roughly coincident with the APVC, is most likely. It is proposed that dacite magmas form from andesitic parents, via fractionation and/or assimilation, within the APMB. Dacites then rise buoyantly to shallow storage levels where they stall and crystallize prior to eruption. Microlites form during subsequent ascent from the storage region to the surface.

Bernard J. Wood Receives 2013 Harry H. Hess Medal: Citation

As Harry Hess recognized over 50 years ago, mantle melting is the fundamental motor for planetary evolution and differentiation. Melting generates the major divisions of crust mantle and core. The distribution of chemical elements between solids, melts, and gaseous phases is fundamental to understanding these differentiation processes. Bernie Wood, together with Jon Blundy, has combined experimental petrology and physicochemical theory to revolutionize the understanding of the distribution of trace elements between melts and solids in the Earth. Knowledge of these distribution laws allows the reconstruction of the source compositions of the melts (deep in Earth's interior) from their abundances in volcanic rocks. Bernie's theoretical treatment relates the elastic strain of the lattice caused by the substitution of a trace element in a crystal to the ionic radius and charge of this element. This theory, and its experimental calibrations, brought order to a literature of badly scattered, rather chaotic experimental data that allowed no satisfactory quantitative modeling of melting processes in the mantle.

P11 島弧ソレアイトマグマの結晶分化作用 : 実験岩石学的研究に基づく再検討(ポスターセッション)

P11 島弧ソレアイトマグマの結晶分化作用 : 実験岩石学的研究に基づく再検討(ポスターセッション)

Preface: EMPG XIV

The Fourteenth International Symposium on Experimental Mineralogy, Petrology and Geochemistry was held in Kiel, Germany, 4–7 March 2012, and was organized by Philip Kegler from the Institute of Geosciences, Department of Mineralogy. More than 260 scientists from 30 countries attended the meeting. Altogether, 230 abstracts were submitted and presented over three full days of two parallel oral sessions and one dedicated poster session. The posters were displayed over the entire time of the conference. Almost 40% of the contributions were presented by graduate students. Plenary lectures were given by Michael Walter, University of Bristol, Bristol, UK, on the subject of ‘Modelling core formation in Earth: regression – useful analytical tool or Freudian …

Late crystallization of K-feldspar and the paradox of megacrystic granites

K-feldspar crystals >5 cm in greatest dimension are common in calc-alkaline granites and granodiorites worldwide. Such megacrysts are generally interpreted as having grown to large sizes early in a magma’s crystallization history while they were largely molten, owing to field relations such as megacryst alignment and megacryst-rich clusters and to crystallographic features such as zonally arranged inclusions and sawtooth Ba zoning. These features are consistent with early growth but do not require it. In contrast, experimental petrology, mineral compositions, and natural examples of partial melting of granite demonstrate that K-feldspar is typically the last major phase to crystallize and that most K-feldspar growth occurs after the magma crosses the rheologic lock-up threshold of ~50 % crystals. The near-absence of K-feldspar phenocrysts in dacite lavas and tuffs, even in highly crystalline ones, demonstrates that natural magmas do not precipitate significant K-feldspar while they are mobile. The highly potassic compositions of megacrysts (and indeed, of K-feldspar in non-megacrystic granites as well) require exsolution of albite component down to temperatures of ~400 °C. The low Ca contents of megacrysts cannot result from exsolution of anorthite and must represent recrystallization of the crystals at low temperature. These mineralogical and experimental constraints require that K-feldspar megacrysts indicate widespread and thorough recrystallization of the host granites and granodiorites.

Magmatic controls on eruption dynamics of the 1950 yr B.P. eruption of San Antonio Volcano, Tacaná Volcanic Complex, Mexico–Guatemala

San Antonio Volcano, in the Tacaná Volcanic Complex, erupted ~1950yr. B.P., with a Pelean type eruption that produced andesitic pyroclastic surges and block-and-ash flows destroying part of the volcano summit and producing a horse-shoe shaped crater open to the SW. Between 1950 and 800yrB.P. the eruption continued with effusive andesites followed by a dacite lava flow and a summit dome, all from a single magma batch. All products consist of phenocrysts and microphenocrysts of zoned plagioclase, amphibole, pyroxene, magnetite±ilmenite, set in partially crystallized groundmass of glass and microlites of the same mineral phases, except for the lack of amphibole. Included in the andesitic blocks of the block-and-ash flow deposit are basaltic andesite enclaves with elongated and ellipsoidal forms and chilled margins. The enclaves have intersertal textures with brown glass between microphenocrysts of plagioclase, hornblende, pyroxene, and olivine, and minor proportions of phenocrysts of plagioclase, hornblende, and pyroxene. A compositional range obtained of blocks and enclaves resulted from mixing between andesite (866°C±22) and basaltic andesite (enclaves, 932°C±22), which may have triggered the explosive Pelean eruption. Vestiges of that mixing are preserved as complex compositional zones in plagioclase and clinopyroxene-rich reaction rims in amphibole in the andesite. Whole-rock chemistry, geothermometry, experimental petrology and modeling results suggest that after the mixing event the eruption tapped hybrid andesitic magma (≤900°C) and ended with effusive dacitic magma (~825°C), all of which were stored at ~200MPa water pressure. A complex open-system evolution that involved crustal end-members best explains the generation of effusive dacite from the hybrid andesite. Amphibole in the dacite is rimmed by reaction products of plagioclase, orthopyroxene, and Fe–Ti oxides produced by decompression during ascent. Amphibole in the andesite, however, lacks such rims. Because the andesite was at 866±22°C and the dacite was at ~825°C, the reaction rims indicate that the andesitic magma ascended at 0.023ms−1 during the explosive phase of the eruption, whereas the dacitic magma rose more slowly at ~0.002–0.004ms−1.

Chronicles of the annual 2012 all-Russia seminar on experimental mineralogy, petrology, and geochemistry

The annual 2012 AllRussia Seminar on Experi� mental Mineralogy, Petrology, and Geochemistry was organized by the Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKhI), Russian Acad� emy of Sciences, and the Institute of Experimental Mineralogy (IEM), Russian Academy of Sciences, under the financial support of the Russian Foundation for Basic Research, project no. 12�05�0601g, and the Earth Science Division of the Academy of Sciences. The Seminar was held in Moscow on April 17 and 18, 2012, and was attended by researchers from more than thirty national research and educational institutions in Moscow, Chernogolovka, Novosibirsk, Miass, Dubna, Kazan, Irkutsk, Omsk, Vladivostok, Makhachkala, and Borok in Yaroslavl oblast. The Seminar was also partic� ipated by foreign scientists from Armenia, Great Brit� ain, Germany, France, and the Czech Republic. The participants presented there more than 146 papers, including 58 at plenary sessions and 100 at poster ones. The Seminar was opened by its Chairman Prof. A.A. Kadik, who outlines the scope of the Seminar. The CoChairman Prof. Yu.A. Litvin greeted and welcomed the participants and expressed regret that the Russian Foundation for Basic Research suspended its financial support for the acquisition and maintenance of research equipment, which shall affect, first of all, equipment for experimental studies.

Moho vs crust–mantle boundary: Evolution of an idea

Abstract The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust–mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P–T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust–mantle boundary in off-craton regions commonly is transitional over a depth range of about 5–20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust–mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U–Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust–mantle sections, and revealed that the crust–mantle boundary can change in depth through time. However, the nature of the crust–mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust–mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15–30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes, and the composition of the convecting mantle.

Mechanisms of bubble coalescence in silicic magmas

Bubble coalescence is an important process that strongly affects magmatic degassing. Without coalescence, bubbles remain isolated from one another in the melt, severely limiting gas release. Despite this fact, very little has been done to identify coalescence mechanisms from textures of magmatic rocks or to quantify the dynamics of bubble coalescence in melts. In this paper, we present a systematic study of bubble-coalescence mechanisms and dynamics in natural and experimentally produced bubbly rhyolite magma. We have used a combination of natural observations aided by high-resolution X-ray computed tomography, petrological experiments, and physical models to identify different types of bubble–bubble interaction that lead to coalescence on the timescales of magma ascent and eruption. Our observations and calculations suggest that bubbles most efficiently coalesce when inter-bubble melt walls thin by stretching rather than by melt drainage from between converging bubble walls. Orders of magnitude are more rapid than melt drainage, bubble wall stretching produces walls thin enough that inter-bubble pressure gradients may cause the melt wall to dimple, further enhancing coalescence. To put these results into volcanogical context, we have identified magma ascent conditions where each coalescence mechanism should act, and discuss the physical conditions for preserving coalescence structures in natural pumice. The timescales we propose could improve volcanic eruption models, which currently do not account for bubble coalescence. Although we do not address the effect of shear strain on bubble coalescence, the processes discussed here may operate in several different eruption regimes, including vesiculation of lava domes, post-fragmentation frothing of vulcanian bombs, and bubbling of pyroclasts in conduits.

The interplay between X-ray powder and electron diffraction: the case of experimental petrology

The interplay between X-ray powder and electron diffraction: the case of experimental petrology

Extra-terrestrial igneous granites and related rocks: A review of their occurrence and petrogenesis

The telluric planets and the asteroid belt display the same internal structure with a metallic inner core and a silicate outer shell. Experimental data and petrological evidence in silicate systems show that granite can be produced by extreme igneous differentiation through various types of igneous processes.On Moon, 4.4–3.9Ga granite clasts display dry mineral assemblages. They correspond to at least 8 discrete intrusive events. Large K/Ca enrichment and low REE abundances in granite relative to KREEP are consistent with silicate liquid immiscibility, a process observed in melt inclusions within olivine of lunar basalts and in lunar meteorites. Steep-sided domes identified by remote sensing can represent intrusive or extrusive felsic formations.On Mars, black-and-white rhythmic layers observed on the Tharsis rise along the flanks of the peripheral scarps of the Tharsis Montes giant volcanoes suggest the possible eruption of felsic pyroclastites. Though no true granites were found so far in the Martian SNC meteorites, felsic glasses and mesostases were identified and a component close to terrestrial continental (granitic) crust is inferred from trace element and isotope systematics.Venus has suffered extensive volcanic resurfacing, whereas folded and faulted areas resemble terrestrial continents. Near large shield volcanoes, with dominant basaltic compositions, steep-sided domes have been interpreted as non-degassed silicic extrusions. The hypothesis of a granitic component is “tantalising”.Extra-terrestrial granite is frequently found as clasts and mesostases in asteroidal meteorites. Porphyritic textures, with alkali feldspar crystals up to several centimetres in size, were observed in silicate enclaves within iron meteorites. In the chondrite clan, polymict breccias can contain granitic clasts, whose provenance is debated. One clast from the Adzhi-Bogdo meteorite yields a 4.53±0.03Ga Pb–Pb age, making it the oldest known granite in the solar system.The vast majority of granitic materials recognised so far in the extra-terrestrial record are characterised by ferroan A-type compositions, characterised by high to very high K2O and medium CaO contents, sodic varieties being exceedingly rare. Textural evidence of graphic quartz–alkali feldspar intergrowths within crystallised products suggests that they are igneous in origin and crystallised quickly from a liquid. In water-depleted to water-free environments, fluorine and chlorine can play significant roles, as their effects on liquidus temperatures and crystallising assemblages are nearly identical to those of water. The distribution of alkalis and alkaline earths cannot be related only to extensive crystal fractionation, but is likely induced by supplementary silicate liquid immiscibility. Medium-temperature silicate liquid immiscibility is well known as a mode of differentiation in experimental petrology studies at very low pressures on systems dominated by Fe, Ti, K, and P as major elements.The ultimate question is, therefore, not whether granite (s.l.) occurs in any given planetary body, but if sufficient volumes of granitic materials could have been produced to constitute stable continental nuclei.

Water migration in a subduction complex based on the data of seismic tomography and experimental petrology

Water migration in a subduction complex based on the data of seismic tomography and experimental petrology

Annual seminar on experimental mineralogy, petrology, and geochemistry of 2011

Annual seminar on experimental mineralogy, petrology, and geochemistry of 2011

Thermodynamic properties of alloys of gold-74/palladium-26 with variable amounts of iron and the use of Au-Pd-Fe alloys as containers for experimental petrology

Iron oxide-alloy equilibration experiments were conducted in H_2-CO_2 gas mixtures at 1 atm and 1125–1240 °C using strips of Au_(74)Pd_(26) (wt%) and produced Au-Pd-Fe alloys with 0.03–13 wt% iron. A thermodynamic calibration for the mixing of Au_(74)Pd_(26) with iron using an asymmetric regular solution leads to WG_(-Fe) = –45.0 ± 1.8 kJ/mol and WG_(-AuPd) = +19.5 ± 7.7 kJ/mol (1σ). Internal oxidation of iron was observed in a reversal experiment, suggesting that oxygen can be transferred across capsule boundaries during high-temperature experiments. This thermodynamic calibration is applicable to a wide range of oxygen fugacities and iron activities relevant to petrological and metallurgical applications at 1 atm and, as previous studies suggest excess volumes in this system are small, it can also be used to predict Fe activities in experiments at elevated pressure (up to 3 GPa). By pre-doping Au-Pd capsules to match Fe activities expected for the sample during an experiment, it is possible to maintain samples with little to no loss of iron. Pre-saturation of the capsule also provides a method for controlling the oxygen fugacity of samples if no formal oxygen buffer is available.

Dense fine-grained aggregates prepared by spark plasma sintering (SPS), an original technique in experimental petrology

We have fabricated dense polyphase mixtures (silicate and oxide minerals, metal, and silicate melt) by Spark Plasma Sintering (SPS), a technique that has only recently been applied to silicates. We describe the SPS method and some of the characteristics of sintered specimens of forsterite, forsterite + MgO, forsterite + metal (Ni or Fe) and forsterite + metal + silicate melt. We show that SPS is a very efficient method to quickly prepare dense (>99 %) polyphase aggregates with homogeneous microstructures (well distributed phases, narrow grain size distributions, polygonal grain boundaries. . .) and small grain sizes with little or no grain growth during sintering. We observe the development of slight Shape Preferred Orientations (SPO), especially for the metal phases, due to the very simple setup we used here. Overall, SPS offers substantial advantages over traditional sintering techniques, making it perfectly suitable for experimental studies in Earth sciences, in particular those involving kinetic processes.

Magma generation and evolution and global tectonics: An issue in honour of Peter J. Wyllie for his life-long contributions by means of experimental petrology to understanding how the Earth works: Foreword

Magma generation and evolution and global tectonics: An issue in honour of Peter J. Wyllie for his life-long contributions by means of experimental petrology to understanding how the Earth works: Foreword