Equilibration Pressures Research Articles

Ferric iron stabilization at deep magma ocean conditions.

Fe2O3 produced in a deep magma ocean in equilibrium with core-destined alloy sets the early redox budget and atmospheric composition of terrestrial planets. Previous experiments (≤28 gigapascals) and first-principles calculations indicate that a deep terrestrial magma ocean produces appreciable Fe3+ but predict Fe3+/ΣFe ratios that conflict by an order of magnitude. We present Fe3+/ΣFe of glasses quenched from melts equilibrated with Fe alloy at 38 to 71 gigapascals, 3600 to 4400 kelvin, analyzed by synchrotron Mössbauer spectroscopy. These indicate Fe3+/ΣFe of 0.056 to 0.112 in a terrestrial magma ocean with mean alloy-silicate equilibration pressures of 28 to 53 gigapascals, producing sufficient Fe2O3 to account for the modern bulk silicate Earth redox budget and surficial conditions near or more oxidizing than the iron-wüstite buffer, which would stabilize a primitive CO- and H2O-rich atmosphere.

A dynamic mid-crustal magma domain revealed by the 2023 to 2024 Sundhnúksgígar eruptions in Iceland.

Mid-crustal magma domains are the source of many basaltic eruptions. Lavas from individual eruptions are often chemically homogeneous, suggesting that they derive from single, well-mixed magma reservoirs. The 2023 to 2024 eruptions at Sundhnúksgígar in the Svartsengi volcanic system in Iceland provide an opportunity to observe the behavior of a mid-crustal magma domain at high spatial and temporal resolution by detailed sampling and geochemical characterization. We observed substantial mantle-derived geochemical variability in the products erupted in the first hours of the December 2023 and January, February, and March to May 2024 eruptions, indicating that the eruptions derived from multiple magma reservoirs, which mineral-melt equilibration pressures place in the mid crust. The unusual presence of geochemical heterogeneity in the mid-crustal magma domain provides insights into how dynamic and complex mid-crustal magma domains can be.

Magmatic water content in HIMU basalts from the Cook-Austral Islands: constraints on degassing processes and source composition from clinopyroxene phenocrysts

The amount of water recycled during subduction is unclear. Water/Ce estimates in HIMU (high-238U/204Pb) basalts are variable, ranging from < 100 to > 250 in glasses and melt inclusions. Because clinopyroxene (cpx) is a common early liquidus phase and the cpx/melt partitioning of water is well constrained, cpx phenocrysts provide an additional constraint on magmatic water contents. We present water and trace element concentrations in HIMU-basalt-hosted cpx phenocrysts from the Austral Islands. Calculated melt [H2O] (up to 4.3 wt.%) and H2O/Ce ratios (22–825) are higher than in olivine-hosted inclusions, as are estimated equilibration pressures. Correlation between estimated melt [H2O] and crystallization or entrapment pressure suggests significant water loss during magma ascent. Most ocean island basalts (OIBs) span a limited range in H2O (~ 1–1.5 wt.%), and low (< 100) H2O/Ce ratios are primarily observed in melts with unusually high [Ce] (up to 350 ppm). Additionally, [H2O] and H2O/Ce in some suites correlate with entrapment pressure despite having quench pressures high enough to prevent significant water loss from open- or closed-system degassing (< 100 MPa). Polybaric “sparging”, whereby low-P melts re-equilibrate with CO2-rich fluids exsolved at higher pressure, may result in water loss at pressures less than CO2 saturation. This may more accurately describe OIB degassing processes than open or closed system degassing. After correcting for degassing, primary Australs melts likely have H2O/Ce of ~ 300–600. If applicable to OIB sources in general, this limits the total water budget of the mantle, including the mantle transition zone, to < 2.4 ocean masses.

Ferric Iron in Eclogitic Garnet and Clinopyroxene from the V. Grib Kimberlite Pipe (NW Russia): Evidence of a Highly Oxidized Subducted Slab

Abstract Estimates of oxygen fugacity of eclogitic rocks are linked to the redox evolution of the oceanic protolith during subduction and its residence in the lithospheric mantle, and, based on knowledge of pressures and temperatures, allow modelling of the speciation of volatile elements and diamond (or graphite) versus carbonate stability. To date, the oxygen fugacity of mantle eclogites has been shown to vary between −6 (Kasai, Congo and Udachnaya, Siberia) and −0.1 (Udachnaya, Siberia) log units (relative to the fayalite–magnetite–quartz buffer, FMQ), linked to the low Fe3+ contents of garnets. In this study, we investigated the Fe oxidation state of coexisting garnet and clinopyroxene hand-picked out of 17 diamond-free high-MgO and low-MgO mantle eclogites (dated at 2.84 Ga) from the Grib kimberlite pipe (East-European platform). Measured Fe3+/∑Fe values range between 0.03 and 0.19 for garnet and 0.18–0.38 for clinopyroxene, the former being higher than what was measured previously in garnets equilibrated at mantle conditions. The Fe3+/∑Fe of the reconstructed bulk rock ranges between 0.10 and 0.15 for high-MgO eclogites and 0.10 and 0.24 for low-MgO eclogites (with uncertainties of ± 0.02 and ± 0.03 in both cases). Thermobarometric calculations result in equilibration pressures and temperatures of 3.0–5.2 (± 0.4) GPa and 720–1050 (± 60) °C for both high-MgO and low-MgO eclogites, slightly lower than previous P–T estimates of mantle eclogites from the Udachnaya kimberlite pipe (Siberian craton). At these conditions, ∆logfo2 (FMQ) calculated using the available oxythermobarometric model varies from −1.7 to −0.6 log units for high-MgO eclogites and from −2.9 to 0.9 log units for low-MgO eclogites. Samples recording ∆logfo2 (FMQ) ≤ −1 log units overlap with North Slave, West Africa and Udachnaya eclogites, with no difference among eclogite types. The average values of −1.2 (± 0.4) log units for high-MgO and −0.6 (± 1.1) log units for low-MgO eclogites suggest different redox conditions of basaltic protoliths during subduction worldwide. Previous geochemical studies on the same rock samples reported evidence of cryptic metasomatism in both garnet and clinopyroxene that we demonstrate being not recorded by their major elements, while modal metasomatism evidenced by the presence of phlogopite as a product of interaction with a kimberlitic melt only affects the MgO of the bulk rock. Therefore, we suggest that high Fe3+/∑Fe ratios for garnet (&amp;gt; 0.10) and for reconstructed bulk rocks in the case of both low-MgO and high-MgO samples cannot be due to metasomatic interaction with an oxidized fluid, but rather are the consequence of Fe3+ redistribution in an unusually oxidized mafic protolith upon metamorphism. Our results highlight the redox variability of eclogites of Archaean age at conditions more oxidized than present-day mid-ocean ridge basalts (MORBs) and imply an oxidizing nature of the convective mantle source where magma was formed with consequent speciation of C in the form of carbonate fluid explaining, therefore, the lack of eclogitic diamonds in V. Grib kimberlite pipe.

Fluid-mineral Equilibrium Under Nonhydrostatic Stress: Insight From Molecular Dynamics

The interpretation of phase equilibria and reactions in geological materials is based on standard thermodynamics that assumes hydrostatic and homogeneous stress conditions. However, rocks and minerals in the lithosphere can support stress gradients and nonhydrostatic stresses. Currently, there is still not an accepted macroscopic thermodynamic theory to include the effect of nonhydrostatic stress on mineral reactions, and the use of several thermodynamic potentials in stressed geological system remains under debate. In experiments under nonhydrostatic stress, it is often difficult to resolve the direct effect of differential stress on phase equilibria because pressure gradients may be developed. Such gradients can affect the metamorphic equilibria at the local scale. Here, we investigate the direct effect of a homogeneous, nonhydrostatic stress field on the solid-fluid equilibrium using molecular dynamics simulations at non-zero pressure and elevated temperature conditions. Our results show that, for simple single-component systems at constant temperature, the equilibrium fluid pressure of a stressed system is always larger than the value of fluid pressure at hydrostatic stress conditions. The displacement of the equilibrium value of the fluid pressure is about an order of magnitude smaller compared to the level of differential stress in the solid crystal. Thus, phase equilibria can be accurately predicted by taking the fluid pressure as a proxy of the equilibration pressure. On the contrary, the mean stress of the solid can deviate substantially from the pressure of the fluid in stressed systems at thermodynamic equilibrium. This has implications on the use of thermodynamic pressure in geodynamic models since the fluid pressure is a more accurate proxy for predicting the location of metamorphic reactions, while the equilibrium density of the solid has to be determined from its mean stress.

Petrology, Age, and Rift Origin of Ultramafic Lamprophyres (Aillikites) at Mount Webb, a New Alkaline Province in Central Australia

AbstractDiamond exploration over the past decade has led to the discovery of a new province of kimberlitic pipes (the Webb Province) in the Gibson Desert of central Australia. The Webb pipes comprise sparse macrocrystic olivine set in a groundmass of olivine, phlogopite, perovskite, spinel, clinopyroxene, titanian‐andradite and carbonate. The pipes resemble ultramafic lamprophyres (notably aillikites) in their mineralogy, major and minor oxide chemistry, and initial 87Sr/86Sr and εNd‐εHf isotopic compositions. Ion probe U‐Pb geochronology on perovskite (806 ± 22 Ma) indicates the eruption of the pipes was co‐eval with plume‐related magmatism within central Australia (Willouran‐Gairdner Volcanic Event) associated with the opening of the Centralian Superbasin and Rodinia supercontinent break‐up. The equilibration pressure and temperature of mantle‐derived garnet and chromian (Cr) diopside xenocrysts range between 17 and 40 kbar and 750–1320°C and define a paleo‐lithospheric thickness of 140 ± 10 km. Chemical variations of xenocrysts define litho‐chemical horizons within the shallow, middle, and deep sub‐continental lithospheric mantle (SCLM). The shallow SCLM (50–70 km), which includes garnet‐spinel and spinel lherzolite, contains Cr diopside with weakly refertilized rare earth element compositions and unenriched compositions. The mid‐lithosphere (70–85 km) has lower modal abundances of Cr diopside. This layer corresponds to a seismic mid‐lithosphere discontinuity interpreted as pargasite‐bearing lherzolite. The deep SCLM (&gt;90 km) comprises refertilized garnet lherzolite that was metasomatized by a silicate‐carbonatite melt.

Linking the Core Heat Content to Earth's Accretion History

AbstractIn this study we use a parameterized model of differentiation in a magma ocean setting, in which the magma ocean depth evolves during accretion, to predict the composition of the primordial core. We couple this chemical model to a thermal evolution model of the accreting metal to estimate the Earth's core heat content at the end of its formation. We find geochemically consistent models. All these scenarios have in common two key features: (a) the average pressure of metal‐silicates equilibration is between 20 and 45 GPa (final pressure between 40% and 60% of CMB pressure); (b) 60%–80% of Earth's mass is accreted as reduced material. The chemical stratification is stable in most cases, though some scenarios result in an unstable compositional stratification. Mixing an initially stratified core requires a small fraction of the energy released after a giant impact. Importantly, the temperature at the Core Mantle Boundary is ranging from 3925 to 4150 K. For example, scenarios in which the magma ocean remains shallow for a large part of the accretion, then gets deeper at the end of accretion can produce chemically coherent models with cooler cores. This suggests that independent constraints on the core temperature could in principle be used as constraints for the differentiation conditions, and core composition. In particular, we find that the abundance of light elements in the core correlates positively with the temperature of the core at the end of accretion, as well as with the average pressure of equilibration during differentiation.

Architecture of the Lesser Antilles Arc Illustrated by Melt Inclusions

Abstract Volatiles are an essential aspect of subduction zones and constraining their cycling through subduction zones is of prime importance to better understand the genesis, transport, storage and eruption of arc magmas. Here we performed an along-arc investigation of the chemical composition of melt inclusions trapped in minerals representative of ten volcanic centers and 23 key explosive eruptions along the presently active Lesser Antilles arc, from Montserrat in the North to St. Vincent in the South. We use the melt inclusion compositions to reconstruct pre-eruptive conditions, especially pre-eruptive magma storage and degassing levels that highlight how the magma plumbing system is organized and works and to discuss magma source characteristics. All major and selected trace elements and volatiles (H2O, CO2, S, halogens (F, Cl, Br)) have been measured on the same melt inclusions when possible. Eruptions dominantly involved andesitic to dacitic magmas (Montserrat, Guadeloupe, Dominica, Martinique, St. Lucia) and basaltic andesite magmas from St. Vincent. Melt inclusions have been used as pressure probes for magmas, for inferring crustal equilibration pressures. We shed light on the systematic occurrence and lateral complexity of a vertical transcrustal magmatic systems feeding active volcanoes. The geochemical view of the architecture of the plumbing system and in particular the Moho's depth is more variable than the view obtained by seismic data along the Lesser Antilles arc. We propose that the discontinuity between the upper and the middle crust is a major magma ponding zone beneath most of the Lesser Antilles islands and that the crustal structure thus imparts a control on the geochemical signature of arc lavas. Melt inclusions are highly differentiated (dacitic to rhyolitic in composition), so they are distant in composition from the primary, mantle-derived magmas, but they provide indirect information about the magmatic sources. The along-arc variability in Y and heavy rare earth element contents of melt inclusions is consistent with the presence of garnet in the mantle source. Our results also indicate an important contribution of oxidized and saline slab-derived fluids to the magma source predominantly in the southern Lesser Antilles that may have implication on the accretionary system behavior. In addition, a high geographical gradient between sediment melt and slab-derived fluid contributions, illustrating high variability in magmas erupted in close spatial association is reported for some islands, such as Martinique and Dominica. Volatile contents are variable for MIs across the arc: the highest H2O (&amp;lt;8 wt%), Cl (up to 3800 ppm) and Br (up to 20 ppm) concentrations occur in MIs from Dominica. However, there is no systematic correlation between MI volatile content and position along the arc. Halogen Cl/F and Cl/Br ratios vary from one island to another, even between the different eruptions, but without any along arc zoning, indicating that halogen fractionation occurred by fluid transfer (variable assimilation rate of fluids derived from seawater) or by heterogeneities of mantle origin inherited from the initial differentiation of the mantle.

Evolution of Hawaiian Volcano Magmatic Plumbing System and Implications for Melt/Edifice and Melt/Lithosphere Interaction: Constraints from Hualālai Xenoliths

Abstract The evolution of Hawaiian magmatic storage and transport systems in response to variations in magma supply over the course of volcano lifespan can have a significant influence on the type and amount of wallrock material that is assimilated by ponded melts prior to eruption. Understanding this plumbing evolution is therefore critical for evaluating the extent to which such melt/wallrock interaction affects the geochemical signals of Hawaiian basalts. We have examined mineral major and trace element and Sr-Nd-Pb-Hf-Os-O isotope variations in a suite of cumulate and lower Pacific crust xenoliths from the Ka‘ūpūlehu flow, Hualālai Volcano, Hawai‘i in order to constrain the depths of magma storage during Hualālai shield- and post-shield-stage volcanism and the effects of edifice and Pacific crust assimilation. Xenoliths range from 1- and 2-pyroxene gabbros to dunites. Pressures of equilibration for gabbroic and pyroxenitic xenoliths, calculated using two-pyroxene and clinopyroxene-only thermobarometry, suggest that most xenoliths, including both shield- and post-shield-stage cumulates, formed within the Pacific lower crust, at pressures &amp;gt;0.24 GPa. However, two gabbros record lower equilibration pressures (&amp;lt;0.2 GPa) and may have formed within the volcanic edifice. Dunite xenoliths also appear to have formed at shallower depths than most gabbro and pyroxenite xenoliths, inconsistent with a single liquid line of descent. These results indicate that, although shallow (intra-edifice) magma chambers are active during Hawaiian shield-stage volcanism, some magmas also pond and fractionate within or near the base of the Pacific crust during the shield stage. Mass and energy constrained geochemical modeling suggests that ponded melts are likely to assimilate significant quantities of wallrock material, with the mass ratio of assimilated material to crystals fractionated approaching one, regardless of depth of ponding. Elevated 187Os/188Os in some evolved post-shield-derived xenoliths are consistent with assimilation of lower Pacific crust, and low δ18O in xenoliths recording shallow equilibration pressures are consistent with edifice assimilation. However, the effects of assimilation on other radiogenic isotopes appear to be limited in most xenoliths and, by inference, in erupted basalts. Melt–wallrock reaction also appears to have modified the composition of the local Pacific crust. Although plagioclase from the lower oceanic crust record unradiogenic Sr-isotopes similar to mid-ocean ridge basalt (MORB), pyroxene Sr-Nd-Hf and whole-rock Os-isotopes have been variably affected by interaction with Hawaiian melts, resulting in a hybrid isotopic composition intermediate between MORB and Hawaiian shield-stage basalts. These hybrid isotopic compositions are qualitatively similar to Hawaiian rejuvenation-stage basalts. Similar hybridization is likely to have altered the isotopic composition of the Pacific lithospheric mantle. Therefore, Pb-isotope differences between MORB and rejuvenation-stage Hawaiian melts do not preclude melt generation within the Pacific lithosphere or asthenosphere. The isotopic signatures of rejuvenation-stage basalts may represent a unique depleted component within the Hawaiian plume, as suggested by previous studies, but requires additional investigation in light of these results.

Magmatic evolution and architecture of an arc-related, rhyolitic caldera complex: The late Pleistocene to Holocene Cerro Blanco volcanic complex, southern Puna, Argentina

Abstract Through the lens of bulk-rock and matrix glass geochemistry, we investigated the magmatic evolution and pre-eruptive architecture of the siliceous magma complex beneath the Cerro Blanco volcanic complex, a Crater Lake–type caldera complex in the southern Puna Plateau of the Central Andes of Argentina. The Cerro Blanco volcanic complex has been the site of two caldera-forming eruptions with volcanic explosivity index (VEI) 6+ that emplaced the ca. 54 ka Campo Piedra Pomez ignimbrite and the ca. 4.2 ka Cerro Blanco ignimbrite. As such, it is the most productive recent explosive volcano in the Central Andes. The most recent eruptions (younger than 4.2 ka) are dominantly postcaldera effusions of crystal-rich domes and associated small explosive pulses. Previous work has demonstrated that andesitic recharge of and mixing with rhyolitic magma occurred at the base of the magma complex, at ~10 km depth. New isotopic data (Sr, Nd, Pb, and O) confirm that the Cerro Blanco volcanic complex rhyolite suite is part of a regional southern Puna, arc-related ignimbrite group. The suite defines a tight group of consanguineous siliceous magmas that serves as a model for the evolution of arc-related, caldera-forming silicic magma systems in the region and elsewhere. These data indicate that the rhyolites originated through limited assimilation of and mixing with upper-crustal lithologies by regional basaltic andesite parent materials, followed by extensive fractional crystallization. Least squares models of major elements in tandem with Rayleigh fractionation models for trace elements reveal that the internal variations among the rhyolites through time can be derived by extensive fractionation of a quartz–two feldspar (granitic minimum) assemblage with limited assimilation. The rare earth element character of local volumes of melt in some samples of the Campo Piedra Pomez ignimbrite basal fallout requires significant fractionation of amphibole. The distinctive major- and trace-element characteristics of bulk rock and matrix of the Campo Piedra Pomez and Cerro Blanco tephras provide useful geochemical fingerprints to facilitate regional tephrochronology. Available data indicate that rhyolites from other neighborhood centers, such as Cueros de Purulla, share bulk chemical characteristics with the Campo Piedra Pomez ignimbrite rhyolites, but they appear to be isotopically distinct. Pre-eruptive storage and final equilibration of the rhyolitic melts were estimated from matrix glass compositions projected onto the haplogranitic system (quartz-albite-orthoclase-H2O) and using rhyolite-MELTS models. These revealed equilibration pressures between 360 and 60 MPa (~10–2 km depth) with lowest pressures in the Holocene eruptions. Model temperatures for the suite ranged from 695 to 790 °C. Integrated together, our results reveal that the Cerro Blanco volcanic complex is a steady-state (low-magmatic-flux), arc-related complex, standing in contrast to the flare-up (high-magmatic-flux) supervolcanoes that dominate the Neogene volcanic stratigraphy. The silicic magmas of the Cerro Blanco volcanic complex were derived more directly from mafic and intermediate precursors through extensive fractional crystallization, albeit with some mixing and assimilation of local basement. Geochemical models and pressure-temperature estimates indicate that significant volumes of remnant cumulates of felsic and intermediate composition should dominate the polybaric magma complex beneath the Cerro Blanco volcanic complex, which gradually shallowed through time. Evolution to the most silicic compositions and final equilibration of some of the postcaldera domes occurred during ascent and decompression at depths less than 2 km. Our work connotes an incrementally accumulated (over at least 54 k.y.), upper-crustal pluton beneath the Cerro Blanco volcanic complex between 2 and 10 km depth. The composition of this pluton is predicted to be dominantly granitic, with deeper parts being granodioritic to tonalitic. The progressive solidification and eventual contraction of the magma complex may account for the decades of deflation that has characterized Cerro Blanco. The presently active geothermal anomaly and hydrothermal springs indicate the Cerro Blanco volcanic complex remains potentially active.

Prolonged Slab-derived Silicate and Carbonate Metasomatism of a Cratonic Mantle Wedge (Maowu Ultramafic body, China)

AbstractMass transfer between crust and mantle at continental margins is a crucial process in shaping mantle heterogeneity and material cycling in deep Earth. Mass transfer is usually archived by the slab-derived and/or asthenosphere-derived component, which metasomatize a cratonic mantle wedge. Clarifying the origin and temporal sequences of these records is a fundamental aim yet is poorly resolved. Comprehensive petrography, whole-rock and mineral compositions [including platinum group elements (PGE)], zircon U–Pb ages, trace elements, and Hf isotopes of the Maowu ultramafic body (comprising harzburgites and garnet orthopyroxenites) in the Dabie orogen (Central China) are presented in this study to decode the complex metasomatic histories beneath the southern North China Craton (NCC). The ultramafic body represents a typical cratonic mantle-wedge fragment with an equilibration pressure of 4·0 ± 1·0 GPa and temperature of 750 ± 50 °C. The harzburgites have high Mg# values (up to 92) and Ni contents (2537–2892 ppm), low Al2O3 (0·26–0·76 wt%) and CaO (0·05–0·32 wt%) contents, and high olivine Fo values (91–93), supporting the origin from a cratonic mantle wedge with partial melting extents of ~20–25 %. Garnet orthopyroxenites occurring as veins in the harzburgites have a wide range of Mg# values (83–91), high Ni contents (963–2353 ppm), and significant enrichment in light rare earth elements and large ion lithophile elements. They show PGE contents and patterns similar to those of the host harzburgites. These characteristics, combined with geochemical modeling, suggest that the garnet orthopyroxenites were produced through the reaction of the harzburgites with silicate melts derived from the continental crust. Three types of zircons were identified in the Maowu ultramafic body. The group-I zircons with U–Pb ages ranging from ~1927 to ~465 Ma were separated from the harzburgites. They are characterized by oscillatory zones, high heavy rare earth element (HREE) contents, a wide range of εHf(t) values (from −24·9 to +21·0), and felsic inclusions (e.g. quartz and plagioclase). They are interpreted as records of the intense silicate-melt metasomatism triggered by the addition of crust-derived silicate sediments (containing Proterozoic detrital zircons) into the NCC mantle wedge. This metasomatism formed the garnet orthopyroxenite veins in the southern NCC mantle wedge. The group-II zircons have dark cores and bright rims and yield a range of U–Pb ages from 421 ± 8 to 256 ± 6 Ma in both the harzburgites and garnet orthopyroxenites. They contain high Th and U contents (up to 5000 ppm) and display steep HREE patterns, negative Eu anomalies, and positive εHf(t) values (+0·6 to +8·2). Carbonates were identified as inclusions in the zircons and as pods or veinlets in the matrix of the harzburgites. These features may reflect a long-term and pervasive metasomatism by oxidized carbonate fluids in the garnet orthopyroxenite-veined mantle wedge, coeval with the secular subduction of the Tethyan slab that carried mainly sedimentary carbonates. The group-III zircons from both the harzburgites and garnet orthopyroxenites show concordant U–Pb ages of 227 ± 6 Ma. They are interpreted to record the Triassic continental collision between the Yangtze Craton and NCC. Collectively, this study provides geochemical, mineralogical, and petrological evidence that the periphery of a cratonic mantle with prolonged fluxing and various metasomatism can archive the complex history along a convergent margin that evolved from oceanic subduction to continental collision.

Perioperative Hemodynamic Monitoring: An Overview of Current Methods.

Perioperative hemodynamic monitoring is an essential part of anesthetic care. In this review, we aim to give an overview of methods currently used in the clinical routine and experimental methods under development. The technical aspects of the mentioned methods are discussed briefly. This review includes methods to monitor blood pressures, for example, arterial pressure, mean systemic filling pressure and central venous pressure, and volumes, for example, global end-diastolic volume (GEDV) and extravascular lung water. In addition, monitoring blood flow (cardiac output) and fluid responsiveness (preload) will be discussed.

Scaling laws for the geometry of an impact-induced magma ocean

Growing protoplanets experience a number of impacts during the accretion stage. A large impactor hits the surface of a protoplanet and produces impact-induced melt, where the impactor's iron emulsifies and experiences metal-silicate equilibration with the mantle of the protoplanet while it descends towards the base of the melt. This process repeatedly occurs and determines the chemical compositions of both mantle and core. The partitioning is controlled by parameters such as the equilibration pressure and temperature, which are often assumed to be proportional to the pressure and temperature at the base of the melt. The pressure and temperature depend on both the depth and shape of the impact-induced melt region. A spatially confined melt region, namely a melt pool, can have a larger equilibrium pressure than a radially uniform (global) magma ocean even if their melt volumes are the same. Here, we develop scaling laws for (1) the distribution of impact-induced heat within the mantle and (2) shape of the impact-induced melt based on more than 100 smoothed particle hydrodynamic (SPH) simulations. We use Legendre polynomials to describe these scaling laws and determine their coefficients by linear regression, minimizing the error between our model and SPH simulations. The input parameters are the impact angle θ (0∘,30∘,60∘, and 90∘), total mass MT (1MMars−53MMars, where MMars is the mass of Mars), impact velocity vimp (vesc−2vesc, where vesc is the mutual escape velocity), and impactor-to-total mass ratio γ (0.03−0.5). We find that the equilibrium pressure at the base of a melt pool can be higher (up to ≈80%) than those of radially-uniform global magma ocean models. This could have a significant impact on element partitioning. These melt scaling laws are publicly available on GitHub (https://github.com/mikinakajima/MeltScalingLaw).

The Effect of Inefficient Accretion on Planetary Differentiation

Abstract Pairwise collisions between terrestrial embryos are the dominant means of accretion during the last stage of planet formation. Hence, their realistic treatment in N-body studies is critical to accurately model the formation of terrestrial planets and to develop interpretations of telescopic and spacecraft observations. In this work, we compare the effects of two collision prescriptions on the core−mantle differentiation of terrestrial planets: a model in which collisions are always completely accretionary (“perfect merging”), and a more realistic model based on neural networks that has been trained on hydrodynamical simulations of giant impacts. The latter model is able to predict the loss of mass due to imperfect accretion and the evolution of nonaccreted projectiles in hit-and-run collisions. We find that the results of the neural network model feature a wider range of final core mass fractions and metal−silicate equilibration pressures, temperatures, and oxygen fugacities than the assumption of perfect merging. When used to model collisions in N-body studies of terrestrial planet formation, the two models provide similar answers for planets more massive than ≈0.1 M ⊕ (Earth masses). For less massive final bodies, however, the inefficient-accretion model predicts a higher degree of compositional diversity. This phenomenon is not reflected in planet formation models of the solar system that use perfect merging to determine collisional outcomes. Our findings confirm the role of giant impacts as important drivers of planetary diversity and encourage a realistic implementation of inefficient accretion in future accretion studies.

Metasomatized eclogite xenoliths from the central Kaapvaal craton as probes of a seismic mid-lithospheric discontinuity

The central region of the Kaapvaal craton is relatively understudied in terms of its lithospheric mantle architecture, but is commonly believed to be significantly impacted by post-Archean magmatism such as the ca. 2056 Ma Bushveld large igneous event. We investigate a collection of 17 eclogite xenoliths from the Cretaceous Palmietfontein kimberlite at the Western Limb of the Bushveld Complex for their mineralogical compositions (major and trace elements, plus Fe3+ contents), as well as stable oxygen and radiogenic Pb isotopic compositions to gain further insights into the nature and evolution of the central Kaapvaal cratonic mantle lithosphere. New U/Pb age determinations on mantle-derived zircon yield a magma emplacement age of ca. 75 Ma for the Palmietfontein Group-1 kimberlite, which means that the entrained eclogite xenoliths may record a protracted metasomatic history from the Proterozoic through to most of the Phanerozoic eon.Garnet δ18O values of up to 6.9‰ and positive Eu anomalies for the bulk rocks suggest seawater-altered oceanic crustal protoliths for the Palmietfontein eclogite xenolith suite, which is typical for the eclogitic components of the Kaapvaal root and other cratonic mantle sections worldwide. However, several features of the Palmietfontein eclogites are commonly not observed in other mantle-derived eclogite xenolith suites. Firstly, the samples studied yield relatively low equilibration pressures and temperatures between 2.7 and 4.5 GPa and 740–1064 °C, indicating a relatively shallow residence between 90 and 150 km depths. Secondly, euhedral coarse amphibole is present in several eclogite nodules where it is in equilibrium with ‘touching’ garnet, supporting eclogite residence within the amphibole stability field at uppermost lithospheric mantle conditions. Thirdly, primary omphacitic clinopyroxene is often overgrown by diopside, and is significantly enriched in incompatible trace elements. The clinopyroxene is also characterized by elevated 206Pb/204Pb of 17.28–19.20 and 207Pb/204 Pb of 15.51–16.27, and these Pb isotopic compositions overlap with those of Mesozoic Group-2 kimberlites from the Kaapvaal craton.Our results show that eclogites reside at ~85 km depth beneath the central Kaapvaal craton as part of a layer that corresponds to an approximately 50 km thick seismically-detected mid-lithospheric discontinuity. Mid-lithospheric discontinuities have been interpreted as metasomatic fronts formed by focussed crystallization of hydrous mineral phases from enriched volatile-bearing melts, and as such the strongly overprinted amphibole-bearing eclogite xenoliths from Palmietfontein may represent a physical expression of such seismically anomalous metasomatic layer at mid-lithospheric depth. Our Pb isotope data suggest that the focussed metasomatism can be attributed to volatile-rich melts reminiscent of potassic Group-2 kimberlites, which have been invoked in MARID-style metasomatic overprinting of the lower lithospheric mantle beneath the western Kaapvaal craton. However, the relatively low fO2 recorded by the Palmietfontein eclogites (minimum FMQ-4.5) suggests that the metasomatism at mid-lithospheric depth was less protracted compared to the more intensive and oxidizing metasomatism typically observed near the base of cratonic mantle roots. While it is possible that Proterozoic magmatic events were responsible for the focussed mid-lithospheric metasomatism of the Kaapvaal mantle, on the basis of the Pb isotope constraints the Palmietfontein eclogites were most likely overprinted during ca. 120 Ma Group-2 kimberlite magmatism.

Metal-silicate mixing by large Earth-forming impacts

Geochemical and isotopic observations constrain the timing, temperature and pressure of Earth's formation. However, to fully interpret these observations, we must know the degree of mixing and equilibration between metal and silicates following the collisions that formed the Earth. Recent fluid dynamical experiments provide initial estimates of this mixing, but they entirely neglect the inertia of planet-building impactors. Here we use laboratory experiments on the impact of a dense liquid volume into a lighter liquid pool to establish scaling laws for mixing as a function of the impactor speed, size, density and the local gravity. Our experiments reproduce the cratering process observed in impact simulations. They also produce turbulence down to small scales, approaching the dynamical regime of planetary impacts. In each experiment, we observe an early impact-dominated stage, which includes the formation of a crater, its collapse into an upward jet, and the collapse of the jet. At later times, we observe the downward propagation of a buoyant thermal. We quantify the contribution to mixing from both the impact and subsequent thermal stage. Our experimental results, together with our theoretical calculations, indicate that the collapse of the jet produces much of the impact-induced mixing. We find that the ratio between the jet inertia and the impactor buoyancy controls mixing. Applied to Earth's formation, we predict full chemical equilibration for impactors less than 100 km in diameter, but only partial equilibration for Moon-forming giant impacts. With our new scalings that account for the impactor inertia, the mass transfer between metal and silicates is up to twenty times larger than previous estimates. This reduces the accretion timescale, deduced from isotopic data, by up to a factor of ten and the equilibration pressure, deduced from siderophile elements, by up to a factor of two.

Multi-stage garnet formation and destruction in Kimberley harzburgitic xenoliths, South Africa

Thirty-nine garnet harzburgites from Kimberley in the Kaapvaal Craton (South Africa) were studied to constrain the origin, age and evolution of sub-cratonic lithospheric mantle (SCLM). In order to avoid chemical overprinting by recent metasomatism, only garnet harzburgites that appeared clinopyroxene-free to the naked eye were sampled. The majority of garnets were, however, in equilibrium with clinopyroxene (24 of 39). Whole rock and mineral major–trace element geochemistry and garnet Sr–Nd–Hf isotope data are presented. Equilibration pressures range from 3.8–6.1 GPa, indicating the harzburgites were derived from a large portion of the SCLM (~115–185 km). High olivine Mg# (~93.4, n = 39) and low whole rock heavy rare earth elements (HREE) contents are consistent with large degrees of partial melting (>45%) and garnet exhaustion leaving a dunitic residue with olivine ≥90%, orthopyroxene ≤10% and HREE <0.01 times chondrite. Mineral modes, whole rock Al2O3 (0.5–3.2 wt%) and SiO2 (43.1–49.1 wt%), however, indicate heterogeneous re-introduction of garnet (≤13%) and orthopyroxene (≤50%). Harzburgites with high garnet and relatively low orthopyroxene modes (mostly ~7–13% and ~ 9–30%; n = 6) are characterised by mildly sinusoidal garnet REE patterns (Tb-Dy minimum and high HREE) and Archaean depleted Hf TDM ages (2.7–3.3 Ga; εHfe: +190 to +709). In contrast, harzburgites with high orthopyroxene and relatively low garnet and modes (~1.5–7.5% and ~ 25–50%; n = 19) are characterised by highly sinuous REE patterns (Ho-Yb minimum and low HREE) and Proterozoic enriched Hf TDM ages (0.7–1.6 Ga; εHfe: −16 to +6). It is inferred that Archaean G10 garnet re-introduction caused a significant increase in HREE, making melt depletion models based on HREE inaccurate. Orthopyroxene addition, a few hundred million years later, most likely at ~2.7 Ga and associated with Ventersdorp magmatic activity, caused partial consumption of garnet and olivine, and changed garnet compositions leading to: 1) Cr/Al ratio increase; 2) HREE decrease; 3) more sinusoidal REE patterns; and 4) un-radiogenic 176Hf/177Hf. Garnets define a Lu-Hf isochron age of 2702 ± 64 Ma (εHfi = +44, n = 31), which is interpreted as a consequence of partial isotopic equilibrium within the SCLM and mixing of the garnet- and orthopyroxene-rich metasomatic components. The low LILE contents and absence of Nb-Ta anomalies are consistent with modal metasomatism caused by intra-plate magmatism. In addition, the REE signatures of metasomatic agents in equilibrium with the garnets suggest that carbonatitic melts and SiO2-rich hydrous melts were responsible for re-introduction of garnet and orthopyroxene, respectively. Sr-Nd isotope systematics were disrupted associated with kimberlite magmatism (Nd isochron: 217 ± 58 Ma, εNdi = +4; n = 34), consistent with recent G10 garnet transformation into G9 garnets (Ca + Fe-enriched). This event may have caused garnet addition (up to 1%), suggesting that garnet was formed or destroyed in at least 4 different events: i) initial extensive polybaric melting, ii) asthenospheric melts re-introducing the bulk of the garnet, iii) orthopyroxene addition and garnet loss, all in the Archaean, and iv) minor garnet addition possibly related to recent kimberlite magmatism prior to eruption.

Metal–silicate partitioning of W and Mo and the role of carbon in controlling their abundances in the bulk silicate earth

The liquid metal–liquid silicate partitioning of molybdenum and tungsten during core formation must be well-constrained in order to understand the evolution of Earth and other planetary bodies, in particular because the Hf–W isotopic system is used to date early planetary evolution. The partition coefficients DMo and DW have been suggested to depend on pressure, temperature, silicate and metal compositions, although previous studies have produced varying and inconsistent models. Additionally, the high cationic charges of W and Mo in silicate melts make their partition coefficients particularly sensitive to oxygen fugacity. We combine 48 new high pressure and temperature experimental results with a comprehensive database of previous experiments to re-examine the systematics of Mo and W partitioning, and produce revised partitioning models from the large combined dataset. W partitioning is particularly sensitive to silicate and metallic melt compositions and becomes more siderophile with increasing temperature. We show that W has a 6+ oxidation state in silicate melts over the full experimental fO2 range of ΔIW −1.5 to −3.5. Mo has a 4+ oxidation state, and its partitioning is less sensitive to silicate melt composition but also depends on metallic melt composition. DMo stays approximately constant with increasing depth in Earth. Both W and Mo become more siderophile with increasing C content of the metal: we therefore performed experiments with varying C concentrations and fit epsilon interaction parameters: εCMo = −7.03 ± 0.30 and εCW = −7.38 ± 0.57.W and Mo along with C are incorporated into a combined N-body accretion and core–mantle differentiation model, which already includes the major rock-forming elements as well as S, and moderately and highly siderophile elements. In this model, oxidation and volatility gradients extend through the protoplanetary disk so that Earth accretes heterogeneously. These gradients, as well as the metal–silicate equilibration pressure, are fitted using a least squares optimisation so that the model Earth-like planet reproduces the composition of the bulk silicate Earth (BSE) in terms of 17 simulated element concentrations (Mg, Fe, Si, Ni, Co, Nb, Ta, V, Cr, S, Pt, Pd, Ru, Ir, W, Mo, and C). The effects of the interaction of W and Mo with Si, S, O, and C in metal are included. Using this model with six separate terrestrial planet accretion simulations, we show that W and Mo require the early accreting Earth to be sulfur-depleted and carbon-enriched so that W and Mo are efficiently partitioned into Earth’s core and do not accumulate in the mantle. When this is the case, the produced Earth-like planets possess mantle compositions matching the BSE for all simulated elements. However, there are two distinct groups of estimates of the bulk mantle’s C abundance in the literature: low (∼100 ppm) and high (∼800 ppm), and all six models are consistent with the higher estimated carbon abundance. The low BSE C abundance would be achievable when the effects of the segregation of dispersed metal droplets produced in deep magma oceans by the disproportionation of Fe2+ to Fe3+ plus metallic Fe is included.

Metasomatic control of hydrogen contents in the layered cratonic mantle lithosphere sampled by Lac de Gras xenoliths in the central Slave craton, Canada

Whether hydrogen incorporated in nominally anhydrous mantle minerals plays a role in the strength and longevity of the thick cratonic lithosphere is a matter of debate. In particular, the percolation of hydrogen-bearing melts and fluids could potentially add hydrogen to the mantle lithosphere, weaken its olivines (the dominant mineral in mantle peridotite), and cause delamination of the lithosphere's base. The influence of metasomatism on hydrogen contents of cratonic mantle minerals can be tested in mantle xenoliths from the Slave Craton (Canada) because they show extensive evidence for metasomatism of a layered cratonic mantle. Minerals from mantle xenoliths from the Diavik mine in the Lac de Gras kimberlite area located at the center of the Archean Slave craton were analyzed by FTIR for hydrogen contents. The 18 peridotites, two pyroxenites, one websterite and one wehrlite span an equilibration pressure range from 3.1 to 6.6 GPa and include samples from the shallow (≤145 km), oxidized ultra-depleted layer; the deeper (∼145–180 km), reduced less depleted layer; and an ultra-deep (≥180 km) layer near the base of the lithosphere. Olivine, orthopyroxene, clinopyroxene and garnet from peridotites contain 30–145, 110–225, 105–285, 2–105 ppm H2O, respectively. Within each deep and ultra-deep layer, correlations of hydrogen contents in minerals and tracers of metasomatism (for example light over heavy rare-earth-element ratio (LREE/HREE), high-field-strength-element (HFSE) content with equilibration pressure) can be explained by a chromatographic process occurring during the percolation of kimberlite-like melts through garnet peridotite. The hydrogen content of peridotite minerals is controlled by the compositions of the evolving melt and of the minerals and by mineral/melt partition coefficients. At the beginning of the process, clinopyroxene scavenges most of the hydrogen and garnet most of the HFSE. As the melt evolves and becomes enriched in hydrogen and LREE, olivine and garnet start to incorporate hydrogen and pyroxenes become enriched in LREE. The hydrogen content of peridotite increases with decreasing depth, overall (e.g., from 75 to 138 ppm H2O in the deep peridotites). Effective viscosity calculated using olivine hydrogen content for the deepest xenoliths near the lithosphere-asthenosphere boundary overlaps with estimates of asthenospheric viscosities. These xenoliths cannot be representative of the overall cratonic root because the lack of viscosity contrast would have caused basal erosion of lithosphere. Instead, metasomatism must be confined in narrow zones channeling kimberlite melts through the lithosphere and from where xenoliths are preferentially sampled. Such localized metasomatism by hydrogen-bearing melts therefore does not necessarily result in delamination of the cratonic root.

Sm-Nd geochronology and petrologic investigation of sub-ophiolite metamorphic sole from the Dinarides (Krivaja-Konjuh, Ophiolite Complex, Bosnia and Herzegovina)

The Dinaridic segment of Neotethys was affected by a widespread shortening and related subduction-accretion-obduction processes that commenced in the middle Jurassic. In the Dinarides, the Krivaja-Konjuh Ophiolite Complex (KKOC) stands as the largest ophiolite complex with a well-exposed metamorphic sole which is the key to understanding the dynamics of intraoceanic subduction initiation in this part of Neotethys. In this contribution we present Sm-Nd geochronology on a granulite facies amphibolite from the KKOC, as well as a detailed petrological description. A five-point isochrone age calculated from clinopyroxene, plagioclase, garnet, amphibole and whole rock is 162 ± 14 Ma (MSWD = 6.2), whereas garnet and whole rock yield 160 ± 7 Ma. Ages calculated from all data points except clinopyroxene are 162 ± 5 Ma (MSWD = 1.09). Petrographic investigations suggest that these ages date granulite facies metamorphic conditions (i.e. peak metamorphism of Grt-Cpx amphibolite) rather than post-peak exhumation or obduction processes. Phase textural relationships are in line with previous research, which indicated a peak metamorphism equilibration pressure and temperature of ~1 GPa and ~800 °C, respectively. Granulite facies conditions are elucidated for an igneous precursor, which underwent a multi-stage metamorphism that gave rise to recrystallization of igneous clinopyroxene and plagioclase, epitaxial growth of amphibole, and garnet blastosis. Taking into account the age of gabbronorite from the youngest segment of the KKOC oceanic crust (Taorcian to Bathonian) and ages of radiolarian assemblages from the KKOC melange (Bajocian to Bathonian), it may be inferred that within ~25 Ma the Dinaridic segment of Neotethys evolved rapidly from active ridge spreading through a stage of intraoceanic subduction and arc magmatism toward sub-ophioliteexhumation and further obduction along the Adria passive margin at the end of the Jurassic era.