Earth's Mantle Research Articles

Hydrogen isotopic evidence for a core component in Baffin Island lavas.

The nature of chemical exchange between Earth's core and mantle is fundamental to understanding their evolution. Tungsten-182 and helium-3 anomalies in volcanic rocks from deeply sourced mantle plumes have been attributed to core-mantle exchange. Hydrogen (H) is potentially abundant in the core. Therefore, H may also be a sensitive tracer of core-mantle exchange. We measured 2H/1H ratios (reported as δD) in olivine-hosted basaltic melt inclusions from a Baffin Island lava to test whether mantle plumes contain H from the core. The average δD value (-144±24 per mil) is lower than some estimates for the average depleted upper mantle (δD≈-60±20 per mil). The low δD composition likely derives from isotopic diffusion or H leakage from the core, not isotopic fractionation during magmatism or crustal contamination. Over geologic time, core-mantle exchange of H may have overprinted the isotopic composition of mantle plume source regions and much of the upper mantle.

Heavy boron isotopes in intraplate basalts reveal recycled carbonate in the mantle.

Recycling of surficial volatiles such as carbon into the mantle plays a fundamental role in modulating Earth's habitability. However, slab devolatilization during subduction could prevent carbon from entering the deep mantle. Boron isotopes are excellent tracers of recycled volatiles, but correlations between boron isotopes and mantle heterogeneity indicators are rarely observed, thereby casting doubt that substantial amounts of volatiles and boron can be recycled into the deep mantle. Here, we show that boron isotopes in two different types of primitive continental intraplate basalts correlate well with mantle heterogeneity indicators, indicating contributions of various subducted crustal components. A common high-δ11B component shared by both types of basalts is best explained as recycled subducted carbonate rather than serpentinite. Our findings demonstrate that subducted carbonate carries heavy B into Earth's deep mantle, and its recycling could account for the high-δ11B signatures observed in intraplate magmas and deeply sourced carbonatites.

Adjoint‐Based Marker‐In‐Cell Data Assimilation for Constraining Thermal and Flow Processes From Lagrangian Particle Records

AbstractGeophysical problems often involve Lagrangian particles that follow surrounding flows and record information about the system, such as the pressure and temperature path recorded in metamorphic rocks. These Lagrangian particles can be useful for constraining unknown parameters, such as their sources and the thermal and flow processes of the surrounding fluid. To use information about Lagrangian particles to constrain unknown parameters about the surrounding fluid in an inverse manner, we have developed a 4D‐Var (four‐dimensional variational) data assimilation for thermal convection in a particle‐grid coupled system. Here we consider particles advected in a thermally convecting, highly viscous fluid that mimics geochemical tracers in the Earth's mantle, and estimate time series of thermal and velocity fields only from the particle records, focusing on their high traceability in the laminar flow. We present preliminary 4D‐Var results using a sufficient amount of synthetic particle position and velocity data. The 4D‐Var run achieves a 60‐Myr time reversal of thermal convection at a horizontal wavelength of 6,000 km, without using any temperature data. For complex convection patterns, the cost function tends not to decrease well, likely indicating that the method is successful when the time reversal is much smaller than the mixing time scale, over which information about the initial particle arrangement is lost. Our framework has the potential to constrain thermal, flow, and mixing processes not only in the Earth's mantle but also in any other laminar flow containing Lagrangian particles that record useful information.

Geochemical data of Al-rich diopside pyroxenites from the Premosello mantle peridotite massif, Ivrea-Verbano Zone, Southern Alps.

Geochemical data of Al-rich diopside pyroxenites from the Premosello mantle peridotite massif, Ivrea-Verbano Zone, Southern Alps.

18.6-yr tidal variations in J2 observed from 48-yr satellite laser ranging (SLR)

SUMMARY Analysis of the 48-yr of satellite laser ranging data of multiple satellites shows that long-term variations in the Earth's dynamical oblateness represented by the second-degree zonal harmonic J2 is best characterized by the superposition of a quadratic trend, 10.5- and 18.6-yr variations. These variations result from climate-related mass changes, tides and core flow-induced variations at the core–mantle boundary. We determined that the global ocean's response to the lunar attraction at the 18.6-yr period is near equilibrium, with an amplitude of 0.4735 ± 0.008 cm and an error of ∼11 per cent relative to the modelled amplitude (0.4224 cm), and ∼2 ± 3 deg of phase lag. The 18.6-yr Love Number was found to be 0.013 75 − i0.005 53 with an error of 2 per cent for both the real and imaginary parts and a phase correction π for the imaginary part of the International Earth Rotation and Reference Systems Service (IERS) 2010 anelasticity model. The nominal frequency-independent anelasticity Love number, k₂, was determined to be 0.3022 ± 0.0001 for the 18.6-yr period, based on a reference frequency of 200 s and α = 0.1514 for mantle anelasticity for mantle anelasticity. This study also reveals a significant gravitational signal (3.06 × 10−11) in J2 obstructs the Earth's mantle anelastic response to the 18.6-yr tidal forces, reflecting in phase shift of π the imaginary part of the IERS 2010 Love number. This signal can be characterized by a positive Love number of 0.011 06 in the modelling of the variation in J2 coupling with the 18.6-yr tide. This signal is possibly produced by the core dynamics, which creates a gravitational signal in J2 with an amplitude of 3.36 × 10−11 at the decadal time scale and could account for ∼70 per cent of the observed 10.5-yr variation

Earth's Deep‐Time Geodynamic Evolution Recorded by Hafnium Isotope Perturbations

AbstractInteractions between Earth's mantle and crust have shaped the planet's evolution through deep time. Hafnium (Hf) isotopes provide a unique fingerprint of magma sources, enabling the tracking of the crucial interaction zone in the upper mantle evolution through more than four billion years of Earth's history. However, previous studies have relied on a combination of evolved and juvenile zircons, making it challenging to distinguish the genuine evolution of mantle properties. Here, we present a global compilation of Hf isotopic analyses of zircons from juvenile crust to track the upper mantle's evolution throughout Earth's history. By employing Singular Spectrum Analysis and Wavelet Analysis for time series, we decompose the complex Hf isotopic evolution curves and determine the respective periods and interpretations of each component. Our analysis reveals a complex and dynamic evolution of the upper mantle, with distinct periods of stability and upheaval. We show that the upper mantle has undergone periodic perturbations through mixing with crustal materials since Earth's formation, primarily caused by plate subduction and weakly influenced by mantle convective cycles. Hf isotopes reveal vigorous mantle convection that propelled plate tectonics during the Hadean, along with numerous supercontinent cycles that originated in the early Mesoarchean and a notable shift in subduction modes during the Neoproterozoic. This Hf isotope survey provides new insights into Earth's tectonic machinery, advancing our understanding of the planet's geological history.

Impact‐Driven Redox Stratification of Earth's Mantle

AbstractPlanetary formation involves highly energetic collisions, the consequences of which set the stage for the ensuing planetary evolution. During accretion, Earth's mantle was largely molten, a so‐called magma ocean, and its oxidation state was determined by equilibration with metal‐rich cores of infalling planetesimals through redox buffering reactions. We test two proposed mechanisms (metal layer and metal droplets) for equilibration in a magma ocean and the resulting oxidation state (Fe3+/ΣFe). Using scaling laws on convective mixing, we find that the metal layer could promote oxidation of a magma ocean, but this layer is too short‐lived to reproduce present‐day mantle Fe3+/ΣFe (2%–6%). Metal droplets produced by the fragmentation of impactor cores can also promote oxidation of a magma ocean. We use Monte Carlo sampling on two possible accretion scenarios to determine the likely range of oxidation states by metal droplets. We find that equilibration between silicate and metal droplets tends toward higher mantle Fe3+/ΣFe than presently observed. To achieve present‐day mantle Fe3+/ΣFe and maintain the degree of equilibration suggested by Hf‐W and U‐Pb systematics (30%–70%), the last (Moon‐forming) giant impact likely did not melt the entire mantle, therefore leaving the mantle stratified in terms of oxidation state after main accretion completes. Furthermore, late accretion impacts during the Hadean (4.5–4.0 Ga) could generate reduced domains in the shallow upper mantle, potentially sustaining surface environments conducive for prebiotic chemistry.

Detectability of oxygen fugacity regimes in the magma ocean world 55 Cancri e at high spectral resolution

ABSTRACT Ultra-short-period exoplanets such as 55 Cancri e (55 Cnc e), hosting dayside magma oceans, present unique opportunities to study surface-atmosphere interactions. The composition of a vaporized mineral atmosphere enveloping the dayside is dictated by that of the surface magma ocean, which in turn is sensitive to its oxygen fugacity (fO$_2$). Observability estimations and characterization of the atmospheric emission of 55 Cnc e have mostly remained limited to low spectral resolution space-based studies. Here, we aim to examine ground-based high-resolution observabilities of a diverse set of mineral atmospheres produced across a grid of mantle fO$_2$s varying over 12 orders of magnitude. We assume a bulk silicate Earth mantle composition and a substellar dayside temperature of T = 2500 K in the near-infrared wavelength region. This spectral range is often featureless for this class of atmospheres at low resolution. Coupling our newly developed simulator for synthesizing realistic observations from high-resolution ground-based spectrographs (Ratri) to a pre-developed high-resolution cross-correlation spectroscopy (HRCCS) analysis pipeline (Upamana), we find that this array of mineral atmospheres would all be detectable with 11 h of observing time of the dayside of 55 Cnc e with CARMENES and each individual scenario can be correctly differentiated within 1$\sigma$. Our analysis is readily able to distinguish between a planet with an Earth-like redox state (with fO$_2$ $\sim$ 3.5 log$_{10}$ units above the iron-wüstite, IW buffer) and a Mercury-like planet (fO$_2$ $\sim$ 5 log$_{10}$ units below IW). We thus conclude that the HRCCS technique holds promise for cataloguing the diversity of redox states among the rocky exoplanetary population.

Variations in Hawaiian Plume Flux Controlled by Ancient Mantle Depletion

AbstractMantle plumes—upwellings of buoyant rock in Earth's mantle—feed hotspot volcanoes such as Hawai‘i. The size of volcanoes along the Hawai‘i–Emperor chain, and thus the magma flux of the Hawaiian plume, has varied over the past 85 million years. Fifteen and two million years ago, rapid bursts in magmatic production led to the emergence of large islands such as Pūhāhonu, Maui Nui and Hawai‘i, but the underlying mechanisms remain enigmatic. Here, we use new radiogenic Ce–Sr–Nd–Hf isotope data of Hawaiian shield lavas to quantify the composition and proportion of the different constituents of the Hawaiian plume over time. We find that most of the Hawaiian mantle source is peridotite that has experienced variable degrees of melt depletion before being incorporated into the plume. We show that the most isotopically enriched LOA‐type compositions arise from the aggregation of melts from more depleted, trace element‐starved peridotite, causing the over‐visibility of melts from recycled crust in the mixture. Our results also show that upwelling of chemically more depleted, and thus less dense, more buoyant mantle peridotite occurred synchronously to an observed burst of magma production. Buoyancy variations induced by variably depleted peridotite may not only control the temporal patterns of volcanic productivity in Hawai‘i, but also those of other plumes world‐wide. The excess buoyancy of depleted peridotite may therefore be an underrated driving force for convective mantle flow, trigger and sustain active upwelling of relatively cool plumes, and control the geometry of mantle upwellings from variable depths.

Structures and properties of Ca-Xe compounds at extreme pressure and temperature.

Calcium, one of the most abundant elements in the Earth's mantle, does not react easily with noble gases (e.g., He and Xe) under ambient conditions. However, high pressure can alter electron configurations in atoms, leading to the formation of unconventional compounds. In this study, we systematically investigate Ca-Xe compounds across pressures of 0-150GPa using calypso structure prediction methods combined with first-principles calculations. We identify four novel Ca-Xe compounds Pm3̄m-CaXe, P4/mmm-CaXe2, I4/m-Ca3Xe, and P4/mmm-Ca2Xe3 that demonstrate stability over a wide pressure range from 37.5 to 150GPa. All these compounds exhibit metallic properties and are dynamically stable, as indicated by the absence of imaginary frequencies in their phonon dispersion spectra. Ionic bonding between Ca and Xe is observed due to electron transfer from Ca to Xe. Abinitio molecular dynamics simulations show that Pm3̄m-CaXe, P4/mmm-CaXe2, and P4/mmm-Ca2Xe3 remain solid up to pressures of 135GPa and temperatures of 4000K. In contrast, I4/m-Ca3Xe undergoes a transition from solid to liquid at temperatures above 3500K due to weakened Ca-Xe bonds. The findings suggest that these Ca-Xe compounds could potentially be synthesized experimentally under high-pressure conditions. The results offer theoretical guidance for discovering new high-pressure Xe compounds and provide valuable insights into Xe chemistry.

Melt–Rock Interaction Experiments Reveal Rapid Microstructural and Chemical Changes at Lower Crustal Conditions

ABSTRACTThe reactive flow of melt through the mantle or crust triggers chemical disequilibrium, driving reactions that significantly alter the mineral assemblages and physical properties of host rocks. However, the degrees of chemical difference required to initiate these reactions and their timescale remain poorly understood. In this study, we present piston–cylinder reaction experiments simulating lower crustal conditions, where largely anhydrous lower crustal granoblastic dioritic gneiss interacts with a hydrous mafic melt, created from the same gneiss but modified by the addition of ~6‐wt.% H2O. Remarkably, reactions occurred within just 12 h, producing microstructures that closely resemble those observed in natural, melt‐fluxed rocks from the lower arc crust in Fiordland, New Zealand. Melt–rock interactions led to the formation of epitaxial, multilayer symplectic coronae of pargasite + plagioclase or quartz partially replacing pre‐existing pyroxene grains. The protolith plagioclase and amphibole are either completely dissolved into the melt or replaced by a modified composition of the same mineral. The melt exhibits compositional variations that correlate with distance from the melt–rock reaction front. Quenched melt chemistry data demonstrate the potential for melt compositions to continuously evolve in response to both crystallisation and melt–rock interactions during reactive flow. Importantly, our findings reveal that melt–rock reactions, initiated by melt not drastically different from the solid rock (protolith), can induce significant changes in rock composition and thus physical properties in a short time. Our findings have broad implications for understanding the compositional evolution of migrating melts and the chemical and mechanical evolution of the Earth's mantle and lower crust in general.

Redox Melting of Garnet Lherzolite: Generation of Carbonated Silicate and Sulfide Melts and Implications for OIB Formation From Chalcophile and Redox‐Sensitive Elements

AbstractUpwellings in the Earth's mantle become sufficiently oxidizing for ‐induced redox melting at depths equivalent to ∼8–5 GPa, generating deep incipient mantle melts. This study simulates the geochemistry of the redox melting process by conducting multi‐anvil experiments at 5 GPa and slightly superadiabatic 1,450°C. By stepwise increasing the oxygen content in a graphite‐ and sulfide‐saturated bulk silicate Earth (BSE)‐like composition, sulfide and carbonated silicate melts were produced and coexist with garnet olivine orthopyroxene clinopyroxene. Carbonated silicate melts contain 31–38 wt.% , 9–17 wt.% , 270–475 ppm S and have an of 0.75–0.77; the sulfide melts have molar metal/(S + O) and Ni/(Fe + Ni) ratios of 1.08–1.23 and 0.59–0.69, respectively. The experiments were doped with chalcophile and/or redox‐sensitive trace elements to derive mineral/carbonated silicate melt/sulfide melt partition coefficients. Sulfide melt/carbonated silicate melt partition coefficients are lithophile for Ga, P, V, Mn, Ge, Cr, Zn and In increasing in this sequence from 0.005 to 0.9, and chalcophile for Cd, Mo, Sn, Tl, Pb, Co, Sb, As, Ni, Bi, Se and Te, increasing from 3 to ∼6000. We use our data to model trace element concentrations in incipient redox melts and apply our results to ocean island basalt (OIB) genesis. Our redox melting model suggests that average concentrations of most trace elements in primitive and Si‐undersaturated OIBs can be well explained by 1%–2% melting of sulfide‐saturated depleted mantle mixed with 10–20 wt.% of recycled oceanic crust that includes minor sediment when retaining some sulfide melt in the source.

Barium Isotope Fingerprint for Recycled Ancient Sediment in the Source of EM1‐Type Continental Basalts

AbstractThe origin of enriched mantle 1 (EM1) endmember, characterized by low 206Pb/204Pb and 143Nd/144Nd ratios in ocean island basalts, has long been debated. This is because melting of surrounding peridotite, together with the EM1 component, can dilute the “EM1 fingerprints” in these rocks. Here, we present barium isotope data for well‐characterized EM1‐type continental basalts from northeast China to constrain their nature and origin. Our results show that these basalts have δ138/134Ba values ranging from −0.1‰ to 0.08‰, which are lower than the depleted MORB mantle. Correlations between δ138/134Ba and K/U, Ba/Th, U/Pb, εNd and 206Pb/204Pb suggest a heterogeneous source involving binary mixing between the lithospheric mantle and an EM1 component. The EM1 component, characterized by light δ138/134Ba and low 206Pb/204Pb ratios, can be attributed to the addition of recycled ancient sediments to the source. This study indicates that Ba isotopes have potential to trace crustal material recycling into Earth's deep mantle.

Modeling of shock wave loading FeO to 1000 GPa

Iron oxide, FeO, is one of the main rock-forming oxides. Research into its thermophysical properties under high-energy loading is necessary to construct an equation of state that is used in modeling the properties of Earth's mantle and core as well as other celestial bodies. The results of calculations of thermodynamic properties of FeO under shock compression up to 1000 GPa are presented. In the phase transition field, calculations for FeO are performed as a mixture of low- and high-pressure phases based on the assumption that components of the mixture are in thermodynamic equilibrium under shock wave loadings. The conditions at the wave front are expressed in Rankin–Hugoniot ratios that express conservation of mass, momentum, and energy. Conservation conditions for momentum and energy flow are written for the mixture overall, while conservation conditions for mass flow are written separately for each component. Supplementing the obtained expressions with the condition of equality of the component temperature values and the equations of state for each component, shock adiabatic curves for a heterogeneous material are obtained. This method allows us to accurately describe the shock-wave loading of FeO, including in the phase transition region. Verification of simulation results is carried out using data obtained from experiments and calculations by other researchers. The considered technique is useful for calculations of similarly complex materials.

Thermoelastic Properties of Iron‐Rich Ringwoodite and the Deep Mantle Aerotherm of Mars

AbstractThe Martian mantle is considered to have a higher Fe/Mg ratio than the Earth's mantle. Ringwoodite, γ‐(Mg,Fe)2SiO4, is likely the dominant polymorph of olivine in the core‐mantle boundary (CMB) region of Mars. We synthesized anhydrous iron‐rich ringwoodite with molar Mg/(Mg + Fe) = 0.44 and determined its thermal equation of state up to 35 GPa and 750 K by synchrotron X‐ray diffraction. Using a third order Birch‐Murnaghan equation of state, we obtain KT0 = 182 (3) GPa, K′ = 4.6 (2), and α0 = 3.18 (6) × 10−5 K−1. Using these results and an updated mineralogical model with an iron‐rich composition of Mg/(Mg + Fe) = 0.75 for the Martian mantle, we estimate ∼1900 K for the temperature of the D1000 seismic discontinuity inside Mars. The resulting adiabat predicts a warm aerotherm, which could explain the presence of partial melt at the CMB of Mars recently detected with seismic data from the 2019 InSight mission.

Unveiling pressure-induced anomalous shear behavior and thermoelasticity of α-Fe2O3 hematite at high pressure.

Unveiling pressure-induced anomalous shear behavior and thermoelasticity of α-Fe2O3 hematite at high pressure.

Constraining the parameters of the Andrade rheology in Earth's mantle with Love numbers of 12 tidal constituents

Constraining the parameters of the Andrade rheology in Earth's mantle with Love numbers of 12 tidal constituents

Strong precursor softening in cubic CaSiO3 perovskite

CaSiO[Formula: see text] perovskite (CaPv) is the last major mineral in the Earth's lower mantle whose elasticity remains largely unresolved. Here, we investigate the elasticity of CaPv using ab initio machine-learning force fields (MLFF). At room temperature, the elasticity of tetragonal CaPv determined by MLFF molecular dynamics (MD) agrees well with experimental measurements after considering temperature induced variations in the hydrostatic structure, proving the effectiveness of the method. We use the MLFF MD in the [Formula: see text] ensemble to establish the tetragonal-cubic phase boundary and confirm that in the lower mantle CaPv is in the cubic phase. The elasticity of cubic CaPv shows distinct temperature dependence at different ranges: it is linear at high temperatures, whereas it exhibits anomalous precursor softening near the tetragonal-cubic phase boundary. The temperature interval of precursor softening widens as the pressure increases and overlaps with the temperature profile of subducted cold slabs near the core-mantle boundary. While cubic CaPv is seismically invisible along the average mantle geotherm, it may induce low-velocity zones with negative temperature anomaly, leading to the view that the large low shear velocity provinces (LLSVPs) may be caused by subducted oceanic crust rich in CaPv with temperature lower than ambient mantle. A cool, rigid LLSVP may help explain the preferential formation of mantle plumes at its margins, as well as its weaker seismic anisotropy.

Spherically symmetric Earth models yield no net electron spin

Terrestrial experiments that use electrons in Earth as a spin-polarized source have been demonstrated to provide strong bounds on exotic long-range spin-spin and spin-velocity interactions. These bounds constrain the coupling strength of many proposed ultralight bosonic dark-matter candidates. Recently, it was pointed out that a monopole-dipole coupling between the Sun and the spin-polarized electrons of Earth would result in a modification of the precession of the perihelion of Earth. Using an estimate for the net spin polarization of Earth and experimental bounds on Earth’s perihelion precession, interesting constraints were placed on the magnitude of this monopole-dipole coupling. Here we investigate the spin associated with Earth’s electrons. We find that there are about 6×1041 spin-polarized electrons in the mantle and crust of Earth oriented antiparallel to their local magnetic field. However, when integrated over any spherically symmetric Earth model, we find that the vector sum of these spins is zero. In order to establish a lower bound on the magnitude of the net spin along Earth’s rotation axis we have investigated three of the largest breakdowns of Earth’s spherical symmetry: the large low shear-velocity provinces of the mantle, the crustal composition, and the oblate spheroid of Earth. From these investigations we conclude that there are at least 5×1038 spin-polarized electrons aligned antiparallel to Earth’s rotation axis. This analysis suggests that the bounds on the monopole-dipole coupling that were extracted from Earth’s perihelion precession need to be relaxed by a factor of about 2000. Published by the American Physical Society 2025

A method for simultaneously determining Earth's magnetic field and mantle conductivity models using MSS-1 and Swarm satellite magnetic data

A method for simultaneously determining Earth's magnetic field and mantle conductivity models using MSS-1 and Swarm satellite magnetic data