Earth's Mantle Research Articles

Modeling liquid transport in the Earth's mantle as two-phase flow: effect of an enforced positive porosity on liquid flow and mass conservation

Abstract. Fluid and melt transport in the solid mantle can be modeled as a two-phase flow in which the liquid flow is resisted by the compaction of the viscously deforming solid mantle. Given the wide impact of liquid transport on the geodynamical and geochemical evolution of the Earth, the so-called “compaction equations” are increasingly being incorporated into geodynamical modeling studies. When implementing these equations, it is common to use a regularization technique to handle the porosity singularity in the dry mantle. Moreover, it is also common to enforce a positive porosity (liquid fraction) to avoid unphysical negative values of porosity. However, the effects of this “capped” porosity on the liquid flow and mass conservation have not been quantitatively evaluated. Here, we investigate these effects using a series of 1- and 2-dimensional numerical models implemented using the commercial finite-element package COMSOL Multiphysics®. The results of benchmarking experiments against a semi-analytical solution for 1- and 2-D solitary waves illustrate the successful implementation of the compaction equations. We show that the solutions are accurate when the element size is smaller than half of the compaction length. Furthermore, in time-evolving experiments where the solid is stationary (immobile), we show that the mass balance errors are similarly low for both the capped and uncapped (i.e., allowing negative porosity) experiments. When Couette flow, convective flow, or subduction corner flow of the solid mantle is assumed, the capped porosity leads to overestimations of the mass of liquid in the model domain and the mass flux of liquid across the model boundaries, resulting in intrinsic errors in mass conservation even if a high mesh resolution is used. Despite the errors in mass balance, however, the distributions of the positive porosity and peaks (largest positive liquid fractions) in both the uncapped and capped experiments are similar. Hence, the capping of porosity in the compaction equations can be reasonably used to assess the main pathways and first-order distribution of fluids and melts in the mantle.

Halogen Cycling in the Solid Earth

Each of the halogens constrains a different aspect of volatile cycling in the solid Earth. F is moderately incompatible in the mantle and has a low mobility at Earth's surface, meaning that it is preferentially retained in the mantle and continental crust. In contrast, Cl, Br, and I are strongly incompatible and highly soluble. Chloride is the dominant anion in seawater and many geofluids and a major component of evaporite minerals. Br and I are essential for life and significantly incorporated into organic matter that accumulates in marine sediments. Surficial fluids circulated into continental and oceanic crust incorporate surface-derived halogens into alteration minerals. As a result, subducting slabs and arc lavas are weakly enriched in F and strongly enriched in Cl, Br, and I. Subduction has maintained mantle Cl and Br concentrations at relatively constant levels since Earth's early differentiation, but mantle I/Cl has decreased over time. ▪Halogen abundances on the early Earth were affected by I partitioning into Earth's core and possible loss of hydrophilic Cl, Br, and I in an early formed ocean.▪Halogens are powerful tracers of subduction zone processes on the modern Earth, with Cl, Br, and I having a dominantly subducted origin in Earth's mantle.▪The deep subduction cycles of Cl, Br, and I are more similar to that of H2O than they are to F, but the geochemical cycle of each halogen differs in detail.▪Halogen abundance ratios and stable isotope ratios vary systematically in Earth's surface reservoirs, meaning that halogens are powerful tracers of geological fluids and melts.

Retraction of: Self-consistent models of Earth's mantle and core from long-period seismic and tidal constraints

Retraction of: Self-consistent models of Earth's mantle and core from long-period seismic and tidal constraints

Pb-изотопная систематика битумов, керогенов и нефтей: от изохронных и дискретных источников до протяженных трендов глобальных компонентов

The paper presents a review of Pb isotope data on bitumens, kerogens, and oils. The diagrams of Pb isotopes distinguish isochron families, discrete clusters, and continuous extended trends of data points. Arguments are given in favor of Pb isotopic homogenization with the output of isochron Pb–Pb dating under hydrothermal conditions during lead separation from uranium into ore minerals simultaneously with the enrichment of bitumen with uranium. From families of data points of oils and kerogen, the Pb isotope diagrams reveal discreteness of source components that have not undergone general Pb isotopic homogenization under catagenesis conditions. Continuous, extended trends in Pb isotopes are identified and interpreted in terms of the global evolution of the Earth's mantle and crust. For oils from Europe and adjacent marine areas, Pb-isotope mixture of components is determined. In North Sea, mixing between Precambrian basement rocks and Jurassic black shales is traced that demonstrates a common European oil component (CEOC) that has a high μ (238U/204Pb) – HIMU and significantly different from the common mantle reservoir (CMR) of intraplate volcanic rocks from Europe with adjacent Africa and Arabia. In contrast to this relationship between components, extended trends of oils from the Liaohe field of Northeast China are similar to those of the ELMU and LOMU mantle components of the Cenozoic volcanic rocks from Asia. It is suggested that bitumen, kerogens, and oils of this field are generated by deep mantle fluid flows. The review was done in frame of the interactive preparation of a paper with master's students of the Geological Faculty of Irkutsk State University.

TO THE 60TH ANNIVERSARY OF THE DEPARTMENT OF EARTH SCIENCES OF THE NATIONAL ACADEMY OF SCIENCES OF UKRAINE. Part 1. Historical outline of the development of natural sciences from the founding of the Academy of Sciences of Ukraine to the establishment of the Department of Earth and Space Sciences of the Academy of Sciences of the Ukrainian SSR (1918–1962)

The history of the formation and development of Earth sciences since the founding of the Ukrainian Academy of Sciences (UAS) contains a significant amount of factual material. Taking into account the limitation of the volume of the journal publication, the authors divided the chronological review of the history of natural sciences in the system of the Academy dedicated to the 60th anniversary of the Department of Earth Sciences of the National Academy of Sciences of Ukraine into three parts. In the first part, the main historical events in dates, facts and personalities of the formation and development of the natural sciences of Ukraine from the founding of the Ukrainian Academy of Sciences in 1918 to the organizational and structural formation of the Department of Earth and Space Sciences of the Academy of Sciences of the Ukrainian SSR in 1963 are listed in chronological order. In the second and third parts, the formation and development of scientific institutions of the Department of Earth Sciences are considered in accordance with (1963–1990) and after (1991–2023), i.e., the acquisition of independence by Ukraine, as well as brief information about the achievements of the members of the Academy. Scientists-naturalists from the moment of establishment of UAS and during its first 45 years passed all stages of its formation and development. Among the outstanding achievements, which became a unique contribution to the development of natural sciences during this period, the following should be included: (a) the substantiation of a new theoretical direction in geological science – tectoorogeny, the doctrine of the Earth's tectonosphere, (b) the beginning of the creation of the concept of the abiogenic (inorganic) origin of oil and gas at extremely high temperatures and pressures in the Earth's upper mantle, (c) studying the deep structure of the Earth’s crust and the upper mantle of the territory of Ukraine by geophysical methods. The above list of key achievements includes only breakthrough ideas and theories. In the text of the article, the content and significance of the main achievements of natural scientists of the Academy are considered in the given biographical references about their authors.

Robust estimates of the ratio between S- and P-wave velocity anomalies in the Earth's mantle using normal modes

Robust estimates of the ratio between S- and P-wave velocity anomalies in the Earth's mantle using normal modes

Partitioning of nickel and cobalt between metal and silicate melts: Expanding the oxy-barometer to reducing conditions

Partitioning of nickel and cobalt between metal and silicate melts: Expanding the oxy-barometer to reducing conditions

Fossil hydrothermal oceanic systems through in-situ B isotopes in ophicarbonates (N. Apennines, Italy)

Fossil hydrothermal oceanic systems through in-situ B isotopes in ophicarbonates (N. Apennines, Italy)

Davemaoite as the mantle mineral with the highest melting temperature.

Knowledge of high-pressure melting curves of silicate minerals is critical for modeling the thermal-chemical evolution of rocky planets. However, the melting temperature of davemaoite, the third most abundant mineral in Earth's lower mantle, is still controversial. Here, we investigate the melting curves of two minerals, MgSiO3 bridgmanite and CaSiO3 davemaoite, under their stability field in the mantle by performing first-principles molecular dynamics simulations based on the density functional theory. The melting curve of bridgmanite is in excellent agreement with previous studies, confirming a general consensus on its melting temperature. However, we predict a much higher melting curve of davemaoite than almost all previous estimates. Melting temperature of davemaoite at the pressure of core-mantle boundary (~136 gigapascals) is about 7700(150) K, which is approximately 2000 K higher than that of bridgmanite. The ultrarefractory nature of davemaoite is critical to reconsider many models in the deep planetary interior, for instance, solidification of early magma ocean and geodynamical behavior of mantle rocks.

CO2‐Undersaturated Melt Inclusions From the South West Indian Ridge Record Surprisingly Uniform Redox Conditions

AbstractThe behavior of Fe3+ during mantle partial melting strongly influences the oxidation state of the resulting magmas, with implications for the evolution of the atmosphere's oxidation state. Here, we challenge a prevailing view that low‐degree partial melts are more oxidized due to the incompatible behavior of Fe3+. Our study is based on measurements of Fe3+/∑Fe along with major, minor, trace and volatile elements in olivine‐ and plagioclase‐hosted melt inclusions of CO2 undersaturated mantle melts in South West Indian Ridge lava. These inclusions record minimum entrapment pressures equivalent to depths up to 10 km below the seafloor, record magma ascent rates of 0.03–0.19 m/s, and display exceptionally high CO2/Ba, CO2/Rb, and CO2/Nb ratios, indicative of a CO2‐rich mantle source. Accounting for fractional crystallization, we find a uniform melt oxidation state (with an Fe3+/ΣFe at 0.140 ± 0.005 at MgO = 10 wt.%) that displays no systematic variation with major, minor, volatile or trace element contents, thus providing no evidence for a relationship between the degree of partial melting and Fe3+/ΣFe. This can be explained by efficient buffering of Fe3+/∑Fe and fO2 of mid‐ocean ridge basalt melts by their surrounding mantle and/or a decrease in the bulk peridotite‐melt Fe2O3 partition coefficient with increasing partial melting. We conclude that changes in the Earth's upper mantle temperature over geological time need not have affected the oxidation state of volcanic products or of the atmosphere.

Partial melt composition of enstatite chondritic mantle around the rheological transition at 23 GPa: Implications for the chemical differentiation of the Earth's mantle

Partial melt composition of enstatite chondritic mantle around the rheological transition at 23 GPa: Implications for the chemical differentiation of the Earth's mantle

Calcium isotopes track volatile components in the mantle sources of alkaline rocks and associated carbonatites

The volatile components CO2 and H2O induce mantle melting and thus exert major controls on mantle heterogeneity. Primitive intraplate alkaline magmatic rocks are the closest analogues for incipient mantle melts and provide the most direct method to assess such mantle heterogeneity. Given the considerable Ca isotope differences among carbonate, clinopyroxene, garnet, and orthopyroxene in the mantle (up to 1 ‰ for δ44/40Ca), δ44/40Ca of alkaline rocks is a promising tracer of lithological heterogeneity. We present stable Ca isotope data for ca. 1.4 Ga lamproites, 590–555 Ma ultramafic lamprophyres and carbonatites, and 142 Ma nephelinites from Aillik Bay in Labrador, eastern Canada. These primitive alkaline rock suites are the products of three stages of magmatism that accompanied lithospheric thinning and rifting of the North Atlantic craton. The three discrete magmatic events formed by melting of different lithologies in a metasomatized lithospheric mantle column at various depths: (1) MARID-like components (mica-amphibole-rutile-ilmenite-diopside) in the source of the lamproites; (2) phlogopite-carbonate veins were an additional source component for ultramafic lamprophyres during the second event; and (3) wehrlites at shallower depths were an important source component for nephelinites during the final event.The Mesoproterozoic lamproites show lower δ44/40Ca values (0.58 to 0.66 ‰) than MORBs (0.84 ± 0.03 ‰, 2se). This cannot be explained by fractional crystallization or melting of the clinopyroxene-dominated source but can be attributed to a source enriched in the alkali amphibole K-richterite, which has characteristically low δ44/40Ca. The δ44/40Ca values of the ultramafic lamprophyre suite during the second rifting stage are remarkably uniform, with overlapping ranges for primary carbonated silicate melts (aillikite: 0.67 to 0.75 ‰), conjugate carbonatitic liquids (0.71 to 0.82 ‰) and silicate-dominated damtjernite liquid (primary damtjernite: 0.68 to 0.72 ‰). This suggests negligible Ca isotope fractionation during liquid immiscibility of carbonate-bearing magmas. Combined with previously reported δ44/40Ca values for carbonatites and kimberlites, our data suggest that carbonated silicate melts in Earth's mantle have δ44/40Ca compositions resolvably lower than those for MORBs (0.74 ± 0.02 ‰ versus 0.84 ± 0.03 ‰, 2se). The δ44/40Ca values of the Cretaceous nephelinites (0.72 to 0.78 ‰) are homogenous and similar to those of the 590–555 Ma ultramafic lamprophyres, suggesting that the wehrlitic source component for the nephelinites formed by mantle metasomatism during interaction with rising aillikite magmas during the second rifting stage. Our results highlight that both K-richterite and carbonate components in mantle sources can result in the systematically low δ44/40Ca values of alkaline magmas, which may explain previously reported low δ44/40Ca values of alkaline rocks and some carbonatites. Our study indicates that Ca isotopes are a robust tracer of lithological variation caused by volatiles in the Earth's upper mantle.

Linking rates of slab sinking to long-term lower mantle flow and mixing

Numerical models of Earth's mantle dynamics that aim to comply with a variety of surface observations and/or modern mantle structure, still predict a widely varying vigour of mantle flow which governs the long-term evolution of mantle structure and mixing. A yet unexplored source of intrinsic information on mantle flow characteristics are the geologically reconstructed average slab sinking rates. Here we evaluate from numerical experiments how average slab sinking rates relate to the vigour of mantle convection and mixing. We use a simplified mantle convection model and show that long-term mantle flow velocity and mixing is strongly sensitive to slab sinking rates. Models tuned to match lower mantle average sinking rates of 10–15 mm/a, yield lower mantle convection rates of only several mm/a. Furthermore, they reveal large unmixed regions in the mid-mantle which preserve 25% of ‘primordial’ lower mantle material after 1000 Ma, which may explain geochemical observations from hotspot volcanoes.

A redox effect on the viscosity of molten pyrolite

The viscosity of molten Earth mantle has been determined for various redox states using very high temperature viscometry at 1 bar. The viscosity-temperature relationship of the most oxidised pyrolite studied here is comparable to that of a previous determination of the viscosity of a peridotite melt. For the first time, the effect of iron redox state on molten mantle viscosity has been determined by calorimetric analysis of the glass transition on extremely carefully characterised glassy samples quenched from conditions of variable fO2 using gas-mixing levitation. There is a clear trend of decreasing viscosity with increasing redox state over the range of Fe3+/ΣFe. = 0.07–0.29. We also observe an increase in glass transition temperatures with increasing melt depolymerisation (i.e., higher NBO/T ratios). Both the negative oxidation dependence of viscosity and glass transition behaviour upon depolymerisation are contradictory to the trends observed from redox viscometry of more silica-rich melts but may be consistent with the broadly diminishing positive redox viscometry trends of melts with increasing basicity.

Heavy Mo isotope enrichment in the Pitcairn plume: Implications for the subduction cycle of anoxic sediments

Heavy Mo isotope enrichment in the Pitcairn plume: Implications for the subduction cycle of anoxic sediments

The Moon-Forming Impact and the Autotrophic Origin of Life.

The Moon-forming impact vaporized part of Earth's mantle, and turned the rest into a magma ocean, from which carbon dioxide degassed into the atmosphere, where it stayed until water rained out to form the oceans. The rain dissolved CO2 and made it available to react with transition metal catalysts in the Earth's crust so as to ultimately generate the organic compounds that form the backbone of microbial metabolism. The Moon-forming impact was key in building a planet with the capacity to generate life in that it converted carbon on Earth into a homogeneous and accessible substrate for organic synthesis. Today all ecosystems, without exception, depend upon primary producers, organisms that fix CO2 . According to theories of autotrophic origin, it has always been that way, because autotrophic theories posit that the first forms of life generated all the molecules needed to build a cell from CO2 , forging a direct line of continuity between Earth's initial CO2 -rich atmosphere and the first microorganisms. By modern accounts these were chemolithoautotrophic archaea and bacteria that initially colonized the crust and still inhabit that environment today.

Automated shear-wave splitting analysis for single- and multi- layer anisotropic media

Shear-wave velocity anisotropy is present throughout the earth. The strength and orientation of anisotropy can be observed by shear-wave splitting (birefringence) accumulated between earthquake sources and receivers. Seismic deployments are getting ever larger, increasing the number of earthquakes detected and the number of source-receiver pairs. Here, we present a new Python software package, SWSPy, that fully automates shear-wave splitting analysis, useful for large datasets. The software is written in Python, so it can be easily integrated into existing workflows. Furthermore, seismic anisotropy studies typically make a single-layer approximation, but in this work we describe a new method for measuring anisotropy for multi-layered media, which is also implemented. We demonstrate the performance of SWSPy for a range of geological settings, from glaciers to Earth's mantle. We show how the package facilitates interpretation of an extensive dataset at a volcano, and how the new multi-layer method performs on synthetic and real-world data. The automated nature of SWSPy and the discrimination of multi-layer anisotropy will improve the quantification of seismic anisotropy, especially for tomographic applications. The method is also relevant for removing anisotropic effects, important for applications including full-waveform inversion and moment magnitude analysis.

Subcretion of altered oceanic crust beneath the SW São Francisco Craton, Brazil – A stable isotope study on diamonds and their inclusions

Subcretion of altered oceanic crust beneath the SW São Francisco Craton, Brazil – A stable isotope study on diamonds and their inclusions

Barium isotope compositions of altered oceanic crust from the IODP Site 1256 at the East Pacific rise

Barium isotope compositions of altered oceanic crust from the IODP Site 1256 at the East Pacific rise

Vestiges of impact-driven three-phase mixing in the chemistry and structure of Earth’s mantle

Highly siderophile elements (HSEs; namely Ru, Rh, Pd, Re, Os, Ir, Pt, and Au) in Earth's mantle require the addition of metals after the formation of Earth's core. Early, large collisions have the potential to deliver metals, but the details of their mixing with Earth's mantle remain unresolved. As a large projectile disrupts and penetrates Earth's mantle, a fraction of its metallic core may directly merge with Earth's core. Ensuing gravitational instabilities remove the remaining projectile's core stranded in Earth's mantle, leaving the latter deprived of HSEs. Here, we propose a framework that can efficiently retain the metallic components during large impacts. The mechanism is based on the ubiquitous presence of a partially molten region in the mantle beneath an impact-generated magma ocean, and it involves rapid three-phase flow with solid silicate, molten silicate, and liquid metal as well as long-term mixing by mantle convection. In addition, large low-shear-velocity provinces in the lower mantle may originate from compositional heterogeneities resulting from the proposed three-phase flow during high-energy collisions.