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The InSight mission deployed one seismic station on Mars, providing a chance to apply single‐station‐based autocorrelation analysis to investigate Martian subsurface structures. However, recent analysis indicated the low‐frequency autocorrelation signals may originate from quasi‐periodic high‐amplitude instrumental "glitches" rather than the reflection response of deep Mars. In this study, we detected and removed these high‐amplitude glitches in raw seismic data and employed autocorrelation on the clean vertical component waveforms filtered between 0.05 and 0.1 Hz. We observed signals at the expected times for the olivine‐wadsleyite transition and core‐mantle boundary (CMB) as estimated by other methods. This result suggests that the low‐frequency autocorrelation signals are the reflection response from the olivine‐wadsleyite transition in the mantle and the Martian CMB region, rather than a noise phenomena. A grid search method to fit the observed PcP waveform was used to identify a layer intermediate in velocity between the Martian mantle and core at the Martian CMB. Plain Language Summary: The InSight mission deployed one seismic station on Mars at the end of 2018 to measure the interior structure of Mars. A recent study autocorrelated the InSight ambient noise data to retrieve reflection signals from subsurface discontinuities. Two seismic signals that reflected from deep within Mars, the olivine‐wadsleyite transition, a pressure‐temperature dependent mineral phase change in the mantle, and the core‐mantle boundary (CMB), are observed. However, some analyses suggested that the arrival times of these signals coincide with the recurrence time of high‐amplitude glitches within the raw seismic data, leading to an incorrect interpretation of the autocorrelation function (ACF). To resolve this issue, we detected and removed the high‐amplitude glitches before further processing the ambient noise data. The autocorrelation analysis of clean continuous vertical‐component waveforms recovers signals at times corresponding to the olivine‐wadsleyite transition and CMB, whereas ACF of glitch‐only waveforms does not. This suggests that signals on the low‐frequency ACF are from the seismic discontinuities at olivine‐wadsleyite transition and CMB rather than being noise artifacts. We further identified velocity layering near Martian CMB by matching the complexity of the PcP signal observed in the ACF of clean data set with synthetic seismograms. Key Points: Autocorrelation of clean Seismic Experiment for Interior Structure waveforms recovers the prominent signals reflected from deep MarsThe autocorrelation tests on raw, clean and glitch‐only data suggest the signals identified are from deep Mars rather than instrumental noiseA velocity transition model of the Martian core‐mantle boundary better fits the observed PcP phase than a sharp velocity drop [ABSTRACT FROM AUTHOR]

Major and trace element abundances, including highly siderophile elements, and 187Os and 182W isotopic compositions were determined for ca. 89 Ma mafic and ultramafic rocks from the islands of Gorgona (Colombia) and Curaçao (Dutch Caribbean). The volcanic systems of both islands were likely associated with a mantle plume that generated the Caribbean Large Igneous Provence. The major and lithophile trace element characteristics of the rocks examined are consistent with the results of prior studies, and indicate derivation from both a chemically highly-depleted mantle component, and an enriched, or less highly-depleted mantle component. Highly siderophile element abundances for these rocks are generally similar to rocks with comparable MgO globally, indicating that the major source components were not substantially enriched or depleted in these elements. Rhenium-Os isotopic systematics of most rocks of both islands indicate derivation from a mantle source with an initial 187Os/188Os ratio between that of the contemporaneous average depleted mid-ocean ridge mantle and bulk silicate Earth. The composition may reflect either an average lower mantle signature, or global-scale Os isotopic heterogeneity in the upper mantle. Some of the basalts, as well as two of the komatiites, are characterized by calculated initial 187Os/188Os ratios 10–15 % higher than the chondritic reference. These more radiogenic Os isotopic compositions do not correlate with major or trace element systematics, and indicate a mantle source component that was most likely produced by either sulfide metasomatism or ancient Re/Os fractionation. Tungsten-182 isotopic compositions measured for rocks from both islands are characterized by variable μ182W values ranging from modern bulk silicate Earth-like to strongly negative values. The μ182W values do not correlate with major/trace element abundances or initial 187Os/188Os compositions. As with some modern ocean island basalt systems, however, the lowest μ182W value (−53) measured, for a Gorgona olivine gabbro, corresponds with the highest 3He/4He previously measured from the suite (15.8 R/R A). Given the lack of correlation with other chemical/isotopic compositions, the mantle component characterized by negative μ182W and possibly high 3He/4He is most parsimoniously explained to have formed as a result of isotopic equilibration between the mantle and core at the core-mantle boundary. [ABSTRACT FROM AUTHOR]

Studies of ocean island basalts have identified a Prevalent Mantle (PREMA) component as a fundamental feature of mantle geochemical arrays; however, its origin and distribution are highly controversial, including its potential link to plumes sourced in low-shear-wave velocity provinces (LLSVPs) above the core-mantle boundary. In this study, we interrogate the compositional systematics of ~ 3500 Cenozoic oceanic and continental sodic basalts to provide insights into the origin and distribution of PREMA. We find that low-degree basaltic melts with high Nb concentrations located away from deep-mantle plumes have PREMA-like Sr-Nd-Hf isotopic signatures, implying that PREMA is highly fusible and not exclusively associated with LLSVPs. Geochemical modelling and mantle convection simulations indicate that PREMA could have been generated soon after Earth accretion, experiencing only minimal melting or enrichment, and then scattered throughout the upper mantle, rather than being the result of mixing between depleted and enriched mantle components. PREMA, the highly fusible Prevalent Mantle now found throughout the mantle, may have been generated soon after Earth's accretion with minimal subsequent modification, according to a combination of composition data from Cenozoic sodic basalts and mantle convection simulations [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Khangai plume is situated under Central and Eastern Mongolia and is a mantle volume with significantly reduced longitudinal (P) wave velocities. The plume has been identified as a result of the analysis of the MITP08 volumetric model of P-wave velocity variations, representing the deviations of P-wave velocities from the average values (δVp), given as a percentage. The lithospheric mantle is thinned to ca. 50 km above the plume. Especially low velocities (δVp ≤ –0.6%) are found in the sublithospheric mantle up to a depth of 400 km. The main body of the plume is located under the Khangai Highland and extends northward to the edge of Southern Siberia. The Khentei branch of the plume that is located SE of the Khentei Highland is connected with the main plume body at depths of 800–1000 km. Branches of the plume and its Khentei branch extend into Transbaikalia. The area of the plume decreases with depth, and its deepest part (1250–1300 km) is located under the southern Khangai Highland. The main body of the Khangai plume is expressed on the land surface by the Cenozoic uplift reaching 3500–4000 m in the southern Khangai Highland. From the SE, the Khangai plume and its Khentei branch territory are limited by Late Cenozoic troughs stretching along the southeastern border of Mongolia. From other sides, the Khangai uplift is bounded by a C-shaped belt of basins. The belt includes the southwestern part of the Baikal Rift Zone, the Tunka and Tuva Basins in the north, the Ubsu-Nur Basin and the Basin of Big Lakes in the west, and the Valley of Lakes in the south. The basins are filled with lacustrine and fluvial deposits of the Late Oligocene to Pliocene. In the Quaternary, the South and Central Baikal Basins, which existed as early as the Early Paleogene, became a part of the Baikal Rift, and the other basins were involved in the general uplift of the region. The structural paragenesis of the Khangai uplift and the surrounding basins is caused by the influence of the Khangai plume. On the territory above the plume, including its Khentei and Transbaikalia branches, the Cenozoic basaltic plume volcanism occurred, inheriting the Cretaceous volcanic manifestations in some places. The structural paragenesis associated with the Khangai plume is combined with the structural paragenesis produced by lithospheric plate interaction. The latter is expressed the best of all by active faults, but developed synchronously to the plume paragenesis. The active fault kinematics shows that the eastern and central parts of the region developed in the transpression conditions and the north-eastern part developed in conditions of extension and transtension. The Khangai plume is connected at depth with the Tibetan plume, which is situated under the central and eastern Tibetan Plateau north of the Lhasa block. The Tibetan plume has the shape of a funnel rising from depths of 1400–1600 km and is accompanied by thinning of the lithosphere and uplift of the land surface. The Khangai and Tibetan plumes represent a specific category of plumes. They rise from the upper Lower Mantle and differ by this from the Upper Mantle plumes and the African and Pacific superplumes rising from the core-mantle boundary. Data are presented on the possible connection of the Khangai and Tibetan plumes with the superplume branches, but independent origin of the plumes is also admitted. [ABSTRACT FROM AUTHOR]

The observed variations in intense geomagnetic flux lobes have a significant impact on regional geomagnetic fields, and produce unique geomagnetic characteristics. To investigate the time‐dependent effect of the Siberian flux lobe on the geomagnetic field in East Asia, we reconstructed a stacked full‐vector paleomagnetic secular variation record (since 2000 BCE) from three sediment cores collected in the Bohai Sea, China. Age models of the studied cores were established through a combination of radiocarbon 14C dating and inter‐profile correlation of mass‐normalized magnetic susceptibility. Rock magnetic results indicate that fine‐grained magnetite is the primary remanent carrier. We found that the paleomagnetic field records in the Bohai Sea correspond more closely with those from the middle latitudes, rather than the low latitudes. This was primarily attributed to the variation of the Siberian flux lobe. This study provides a better understanding of the contrasting patterns of regional geomagnetic fields in East Asia, and emphasizes the significant role played by the Siberian flux intensity lobe in shaping their formation. Plain Language Summary: The Earth's magnetic field is in a constant state of flux, both temporally and spatially, and plays a crucial role in protecting our planet from solar wind and cosmic rays. The long‐term variation of the Earth's magnetic field is closely linked with the magnetic flux patch situated at the core‐mantle boundary. However, our understanding of the evolution of magnetic flux patches has been limited by the use of short‐term instrumental data and discrete archeomagnetic data. In this paper, we reconstruct a ∼4,000‐year high‐resolution full‐vector paleomagnetic record from sediments in the Bohai Sea, China. Our findings reveal a clear contrast in the paleomagnetic variations between the middle and low latitudes of East Asia. We proposed that the Siberian flux intensity lobe likely played an important role in the observed paleomagnetic behavior discrepancy between the low‐ and mid‐latitudes of East Asia. Key Points: A multi‐decadal resolution paleomagnetic record spanning approximately 4,000 years has been derived from sediments in the Bohai Sea, ChinaThe paleomagnetic behavior differs between middle and low latitudes across East Asia, indicating the variation of the Siberian flux lobeThe disparity in inclination between the Chinese and Levantine spikes implies that these spikes arise from separate magnetic flux patches [ABSTRACT FROM AUTHOR]

We present a new data set of nearly 100 earthquakes which show clear evidence of the Hawaiian ultra-low velocity zone (ULVZ) in the S   core-diffracted phase (Sdiff), representing the most comprehensive Sdiff data set of a ULVZ to date. Using a Bayesian inversion approach, as outlined in Martin et al., and a subset of the data set, we characterise the 2-D morphology and velocity of the Hawaiian ULVZ. The results suggest that the ULVZ is smaller than previously estimated, with an elliptical shape, and oriented along the direction of the large low-shear velocity province boundary. Using forward modelling, we infer that the ULVZ has a height of 25 km and shear velocity reduction of 25 %. [ABSTRACT FROM AUTHOR]

Ultra-low velocity zones (ULVZs) are patches of extremely slow seismic velocities on the core–mantle boundary (CMB). Here, we target them using the postcursors to S core-diffracted phases (Sdiff) caused by ULVZs. We use traveltimes of these postcursors to make probabilistic maps using a reversible-jump Markov chain Monte Carlo inversion setup. For the forward model, we extend 2-D wave front tracking (2DWT) software, previously developed for surface wave multipathing studies, to the CMB. The 2DWT is able to model the full multipathing behaviour of Sdiff postcursors and compute arrival times for a given ULVZ input velocity structure on the order of a few CPU seconds, as opposed to 100s of CPU hours required for 3-D full waveform synthetics. We validate the method using synthetic data sets produced by the 2DWT, as well as 3-D full waveform synthetics, using a parametrisation formed from a collection of ellipses. We also test idealistic data coverage versus a case of more realistic coverage. We show ULVZ size and velocity reduction can typically be well recovered, and our maps show the inherent trade-off between these parameters around the edge of the ULVZ. Our method cannot directly constrain ULVZ height; tests show that it underestimates ULVZ velocity reductions and overestimates ellipticity for thinner ULVZs due to neglecting mantle effects. [ABSTRACT FROM AUTHOR]

The Tethyan evolution depicts the continuous process of landmasses separating from the Gondwana continent in the south, drifting northwards, and subsequently colliding with the continents in the north over the past 500 million years. In this process, the Tethyan oceans that formed between the landmass and the southern or northern continents underwent growth, evolution, and eventual closure with the early Cenozoic India-Eurasia collision. However, the Tethyan lithosphere did not disappear but rather continued to evolve after entering into the deep Earth. The current position, morphology, and volume of the subducted Tethyan oceanic slabs in the deep mantle record the latest moment of this continuous evolution, providing critical constraints for Tethyan studies. This paper summarizes and analyzes the results of global-scale whole-mantle seismic tomography in the past nearly two decades, revealing a northwest-southeast seismically high-velocity anomaly, which is linearly distributed at depths of 1000–2000 km beneath the Tethyan realm and referred to as the Tethyan anomaly. By searching for an optimal linear combination of previous global seismic tomographic models to best match the known subducted slabs in the upper mantle, we observe that the Tethyan anomaly extends approximately 8700 km in length and 2600 km in width, exhibiting a parallel structure with northern and southern branches. Combining geological records of oceanic subduction initiation and previous geodynamic studies, this study suggests that the main body of the Tethyan anomaly represents the remnants of the subducted Neo-Tethyan oceanic slabs, which subducted from the Late Jurassic to the early Cenozoic. The northern branch consists of subducted slabs from the Neo-Tethys beneath the southern margin of Eurasia, while the southern branch likely reflects the intra-oceanic subducted slabs of Neo-Tethys during the Cretaceous. The western portion of the Tethyan anomaly may reflect remnants of Paleo-Tethys, while the eastern portion, towards India and the Bay of Bengal, shows signs of subduction towards the core-mantle boundary. Finally, this study discusses the future prospects of whole-mantle seismic tomographic studies focusing on the Tethyan realm. [ABSTRACT FROM AUTHOR]

Temporal trends in the paleomagnetic dipole moment exhibit the property of positive skewness. On average, positive trends are larger and occur less frequently than negative trends over timescales of several tens of kyr. We explore the origin of this property using numerical geodynamo models. A suite of models reveals that skewness arises for a restricted set of boundary conditions. Models driven by heat flow at the top and bottom boundaries exhibit very little skewness, whereas models driven solely by heat flow on the lower boundary produce significant positive skewness. Further increases in skewness occur in the presence of thermal stratification at the top of the core. The level of skewness in the geodynamo models is correlated with estimates of upwelling near the core‐mantle boundary. Sustained upwelling is expected to increase magnetic‐flux expulsion, contributing to higher levels of skewness. Similar behavior is recovered from stochastic models in which the dipole is generated by a random series of cyclonic convection events. Skewness in the stochastic models is quantitatively similar to estimates from the geodynamo models when the average recurrence time of the convection events is 100 years. Extending the stochastic models to the paleomagnetic field implies a longer recurrence time of 1,000 years or more. We interpret this recurrence time in terms of the timing of flux‐expulsion events rather than individual convective events. Abrupt increases in the dipole moment from flux expulsion can produce skewed trends on timescales of tens of kyr. Plain Language Summary: Paleomagnetic observations suggest that the dipole field grows and decays at different rates. Abrupt growth of the dipole is often followed by slower decay, particularly when averaged over short‐period fluctuations. Geodynamo models are capable of reproducing this behavior, but only with a restricted set of the boundary conditions. Many features of the geodynamo models are captured in stochastic models when the dipole generation is represented as a series of cyclonic convection events. The average recurrence time for the cyclonic convection events is the main factor in setting the level of asymmetry. Extending these results to the paleomagnetic field implies a recurrence time of several kyr. Such long recurrence times cannot be attributed to individual convection events when the timescale for fluid to rise through the core is only 100 years. Instead, we attribute the long recurrences times to magnetic‐flux expulsion. Large flux‐expulsion events occurring on kyr timescales are sufficient to account for the observed asymmetry. Key Points: Skewed dipole trends are predicted in geodynamo models under a restricted set of boundary conditionsSkewness in the models is correlated with fluid upwelling and magnetic‐flux expulsion at the core‐mantle boundaryTrends in the paleomagnetic field imply large flux‐expulsion events on millennial timescales [ABSTRACT FROM AUTHOR]

In seismic tomography, traveltime information of seismic body phases is commonly used to invert the seismic velocities of the subsurface structure. At long periods or for later seismic phases, the arrival time of seismic phases lack definitive onset and a direct picking of the absolute arrival time has large uncertainty and reproducibility. A common practice is to estimate the relative delay between the observed and synthetic signals that maximizes the correlation coefficient. For that aim, we must first select appropriate time windows around the candidate signals. To improve the ability to detect and extract weak signals, we develop a new morphological time window selection (MTWS) algorithm that adapts to the shape of signals and has robust performance in automated processing of massive data. The MTWS method consists of two successive steps. First, we detect the major peaks on the waveform envelope using a maximum filter. Secondly, we solve for the beginning and end of the time windows surrounding the peaks straightforwardly from simple geometrical equations. The efficiency and robustness of the MTWS algorithm make it very suitable for automated processing of huge data sets. We demonstrate the implementation of the method with both synthetic and observed long period (20–40 s) SH waves. From ∼100   000 traces of transverse-component seismograms recorded by global seismic networks over the course of a year, we obtain ∼15   000 S diff, ∼7500 ScS and also some ScS multiples. The global map of S diff correlation time delays shows consistent patterns with the shear wave velocity perturbations on the core–mantle boundary in the recent tomographic models. [ABSTRACT FROM AUTHOR]

Based on the first-principles method combined with Special Quasi-random Structures package, we investigated the effects of impurities distributions on the perovskite (Pv)–post-perovskite (PPv) phase transition pressures of Fe- and Al-bearing MgSiO3. 61 different distribution configurations were calculated. The results show that the distribution has marginal effect on the Pv–PPv phase transition pressure of Fe2+-bearing MgSiO3. However, the separate of Al3+Al3+ ions can significantly increase the Pv–PPv phase transition pressure to that higher than the core–mantle boundary (CMB) pressure. In the most disordered structures of Al3+Al3+-bearing case constructed by SQS, the Pv–PPv phase transition pressure is higher than 400 GPa. Based on our previous result, we proposed that only Fe2+-bearing MgSiO3 can induce the discontinuous increase in shear wave velocity at the CMB, while Al3+Al3+-, Fe3+Al3+- and Fe3+Fe3+-bearing MgSiO3 cannot. [ABSTRACT FROM AUTHOR]

The magnetic effects of two similar underwater earthquakes with magnitudes of 6.0 and 7.3, which occurred on March 16, 2022, were considered in (Adushkin et al., 2023). According to the data of INTERMAGNET magnetic observatories, these earthquakes were found to be accompanied (with a delay of ~55 min) by variations in the Earth's magnetic field in the form of a train of quasi-periodic oscillations with an amplitude of ~2–8 nT and a period of ~30 min at distances of ~210 to ~3000 km from the epicenter. It was suggested in the aforementioned study that this magnetic effect is caused by a disturbance of the geodynamo as a result of the impact of seismic waves propagating deep into Earth. This interesting hypothesis requires a detailed discussion from different points of view. A more detailed analysis of the pattern of geomagnetic field disturbance at all latitudes, performed by us, leads to a conclusion that the found quasi-periodic disturbance is a mid-latitude response to auroral electrojet variations and is not related to the earthquake. According to our estimates, variations with a source at the core–mantle interface on a time scale less than one year cannot manifest themselves on the Earth's surface at all. [ABSTRACT FROM AUTHOR]

Mare‐basalt volcanism is concentrated on the lunar nearside. A plausible explanation for this asymmetric distribution is long‐wavelength (spherical harmonic degree‐1) mantle convection driven by upwellings of the overturned ilmenite‐bearing magma ocean cumulates (IBCs). The pattern of lunar mantle convection depends in part on the rheological properties of ilmenite. This study explores the effect of pressure‐dependent ilmenite viscosity on the instability of an overturned IBC layer initially at the core‐mantle boundary and the pattern of lunar mantle convection through three‐dimensional numerical simulations. We show that the convective patterns are sensitive to the activation volume for viscous flow. An effective activation volume of 10 cm3/mol would reduce the internal convection in the overturned IBC layer and promote the hemispherical upwelling. However, when the activation volume is too small, vigorous convection in the overturned IBC layer would inhibit heat from concentrating on one hemisphere. When the activation volume is too large, the size of the upwelling plumes is restricted, preventing a stable long‐wavelength structure in the upper mantle. Decompression melting during asymmetric upwelling would produce the localization of mare basalts on the lunar surface. Plain Language Summary: Titanium‐rich mare basalts are concentrated on the surface of the lunar nearside. This asymmetry in mare basalts on the lunar surface likely holds important clues for the evolution of the Moon and potentially other planetary objects. In this study, we present the first 3D numerical models of convection in the lunar mantle that use pressure‐dependent rheology and assess the importance of such rheology on lunar plume evolution. Our models show that pressure‐dependent rheology can significantly affect lunar plume evolution and that an effective activation volume of 10 cm3/mol produces a hemispherical plume structure relevant to the asymmetric distribution of mare basalts on the lunar surface today. If the activation volume is too small, strong convection would exhaust the heat. If the activation volume is too large, the upwelling plumes would be insufficient. The value of 10 cm3/mol is also consistent with the values determined by recent rock deformation experiments on ilmenite, which is an important mineral found within the lunar mantle. This study highlights the importance of pressure‐dependent rheology on lunar mantle dynamics and likely has important implications for mantle dynamics of other planetary mantles. Key Points: We apply pressure‐dependent ilmenite rheology to mantle convection dynamicsAn effective activation volume of 10 cm3/mol facilitates long‐wavelength convectionIncreased or reduced activation volume leads to different mantle convection evolutions [ABSTRACT FROM AUTHOR]

Heat flux across the core-mantle boundary (CMB) is an important variable of Earth's thermal evolution and dynamics. Seismic tomography provides access to seismic heterogeneities in the lower mantle, which can be related to present-day thermal heterogeneities. Alternatively, mantle convection models can be used to either infer past CMB heat flux or to produce statistically realistic CMB heat flux patterns in self-consistent models. Mantle dynamics modifies the inertia tensor of the Earth, which implies a rotation of the Earth with respect to its spin axis, a phenomenon called true polar wander (TPW). This rotation must be taken into account to link the dynamics of the mantle to the dynamics of the core. In this study, we use two recently published mantle convection models to explore the impact of TPW on the CMB heat flux over long timescales (~ 1 Gyr). One of the mantle convection models is driven by a plate reconstruction, while the other self-consistently produces a plate-like behavior. We compute the geoid in both models to correct for TPW. In the plate-driven model, we compute a total geoid and a geoid in which lateral variations of viscosity and temperature are suppressed above 350 km depth. We show that TPW plays an important role in redistributing the CMB heat flux, notably at short time scales (≤ 10 Myr). Those rapid variations modify the latitudinal distribution of the CMB heat flux, which is known to affect the stability of the magnetic dipole in geodynamo simulations. A principal component analysis (PCA) is computed to obtain the dominant CMB heat flux pattern in the different cases. These heat flux patterns can be used as boundary conditions for geodynamo models as representative of the mantle convection cases studied here. We note that the geoids produced by the two models are widely different from each other and from the observed present-day geoid.Work thus still needs to be done to improve the computation of the geoid in mantle convection models related to plate-tectonics. [ABSTRACT FROM AUTHOR]

SUMMARY: A series of models of the Earth magnetic field and core surface flow have been simultaneously and sequentially co-estimated from year 1999 to 2022. The models were derived from magnetic satellite and ground observatory data using a linear Kalman filter approach and prior statistics based on numerical dynamo simulations. The core field and secular variation model components present the same characteristics as the most recent core field models with slightly higher resolution in time. A principal component analysis of the core surface flow series of models shows that the largest flow variations are observed at high latitudes and under the western part of the Pacific Ocean. Filtering out the flow variation periods longer than ∼11.5 yr leads to a filtered azimuthal flow that presents ∼7 yr periodicities with patterns propagating westward by ∼60° longitude per year. These patterns are present mainly at mid- and equatorial latitudes. They are compatible with a perturbation of the main flow made of small columnar flows with rotation axis intersecting the core–mantle boundary between 10° and 15° latitudes, and flow speed of less than 5 km yr–1. Present at all longitudes, these columnar flows are particularly strong under the Pacific Ocean after 2013. They can also be clearly identified under the Atlantic Ocean from 2005 to 2015. [ABSTRACT FROM AUTHOR]

Thermal conductivity plays an important role in the thermochemical evolution of Earth's mantle. Recent mineral physics studies suggest that the thermal conductivity of the mantle varies with pressure and composition, and this may play an important role in the evolution of the Earth's mantle. Meanwhile, the rheology of the deep mantle is also supposed to be composition-dependent. However, the dynamic influences of these factors remain not well understood. In this study, we performed numerical experiments of thermochemical mantle convection in 2-D spherical annulus geometry to systematically investigate the effects of depth- and composition-dependent thermal conductivity and the compositional viscosity ratio on the long-term evolution of the large thermochemical structure of primordial material in Earth's mantle. Our results show that increasing the depth-dependent thermal conductivity leads to a larger core-mantle boundary (CMB) heat flow and allows the formation of more stable large thermochemical piles (e.g., Large Low Shear Velocity Provinces, LLSVPs); while decreasing the composition-dependent thermal conductivity would slightly destabilize the primordial thermochemical piles, increase the altitude of these piles and the temperature differences between the piles and the ambient mantle. If the primordial mantle material is compositionally more viscous (e.g., 20 times than that of the ambient mantle), the long-term stability of the thermochemical piles of primordial material decreases, and this destabilizing effect will be enhanced by decreasing the composition-dependent thermal conductivity. As a result, the thermochemical piles would be unstable in the core-mantle boundary region. Therefore, our study indicates that the combined effects of depth- and composition-dependent thermal conductivity and compositional viscosity ratio are pronounced to the thermochemical evolution of the mantle. [ABSTRACT FROM AUTHOR]

Carbonate melts have been proposed to exist in the lower mantle, but their interaction with other lower mantle melt compositions is poorly understood. To understand miscibility in the carbonate‐silicate‐metal melt system, we simulate endmember, binary, and ternary melt mixtures and study how their Gibbs free energies of mixing evolve with pressure. We find that carbonate‐metal and carbonate‐silicate melts have miscibility gaps that close with increasing pressure, while silicate‐metal melts are immiscible at all lower‐mantle pressures. Extending this analysis to the core‐mantle boundary, we suggest three miscible melt fields near the endmember carbonate, silicate, and iron melt compositions. Analysis of the densities of these miscible melt compositions indicates that some carbonate‐rich and some silicate‐rich melt compositions are gravitationally stable at the core‐mantle boundary and could be candidate compositions to explain ultra‐low velocity zones. Additionally, we evaluate the speciation of an example immiscible melt composition at various pressures throughout the mantle and identify reduced carbon species that would be expected to form in the melt. Our analysis reveals that a majority of Earth's carbon could have been transported to the core during core‐mantle differentiation and that much of Earth's carbon may be stored in the deep interior today. Plain Language Summary: Understanding the storage and cycling of carbon in the Earth's deep interior improves our knowledge of the Earth's formation and evolution throughout geologic time. Carbon‐bearing melts are candidate phases for carbon storage in the lower mantle and may react and mix with other melt phases at places such as the core‐mantle boundary. The extent of mixing upon reaction is dependent on the thermodynamic properties of the mixture components and determines the possible range of compositions, structures, and densities of multicomponent melt mixtures. To determine possible melt compositions that may arise from mixtures of carbonate, silicate, and iron melts in the lower mantle and their physical and chemical properties, we performed molecular simulations to determine whether a mixture will separate or stay mixed. We find that carbonate melts mix with silicate and iron melts at all lower mantle pressures, and that mixing in the carbonate‐silicate‐iron melt system increases with pressure. Additionally, we find that certain melt mixtures have densities at the core‐mantle boundary that make them candidate compositions to explain ultra‐low velocity zones. Finally, we find that carbon has an affinity for iron that leads to the formation of carbide‐like structures that may have allowed carbon to become sequestered in the Earth's core during core formation. Key Points: Carbonate‐iron and carbonate‐silicate melts have miscibility gaps that close with increasing pressureCarbonate‐silicate‐iron melts may contribute to the existence of ultra‐low velocity zones at the core‐mantle boundaryCarbon's affinity for iron indicates that much of Earth's carbon could have been transported to the core during core‐mantle differentiation [ABSTRACT FROM AUTHOR]

Iron hydride in Earth's interior can be formed by the reaction between hydrous minerals (water) and iron. Studying iron hydride improves our understanding of hydrogen transportation in Earth's interior. Our high-pressure experiments found that face-centered cubic (fcc) FeH x (x ≤ 1) is stable up to 165 GPa, and our ab initio molecular dynamics simulations predicted that fcc FeH x transforms to a superionic state under lower mantle conditions. In the superionic state, H-ions in fcc FeH become highly diffusive-like fluids with a high diffusion coefficient of ∼3.7 × 10−4 cm2 s−1, which is comparable to that in the liquid Fe-H phase. The densities and melting temperatures of fcc FeH x were systematically calculated. Similar to superionic ice, the extra entropy of diffusive H-ions increases the melting temperature of fcc FeH. The wide stability field of fcc FeH enables hydrogen transport into the outer core to create a potential hydrogen reservoir in Earth's interior, leaving oxygen-rich patches (ORP) above the core mantle boundary (CMB). [ABSTRACT FROM AUTHOR]

The inference of fluid motion below the core–mantle boundary from geomagnetic observations presents a highly non-unique inverse problem. We propose a new method that provides a unique local estimate of the velocity field, assuming quasi-geostrophic flow in the core interior (which implies equatorial mirror symmetry) and negligible magnetic diffusion. These assumptions remove the theoretical underdetermination, enabling us to invert for the flow at each point of a spherical grid representing the core surface. The unreliable reconstruction of small-scale flows, which arises because only large-scale observations are available, is mitigated by smoothing the locally estimated velocity field using a Gaussian process regression. Application of this method to synthetic data provided by a state-of-the-art geodynamo simulation suggests that using this approach, the large-scale flow pattern of the core surface flow can be well reconstructed, while the flow amplitude tends to be underestimated. We compare these results with a core flow inversion using a Bayesian framework that incorporates statistics from numerical geodynamo models as prior information. We find that whether the latter method provides a more accurate recovery of the reference flow than the local estimation depends heavily on how realistic/relevant the chosen prior information is. Application to real geomagnetic data shows that both methods are able to reproduce the main features found in previous core flow studies. [ABSTRACT FROM AUTHOR]

The Earth's rotation exhibits periodic variations as a result of gravitational torques exerted by the Sun and the Moon and of angular momentum exchange of the solid Earth with the Earth's atmosphere and hydrosphere. Here, we aim at determining the complementary effect of the deep interior on variations in the length-of-day (LOD) and focus on the influence of topography at the core–mantle boundary (CMB). For this purpose, we have developed an analytical approach for solving the Navier–Stokes equation for global rotational motions and inertial waves, based on and extending the approach of Wu & Wahr (1997). An advantage of the analytical approach is that it allows to identify the frequencies and topographic spherical harmonics degrees and orders where resonance can happen, as well as to quantify the total amplifications in the tidal effects on LOD variations. Although the resonances are found to be sometimes quite near tidal frequencies, we show that they are not sufficiently close to induce significant perturbations in LOD variations, except for two of the tides, the fortnightly and monthly tides Mf and Mm. Our results go beyond the findings of Wu & Wahr (1997), extending them to a much wider range of degrees and orders of topographic coefficients. We show that there is an amplification in Mf and Mm induced by the degree 18-order 10 and by the degree 7-order 1 of the topography, respectively. Our approach is generic in the sense that it can be applied to other orientation changes of the Earth as well as to other planets. [ABSTRACT FROM AUTHOR]

We analyzed the Earth's long-term polar motion using the time series IERS EOP C04 (International Earth Rotation and Reference Systems Service -- IERS; Earth Orientation Parameters -- EOP; Combination of four (04) techniques -- C04), from 1984 to 2023, to determine the variation of the Chandler wobble amplitude. To compare the results based on the C04 with the so-called Belgrade latitude data (Belgrade Lunette Zenithale { BLZ series 1949-1985) results, we calculated the latitude variations at the BLZ point using the C04 coordinates (x, y). The secular part of these latitude variations was determined by applying the least-squares method (LSM) and removed from the data to obtain the residuals. We used Direct Fourier transforms to extract annual and semiannual oscillations and to remove them from the residuals (resulting in a new set of residuals). These new residuals were divided into 33 independent 1.2-year subintervals. For each subinterval, we calculated the amplitude, period, and phase of the Chandler nutation using LSM. The quasi-periodic instability of 33 values of the Chandler wobble amplitude is detected with a period of 54.5 years using LSM (it was 38.5 years from the BLZ data 1949-1985); the amplitude of that quasi-periodic variation is 0."087 (0."06 from BLZ data). The amplitude of the Chandler nutation varies between minimum of 0."012 (at 2019.3) and a maximum of 0."23 (at 1994.1); the period is stable, but the phase is not stable. We applied the Abbe's criterion to explain the variability in 33 values of the Chandler wobble amplitude and the hypothesis that there is no trend in these 33 values is rejected based on the criterion. The obtained amplitude modulation is in accordance with previous studies, but also with our own results based on the BLZ data. Probably, the cause lies in the hydro-atmospheric circulation that could in uence calculated quasi-periodic variation. A possible explanation can be found in the change in core-mantle electromagnetic coupling (in agreement with the last few years' investigations). In recent papers, it has been indicated that the effects of geomagnetic jerks are more important for exciting a free nutation than the net effect of atmosphere and oceans. [ABSTRACT FROM AUTHOR]

Parameterised by the Love number k2 and the tidal quality factor Q, and inferred from lunar laser ranging (LLR), tidal dissipation in the Moon follows an unexpected frequency dependence often interpreted as evidence for a highly dissipative, melt‐bearing layer encompassing the core‐mantle boundary. Within this, more or less standard interpretation, the basal layer's viscosity is required to be of order 1015–1016 Pa s and its outer radius is predicted to extend to the zone of deep moonquakes. While the reconciliation of those predictions with the mechanical properties of rocks might be challenging, alternative lunar interior models without the basal layer are said to be unable to fit the frequency dependence of tidal Q. The purpose of our paper is to illustrate under what conditions the frequency‐dependence of lunar tidal Q can be interpreted without the need for deep‐seated partial melt. Devising a simplified lunar model, in which the mantle is described by the Sundberg‐Cooper rheology, we predict the relaxation strength and characteristic timescale of elastically accommodated grain boundary sliding in the mantle that would give rise to the desired frequency dependence. Along with developing this alternative model, we test the traditional model with a basal partial melt; and we show that the two models cannot be distinguished from each other by the available selenodetic measurements. Additional insight into the nature of lunar tidal dissipation can be gained either by measurements of higher‐degree Love numbers and quality factors or by farside lunar seismology. Plain Language Summary: As the Moon raises ocean tides on the Earth, the Earth itself gives rise to periodic deformation of the Moon. Precise measurements of lunar shape and motion can reveal those deformations and even relate them to our natural satellite's interior structure. In this work, we discuss two interpretations of those measurements. According to the first one, the lunar interior is hot and a small part of it might have melted, forming a thick layer of weak material buried more than 1,000 km deep under the lunar surface. According to the second one, there is no such layer, and the measured deformation can be explained by the behavior of solid rocks at relatively low temperatures. We show that the two possibilities cannot be distinguished from each other by the existing data. Key Points: A lunar mantle governed by the Andrade model fits selenodetic constraints only with a very weak frequency dependence of tidal dissipationWe seek the parameters of two more complex models that may explain the anomalous frequency dependence of tidal Q measured by lunar laser rangingBoth a dissipative basal layer and elastically accommodated grain‐boundary sliding in the deep mantle can result in the same tidal response [ABSTRACT FROM AUTHOR]

Ultralow‐velocity zones (ULVZs) have been studied using a variety of seismic phases; however, their physical origin is still poorly understood. Short period ScP waveforms are extensively used to infer ULVZ properties because they may be sensitive to all ULVZ elastic moduli and thickness. However, ScP waveforms are additionally complicated by the effects of path attenuation, coherent noise, and source complexity. To address these complications, we developed a hierarchical Bayesian inversion method that allows us to invert ScP waveforms from multiple events simultaneously and accounts for path attenuation and correlated noise. The inversion method is tested with synthetic predictions which show that the inclusion of attenuation is imperative to recover ULVZ parameters accurately and that the ULVZ thickness and S‐wave velocity decrease are most reliably recovered. Utilizing multiple events simultaneously reduces the effects of coherent noise and source time function complexity, which in turn allows for the inclusion of more data to be used in the analyses. We next applied the method to ScP data recorded in Australia for 291 events that sample the core‐mantle boundary beneath the Coral Sea. Our results indicate, on average, ∼12‐km thick ULVZ with ∼14% reduction in S‐wave velocity across the region, but there is a greater variability in ULVZ properties in the south than that in the north of the sampled region. P‐wave velocity reductions and density perturbations are mostly below 10%. These ScP data show more than one ScP post‐cursor in some areas which may indicate complex 3‐D ULVZ structures. Plain Language Summary: Studies of the Earth's deep interior using seismic energy generated by earthquakes show the presence of small‐scale structures at the core‐mantle boundary (CMB) known as ultralow‐velocity zones (ULVZs). The seismic waves traveling through these features are inferred to be slowed down by as much as 50% with respect to normal mantle material. However, it is challenging to determine the physical composition of these ULVZs and how they are linked to other structures in the Earth's interior because we don't have precise knowledge on their physical properties. To understand their origins, we need to estimate their physical properties (i.e., velocity and density) as accurately as possible. This study focuses on the development and application of a probabilistic approach that can provide an unbiased estimate of seismic velocity and density. Our new approach can take data from multiple events simultaneously and incorporates data noise and possible absorption of seismic energy along the path. Application of this approach to real data that sample the CMB beneath the Coral Sea show a wide spread ULVZ with much less lateral variation in material parameters in comparison to solutions using single events. We also find observations that may be linked to 3‐D ULVZ structure. Key Points: We developed a Bayesian waveform inversion approach that combines ScP arrivals from multiple events and incorporates path attenuationFailure to include attenuation in the inversion can yield incorrect ultralow‐velocity zone (ULVZ) elastic parametersLateral variation of ULVZ parameters beneath the Coral Sea may be affected by 2‐/3‐D ULVZ shape [ABSTRACT FROM AUTHOR]

Mantle convection plays a key role in magmatism and volcanism on Earth. The final distribution of deep mantle material upwelled into the asthenosphere cannot be clearly tracked using seismic imaging techniques. Where mid-ocean ridges and plumes interact, the along-ridge variations in plume-affected basalts constrain the spatial extent of the plume-related flow in the asthenosphere. These variations are helpful for revealing convection throughout the mantle from the core-mantle boundary (CMB) to the bottom of the lithosphere. In this study, regional geophysical data, as well as the results of geochemical independent component analysis of radiogenic Sr–Nd-Pb isotopes of South Mid-Atlantic Ridge (SMAR) basalts, were used to analyze the distribution characteristics of the plume-affected asthenosphere beneath the South Atlantic Ocean. We determined that the ridge scope of the Ascension plume-influenced SMAR segments is bounded by the Ascension transform fracture (~ 7.5°S) to the north and the Bode Verde transform fracture (~ 11.1°S) to the south, while the Saint Helena plume-contaminated SMAR segments are bounded by the Cardno transform fracture (~ 14.2°S) to the north and the Trinidade transform fracture (~ 20.8°S) to the south. Furthermore, we determined that the melt extraction process taking place between the mantle plume and ridge system may weaken the plume-related geochemical signals of these plume-affected MORBs. Our results suggest that the distribution of plume-related asthenosphere under the South Atlantic is influenced by large transform faults that block the propagation of the plumes along the bottom of the lithosphere, as well as the propagation of plume-affected materials along the ridge system. [ABSTRACT FROM AUTHOR]

The origin of the Earth's lowest geoid, the Indian Ocean geoid low (IOGL) has been controversial. The geoid predicted from present‐day tomography models has shown that mid to upper mantle hot anomalies are integral in generating the IOGL. Here we assimilate plate reconstruction in global mantle convection models starting from 140 Ma and show that sinking Tethyan slabs perturbed the African Large Low Shear Velocity province and generated plumes beneath the Indian Ocean, which led to the formation of this negative geoid anomaly. We also show that this low can be reproduced by surrounding mantle density anomalies, without having them present directly beneath the geoid low. We tune the density and viscosity of thermochemical piles at core‐mantle boundary, Clapeyron slope and density jump at 660 km discontinuity, and the strength of slabs, to control the rise of plumes, which in turn determine the shape and amplitude of the geoid low. Plain Language Summary: The origin of the deepest geoid on Earth, the Indian Ocean geoid low (IOGL), is debated. Several competing hypotheses exist, amongst which, a recent study employing tomography models suggested that hot anomalies at mid to upper mantle depths are crucial in generating this elusive feature. Assimilating plate motion in global mantle convection models from the Mesozoic till the present day, we attempt to trace the formation of this geoid low. We show that flow induced by downwelling Tethys slabs perturbs the African Large Low Shear Velocity province and gives rise to plumes that reach the upper mantle. These plumes, along with the mantle structure in the vicinity of the geoid low, are responsible for the formation of this negative geoid anomaly. Exploring a wide model parameter space, such as the density and intrinsic viscosity of the thermochemical piles, Clapeyron slope and density jump at 660 km depth, strength of slabs, we show that plumes are integral in generating the IOGL. The contribution of lower mantle Tethys slabs is secondary but also necessary in generating this geoid low. Key Points: Employing time dependent global mantle convection models since the Cretaceous we simulate the origin of the enigmatic Indian Ocean geoid lowPlumes forming along the edges of the African Large Low Shear Velocity province (LLSVP) control the regional geoid in the Indian OceanThese plumes, in turn are generated by lower mantle Tethyan slabs that perturb the African LLSVP [ABSTRACT FROM AUTHOR]

We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars' core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars' core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core-mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars' core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution. [ABSTRACT FROM AUTHOR]

Seismic anisotropy has been detected at many depths of the Earth, including its upper layers, the lowermost mantle and the inner core. While upper mantle seismic anisotropy is relatively straightforward to resolve, lowermost mantle anisotropy has proven to be more complicated to measure. Due to their long, horizontal ray paths along the core–mantle boundary (CMB), S waves diffracted along the CMB (S diff) are potentially strongly influenced by lowermost mantle anisotropy. S diff waves can be recorded over a large epicentral distance range and thus sample the lowermost mantle everywhere around the globe. S diff therefore represents a promising phase for studying lowermost mantle anisotropy; however, previous studies have pointed out some difficulties with the interpretation of differential SHdiff–SVdiff traveltimes in terms of seismic anisotropy. Here, we provide a new, comprehensive assessment of the usability of S diff waves to infer lowermost mantle anisotropy. Using both axisymmetric and fully 3-D global wavefield simulations, we show that there are cases in which S diff can reliably detect and characterize deep mantle anisotropy when measuring traditional splitting parameters (as opposed to differential traveltimes). First, we analyze isotropic effects on S diff polarizations, including the influence of realistic velocity structure (such as 3-D velocity heterogeneity and ultra-low velocity zones), the character of the lowermost mantle velocity gradient, mantle attenuation structure, and Earth's Coriolis force. Secondly, we evaluate effects of seismic anisotropy in both the upper and the lowermost mantle on SHdiff waves. In particular, we investigate how SHdiff waves are split by seismic anisotropy in the upper mantle near the source and how this anisotropic signature propagates to the receiver for a variety of lowermost mantle models. We demonstrate that, in particular and predictable cases, anisotropy leads to S diff splitting that can be clearly distinguished from other waveform effects. These results enable us to lay out a strategy for the analysis of S diff splitting due to anisotropy at the base of the mantle, which includes steps to help avoid potential pitfalls, with attention paid to the initial polarization of S diff and the influence of source-side anisotropy. We demonstrate our S diff splitting method using three earthquakes that occurred beneath the Celebes Sea, measured at many transportable array stations at a suitable epicentral distance. We resolve consistent and well-constrained S diff splitting parameters due to lowermost mantle anisotropy beneath the northeastern Pacific Ocean. [ABSTRACT FROM AUTHOR]

In 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. Plain Language Summary: We coupled a parameterized model of mantle/core segregation with a thermal model evolution for metallic alloys in order to link the composition of the core to its temperature. We find that geochemically coherent models yield a range of temperature at the core‐mantle boundary between 3925 and 4125 K. These temperatures correlate positively with the average pressure of equilibrium and the light elements abundances in the core. Enhancing the thermal model could then help to constrain the Earth's core composition through its temperature. Key Points: We built a thermal model of core evolution linked to accretion historyGeochemically coherent model yield cool cores, unless high amount of dissipation energy is transferred to the metalSome stratified core model are less stable than mixed model [ABSTRACT FROM AUTHOR]

The article presents a study which explores about globally distributed subducted materials along the Earth's core-mantle boundary, along with its implications for ultralow velocity zones (ULVZs) . It mentions that subducted materials, advected along the core-mantle boundary (CMB), providing an explanation for the distribution and range of reported ULVZ properties.

The heat extracted from the core by the overlying mantle across the core‐mantle boundary controls the thermal evolution of the core. This in turn leads to the solidification of the inner core in association with the exsolution of light alloying elements into the liquid outer core. Although the temperature (T) at the inner core boundary (ICB) would be adjusted to account for the effects of the light elements, the melting T of Fe places an upper bound at the ICB and it is a vital point in the thermal profile of the core. Here, we determine the melting T of Fe in the multi‐anvil press by characterizing the interface of Fe‐W interaction. Our data place a tighter constraint on the melting curve of Fe between 8 and 21 GPa, that is directly applicable to small planetary bodies and serves as an anchor for melting curve of Fe at higher pressure. Plain Language Summary: The melting temperature (T) of Fe is a fundamental parameter in constraining the thermal structure and evolution of the cores of the rocky planets and their satellites. Here, we precisely determine the melting T of Fe by characterizing the inter‐metallic diffusive interaction between Fe‐W at the melting transition using a new method "inter‐metallic fast diffusion" in multi‐anvil press. We measured the melting T of Fe at various fixed pressures between 8 and 21 GPa. We determined the melting T within an uncertainty of about 30 K, which is higher in precision than the reported errors in previous studies. Our data set provides a tighter constraint on the melting curve of Fe measured in the large‐volume press. In addition, we used the data set to critically evaluate the melting curve of Fe up to 80 GPa which has a large discrepancy in the existing melting data produced in laser‐heated diamond anvil cell. Key Points: The melting curve of Fe was precisely measured up to 21 GPa in multi‐anvil press by Characterizing the interface of Fe‐W interactionWe used our data set to critically evaluate the melting curve of Fe up to about 80 GPa which provided an independent check on diamond anvil cell datasets [ABSTRACT FROM AUTHOR]

We report the measurements of the thermal conductivity (κ) of iron (Fe) and nickel (Ni) at high pressures and high temperatures near the core–mantle boundary (CMB) of Mercury and Mars. κ values are estimated from the temperature measurements across the sample surface in a laser-heated diamond anvil cell (LHDAC) and using the COMSOL software. In both metals, values of κ drop suddenly at the melting temperature and can be used as another helpful technique to estimate melting temperatures at high pressures. We have obtained the thermal conductivity values of Fe and Ni at the CMB of Mercury to be about (60–70) ± 28 W m−1 K−1 and (65–70) ± 28 W m−1 K−1, respectively. Similarly, in the case of Mars CMB pressure and temperature conditions, the thermal conductivities of Fe and Ni are found to be 80 ± 32 W m−1 K−1 and (65–70) ± 28 W m−1 K−1, respectively. Using the obtained thermal conductivity values of Fe and Ni, we have estimated the adiabatic heat conduction at the outer core of Mercury and Mars, to be about (59–69) ± 28 mW m−2 and (61–72) ± 29 mW m−2, respectively. Both these values are much larger than the values predicted recently from the estimation of electronic thermal conductivity. [ABSTRACT FROM AUTHOR]

New high-precision trace-element analyses of magmatic olivines point to a pyroxenitedominated source for recent alkali basalts erupted above slab windows formed along the Antarctic Peninsula. Melting occurred at ambient mantle temperature, and basalts have geochemical compositions that are indistinguishable from ocean-island basalts (OIBs). We propose that the pyroxenite component originally resided in the upper mantle beneath the subducted slab; formation of a slab window allowed limited decompression and the generation of melts of garnet-pyroxenite, but little or no melting of mantle peridotite. The pyroxenite component in the mantle formed ca. 550 Ma, an age that does not require long-term recycling of subducting slabs to the core-mantle boundary. Enriched mid-ocean ridge basalt (E-MORB) from the adjacent extinct Phoenix Ridge owes its enriched trace-element compositions to mixing between small melt fractions of pyroxenite and peridotite during a period of decreased spreading rate prior to the death of the ridge ca. 3.3 Ma. It is likely that the variable trace-element enrichment seen in East Pacific Rise E-MORB distal from hotspots results from the same process of interactions between small-melt-fraction (<∼5%) melts of pyroxenite and peridotite. [ABSTRACT FROM AUTHOR]

The formation of a new ocean basin provides a unique observational window into the structure and deformation of the oceanic lithosphere. This study offers a detailed 1‐D vertically polarized shear‐wave velocity model of the young Japan Basin by interpreting S receiver functions, seafloor Rayleigh wave ellipticities and phase velocities in a Bayesian trans‐dimensional framework. The models suggest a distinct discontinuity in the mid‐lithosphere. Additional analyses indicate that the upper layer is characterized by strong positive radial anisotropy, while the lower layer is more isotropic. We interpret that the upper layer was formed during the back‐arc opening at 20–15 Ma, where the olivine lattice‐preferred orientation (LPO) fabric induced by passive upwelling contributes to the positive radial anisotropy. The lower, less anisotropic layer may be solidified after the sudden cessation of the opening. Small‐scale convection (SSC) from such a major tectonic event could randomize the LPO enough to weaken radial anisotropy before cooling down the asthenosphere, leaving a radially anisotropic discontinuity in the present‐day mid‐lithosphere. The proposed layered evolution history of the lithosphere beneath the Japan Basin illuminates an important role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Such an SSC‐induced radial anisotropy drop could also occur at the base of the lithosphere in regions with ongoing seafloor spreading and enhance the velocity drop of horizontally polarized shear waves. Thus, the role of SSC is non‐negligible in explaining the sharpness of the Gutenberg discontinuity detected by SS precursors beneath the oceanic lithosphere. Plain Language Summary: The formation of the oceanic lithosphere is associated with a relatively simple mantle convection process called seafloor spreading, but may also be affected by more complex, localized processes such as small‐scale mantle convection. To decipher the evolution history of the lithosphere of the Japan Basin, the Sea of Japan, this study collects earthquake waveforms from broadband ocean‐bottom seismometers and offers a detailed 1‐D seismic structural model beneath the Japan Basin by interpreting the multiple seismological observables in a trans‐dimensional Bayesian framework. Our seismic velocity model and associated analysis reveal that the oceanic lithosphere of the Japan Basin is seismically more complex than expected. The upper and lower parts of the lithosphere show distinct seismic anisotropy properties. We propose a layered evolution model for the lithosphere of the Japan Basin, in which small‐scale convection followed a normal seafloor spreading, and resulted in a structural discontinuity in the present‐day mid‐lithosphere. The proposed model highlights the role of the small‐scale convection in modifying the structural fabrics of the asthenosphere in terms of radial anisotropy. Key Points: We construct detailed 1‐D Vsv models of the Japan Basin by trans‐dimensional inversion of multiple observables extracted from ocean‐bottom seismometers recordsOur analysis reveals a mid‐lithosphere discontinuity arising from strong positive radial anisotropy in the upper lithosphereA layered evolution mode associated with small‐scale convection is proposed for the lithosphere of the Japan Basin [ABSTRACT FROM AUTHOR]

Earth's core‐mantle boundary (CMB) shows a complex structure with various seismic anomalies such as the large low shear‐wave velocity provinces (LLSVPs) and ultra‐low velocity zones (ULVZs). As these structures are possibly induced by chemically distinct material forming a layer above the CMB, models of mantle convection made ad hoc assumptions to simulate the dynamics of this layer. In particular, density and mass were prescribed. Both conditions are critical for the dynamics but hardly constrained. Core‐mantle interaction is considered as one possible origin for this dense layer. For example, diffusion‐controlled enrichment of iron has been proposed. We here apply a chemical gradient between the mantle and the denser core to analyze the penetration of dense material into the mantle. As such, we employ 2D Cartesian models where a thermochemical layer at the base of the mantle develops self‐consistently by a diffusive chemical influx. Our simulations indicate that chemical diffusion is strongly affected by the convective mantle flow. This convection‐assisted diffusion yields a compositional influx mainly in the areas where slabs spread over the bottom boundary and sweep dense material aside to form accumulations with rising plumes atop. Like for a prescribed dense layer this process leads to chemically distinct piles, which are typically smaller (therefore more suited to explain ULVZs) but more persistent due to the constant chemical influx. Combining the influx scenario with the primordial layer can possibly explain the simultaneous existence of LLSVPs and ULVZs along with the observation of a core‐like isotopic composition in the mantle. Plain Language Summary: The core‐mantle boundary (CMB) shows a complex structure. Seismologists have observed features that are possibly denser than their surroundings. These structures form from a dense layer above the CMB. Therefore typical mantle convection models have assumed an initial dense basal layer. The thickness and density of this prescribed layer are crucial but hardly constrained. Here we investigate core‐mantle interaction as one possible origin for this layer and employ 2D Cartesian models of mantle convection that consider a diffusive chemical gradient between the iron‐rich core and the silicate mantle. Our simulations show that the diffusive influx is coupled to the convective mantle flow. Convection‐assisted diffusion gives a larger influx beneath slabs spreading over the CMB. Additionally, as in the models with a prescribed layer, the rising plumes pull dense material up and form piles. In this study, however, the constant chemical influx leads to piles existing for longer times. The piles are typically smaller but can maybe in combination with a primordial layer explain different seismologically observed structures and the presence of core material in the mantle. Key Points: We analyze convection‐assisted core‐mantle interaction in thermochemical mantle convection modelsDense material penetrates into the mantle as a result of a basal diffusive chemical influx, where penetration is promoted by convectionSmall piles form with some of the dense core material being entrained by plumes [ABSTRACT FROM AUTHOR]

The large low‐shear‐velocity provinces (LLSVPs) are thought to be thermo‐chemical in nature, with recycled oceanic crust (OC) being a contender for the source of the chemical heterogeneity. The melting process which forms OC concentrates heat producing elements (HPEs) within it which, over time, may cause any collected piles of OC to destabilize, limiting their suitability to explain LLSVPs. Despite this, most geodynamic studies which include recycling of OC consider only homogeneous heating rates. We perform a suite of spherical, three‐dimensional mantle convection simulations to investigate how buoyancy number, geochemical model and heating model affects the ability of recycled OC to accumulate at the core‐mantle boundary. Our results agree with others that only a narrow range of buoyancy numbers allow OC to form piles in the lower mantle which remain stable to present day. We demonstrate that heterogeneous radiogenic heating causes piles to destabilize more readily, reducing present day CMB coverage from 63% to 47%. Consequently, the choice of geochemical model can influence pile formation. Geochemical models which lead to high internal heating rates can cause more rapid replenishment of piles, increasing their longevity. Where piles do remain to present day, first order comparisons suggest that old (hot) OC material can produce seismic characteristics, such as Vs anomalies, similar to those of LLSVPs. Given the range of current density estimates for lower mantle mineral phases, subducted OC remains a contender for the chemical component of thermo‐chemical LLSVPs. Plain Language Summary: Large, pile‐like structures at the base of Earth's mantle may be partially composed of accumulations of recycled oceanic crust. When oceanic crust is formed, heat producing elements are concentrated within it. This causes oceanic crust to experience relatively high heating rates compared to surrounding material when it is recycled into the mantle. A consequence of the high heating rates is that piles of oceanic crust may become unstable and so may not survive to present day. We conduct three‐dimensional numerical mantle simulations to investigate how the excess chemical density of recycled oceanic crust affects the survival of piles. In line with previous work, we find only a narrow range of excess chemical densities allow the survival of piles to the present day. Piles are more readily destroyed when internal heating is controlled by the concentration of heat producing elements compared to when internal heating is distributed evenly through the mantle. Consequently, assumptions made in the geochemical model, which controls the distribution of heat producing elements, can affect the long‐term stability of piles. Key Points: Heterogenous heating rates cause piles to destabilize more rapidly than homogeneous heating ratesA narrow range of buoyancy numbers allows piles to persist to present day without being destroyed or forming a layerFaster mantle processing rates can replenish piles more efficiently, increasing their longevity [ABSTRACT FROM AUTHOR]

The long-term evolution of the mantle is simulated using 2D spherical annulus geometry to examine the effect of heterogeneous thermal conductivity on the stability of reservoirs of primordial material. Often in numerical models, purely depth-dependent profiles emulate mantle conductivity (taking on values between 3 and 9 Wm-1K-1). This approach synthesizes the mean conductivities of mantle materials at their respective conditions in situ. However, because conductivity also depends on temperature and composition, the effects of these dependencies on mantle conductivity are masked. This issue is significant because dynamically evolving temperature and composition introduce lateral variations in conductivity, especially in the deep mantle. Minimum and maximum variations in conductivity are due to the temperatures of plumes and slabs, respectively, and depth dependence directly controls the amplitude of conductivity (and its variations) across the mantle depth. Our simulations allow assessing the consequences of these variations on mantle dynamics, in combination with the reduction in thermochemical pile conductivity due to its expected high temperatures and enrichment in iron, which has so far not been well examined. The mean conductivity ratio from bottom to top indicates the relative competition between the decreasing effect with increasing temperature and the increasing effect with increasing depth. We find that, when depth dependence is stronger than temperature dependence, a mean conductivity ratio >2 will result in long-lived primordial reservoirs. Specifically, for the mean conductivity profile to be comparable to the conductivity often assumed in numerical models, the depth-dependent ratio must be at least 9. When conductivity is underestimated, the imparted thermal buoyancy (from heat-producing element enrichment) destabilizes the reservoirs and influences core–mantle boundary coverage configuration and the onset of dense material entrainment. The composition dependence of conductivity only plays a minor role that behaves similarly to a small conductivity reduction due to temperature. Nevertheless, this effect may be amplified when depth dependence is increased. For the cases we examine, when the lowermost mantle's mean conductivity is greater than twice the surface conductivity, reservoirs can remain stable for very long periods of time, comparable to the age of the Earth. [ABSTRACT FROM AUTHOR]

The transportation of magma in sedimentary basins often occurs through extensive dyke‐sill networks. The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate. Based on 2D seismic reflection, we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin (ZJNB). The results show that sixty‐nine sills and fourteen forced folds have been identified. The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface. The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca. 0.2 Ma. The spatial and temporal occurrences of intrusions imply that the strong post‐rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core‐mantle boundary. Furthermore, these forced folds could produce several types of hydrocarbon traps, due to accommodation through bending and uplift of the overlying rock and free surface, but it is critical to evaluate the effect of such emplacement when setting exploration targets. [ABSTRACT FROM AUTHOR]

Recent theoretical studies suggest that the physical and rheological mantle properties in massive rocky planets fall outside conventional behaviors inferred for mantle properties at the Earth's mantle pressures. The vacancy diffusion occurring at low pressures is assumed to be followed by interstitial diffusion above ∼0.1 TPa resulting in viscosity reduction at higher pressures. In addition, the dissociation transition of MgSiO3 post‐perovskite (pPv) into new phases of minerals at 0.9 and 2.1 TPa, both with large negative Clapeyron slopes, has further impact(s) on the style of circulation in the mantle of super‐Earth planets. Further, the electronic contribution of conductivity increases exponentially with temperature at temperatures ∼5000 K and higher. We employ 3D‐controlled volume spherical convection models to explore the style of mantle circulation in large rocky super‐Earth planets with different core temperatures. Our numerical models resembling a GJ 876 d size super‐Earth reveal that due to the buffering influence of the pPv‐dissociation transition at ∼0.9 TPa, for deep mantle viscosities lower than ∼1022 Pa.s a small‐scale convective layer may develop at the top of the core‐mantle boundary (CMB). Penetrative superplumes originating from deep mantle‐layered regions can maintain the heat flux from the CMB required for the planet's geodynamo, and can survive for billions of years reaching shallow depths of the mantle without significant lateral migration. The strength of the focused penetrative superplumes that can potentially sustain surface volcanism and plate tectonics is enhanced with increasing CMB temperature, but diminished by higher rates of internal heating. Key Points: Superplumes originating from the deep mantle can maintain active tectonism in massive super‐Earth planets [ABSTRACT FROM AUTHOR]

The origin of widespread volcanism far from plate boundaries and mantle plumes remains a fundamental unsolved question. An example of this puzzle is the Anatolian region, where abundant intraplate volcanism has occurred since 10 Ma, but a nearby underlying plume structure in the deep mantle is lacking. We employed a combination of seismic and geochemical data to link intraplate volcanism in Anatolia to a trail of magmatic centers leading back to East Africa and its mantle plume, consistent with northward asthenospheric transport over a ∼2,500 km distance. Joint modeling of seismic imaging and petrological data indicates that the east Anatolian mantle potential temperature is higher than the ambient mantle (∼1,420°C). Based on multiple seismic tomography models, the Anatolian upper mantle is likely connected to East Africa by an asthenospheric channel with low seismic velocities. Along the channel, isotopic signatures among volcanoes are consistent with a common mantle source, and petrological data demonstrate similar elevated mantle temperatures, consistent with little cooling in the channel during the long‐distance transport. Horizontal asthenospheric pressure gradients originating from mantle plume upwelling beneath East Africa provide a mechanism for high lateral transport rates that match the relatively constant mantle potential temperatures along the channel. Rapid long‐distance asthenospheric flow helps explain the widespread occurrence of global intraplate magmatism in regions far from deeply‐rooted mantle plumes throughout Earth history. Plain Language Summary: Volcanoes that exist in the middle of tectonic plates are often thought to be produced by plumes of high temperature mantle that originate deep within the Earth, near the core‐mantle boundary. However, while many of these "intraplate" volcanoes share chemical compositions with plume‐related volcanism, their close connection to a deep mantle upwelling is not clear for all locations. In this study, we jointly analyze images of the Earth's interior structure from earthquake waves and the chemical properties of erupted magmas to make the case that: (a) the volcanoes in the Anatolia region are fed by a mantle plume that lies beneath the East African Rift system, and (b) upper mantle is transported horizontally over ∼2,500 km from Africa to Anatolia without significant cooling. We modeled mantle transport driven by a hot upwelling mantle plume and found that it is fast enough to explain the apparent lack of cooling. These results suggest that mantle plumes can affect a much larger volume of the Earth than is commonly assumed. Key Points: Upper mantle partial melting prevails beneath the Anatolian region based on seismic receiver functionsPlume‐originated asthenosphere is transported from East Africa to Anatolia while preserving elevated temperature based on basalt samplesTransport over ∼2,500 km is facilitated by reduced viscosity due to high temperature and possibly takes only ∼10 Myr [ABSTRACT FROM AUTHOR]

Proton self diffusion coefficients for bridgmanite at lower mantle conditions are calculated from ab initio molecular dynamics simulations. We find that the proton self diffusion coefficient, D self is nearly constant ∼ 10−8 m2 s−1 along the lower mantle geotherm but increases by nearly one order of magnitude from ∼10−10 m2 s−1 to ∼ 10−9 m2 s−1 along a cold slab geotherm to about 1800 km depth. These rates imply that the proton diffusion length scale is less than 10 km in lower mantle peridotite in the 150-200 million years timescale for slab material to sink through the lower mantle. Cold wet slabs probably lose less than one percent of their total water content to the ambient mantle on their journey through the lower mantle, indicating that recycled water is far from homogeneously distributed since slab delivery is highly heterogeneous. We estimate that 0.1 to 0.3 ocean masses (<100 ppm wt%) of recycled water may be currently stored in slab remnant materials within the lower mantle. This water is likely not entrained by plumes but is instead captured by background mantle flow before returning to the mid-ocean ridges. By contrast, deep-rooted mantle plumes may entrain materials containing primordial-like water from the lowermost mantle or the core, and preserve these anomalies in fairly small-scale heterogeneities. Over the age of the Earth, the proton diffusion length scale is a few tens of km, which places constraints on the size of possible primordial water reservoirs isolated from convective mixing, and indicates little flux of water across the core-mantle boundary. • Ab initio calculations show that protons diffuse ∼10−8 m2s−1 in bridgmanite. • Slabs lose little water in the lower mantle and thus water is stored heterogeneously. • Less than 0.3 ocean masses of recycled water are stored in lower mantle slabs. • Stiff cold zones surround subducted water and limit hydrous interaction with the core. • Traces of primordial water from the lowermost mantle may be carried upwards by plumes. [ABSTRACT FROM AUTHOR]

Paleomagnetic studies of meteorites over the past two decades have revealed that the cores of multiple meteorite parent bodies, including those of certain chondritic groups, generated dynamo fields as they crystallised. However, uncertainties in the direction and mode of core solidification in asteroid-sized bodies have meant using the timings and durations of these fields to constrain parent body properties, such as size, is challenging. Here, we use updated equations of state and liquidus relationships for Fe-FeS liquids at low pressures to calculate the locations at which solids form in these cores. We perform these calculations for core-mantle boundary (CMB) pressures from 0–2 GPa, and Fe-FeS liquid concentrations on the iron-rich side of the eutectic, as well as two values of iron thermal expansivity that cover the measured uncertainties in this parameter, and adiabatic and conductive cooling of these cores. We predict inward core crystallisation from the CMB in asteroids due to their low < 0.5 GPa pressures regardless of the uncertainties in other key core parameters. However, due to low internal pressures in these cores, remelting of any iron snow, as proposed to generate Ganymede's present-day field, may be unlikely as the cores are approximately isothermal. Therefore a different mode of inward core solidification is possibly required to explain compositionally-driven dynamo action in asteroids. Additionally, we identify possible regimes at higher > 0.6 − 2 GPa pressures in which crystallisation can occur concurrently at the CMB and the centre. • The direction of core solidification controls the possible dynamo driving mechanisms. • However, the direction of solidification in asteroid cores is currently uncertain. • We predict that asteroid cores solidified inwardly from the core-mantle boundary. • Due to their low pressures, a new mechanism is needed to drive last-stage asteroid core dynamos. [ABSTRACT FROM AUTHOR]

In recent decades, ultra-low velocity zones (ULVZs) – thin patches of strongly reduced seismic velocity atop the core-mantle boundary (CMB) – have been inferred from observations of a variety of seismic phases. One such phase is Sdiff and its out-of-plane postcursory energy, Sdiff+. In this study, we present a high quality dataset of Sdiff and Sdiff+ which shows evidence of a ULVZ in the central Pacific, roughly between Hawaii and Marquesas. The observed Sdiff+ have an unusually short dominant period (5–12 seconds) compared to previous Sdiff+ observations, which is indicative of a ULVZ that is approximately 10–15 km thick. We analyse this high frequency dataset using the 2D Wavefront Tracker (2DWT) Bayesian inversion methodology to generate a probabilistic ensemble of ULVZ models. As a result of the uniazimuthal coverage of data, there is a strong southwest-northeast trade-off, but there is a slight preference for the ULVZ to be located just outside the Pacific large low velocity province (LLVP) boundary, roughly centred 20° north of Marquesas and 20° southeast of Hawaii. The 2DWT inversion of Sdiff+ travel times suggest that the ULVZ can be approximated as a cylindrical structure; either as a larger and weaker anomaly (radius 280 km, dVs -20%) close to the LLVP, or a smaller and stronger anomaly (radius 180 km, dVs -30%) further away from the LLVP. Unlike previous broad-scale ULVZs modelled with Sdiff+, this ULVZ is thinner, might lie outside of an LLVP, and lacks a potential relationship to a mantle plume. [ABSTRACT FROM AUTHOR]

Earth's geodynamo has operated for over 3.5 billion years. The magnetic field is currently powered by thermocompositional convection in the outer core, which involves the release of light elements and latent heat as the inner core solidifies. However, since the inner core nucleated no more than 1.5 billion years ago, the early dynamo could not rely on these buoyancy sources. Given recent estimates of the thermal conductivity of the outer core, an alternative mechanism may be required to sustain the geodynamo prior to nucleation of the inner core. One possibility is a silicate dynamo operating in a long-lived basal magma ocean. Here, we investigate the structural, thermal, buoyancy, and magnetic evolution of an Earth-like terrestrial planet. Using modern equations of state and melting curves, we include a time-dependent parameterization of the compositional evolution of an iron-rich basal magma ocean. We combine an internal structure integration of the planet with energy budgets in a coupled core, basal magma ocean, and mantle system. We determine the thermocompositional convective stability of the core and the basal magma ocean, and assess their respective dynamo activity using entropy budgets and magnetic Reynolds numbers. Our conservative nominal model predicts a transient basal magma ocean dynamo followed by a core dynamo after 1 billion years. The model is sensitive to several parameters, including the initial temperature of the core-mantle boundary, the parameterization of mantle convection, the composition of the basal magma ocean, the radiogenic content of the planet, as well as convective velocity and magnetic scaling laws. We use the nominal model to constrain the range of basal magma ocean electrical conductivity and core thermal conductivity that sustain a dynamo. This highlights the importance of constraining the parameters and transport properties that influence planetary evolution using experiments and simulations conducted at pressure, temperature, and composition conditions found in planetary interior, in order to reduce model degeneracies. [Display omitted] • The structural, thermal, buoyancy, and magnetic evolution of an Earth-like planet is investigated • The planet evolution includes a transient iron-rich basal magma ocean with a time-dependent composition • The nominal model predicts a basal magma ocean dynamo followed by a core dynamo after 1 billion years • An early silicate dynamo is possible with an electrical conductivity larger than 21,500 S/m • An early core dynamo is not possible with a thermal conductivity larger than 15.8 W/m/K [ABSTRACT FROM AUTHOR]

The "new core paradox" suggests that the persistence of the geomagnetic field over nearly all of Earth history is in conflict with the core being highly thermally conductive, which makes convection and dynamo action in the core much harder prior to the nucleation of the inner core. Here we revisit this issue by exploring the influence of six important parameters on core evolution: upper/lower mantle viscosity ratio, core thermal conductivity, core radiogenic heat rate, mantle radiogenic heating rate, central core melting temperature, and initial core‐mantle boundary (CMB) temperature. Each parameter is systematically explored by the model, which couples mantle energy and core energy‐entropy evolution. A model is "successful" if the correct present‐day inner core size is achieved and the dynamo remains alive, as implied by the paleomagnetic record. In agreement with previous studies, we do not find successful thermal evolutions using nominal parameters, which includes a core thermal conductivity of 70 Wm−1K−1, zero core radioactivity, and an initial CMB temperature of 5,000 K. The dynamo can be kept alive by assuming an unrealistically low thermal conductivity of 20 Wm−1K−1 or an unrealistically high core radioactive heat flow of 3 TW at present‐day, which are considered "unsuccessful" models. We identify a third scenario to keep the dynamo alive by assuming a hot initial CMB temperature of ∼6,000 K and a central core liquidus of ∼5,550 K. These temperatures are on the extreme end of typical estimates, but should not be ruled out and deserve further scrutiny. Plain Language Summary: The cooling of Earth over geological time is of interest to many scientific disciplines and has been studied intensively. Maintaining the geomagnetic field requires continuous core cooling to drive fluid motion in Earth's liquid iron outer core. Recent studies have shown that the materials that make up Earth's core can conduct heat very efficiently, which makes fluid motion in the core more difficult. In this study we investigate the thermal and magnetic evolution of Earth using a core‐mantle cooling model. In particular, we investigate how several important aspects of Earth's interior that control its thermal and magnetic evolution over 4.5 billion years. In agreement with previous studies, we confirm that typical models fail to reproduce the thermal and magnetic evolution found in the geological record. We identify a potentially new solution that invokes (a) that the core is initially super hot following the formation of the Earth, and (b) that the melting temperature of the core material is lower than most estimates. This potential solution should be investigated further by studying the initial core temperature following planet formation and careful measurement of the melting temperatures of iron alloys. Key Points: Using nominal thermal evolution parameters the geodynamo is predicted to die prior to inner core nucleationKeeping it alive requires either a low thermal conductivity (20 W/m/K), a high core radioactivity (3 TW), or a hot initial core (6,000 K)A relatively low core melting temperature of 5,300 K correlates with higher ohmic dissipation prior to inner core nucleation [ABSTRACT FROM AUTHOR]

Shear‐wave splitting measurements are commonly used to resolve seismic anisotropy in both the upper and lowermost mantle. Typically, such techniques are applied to SmKS phases that have reflected (m‐1) times off the underside of the core‐mantle boundary before being recorded. Practical constraints for shear‐wave splitting studies include the limited number of suitable phases as well as the large fraction of available data discarded because of poor signal‐to‐noise ratios (SNRs) or large measurement uncertainties. Array techniques such as beamforming are commonly used in observational seismology to enhance SNRs, but have not been applied before to improve SmKS signal strength and coherency for shear wave splitting studies. Here, we investigate how a beamforming methodology, based on slowness and backazimuth vespagrams to determine the most coherent incoming wave direction, can improve shear‐wave splitting measurement confidence intervals. Through the analysis of real and synthetic seismograms, we show that (a) the splitting measurements obtained from the beamformed seismograms (beams) reflect an average of the single‐station splitting parameters that contribute to the beam; (b) the beams have (on average) more than twice as large SNRs than the single‐station seismograms that contribute to the beam; (c) the increased SNRs allow the reliable measurement of shear wave splitting parameters from beams down to average single‐station SNRs of 1.3. Beamforming may thus be helpful to more reliably measure splitting due to upper mantle anisotropy. Moreover, we show that beamforming holds potential to greatly improve detection of lowermost mantle anisotropy by demonstrating differential SKS–SKKS splitting analysis using beamformed USArray data. Plain Language Summary: When earthquakes occur, seismic waves are produced that travel through the deep Earth to distant seismic stations. In some portions of the Earth, seismic waves traveling in different directions or with different vibration directions travel at different speeds. This phenomenon is known as seismic anisotropy and results from individual mineral crystals aligning with mantle flow. Therefore, by measuring seismic anisotropy, we can obtain insights into how Earth's mantle flows, a process called mantle convection. In this work, we show that seismic anisotropy can be inferred from recordings of seismic phases that are summed (or stacked) across a number of spatially separated stations (seismic arrays). The resulting stacks are also called beams. Beams have an increased signal clarity compared to single‐station seismograms, leading to several advantages for analyses of seismic anisotropy. For example, the increased signal strength in beams allows for the usage of weaker seismic phases, which are not commonly used for measuring seismic anisotropy. Moreover, measurements made on beamformed data are more robust. This new technique enables us to suggest new directions for lowermost mantle anisotropy analyses. Key Points: Major limitations for shear‐wave splitting measurements are the limited number of suitable phases and low signal‐to‐noise ratios (SNRs)Beamforming enhances the SNR, enabling us to use unusual seismic phases and a larger data fraction for shear‐wave splitting measurementsThis holds potential for investigations of mantle anisotropy, particularly in the lowermost mantle [ABSTRACT FROM AUTHOR]

The origin of the Cameroon Volcanic Line (CVL), which is difficult to explain with traditional plate tectonics and mantle convection models because the volcanism does not display clear age progression, remains widely debated. Existing seismic tomography models show anomalously slow structure beneath the CVL, which some have interpreted to reflect upper mantle convective processes, possibly associated with edge-driven flow related to the neighboring Congo Craton. However, mid- and lower mantle depths are generally not well resolved in these models, making it difficult to determine the extent of the anomalous CVL structure. Here, we present a new P-wave velocity model for the African mantle, developed with the largest collection of travel-time residuals recorded across the continent to date and an adaptive model parameterization. Our extensive data set and inversion method yield high resolution images of the mantle structure beneath western Africa, particularly at the critical mid- and lower mantle depths needed to further evaluate processes associated with the formation of the CVL. Our new model provides strong evidence for a connection between the African Large Low Velocity Province, centered in the lower mantle beneath southern Africa, and the continental portion of the CVL. We suggest that seismically slow material generated near the core-mantle boundary beneath southern Africa moves northwestward under the Congo Craton. At the northern edge of the craton, the hot, buoyant material rises through the upper mantle, causing the CVL volcanism. Consequently, CVL magmatism can be linked to large-scale mantle processes rooted in the deep mantle. [ABSTRACT FROM AUTHOR]