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Recent palaeomagnetic and seismological studies have strengthened the suggestion that the Moon once possessed a core dynamo. Despite its importance as a constraint on lunar evolution, there is currently no consensus on how such a dynamo was driven. Two groups working independently have arrived at the idea that the lunar dynamo was powered by mechanical stirring of the liquid core. Dwyer et al. investigate the mechanism of a dynamo driven by continuous mechanical stirring arising from the differential motion between the solid silicate mantle and the liquid core beneath. They show that the fluid motions and the power required to drive a dynamo operating continuously for more than 1 billion years are readily obtained by such mechanical stirring. Le Bars et al. propose a model whereby the dynamo action comes from impact-induced changes in the Moon's rotation rate. They show that basin-forming impact events are energetic enough to have unlocked the Moon from synchronous rotation, and that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core–mantle boundary, could have powered a lunar dynamo. The origin of lunar magnetic anomalies1,2,3,4,5 remains unresolved after their discovery more than four decades ago. A commonly invoked hypothesis is that the Moon might once have possessed a thermally driven core dynamo3, but this theory is problematical given the small size of the core and the required surface magnetic field strengths6. An alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins7, but many magnetic anomalies exist that are not associated with basin antipodes. Here we propose a new model for magnetic field generation, in which dynamo action comes from impact-induced changes in the Moon’s rotation rate. Basin-forming impact events are energetic enough to have unlocked the Moon from synchronous rotation8, and we demonstrate that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core–mantle boundary9, could have powered a lunar dynamo. Predicted surface magnetic field strengths are on the order of several microteslas, consistent with palaeomagnetic measurements5, and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins.

In order to better constrain the Late Paleozoic tectonic evolution of the SW Central Asian Orogenic Belt, we conducted field structural investigations, zircon U-Pb dating, whole-rock geochemical and Sr-Nd isotopic studies on the meta-sedimentary rocks and intruding granites and mafic dykes in the Dahalajunshan area, southern Yili Block of NW China. Our results allow us to recognize five tectonic/magmatic events. Field-scale and microscopic structures of the low-grade meta-sedimentary rocks showed a regional top-to-the-SE thrusting (Event 1). Undeformed granites that contain dioritic enclaves (Event 2) crosscut the regional foliations and thus post-date Event 1 after ca. 379–369 Ma. Mafic dykes intruded all these rocks after ∼328 Ma (Event 4–1), posterior to brittle-ductile thrusting (N-S contraction) (Event 3) and prior to normal faulting (N-S extension) (Event 4–2). All the magmatic rocks formed in a subduction-related setting. The granites and dioritic enclaves derived from a mixing of crustal- and mantle-derived sources variously modified by slab-derived hydrous melts. The primary magma of the diabase dykes derived from a mantle source modified by the slab fluids with 5% crustal contamination. Variation from regional compression (ductile and brittle-ductile thrusting) to extension (normal faulting) and increasing mantle input in arc-related magmatism reveals a transition from Early Paleozoic advancing subduction (events 1 to 3) to Late Paleozoic retreating subduction (events 4–1 and 4–2) of the Junggar oceanic plate beneath the Yili Block.

International journal of earth sciences (2022). doi:10.1007/s00531-022-02174-5, Published by Springer, Berlin ; Heidelberg

Due to the high density at mantle depths, subducted oceanic crust rarely exhumes to the surface of Earth, making it challenging to determine the evolution and dynamic behavior of oceanic crust. The Sumdo eclogite-bearing metamorphic belt, located between the north and south Lhasa terranes in Tibet, is a natural laboratory for studying the metamorphic evolution of oceanic eclogites. We combined phase equilibrium modeling with detailed petrological investigations for the newly discovered Xilang eclogite from this belt and obtained near-peak metamorphic conditions of 539 °C at 1.84 GPa and a steep exhumation P–T path. These values are much lower than published for the other areas of this belt. Quartz inclusions sealed in garnet from high-pressure rocks are known to preserve residual pressures during exhumation, which can be used to reexamine the peak metamorphic conditions of eclogites in the Sumdo metamorphic belt. We analyzed quartz from three different areas in the belt, including Xilang, Jilang, and Xindaduo, with laser Raman micro spectroscopy. Xilang eclogite preserved the highest residual pressure of 0.53 ± 0.07 GPa in the quartz stability field. A systematic comparison of the residual pressures of different eclogites revealed that not only the peak metamorphic conditions but also the exhumation rate of the host rocks controlled the residual pressure. Hence, the Xilang eclogite may record lower peak P–T conditions, because it exhumed differently than the eclogites from the other areas in the Sumdo metamorphic belt. Combined with numerical modeling, the residual pressures obtained by Raman spectroscopy may be a new way to compare the metamorphic conditions of eclogites and to obtain geochronological information in addition to isotopic investigations.

Geodynamic processes in Antarctica such as glacial isostatic adjustment (GIA) and post-seismic deformation are measured by geodetic observations such as global navigation satellite systems (GNSS) and satellite gravimetry. GNSS measurements have comprised both continuous measurements and episodic measurements since the mid-1990s. The estimated velocities typically reach an accuracy of 1 mm a −1 for horizontal velocities and 2 mm a −1 for vertical velocities. However, the elastic deformation due to present-day ice-load change needs to be considered accordingly. Space gravimetry derives mass changes from small variations in the inter-satellite distance of a pair of satellites, starting with the GRACE (Gravity Recovery and Climate Experiment) satellite mission in 2002 and continuing with the GRACE-FO (GRACE Follow-On) mission launched in 2018. The spatial resolution of the measurements is low (about 300 km) but the measurement error is homogeneous across Antarctica. The estimated trends contain signals from ice-mass change, and local and global GIA signals. To combine the strengths of the individual datasets, statistical combinations of GNSS, GRACE and satellite altimetry data have been developed. These combinations rely on realistic error estimates and assumptions of snow density. Nevertheless, they capture signals that are missing from geodynamic forward models such as the large uplift in the Amundsen Sea sector caused by a low-viscous response to century-scale ice-mass changes.

The Mascarene Islands in the western Indian Ocean, encompassing La Réunion, Mauritius, and Rodrigues, are the recent (, Geochimica et Cosmochimica Acta, 355, ISSN:0016-7037, ISSN:1872-9533

The Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response timescale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modelling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and palaeosea-level investigations of Antarctica provide quantitative ways of independently assessing the 3D mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

International audience; We present a new numerical modelling study of subduction initiation at (hyper-extended) magma-poor and magma-rich continental passive margins. In particular, we test how the structure and rheological stratification of these two end-member types control the formation and thermo-mechanical evolution of subduction zones. The serpentinization of mantle lithosphere in a magma-poor continental rifted margin leads to rheological decoupling at the base of the continental crust, which induces shear localization during subsequent shortening. Under these conditions, a shear zone propagates into the mantle lithosphere and leads to subduction initiation at the transition between ocean and passive margin. In contrast, a magma-rich rifted continental margin is rheologically coupled, which creates a buttressing effect and transfer of deformation into the oceanic domain during shortening, where the subduction zone initiates. These results are quantitatively compared and in agreement with the geological record of subduction initiation in the Alps and Dinarides – Hellenides, where the relics of end-member types of continental rifted margins of the same Adriatic micro-continent bordering the Alpine Tethys and Neotethys oceans, respectively, are observed.

The Qinling Orogenic Belt (QOB) is an important tectonic belt in eastern Asia, which is believed to have been formed by the intracontinental collision between the North China Craton and South China Block. By analyzing radial P-wave receiver functions recorded by 239 broadband stations, we investigate the crustal thickness and Vp/Vs ratio maps under the QOB and its adjacent regions using the H-k and common-conversion-point (CCP) stacking methods. The crustal thickness (H) and Vp/Vs ratios (k) showed significant lateral variations. The assessment of crustal isostatic compensation reveals that the topography of the Dabashan and central QOB are compensated by crustal thickness, although the later may not be fully compensated. The crust of the western and eastern QOB are possibly in a non-Airy-type isostasy state, and the low-density uppermost mantle may play an important role in compensating their elevations. The Dabashan and the region to the south have thick crustal thickness and high Vp/Vs ratios, while the east QOB have thin crustal thickness and low Vp/Vs ratios. The CCP images reveal two strong positive amplitudes at depths consistent with the Moho interface near the Ankang fault. These observations indicate complex lower crustal structure and suggest the existence of eclogitized lower crust beneath Dabashan and lower crust delamination beneath east QOB. We also observe a continuous area with thick crust and high Vp/Vs ratios that covers the Dabashan, Hannan–Micang Dome, Shennong–Huangling Dome and their surrounding regions. This area shows consistency in location with a rapidly uplifted area since approximately 15 Ma, which—with other geological studies—implies the asthenospheric flux from the Tibetan Plateau. The asthenosphere flow may have eroded the lithosphere beneath the Dabashan and promoted the lower crustal eclogization.

Glacial isostatic adjustment is largely governed by the rheological properties of the Earth's mantle. Large mass redistributions in the ocean–cryosphere system and the subsequent response of the viscoelastic Earth have led to dramatic sea level changes in the past. This process is ongoing, and in order to understand and predict current and future sea level changes, the knowledge of mantle properties such as viscosity is essential. In this study, we present a method to obtain estimates of mantle viscosities by the assimilation of relative sea level rates of change into a viscoelastic model of the lithosphere and mantle. We set up a particle filter with probabilistic resampling. In an identical twin experiment, we show that mantle viscosities can be recovered in a glacial isostatic adjustment model of a simple three-layer Earth structure consisting of an elastic lithosphere and two mantle layers of different viscosity. We investigate the ensemble behaviour on different parameters in the following three set-ups: (1) global observations data set since last glacial maximum with different ensemble initialisations and observation uncertainties, (2) regional observations from Fennoscandia or Laurentide/Greenland only, and (3) limiting the observation period to 10 ka until the present. We show that the recovery is successful in all cases if the target parameter values are properly sampled by the initial ensemble probability distribution. This even includes cases in which the target viscosity values are located far in the tail of the initial ensemble probability distribution. Experiments show that the method is successful if enough near-field observations are available. This makes it work best for a period after substantial deglaciation until the present when the number of sea level indicators is relatively high.

Geological processes at subduction zones control seismicity, plutonism and volcanism, and geochemical cycling between the oceans, crust, and mantle. The down-going plate experiences metamorphism, and the associated dehydration and fluid flow alters the physical properties of the plate interface and mantle wedge, as well as controlling the composition of material descending into the mantle. Any direct study of slab evolution during subduction is inhibited by the prohibitive depths at which these processes occur. To examine these processes we use serpentinite mud volcanoes in the Mariana forearc, that permit sampling of serpentinite materials and their pore waters that ascend from the subduction channel. We present new pore water chemical data from the summit and flanks of three serpentinite mud volcanoes that were drilled during International Ocean Discovery Program Expedition 366 which are reflective of reactions within the crust and mantle during the early, shallow (

The connection between multi-plate convergence and Mesozoic metallogenic explosion in the western Pacific continental margin is a frontier theme of research. A key to understanding of the Mesozoic tectonics in South China involves the spatio-temporal distribution and tectonic control of Mesozoic deposits in this region. The Zhejiang Province in South China is located in the middle segment of the western Pacific metallogenic belt, where tectono-magmatic and metallogenic activities during the Yanshanian Period (Jurassic-Cretaceous) were frequent and intense. This region is an ideal window for investigating oceanic slab subduction and recycling, continental marginal magmatism, deep geological processes, and mineralization in the western Pacific continental margin. Here we present a comprehensive synthesis of information from petrology, isotope geochronology, geochemistry, igneous geology, and tectonics of the Zhejiang metallogenic deposits to evaluate the spatio-temporal distribution and formation mechanism of the Yanshanian mineral deposits. The early Yanshanian deposit types are mainly Fe or Pb–Zn ores, which are distributed in the northwestern Zhejiang region. The ore-bearing magmatic rocks in this period are highly fractionated I-type granites, which originated from continental crust together with depleted mantle materials. In the mid-Yanshanian, Mo deposits are the main type and are distributed throughout the region. Magma types in this period are relatively diverse, most are S-type granites, which were derived from the remelting of old continental crust and mixed with juvenile mantle-derived and crust-derived magmas. The late Yanshanian deposit types are mainly W–Sn, which are distributed in the southeastern part of the Zhejiang Province. The ore-bearing magma has the characteristics of A-type granite with mantle origin. Combined with numerical simulation, we discuss the deep processes of Mesozoic metallogenic explosion in South China. We correlate the early Yanshanian mineralization with flat subduction of the Paleo-Pacific Plate and the foundering of the oceanic slab; the mid-Yanshanian mineralization is associated with the destruction and thinning of lithospheric mantle caused by mantle melting related to the sharp subduction; and the late Yanshanian mineralization witnessed a decrease in the volume of mantle materials and the eastward retreat of the trenches.

Chromium isotope compositions have been determined for 42 mantle-derived xenoliths from Cameroon, France, Mongolia, Russia and the USA. The samples are mainly spinel and garnet lherzolites, or harzburgites, and yield δ53CrNIST979 from -0.33 to 0.43 ‰, within the range of previously reported compositions, -0.51 to 0.74 ‰ (Xia et al., 2017). Partial melting has been proposed as a process that alters the δ53Cr of the mantle residue. New non-modal melting models show that the compatible nature of Cr is inconsistent with large changes in the residue’s isotopic composition. The fractionation during melting is constrained by calculated Δ53Crmantle-melt-values

As relics of ancient ocean lithosphere, ophiolites are the most important petrological evidence for marking the sutures and also play a key role in reconstructing plate configuration. They also provide valuable windows for studying crustal accretion and mantle processes occurring at modern ocean ridges. Abundant ophiolites are distributed along the Yarlung-Tsangpo suture and represent the relics of ocean lithosphere of the Neo-Tethys. They are characterized by an incomplete litho-stratigraphy, of which the mantle section is much thicker than the crustal section. Ocean crustal rocks outcropped in the Yarlung-Tsangpo ophiolites are much thinner than normal ocean crusts (~ 7 km) or even absent. Tectonic settings from which the Yarlung-Tsangpo ophiolites originated remain highly controversial, although an origin of the supra-subduction zone is prevailing. Moreover, their incomplete litho-stratigraphy has been commonly attributed to tectonic dismemberment during the late-stage emplacement after their formation. Nevertheless, such an incompleteness resembles the ocean lithosphere generated at modern ultraslow spreading ridges, such as the Southwest Indian Ridge (SWIR). In this paper, we present several lines of evidence that support the formation of the Yarlung-Tsangpo ophiolites at ultraslow spreading ridges, during which detachment faults were developed. This suggests that the Yarlung-Tsangpo ophiolites might represent the ocean core complexes (OCC) in the Neo-Tethys Ocean. The OCC with high topography in the seafloor were clogged in the trench and preserved as ophiolites through Indo-Eurasia collision. The clogging resulted in the demise of an old subduction and a new subduction was re-initiated beneath the clogged OCC.

Late accretion occurred through addition of massive impactors to Earth, leading to potential heterogeneity in the distribution of highly siderophile elements (HSE: Os, Ir, Ru, Pt, Pd, Re) within the mantle. Abyssal peridotites sample the present-day convecting mantle, which make them useful for examining the distribution of the HSE within the mantle. Here we report new HSE abundance data and 187Os/188Os ratios, in conjunction with mineral chemistry and bulk rock major- and trace-element compositions for abyssal peridotites from the fast-spreading Pacific Antarctic Ridge (PAR) and East Pacific Rise (Hess Deep), and for slow to intermediate spreading ridges from the Southwest Indian Ridge, Central Indian Ridge and Mid-Atlantic Ridge. These analyses expand the global abyssal peridotite Os isotope and HSE database, enabling evaluation of potential variations with spreading rate, from ultraslow ( 2 wt.%, the average composition of the primitive mantle is 0.3 ppb Re, 4.9 ppb Pd, 7.1 ppb Pt, 7.2 ppb Ru, 3.8 ppb Ir and Os, showing no Pd/Ir, but a positive Ru/Ir anomaly, relative to chondrites. There is ∼50% variation of the HSE abundances in the oceanic mantle, with much of this variation being observed at small length scales (

Buried craters within tens of meters of lunar regolith are rarely studied but are significant for understanding the evolution of surface processes on the Moon. Here, we first report the evidence of an intact buried crater within the layered strata at Chang'E-4 (CE-4) landing site revealed by the lunar penetrating radar (LPR). The time-frequency comparative analysis method based on the variational mode decomposition (VMD) and the rock quantitative analysis method based on the local unit correlation (LUC) are proposed and applied to the processing and analysis of LPR data within 15 lunar days. The results presented by the two methods provide evidence of a buried crater at the CE-4 landing site and simultaneously reveal the rock-concentrated structure within the buried crater. According to the results, it is considered that the filling materials within the buried crater have survived the impaction and gardening during the formation of the overlying fine-grained regolith. Recent works have proposed that the near-surface material at the CE-4 landing site is mainly the lunar mantle materials excavated from the nearby Finsen crater. Therefore, the buried crater probably preserves the initial lunar mantle materials.

Active/recent volcanism indicates the presence of high-enthalpy resources at depth, but sometimes there is not any evidence of endogenous fluids manifestations at surface, that confirms the presence of an active geothermal system. In this study we present an extensive study of published and new diffuse 4He and 3He emission and thermal energy released data from fifteen volcanic systems, confirming a direct relationship between diffuse helium emissions and thermal energy released associated with the rise of mantle fluids. The results are useful to infer the existence of deep and/or hidden geothermal resources and to estimate roughly its potential at those areas without obvious geothermal manifestations at the surface, but with measureable anomalous emissions of 4He and 3He. Tracing diffuse He emission anomalies at the surface environment of volcanic systems provides very important information for the exploration and discovery of geothermal resources at those areas where the resources are either hidden or lie at great depth.

The mechanism and timing of crustal growth and differentiation on early Earth are debated. Evidence of crustal differentiation is detectable as deviations from Earth’s assumed chondritic uniform reservoir (CHUR) as crust is extracted from the mantle leading to a melt-depleted reservoir. For the long-lived zircon Lu-Hf system, no incontrovertible evidence of significant mantle depletion >3.8 Ga exists. We conduct combined U-Pb and Lu-Hf isotopic analyses for the detrital zircon from the Caozhuang supracrustal sequence in North China. The zircon Hf isotopic compositions are broadly scattered along the CHUR evolution line. However, given the possibility of potential systematic biases in zircon petrogenesis and the unique tectonic setting of early Earth, we posit that magmatism controlled by the nascent forms of plate tectonics during the Eoarchean could have likely hidden the degree of ancient crust-mantle differentiation. The non-depleted zircon Hf isotopes observed in North China and globally during early Earth may in verity imply the existence of ubiquitous depleted mantle domains at that time.

It is well known that water significantly lowers mantle solidi. But it turns out this paradigm is not always true. Here, we studied the interaction of K-rich carbonate melts with the natural garnet lherzolite from the Udachnaya kimberlite (Russia) in the presence of water at 3.0–6.5 GPa, corresponding to depths of 100–200 km. We found that at ≤ 1100 °C, the metasomatic interaction consumes garnet, orthopyroxene, and melt to produce phlogopite ± K-richterite + magnesite ± dolomite. Besides, primary clinopyroxene is replaced by one with a lower amount of jadeite component. Thus, the addition of water to the K-rich carbonate melt, infiltrating the subcontinental lithospheric mantle, should yield its partial or complete disappearance accompanied by phlogopitization and carbonation. The studied systems have H2O/K2O = 2, like that in phlogopite, and therefore correspond to carbonated phlogopite peridotite under fluid-absent conditions. At 4.0–6.5 GPa, the solidus of carbonated phlogopite peridotite is controlled by the following reaction: phlogopite + clinopyroxene + magnesite = garnet + orthopyroxene + olivine + hydrous K-carbonatite melt, which is bracketed between 1100 and 1200 °C. At 3 GPa, the solidus temperature decreases to about 1050 °C presumably owing to the Ca-Mg exchange reaction, clinopyroxene + magnesite = orthopyroxene + dolomite, which stabilizes dolomite reacting with phlogopite at a lower temperature than magnesite. Our results suggest that the phlogopite- and carbonate-rich metasomatic vein networks, weakening rigid lithosphere and promoting continental rifting, could be formed as a result of infiltration of hydrous K-carbonatite melt at the base of subcontinental lithospheric mantle. Stretching and thinning of the cratonic lithosphere make geotherms warmer and shifts their intersections with the solidus of carbonated phlogopite peridotite to shallower depths. Consequently, the successive erosion of the continental lithosphere and ascent of the lithosphere-asthenosphere boundary during continental rifting should be accompanied by remelting of phlogopite-carbonate metasomes, upward percolation of K-rich melt, and its solidification at the front of the magmatic-metasomatic mantle system.

The sudden eruption of submerged calderas can potentially pose imminent danger to nearby communities. Hence, it is crucial to closely monitor the changes in volatile effluents in these environments. Unlike subaerial volcanoes, underwater volcanic activity is difficult to observe. Wakamiko, a submerged caldera in southern Japan shares a magma source with the active subaerial volcano, Mt. Sakurajima . Following years of inactivity, the volcanic eruptions in Mt. Sakurajima became more frequent in 2009; however, it is undetermined how the neighboring Wakamiko caldera has behaved in relation to this upsurge in activity. In this study, we assess the state of hydrothermal venting inside Wakamiko following recent disturbances in Mt. Sakurajima. Based on gas bubbles, seawater and sediment pore water measurements of samples obtained in 2015, it appears that acidic fluids enriched in 3He continue to be discharged to the seafloor. Excess 3He in the water column shows no apparent change since 2010; however, the helium isotopic ratio of the magmatic source continues to be elevated at ∼7.2 Ra. This ratio for the magmatic component is higher than previously observed in 1986 (∼6 Ra). The difference could be related to changes in the degassing activity as well as the mantle composition of the magmatic source. Using the new data from sediment pore water, we estimate the diffusive fluxes of 3He and 4He through the seafloor at 16.05 atoms cm-2s-1 and 1.52 x 106 atoms cm-2s-1, respectively. We also calculated the vent 3He flux at 3.38 x104 atoms cm-2s-1. With the use of the 3He flux, we calculated the diffusive CO2 flux from Wakamiko at 1.41 x 106 mol yr-1 and the vent flux at 3.72 x 108 mol yr-1. The available data that we have are still limited and a more frequent and longer observation is necessary to deduce the temporal changes in Wakamiko and its relation to the volcanic activity of Mt. Sakurajima.

The current stress state of the Earth's crust in Central Asia depends entirely on the interaction of the Eurasian plate with the Indian and Arabian plates. Moreover, an essential role in this action is played by the subduction process in the Pamir-Hind Kush zone. In this region, deep earthquakes and anomalies in seismic velocities indicate subduction of the Indian Plate. To determine the effect of earthquakes on the stress state of the Earth's crust in Central Asia, we analyzed the hypocenters according to the available data over a hundred years. Taking the envelope of the hypocenters as the surface of the subducted indenter, we analyzed its penetration into the mantle. Instead of the pushing force of the indenter, the velocity of the Indian plate is taken into consideration. A model of the stresses is constructed on the equations of creeping motion of a viscous incompressible fluid. The stress variation in the Earth's crust and mantle was calculated as the stress difference before and after the earthquake. The mechanism of earthquakes is modelled by an introduction of equivalent volume forces in the equilibrium equations corresponding to a couple dipoles without a moment. The equations of creeping motion are numerically solved using boundary element methods. Numerical experiments with different physical model parameters for the Earth's crust and mantle were conducted. To introduce the negative buoyancy of the subducting plate, partial eclogitization of the rocks in the collision zone was assumed. As a result, a certain combination of stiffness and density was determined for the lithosphere and mantle, which explained the peculiarities of this region. The influence of crustal and mantle earthquakes in the Pamir-Hindu Kush region on the change in background stresses in Central Asia was analyzed which are not higher than 2–3%.

The origin of enriched mantle 1 (EM1) component in the mantle has long been debated. EM1 source of basalts has been variously attributed to recycled sub-continental lithosphere, recycled lower continental crust, or recycled oceanic crust plus pelagic sediments. Molybdenum stable isotope systematics has the potential to resolve this debate, because of the significant isotopic differences between mantle and crustal reservoirs. Here we present molybdenum isotope data for EM1-type continental intraplate basalts from Nuominhe (NMH), Northeast China. The NMH basalts display significant variations in both δ98/95Mo (98Mo/95Mo ratio relative to NIST SRM 3134, −0.49 to −0.15‰) and Mo/Ce (0.009 to 0.037), and strong correlations between δ98/95Mo, Mo/Ce and Hf isotope and trace elements. EM1 end-member of the NMH basalts shows the lightest δ98/95Mo and lowest Mo/Ce values. The involvement of continental crust and sub-continental lithospheric mantle cannot account for the light Mo isotopic compositions of the basalts. By contrast, the recycled oceanic crust with pelagic sediments, characterized by low δ98/95Mo and Mo/Ce values, is the satisfactory candidate for the EM1 component in the NMH basalts. Our results also suggest a residual slab reservoir with light δ98/95Mo values (

The metasomatized sub-continental lithospheric mantle (SCLM) is increasingly proposed to play a key control in the formation of giant gold (Au) deposits. However, the extent of Au enrichment in metasomatized SCLM and the Au contents of its derivative partial melts remain poorly constrained. Lamprophyres are derived from low-degree melting of metasomatic and fusible components in the SCLM, and could provide fundamental information about the metasomatized source and metal release compared to mantle peridotites and/or pyroxenites. The giant Jiaodong Au province (> 5000 tons, ∼ 120 Ma) in the eastern part of the North China Craton (NCC) is an ideal locality to assess the Au endowment of metasomatized SCLM which may serve as the source of Au, as indicated by the presence of mantle-dominated volatiles in auriferous fluids associated with the deposits. Based on detailed petrological studies, we analyzed Au, S, Cu and platinum-group element (PGE) contents of the SCLM-derived lamprophyres that are temporally (130–121 Ma) and spatially associated with the Jiaodong lode Au deposits. The lamprophyre dykes were emplaced in the deep crust and did not experience significant degassing and sulfide segregation, and the sulfide saturation occurred at a late stage during magma cooling, as demonstrated by sulfide petrography, S contents, Cu/S and Cu/Pd ratios of the lamprophyres. The relatively oxidized (ΔFMQ +1 – +2), hydrous (2–4 wt.% H2O) lamprophyres display variable and generally low Au contents (0.04–3.59 ng/g, mainly 1–3 ng/g, n = 31), as well as low PGE and Cu contents. Their high Au/Cu(N) and Au/Pd(N) ratios together with high Ba/Nb indicate a discernible Au addition to their source, resulting from multi-stage mantle metasomatism related to subduction. However, the average Au contents of the metasomatized SCLM before large-scale Au mineralization are heterogeneous and overall in a range of 0.5–1.5 ng/g. The values are higher than that of depleted SCLM (

The high-pressure solid phase of water known as ice VII has recently attracted a lot of attention when its presence was detected in large exoplanets, their icy satellites, and even in Earth's mantle. Moreover, a transition of ice VII to the superionic phase can be triggered by external electric fields. Here, we investigate the dielectric responses of ice VII to applied oscillating electric fields of various frequencies employing non-equilibrium ab initio molecular dynamics. We focus on the dynamical properties of a dipole-ordered ice VII structure, for which we explored external-field-induced electronic polarisation and the vibrational spectral density of states (VDOS). These analyses are important for the understanding of collective motions in the ice-VII lattice and the electronic properties of this exotic water phase.

Assessing the water abundance and hydrogen isotopic signature (δD) of the Martian interior dictates our understanding of the formation of inner solar-system planets, the origin of their volatiles, Martian volcanic history, and the potential for life-bearing environments on the surface of the red planet. Although several Martian meteorites, representing the planet's crust, have been analyzed before for this assessment, little is known about the effect of shock on recorded hydrogen (H) in their mineral phases. Here, hydrogen contents and isotopes are measured by secondary ion mass spectrometry (SIMS) in an enriched olivine-phyric shergottite, Larkman Nunatak (LAR) 06319, containing impact-melted zones. Systematic 100 μm-long traverses in pyroxene and maskelynite grains reveal decreases of hundreds of µg/g H2O and increases in δD of thousands of ‰ towards the contact with impact-melted zones, which is interpreted as H diffusive loss during shock-melting. Diffusion modeling reveals that temperatures high enough to permit H diffusion following shock were maintained near the impact-melted zone for a few minutes. By comparison, the interior of pyroxenes > 200 μm away from impact-melted zones have some of the highest H content with 170-480 µg/g H2O and the lowest δD with ∼300 ‰. The latter values, obtained on the most Mg-rich, i.e. earliest crystallized pyroxenes, are used to estimate that the enriched shergottite mantle source contains 300-1000 µg/g H2O and has a δD of ∼300 ‰. This δD is similar to that of depleted shergottite and nakhlite mantle sources, but higher than Earth’s upper mantle, suggesting slightly different water source materials for the two planets. The enriched shergottite mantle source has ∼10 times more water than that inferred for the depleted shergottite source and for Earth’s upper mantle. The high water content and wide range of δD in olivine (from 90 µg/g H2O and 2700‰ to 1350 µg/g H2O and -14‰) is interpreted as overprinting by a combination of Martian and terrestrial surface alteration. Finally, the high δD recorded in the impact-melt produced glass (3350-4700 ‰), its moderate water content (100-230 µg/g H2O), and the presence of vesicles, are likely the result of incorporation of Martian surficial material (ice and atmospheric gases) and degassing during shock melting. This study shows that shock can induce H loss from minerals, accompanied by > 1000 ‰ δD increases. Additionally, although it confirms that the Martian mantle may be heterogeneous in its water content, it implies that the Martian mantle is homogeneous within uncertainties for δD.

We report stable Ni isotope compositions (��������/������Ni, relative to SRM986) for mafic lavas with a range of -0.16 ��� to +0.20 ��� (n=44), similar to that of peridotite samples. Ocean island basalts (OIB) have been analysed from Iceland (n=6), the Azores (n=3), the Gal��pagos Islands (n=2), and L����ihi, Hawaii (n=1). Samples from Iceland (average ��������/������Ni = +0.13��0.16���, 2s, n=7) display the greatest range in Ni isotope compositions from a single OIB location in this work, of +0.01 ��� to +0.23 ���. Samples from the Azores (average ��������/������Ni = -0.10��0.10 ���, 2s) and Gal��pagos (average ��������/������Ni = -0.01��0.04 ���, 2s) are generally isotopically lighter. The single L����ihi sample has a ��������/������Ni of +0.17 ���. The lightest analysed bulk rock ��������/������Ni in this work, -0.16 ���, is from the Azores island, Pico. Enriched mid ocean ridge basalts (E-MORB), which have (La/Sm)_N>1, are isotopically lighter than normal type MORB (N-MORB), as shown by data from the Mid Atlantic Ridge (n=9) and East Pacific Rise (n=3). All E-MORB average ��60/58Ni = +0.00��0.06 ��� (2s, n=7), whereas N-MORB average ��60/58Ni = +0.14��0.10 ��� (2s, n=5). A suite of 15 mafic samples from the Cameroon Line, comprising lithologies ranging from nephelinites to hypersthene-normative basalts, have Ni isotope compositions that are identical within analytical uncertainty (average ��������/������Ni = +0.08��0.06 ���, 2s). Similarly, MORB samples display no relationship between ��������/������Ni and geochemical indicators of degree of partial melting or fractional crystallisation. Host lavas for two previously analysed ultramafic xenolith suites have ��������/������Ni identical to the average ��������/������Ni of their respective xenolith suites. This is consistent with previously published evidence from peridotites and komatiites that Ni isotopes are not greatly fractionated by melting. Therefore, mafic rocks may preserve the ��������/������Ni of their mantle source. Sampling a greater volume of mantle, their average Ni isotope composition +0.07��0.17 ��� (2s, n=44) may also be a better representation of the Bulk Silicate Earth (BSE), than estimates based purely on peridotites. The ��������/������Ni of MORB co-varies with La/Sm, Rb/Sr, europium anomaly (Eu/Eu*), and K���O/(K���O+Na���O). The relationships between these parameters and ��������/������Ni are consistent with mixing between two model endmembers. One could be depleted MORB or depleted MORB mantle (DMM) with a relatively heavy Ni isotope composition; the other a more enriched endmember that has isotopically lighter ��������/������Ni. The link between lighter ��������/������Ni and enriched lithologies in the mantle is further supported by published evidence of light Ni isotope compositions associated with some pyroxenite xenoliths. However, the curvature of the apparent mixing arrays defined by basalts is hard to reconcile with admixing of geochemically enriched but isotopically fractionated oceanic crustal lithologies. High [Ni] enriched magmas such as kimberlites may be a closer match to the enriched endmember. However, this needs further study.

Oxygen fugacity controls the behavior of multivalent elements and compositions of C-O-H fluids in Earth’s mantle, which further affects the cycling of materials between the deep interior and surfac...

The competition between the impact of inherited weaknesses and plate kinematics determines the location and style of deformation during rifting, yet the relative impacts of these “internal” and “external” factors remain poorly understood, especially in 3D. In this study we used brittle-viscous analogue models to assess how multiphase rifting, i.e., changes in plate divergence rate or direction, and the distribution of weaknesses in the competent mantle and crust influence rift evolution. We find that the combined reactivation of mantle and crustal weaknesses without kinematic changes creates complex rift structures. Divergence rates affects the strength of the weak lower crustal layer and hence the degree of mantle-crustal coupling. In this context slow rifting decreases coupling, so that crustal weaknesses can easily localize deformation and dominate surface structures, whereas fast rifting increases coupling so that deformation related to mantle weaknesses can have a dominant surface expression. Through a change from slow to fast rifting mantle-related deformation can overprint previous structures that formed along (differently oriented) crustal weaknesses. Conversely, a change from fast to slow rifting may shift deformation from mantle-controlled towards crust-controlled. When changing divergence directions, structures from the first rifting phase may control where subsequent deformation occurs, but only when they are well developed. Alternatively, they are ignored during subsequent rifting. We furthermore place our results in a larger framework of brittle-viscous rift modelling results from previous experimental studies, showing the importance of genral lithospheric layering, divergence rate, the type of deformation in the mantle, and finally upper crustal structural inheritance. The interaction between these parameters can lead to a large variety of deformation styles that may often lead to comparable end products. Therefore, detailed investigation of faulting and to an equal extent basin depocenter distribution over time is required to properly determine the evolution of complex rift systems. These insights provide a strong incentive to revisit various natural examples.

We report systematical zircon U–Pb datings, Hf isotopic data, major and trace element date on the Zhangshiying (ZSY) and the Taishanmiao (TSM) two plutons at the southern margin of the North China Craton (NCC), in order to investigate their petrogenesis and geological evolution. LA-ICP-MS U–Pb zircon of the ZSY and TSM granites dating yield a weighted mean 206Pb/238U age of 122.8 ± 1.5 Ma and 112.1 ± 3.2 Ma. The ZSY quartz syenite enriched in SiO2 (65.59–68.1 wt.%), Al2O3 (15.39–15.64 wt.%), high Sr (468–666 ppm), Sr/Y (35–45), (La/Yb)N (20.1–22.1) ratios, low Y(13.1–16.6 ppm), Yb (1.46–1.77 ppm), depleted in Nb, Ta, P, Ti, Mg, Y and negligible Eu anomalies, which suggesting that the quartz syenite are similar to adakitic rocks. Zircons from this pluton give eHf(t) values from −17.6 to −5.7 with an average of −15.2, and their TDM2 ages (1.29–1.91 Ga) are much younger than the basement rocks of the south margin of the NCC, which indicate that the ZSY quartz syenite were generated by partial melting of thickened lower crust with minor involvement of mantle-derived materials. The TSM pluton has characteristic of A-type granite, such as, high SiO2 (69.7–71.87 wt.%), total alkalis (Na2O + K2O = 8.5 to 9.41 wt.%), HFSE (Zr, Nb, Ga, Y), low CaO (0.27–1.25 wt.%), Ba, Sr and Eu. Their eHf(T) values ranges from −12.4 to −1.6 with an average of −7.6 and TDM2 ranges from 1.10 to 1.63 Ga with an average of 1.38 Ma. We propose that the TSM granites results from partial melting of tonalitic crustal sources with a plagioclase-rich residual at high temperatures and low pressure. Materials input from the mantle also is involved for the higher eHf(t) values than tonalitic crustal at the southern margin of NCC and high temperatures. Our results suggested that the thickened LCC at the south margin of the NCC is still existence before the intrusive of the ZSY adakitic rocks (∼123 Ma). During the intrusive of the TSM granites (∼112 Ma) it turns to extensional environment. This extensional event reflects the background of lithospheric thinning and decratonization of NCC.

The theory of plate tectonics is widely accepted by scientists and provides a robust framework with which to describe and predict the behavior of Earth’s rigid outer shell – the lithosphere – in space and time. Expressions of plate tectonic interactions at the Earth’s surface also provide critical insight into the machinations of our planet’s inaccessible interior, and allow postulation about the geological characteristics of other rocky bodies in our solar system and beyond. Formalization of this paradigm occurred at a landmark Penrose conference in 1969, representing the culmination of centuries of study, and our understanding of the “what”, “where”, “why”, and “when” of plate tectonics on Earth has continued to improve since. Here, we summarize the major discoveries that have been made in these fields and present a modern-day holistic model for the geodynamic evolution of the Earth that best accommodates key lines of evidence for its changes over time. Plate tectonics probably began at a global scale during the Mesoarchean (c. 2.9–3.0 Ga), with firm evidence for subduction in older geological terranes accounted for by isolated plate tectonic ‘microcells’ that initiated at the heads of mantle plumes. Such early subduction likely operated at shallow angles and was short-lived, owing to the buoyancy and low rigidity of hotter oceanic lithosphere. A transitional period during the Neoarchean and Paleoproterozoic/Mesoproterozoic was characterized by continued secular cooling of the Earth’s mantle, which reduced the buoyancy of oceanic lithosphere and increased its strength, allowing the angle of subduction at convergent plate margins to gradually steepen. The appearance of rocks during the Neoproterozoic (c. 0.8–0.9 Ga) diagnostic of subduction do not mark the onset of plate tectonics, but simply record the beginning of modern-style cold, deep, and steep subduction that is an end-member state of an earlier, hotter, mobile lid regime

Many of the peculiar features of the Mesoproterozoic (1.6–1.0 Ga) are related to the assembly of the first supercontinent Nuna, and some may not be distinctive of this time period. A high frequency of A-type granites at 1.6–1.4 Ga may be due, in part, to sampling biases. The overall increase in frequency in A-type granites beginning at 1.9 Ga may track the propagation of plate tectonics especially in the Great Proterozoic Accretionary Orogen. Increases in alkali and related elements in granitoids at 2.4–2.0 Ga may reflect widespread propagation of subduction as plate tectonics spread around the globe, and increases in HREE, Nb, Ti and Sc in granitoids may be related to decreasing importance of restitic garnet in granitoid sources as Earth transitioned from TTG to calc-alkaline magmatic regimes. Related to possible global mantle events at 1.9, 1.0 and 0.6 Ga are peaks in frequency of LIP and zircon ages related to supercontinent assembly. Mesoproterozoic paleomagnetic data that require at least 12 passive margins during this time. An increase in plate speed with time since 2 Ga may reflect a decreasing viscosity contrast across the lithosphere-asthenosphere boundary in response to a cooling mantle or/and thinning of the lithosphere and corresponding increases in heat flux with time. A relatively constant 87Sr/86Sr of seawater between 1.9 and 1.0 Ga may have resulted from a balance between weathered juvenile and reworked crustal sources as well as enhanced seafloor weathering of oceanic basalts. Mostly positive eHf(t) in detrital zircons and eNd(t) granitoids during the Mesoproterozoic suggest significant juvenile crustal input. However, the sparsity of crust of this age today probably results from recycling of large volumes of continental crust into the mantle in peripheral accretionary orogens during the breakup of Nuna at 1.4–1.2 Ga.

We conducted a petrologic study of apatite within eight unbrecciated, non-cumulate eucrites and two monomict, non-cumulate eucrites. These data were combined with previously published data to quantify the abundances of F, Cl, and H2O in the bulk silicate portion of asteroid 4 Vesta (BSV). Using a combination of apatite-based melt hygrometry/chlorometry and appropriately paired volatile/refractory element ratios, we determined that BSV has 3.0–7.2 ppm F, 0.39–1.8 ppm Cl, and 3.6–22 ppm H2O. The abundances of F and H2O are depleted in BSV relative to CI chondrites to a similar degree as F and H2O in the bulk silicate portion of the Moon. This degree of volatile depletion in BSV is similar to what has been determined previously for many moderately volatile elements in 4 Vesta (e.g., Na, K, Zn, Rb, Cs, and Pb). In contrast, Cl is depleted in 4 Vesta by a greater degree than what is recorded in samples from Earth or the Moon. Based on the Cl-isotopic compositions of eucrites and the bulk rock Cl/F ratios determined in this study, the eucrites likely formed through serial magmatism of a mantle with heterogeneous δ37Cl and Cl/F, not as extracts from a partially crystallized global magma ocean. Furthermore, the volatile depletion and Cl-isotopic heterogeneity recorded in eucrites is likely inherited, at least in part, from the precursor materials that accreted to form 4 Vesta and is unlikely to have resulted solely from degassing of a global magma ocean, magmatic degassing of eucrite melts, and/or volatile loss during thermal metamorphism. Although our results can be reconciled with the past presence of wide-scale melting on 4 Vesta (i.e., a partial magma ocean), any future models for eucrite petrogenesis involving a global magma ocean would need to account for the preservation of a heterogeneous eucrite source with respect to Cl/F ratios and Cl isotopes.

Deep, carbonate-rich melts are key constituents of kimberlites and are crucial for understanding the cycle of volatile elements in the mantle. On the Siberian craton, the Udachnaya-East kimberlite hosts extremely well-preserved nodules composed of chlorides + carbonates + sulfates, that do not present any relict sedimentary textures. These salty nodules display textures that are commonly observed in quenched liquids and may thus represent the very last stage liquid of the kimberlite. Alternatively, they could represent assimilated sedimentary material, or even post-magmatic hydrothermal alteration, because kimberlites are known to ascend through the lithosphere while assimilating material from their wall rocks. Here we focus specifically on those chloride-carbonate nodules, which are composed of 70% chloride + 30% alkali-carbonate and sulfate, and used two radiogenic systems (Rb-Sr, Sm-Nd) and the isotopic composition of sulfur, in addition to their major and trace element compositions (n = 3). We then compared the results with the same geochemical data on host kimberlites (n = 4), sedimentary cover (n = 3) and hydrothermal veins (n = 3). Taken together, our results show that the nodules are not the product of a contamination by the Cambrian sedimentary cover. Trace element patterns of the nodules display extreme enrichments in the same elements that are relatively depleted in the host kimberlite but also in kimberlites worldwide (K, Rb, Sr, Pb), suggesting that chloride-carbonate nodules are snapshots of the latest stage liquid present in the kimberlite system. Their isotopic compositions (Rb-Sr, Sm-Nd and δ34S) are consistent with a common magmatic source with their host kimberlite. We propose that chloride-carbonate nodules record a missing compositional endmember, which could explain the trend towards more radiogenic Sr isotope ratios at nearly constant Nd signatures observed in their host kimberlite, as well as in other kimberlites worldwide. This observed trend suggests the presence of a recycled component with high Rb/Sr (such as salts or terrigenous sediments) in the mantle sampled by some kimberlites, either in the lithosphere or the asthenosphere. This study highlights that the role of alkalies and halogens may have been underestimated in the genesis of kimberlites at depths where diamonds are stable, as well as in more evolved magmatic stages. Segregations of chlorides and carbonates occur specifically in sulfate-bearing kimberlites, which may thus sample a mantle domain in which sulfates with δ34S > 0‰ are dominant. The existence of such a reservoir could explain the apparent imbalance observed between the chondritic value (δ34S of 0‰) and the negative S isotopic compositions of mantle sulfides (MORB and peridotites).

Pyrite corona nodules from the ∼2.7 Ga Kapai Slate, a thin, sulfidic carbonaceous shale horizon interbedded with basaltic lava flows in the Yilgarn Craton, Western Australia, have concentric compositional and isotopic zoning with distinctive textural differences between cores and mantles. The sieved-textured cores are enriched in highly compatible trace elements, incl. Ni, As, Ag, Te, Sb, Bi and Pb, and depleted in incompatible Mo and Tl, whereas the radiating-textured mantles are strongly depleted in compatible elements and enriched in incompatible elements, relative to the cores. A striking feature of the data is that both the compatible and incompatible elements are linearly correlated, with correlation coefficients as high as 0.99. A marked drop in the concentration of compatible elements and an increase in incompatible elements at the core-mantle boundary is attributed to a sudden change in the rate of growth of the nodules produced by eruption of the voluminous overlying Paringa Basalt. The weight of the basalt produced sudden compaction of the unconsolidated clays below resulting in upward advection of pore fluid, which thinned the boundary layer around the growing nodules, leading to a marked increase in the rate of pyrite growth. Rapid pyrite growth led to a dramatic depletion in highly compatible elements, and to a build-up in incompatible elements, in the boundary layers around the growing nodule mantles, which resulted in extreme depletion of compatible elements, and enrichment in incompatible elements in the nodule mantles, relative to the cores. The corona nodules are also isotopically zoned with cores that have higher δ34S, with small positive Δ33S values, and mantles that have lower δ34S and higher Δ33S. The increase in Δ33S towards the rims is attributed to S8 being advected to the growing mantles by upward fluid movement during sudden compaction, and the decrease in δ34S to the lighter S isotope, with its higher reactivity and diffusivity, being preferentially incorporated into the fast growing pyrite mantle. The extreme changes in the growth rates of the Kapai Slate corona pyrite nodules provide a new constraint on the partition coefficients of the trace elements between Archean ocean water and sedimentary pyrite. The compatibility of the analysed trace elements decreases in the order Bi > Te > Sb > Ag > Cu > Pb > Ni ≈ As > (Co, Zn, Se, Cd, Mn, W) > Tl > Mo, which is consistent with the order obtained from modern sedimentary pyrites by Large et al. (2014), except for the redox-sensitive elements Mn, Tl and Mo. These differences are attributed to the lower oxygen content of the Archean atmosphere and oceans.

The alkalinity of ocean island basalts (OIB), which form by upwelling thermo-chemical instabilities in the mantle, is often associated with the degree of melting. Yet it remains to be tested if alkalinity and the degree of melting are systematically associated with enriched mantle components. The Tasmantid Seamounts, which are fossil remnants of the Tasmantid mantle plume, comprise a north-south age-progressive submarine volcanic chain in the Coral and Tasman Seas East of Australia. Dredged seafloor lavas from nine seamounts along the seamount chain, ranging in age from 50 to 6.5 Ma, show a dichotomy in alkalinity, similar to those observed in other hotspot areas such as Hawai’i or Pitcairn. In radiogenic Sr-Nd-Hf-Pb isotope systematics, Tasmantid Seamount lavas form a continuum between EM1 and PREMA and are thus part of the prevalent EM1-PREMA association in the Pacific. However, their radiogenic Pb isotope systematics mark the Tasmantid plume as an individuum with no resemblance to any other plume. In stable Fe isotopes (expressed as δ57FePrim, which is the Fe isotopic composition calculated to primitive lavas along a liquid line of descent) alkali basalts are, on average, isotopically heavier than tholeiitic lavas, ranging in δ57FePrim from +0.10 to +0.21‰, unrelated to radiogenic isotope systematics, but with co-variations of δ57FePrim and Ti* (which is the primitive melt Ti content). These systematics point towards residual garnet as a key factor and thus indicate a solely petrologic relation between degrees of melting and Fe isotopes. Tholeiitic lavas exhibit a near-depleted mantle like isotopic composition (ranging in δ57FePrim from −0.01 to +0.22‰, median at δ57FePrim + 0.04‰), yet with values of up to δ57FePrim + 0.22‰ that require an isotopically heavy source of unknown origin. The lack of systematics between alkalinity and radiogenic isotope signatures indicates that temperature is the likely driving force for variable melting degrees in some samples over others. Based on these observations, we surmise that tholeiitic lavas form in the plume centre whereas alkaline lavas form at the cooler rim of the conduit. Mixing between melts and associated enriched components in the Tasmantid mantle plume may occur but, at least for alkaline lavas, only on a small scale.

The chemical composition of erupted basalts provides a record of the thermo-chemical state of their source region and the melting conditions that lead to their formation. Here we present the first probabilistic inversion framework capable of inverting both trace and major element data of mafic volcanic rocks to constrain mantle potential temperature, depth of melting, and major and trace element source composition. The inversion strategy is based on the combination of (i) a two-phase multi-component reactive transport model, (ii) a thermodynamic solver for the evolution of major elements and mineral/liquid phases, (iii) a disequilibrium model of trace element partitioning and (iv) an adaptive Markov chain Monte Carlo algorithm. The mechanical and chemical evolution of melt and solid residue are therefore modelled in an internally- and thermodynamically-consistent manner. We illustrate the inversion approach and its sensitivity to relevant model parameters with a series of numerical experiments with increasing level of complexity. We show the benefits and limitations of using major and trace element compositions separately before demonstrating the advantages of a joint inversion. We show that such joint inversion has great sensitivity to mantle temperature, pressure range of melting and composition of the source, even when realistic uncertainties are assigned to both data and predictions. We further test the reliability of the approach on a real dataset from a well-characterised region: the Rio Grande Rift in western North America. We obtain estimates of mantle potential temperature ( ∼ 1340 °C), lithospheric thickness ( ∼ 60 km) and source composition that are in excellent agreement with numerous independent geochemical and geophysical estimates. In particular, this study suggests that the basalts in this region originated from a moderately hot upwelling and include the contribution from a slightly depleted source that experienced a small degree of melt or fluid metasomatism. This component is likely associated with partial melting of the lower portions of the lithosphere. The flexibility of both the melting model and inversion scheme developed here makes the approach widely applicable to assessing the thermo-chemical structure and evolution of the lithosphere-asthenosphere system and paves the way for truly joint geochemical-geophysical inversions.

This work is devoted to studying the velocity structure of the mantle of the border area of the East European and West European platforms in the crust separated by the Teiserre-Tornquist zone. The mantle under the territory of Poland and Western Ukraine is being investigated. The work uses a three-dimensional P-velocity model of the mantle, constructed using the Taylor approximation method developed by V. S. Geyko. The method’s advantages are independent of the initial approximation (reference model) and the best approximation of nonlinearity. In this area, the exploration depth is 2500 km south of 50 °NL and 1700 km north of 50 °NL. A detailed analysis of horizontal sections of a 3D P-velocity model of the mantle up to a depth of 850 km with a step of 50 km has been carried out. The change in the spatial distribution of the zero seismic velocity boundary is analyzed throughout the depths. This boundary separates the high-velocity upper mantle of the East European Platform and the low-velocity upper mantle of the West European Platform. At the depths of the transition zone of the upper mantle, this boundary separates the low-velocity upper mantle of the East European platform and the high-velocity upper mantle of the West European platform (in this geosphere, a velocity inversion has occurred with respect to the upper mantle). In latitudinal sections, two inclined layers are distinguished. One of them is associated with the upper mantle under the DDV and reaches the mantle under the Carpathians, where it begins to plunge into the high-velocity transition zone of the upper mantle. The second layer is associated with the mantle under the northwestern end of the Baltic syneclise, which extends to the mantle under the Presudet monocline, where it also plunges into the high-velocity transition zone of the upper mantle. In longitudinal sections, inclined layers are distinguished, extending from the mantle under the South Scandinavian megablock of the Baltic Shield to the mantle under the Bohemian massif and the Carpathians, where they plunge into the high-velocity transition zone of the upper mantle. In the study area, three super-deep fluids were identified, characterized by increased stratification of the medium (alternation of higher and lower velocities). The first includes the well-known oil and gas fields of the Central European oil and gas basin (Pomorie and Presudet monocline (Poland)). The second is associated with oil and gas fields of the North Ciscarpathian oil and gas basin (southeastern Poland) and the Carpathian oil and gas basin (Western Ukraine). The extracted super-deep fluid in the mantle of the Baltic Sea corresponds to both the Gdansk Gulf of the Baltic Sea and the Kaliningrad fields (southeast of the Baltic Sea).

The question of the existence of foci of deep earthquakes in the region of the Crimea-Black Sea-Caucasus is extremely important from the point of view of the geodynamics of the region. Previously it was thought that only crustal earthquakes could occur in this region. Recently, results have been obtained that show that earthquakes with depths of at least 300 km occur in this region. The article discusses the question of how plausible these results are and why they were not obtained earlier. Seven specific examples of the ambiguous determination of the depth of earthquake hypocenters in the Crimea-Black Sea-Caucasus region are considered. These examples clearly show that determining the coordinates of earthquake hypocenters using algorithms based on the Geiger method does not allow one to uniquely determine the depth of the hypocenters. The article gives an idea of the authors about the origin of mantle earthquakes in the Caucasian and Crimean-Black Sea regions. For the Caucasus region, mantle earthquakes are associated with two reasons: submersion of the lithospheric layer; in the asthenospheric layer, represented in the seismotomographic sections by a low-velocity anomaly, the nature of earthquake foci is associated with fluids formed during phase transition reactions. In the Crimean-Black Sea region, earthquake foci are located in the lithosphere layer, and the sliding of the lithosphere along the less viscous underlying layer of the upper mantle causes tectonic movements in the lithosphere accompanied by earthquakes. In addition, to determine the coordinates of the hypocenters of the Crimean and Caucasian earthquakes during routine processing, hodographs were used for depths not exceeding 35 km for the Crimea and 50 km for the Caucasus and 150 for the North Caucasus. This circumstance is the main reason why deep earthquakes could not be detected.

The Earth’s accretion process is accompanied by a large number of collisions. It is widely accepted that collisions dominate the Earth’s late accretion stage. Among all these collisions, there is a special type of collision called Core-merging giant impact (CMGI), in which much or most the impactor’s core merges directly with the proto-Earth’s core. This core-merging scenario plays an important role in the Earth’s accretion process and deeply affects the formation of the Earth’s core and mantle. However, because CMGI is a small probability event, it has not been fully studied. Here we use the SPH method to comprehensively study all possible CMGIs in the Earth’s accretion history. We find that CMGI only occurs in the initial conditions with small impact angle, small impact velocity and big impactor. We further discuss the implications of CMGI. We are confident that CMGI inevitably causes the chemical disequilibrium of the Earth's core and mantle. The CMGI process also brings many light elements into the Earth’s core. In particular, if the Moon-forming giant impact is a CMGI, then CMGI can also explain the abnormal content of HSEs in the Earth’s current mantle.

This chapter reviews the geochemistry and petrology of mantle peridotite xenoliths from across Antarctica, including parameters that are of most relevance to geophysical studies. This Memoir is the first time such a complete overview of the chemistry of Antarctic mantle xenoliths has been available and Antarctica should no longer be the ignored continent in studies of mantle xenoliths in volcanic rocks. Xenoliths indicate that the chemistry, heat flow and water content of the Antarctic lithospheric mantle varies regionally at scales of one to thousands of kilometres. The prevalence of variability in xenoliths suggests that the Antarctic mantle is ubiquitously heterogeneous. This has important, yet unquantified, implications for interpreting geophysical data and for reference Earth models used in Antarctic geophysical studies. Information about and interpretations of Antarctic mantle xenoliths can be linked to studies from once adjacent continental blocks in Africa, India, Australia, New Zealand and South America. Together, this can improve understanding of the mantle contribution to glacial isostatic adjustment and geodynamic models to show how the Antarctic mantle fits with adjacent continents in the puzzle of lithospheric blocks. Numerous, fundamental and important research questions remain unanswered making further study of the Antarctic mantle an exciting prospect for future research.

SUMMARY There is mounting evidence for the presence of seismic reflectors in the mantle at a depth of around 1000 km, however, the cause for these reflectors is not yet well established and published observations show a range of depth estimates for these structures. Discussion is also still ongoing whether it is one global or several different reflectors. Here, we investigate the presence of seismic reflectors beneath the North Atlantic using a large number of PP and SS underside reflections. We analyse over 2600 earthquakes with Mw ≥ 5.7 and use array seismic methods to improve the visibility of the small-amplitude reflected signals. The measured time lag between PP/SS arrivals and their corresponding precursors on robust stacks are used to estimate the depth of the reflector. Our results reveal the presence of mid-mantle structure beneath the North Atlantic in a depth range of ∼700–1300 km, consistent for both P- and S-wave observations. The reflector depth is shallower than 1000 km beneath the southern part of the investigation area and deepens seemingly abruptly towards the northern part of the North Atlantic. We find polarity variations in a region of strong depth change which we assume to be due to wave interference. Using 3-D waveform modelling, we implement models with strong topography as well as models with two overlapping reflectors and two separated reflectors and show that a large step in reflector depth over a short lateral distance, as imaged with our data set, can be resolved, while the discrimination between strong topography and two overlapping and separated reflectors, respectively, is also possible. The variations in precursor polarity can also be observed in our synthetic data in the region of strong topography confirming our assumption of wave interference for generating apparent precursor polarity and waveform changes. While the opposite polarity can be produced by the two overlapping reflectors as well, the strong topography model is preferred in this region, since we do detect only one reflected signal in our observations.

Subduction is the major plate driving force, and the strength of the subducting plate controls many aspects of the thermochemical evolution of Earth. Each subducting plate experiences intense normal faulting1–9 during bending that accommodates the transition from horizontal to downwards motion at the outer rise at trenches. Here we investigate the consequences of this bending-induced plate damage using numerical subduction models in which both brittle and ductile deformation, including grain damage, are tracked and coupled self-consistently. Pervasive slab weakening and pronounced segmentation can occur at the outer-rise region owing to the strong feedback between brittle and ductile damage localization. This slab-damage phenomenon explains the subduction dichotomy of strong plates and weak slabs10, the development of large-offset normal faults6,7 near trenches, the occurrence of segmented seismic velocity anomalies11 and distinct interfaces imaged within subducted slabs12,13, and the appearance of deep, localized intraplate areas of reduced effective viscosity14 observed at trenches. Furthermore, brittle–viscously damaged slabs show a tendency for detachment at elevated mantle temperatures. Given Earth’s planetary cooling history15, this implies that intermittent subduction with frequent slab break-off episodes16 may have been characteristic for Earth until more recent times than previously suggested17. Numerical subduction models used to determine the consequences of bending-induced plate damage show that slab weakening and segmentation can occur at the outer-rise region of the subducting plate.