The great sulfur depletion of Earth’s mantle is not a signature of mantle–core equilibration

The extreme depletion of the Earth’s mantle in sulfur is commonly seen as a signature of metal segregation from Earth’s mantle to Earth’s core. However, in addition to S, the mantle contains other elements as volatile as S that are hardly depleted relative to the lithophile volatility trend although they are potentially as siderophile as sulfur. We report experiments in metal-sulfide–silicate systems to show that the CI normalized abundances of S, Pb, and Sn in Earth’s mantle cannot be reproduced by element partitioning in Fe ± S–silicate systems, neither at low nor at high pressure. Much of the volatile inventory of the Earth’s mantle must have been added late in the accretion history, when metal melt segregation to the core had become largely inactive. The great depletion in S is attributed to the selective segregation of a late sulfide matte from an oxidized and largely crystalline mantle. Apparently, the volatile abundances of Earth’s mantle are not in redox equilibrium with Earth’s core.     

On thermochemical mantle plumes with an intermediate thermal power that erupt on the Earth’s surface

The relative plume thermal power Ka = N/N₁ is used (N is the thermal power transferred from the plume base to its conduit and N₁ is the thermal power transferred from the plume conduit into the surrounding mantle in the steady-state heat conduction regime). Thermochemical mantle plumes with small (Ka < 1.15) and intermediate (1.15 < Ka < 1.9) thermal powers are formed at the core–mantle boundary beneath cratons in the absence of horizontal free-convection mantle flows beneath them, or in the presence of weak horizontal mantle flows. Thermochemical plumes reach the Earth’s surface when their relative thermal power is Ka > 1.15. The thermal and hydrodynamical structure of the plume conduit ascending from the core–mantle interface to the level from which the magmatic melt erupts on the Earth’s surface is presented. The model of two-stage eruption of the melt from the plume conduit to the surface is considered. The critical height of the massif above the plume roof, at which the eruption conduit supplying magmatic melt to the surface forms, is determined. The volume of melt erupting through the eruption conduit to the surface is estimated. The dependence of depth Δx from which the melt is transported to the surface on the plume diameter for a kinematic viscosity of ν = 0.5–2 m²/s is presented. In the case when the value Δx is larger than the depth starting from which diamond is stable (150 km), the melt from the plume conduit can transport diamonds to the Earth’s surface. The melt flow in the eruption conduit is considered as a turbulent flow in a cylindrical duct. The velocity of the melt flow in the eruption conduit and the time for the melt to be transported to the surface from a depth of Δx = 150 km for a kinematic viscosity of the melt in the eruption conduit ν_v = 0.01–1 m²/s are determined. Tangential stress on the eruption conduit sidewall is estimated in cases of melt flow both in smooth and rough conduits.     

Fluorine and chlorine in mantle minerals and the halogen budget of the Earth’s mantle

The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth’s upper mantle and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (≥0.4 µg/g F and ≥0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine ~ orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4–31 µg/g F and 0.14–0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1–9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that nearly all MORB may be somewhat contaminated by seawater-rich material and that the Cl content of DMM could be overestimated. With this study, we demonstrate that the halogen contents of natural peridotite minerals are a unique tool to understand the cycling of halogens, from ridge settings to subduction zones.     

Changes in the temperatures of perennially frozen rocks due to pollution of the earth’s surface by coal dust in the territory of the Pechorsk coal basin

A quantitative estimate of the influence on the temperature mode of perennially frozen rocks in the Pechorsk coal basin caused by pollution of the surface by coal dust was undertaken.     

El Ni?o as a consequence of the global oscillation in the dynamics of the earth’s climatic system

During study of the physical nature and potential precursor features of the El Ni?o phenomenon in the Pacific, it was found that a negative large-scale temperature anomaly on the Indian Ocean surface may be one of its significant precursors. This anomaly appears prior to the occurrence of El Ni?o and is accompanied by growth in atmospheric pressure. It gradually extends eastwards along the equator until the zone of planetary convection in the area of the Indonesian Region. The west wind that emerges on the eastern peripherals of the mentioned pressure anomaly leads to reversal of the Pacific segment of the Walker equatorial atmospheric circulation and to a subsequent change in the zonal thermal dipole polarity in the tropical zone of the Pacific (the latter means culmination of the El Ni?o phenomenon). In addition to the mentioned thermobaric anomaly in the Indian Ocean, other obvious signs of large-scale pressure anomalies have been found in the global atmospheric pressure field; these anomalies may be interpreted as manifestations of the intradecadal global oscillation in the dynamics of the modern climatic system. It is suggested that the whole known complex of events related to the El Ni?o phenomenon in the Pacific is a consequence and a regional link of the planetary structure of this global atmospheric phenomenon.     

Ca- and Mg-perovskite phases in the Earth’s mantle as a probable reservoir of Al: Computer-simulation evidence

Semi-empirical and quantum chemical studies of Al atom energy in CaSiO₃ and MgSiO₃ with the perovskite-type structure at pressures and temperatures of the Earth’s mantle are reported. The phase diagram for CaSiO₃ is reproduced and refined. Probable mechanisms of Al incorporation in the structures studied are considered. According to the results of the calculations, Al is preferably incorporated into MgSiO₃, rather than into CaSiO₃. Evaluation of the isomorphic capacity of perovskite phases in relation to Al shows that the Al content in MgSiO₃ may reach 2.4 mol % at 120 GPa and 2400 K. CaSiO₃ cannot be a source of Al atoms in the Earth’s mantle.     

Analysis of an oasis microclimate in China’s hyperarid zone

The microclimate of a desert oasis in China’s hyperarid zone was monitored, analysed and compared to that of nearby forested lands. Factors associated with differences in photosynthetically active radiation (PAR) between clear, cloudy and dust storm days are discussed. Desert oases were shown to fulfill ecological functions such as altering solar radiation, adjusting near-ground and land surface temperatures, reducing temperature differences, lowering wind velocity, and increasing soil and atmospheric humidity. Total solar radiation within the oasis was roughly half that above the forest canopy. During the growing season, air temperatures in Populus euphratica Olivier and Tamarix ramosissima Ledeb. woodlands were, on average, 1.62 and 0.83°C lower, respectively, than that in surrounding woodlands. The greater the forest cover, the greater was the difference in temperature. Air temperature was higher at the upper storey than that at the lower storey of the community, i.e., air temperature increased with increasing height above the soil surface. During the growing season, relative humidity was higher in woodlands than in surrounding areas: relative humidity in P. euphratica and T. ramosissima woodlands were, on average, 8.5 and 4.2% higher, respectively, than that in the surrounding area. Mean wind velocity in the P. euphratica forest land was 0.33 m/s, 2.31 m/s lower than that in the surrounding area. On dust storm days PAR and total radiation, Q, were significantly lower than that on cloudy or clear days. Their ratio, η _Q  = PAR/Q, was larger and much more variable on dust storm days than that on clear or cloudy days.     

Thermoelectric characteristics of semiconductor minerals in earth’s deep crust and their seismogenic significance

Geo-electric anomalies are generated during the process of stress accumulation and release associated with earthquakes. However, the mechanism of these anomalies remains equivocal. Based on the analysis of thermoelectric characteristics of semiconductor minerals of the earth’s deep crust such as graphite, ferrosilicon alloy, magnetite etc., we perform finite element analysis to evaluate the principles governing the thermoelectric power generated by minerals and rocks. The results show that graphite, ferrosilicon alloy and magnetite all exhibit Seebeck effect and can be superimposed. And the thermo-electric field can be enhanced with the activation temperature increases, the content of thermoelectric minerals increases, the size of aggregates increases, and the spacing of thermoelectric minerals grains decreases. Seismogenic processes would generate a similar thermal gradient. The natural semiconductor minerals in this thermal field show a thermoelectric effect, forming a thermoelectric field that interferes with the background electric field. This study indicates that thermoelectric effect may have an important influence on the formation of geoelectric field.     

Rift induced delamination of mantle lithosphere and crustal uplift: a new mechanism for explaining Rwenzori Mountains’ extreme elevation?

With heights of 4–5 km, the topography of Rwenzori Mountains, a large horst of old crustal rocks located inside a young passive rift system, poses the question “Why are the Rwenzori Mountains so high?”. The Cenozoic Western Rift branch of the East African Rift System is situated within the Late Proterozoic mobile belts between the Archean Tanzania Craton and Congo Craton. The special geological setting of the massif at a rift node encircled by the ends of the northern Western Rift segments of Lake Albert and Lake Edward suggests that the mechanism responsible for the high elevation of the Rwenzoris is related to the rifting process. Our hypothesis is based on the propagation of the rift tips, surrounding the stiff old lithosphere at Rwenzori region, thereby triggering the delamination of the cold and dense mantle lithosphere (ML) root by reducing viscosity and strength of the undermost lower crust. As a result, this unloading induces fast isostatic pop-up of the less dense crustal Rwenzori block. We term this RID—“rift induced delamination of Mantle Lithosphere”. The physical consistency of the RID hypothesis is tested numerically. Viscous flow of 2D models is approximated by a Finite Difference Method with markers in an Eulerian formulation. The equations of conservation of mass, momentum and energy are solved for a multi-component system. Based on laboratory data of appropriate rock samples, a temperature-, pressure- and stress-dependent rheology is assumed. Assuming a simple starting model with a locally heated ML, the ML block between the weakened zones becomes unstable and sinks into the asthenosphere, while the overlying continental crust rises up. Thus, RID seems to be a viable mechanism to explain geodynamically the extreme uplift. Important conditions are a thermal anomaly within the ML, a ductile lower crust with visco-plastic rheology allowing significant strength reduction and lateral density variations. The special situation of a two-sided rifting or offset rift segments to decouple the ML laterally from the surrounding continental lithosphere seems to be most decisive. Further support for the RID mechanism may come from additional crustal thickness and an extensive stress field. Some parameters, such as the excess temperature and yield stress, are very sensitive, small changes determine whether delamination takes place or not.     

Older people’s psychosocial needs in a post-disaster rural community of China: an exploratory study

Older people are arguably one of the most vulnerable groups during a disaster. Existing studies either in China or in other countries predominantly focus on the more Western, pathology-based mental health approach in addressing the impact of disasters on older victims and their needs. However, the concept of ‘psychosocial’ recognises that problems caused by emergencies can simultaneously be of a social nature and a psychological one. This concept emerged from a growing critique on individual oriented mental health approach in disaster contexts. The present study was conducted to explore older people’s needs from a psychosocial perspective. The research site was a Chinese rural community located in the epicentre of ‘5.12’ Wenchuan earthquake (Ms = 8.0) occurred in 2008. The authors conducted content analyses on the qualitative in-depth interviews with 10 (5 males and 5 females) out of 30 older persons from this community. The findings revealed three major psychosocial problems: (1) constant fear of recurring debris flows; (2) sense of helplessness; and (3) disruption to previous social network. Indubitably, the participants reported family members and neighbours as their major sources of social support in emergency situations. This exploratory study argues that older people being exposed to disasters will not only develop psychological problems but also suffer disruption to their social support network and puts forward that empowering family and strengthening community cohesion are important initiatives for helping professionals to promote older people’s psychosocial well-being and enhance their resilience to natural disasters.     

Making a new area in Xiong’an: Incentives and challenges of China’s “Millennium Plan”

On April 1, 2017, China announced to initiate the Xiong’an New Area (XNA) plan, which is a national-level strategy aimed at alleviating the pressures felt by Beijing and promoting the integration of the Beijing-Tianjin-Hebei (BTH) city-region. In China, a city-region can be viewed as an outcome of state spatial selectivity that aims to manage crises and maintain governance through strong state involvement. This paper attempts to provide a broad view of the XNA plan by examining it in the context of China’s long-term efforts to coordinate the BTH region, explaining the incentives associated with choosing Xiong’an, and analyzing the challenges the plan has faced. Considering that theoretical insights based on Western experience may not be applicable to China, this paper can contribute to the debate revealing the logics of city-region building in different contexts.     

Evolution of manganese ore genesis in the earth’s geological history and the role of the biosphere

The formation of manganese rocks and ores occurred during the whole geological history of the Earth. Five metallogenic epochs (Early to Middle Proterozoic, Late Proterozoic, Early to Middle Paleozoic, Late Paleozoic, and Meso-Cenozoic) and 7 very important phases (Early, Middle, and Late Proterozoic, Early to Middle Paleozoic, Late Paleozoic, Late Mesozoic, and Meso-Cenozoic) can be distinguished. The phases of manganese ore genesis at many stratigraphic levels are closely related to the global climatic and tectonic reconstructions (the breakup of the continent of Gondwana and periods of glaciations and aridization) and biotic events (mass extinction of organisms). Based on carbon isotopic composition in manganese carbonates, participation of oxidized organic carbon is established.