Earth Transition Research Articles

Tectonic and climatic controls on sediment transport to the Southeast Indian Ocean during the Eocene: New insights from IODP Site U1514

The Eocene was a critical period of global plate reorganization and it also saw the Earth's climate transition from the warmhouse state to the coolhouse state. Reconstructing the Eocene sedimentary history in the climate-sensitive Southern Ocean is important for understanding paleoenvironmental changes in response to the accelerated Australia/Antarctica separation and global cooling throughout the middle and late Eocene. Here, we present the first detailed multiproxy record of a continuous sequence from International Ocean Discovery Program (IODP) Site U1514 in the Mentelle Basin off southwestern Australia. Our aim is to reconstruct the sediment provenances and paleoenvironmental evolution in response to the abovementioned climatic and tectonic changes in the mid-high southern latitudes during the Eocene. Provenance analyses based on Sr-Nd isotopes, trace elements, and clay mineral assemblages suggest that Eocene sediments at Site U1514 predominantly originated from the southwestern Australian continent and the Naturaliste Plateau. Sediment provenance variations during the middle Eocene indicate that the onset of fast separation between Australia and Antarctica at 43 Ma caused an increased supply of volcanic materials from the Naturaliste Plateau between 43 and 38 Ma. Terrigenous inputs to the Mentelle Basin during the middle Eocene were primarily controlled by paleoclimate changes rather than tectonic processes because coeval clay mineralogical changes (higher kaolinite/smectite ratio and MARkaolinite) indicate a period of stronger physical erosion and chemical weathering on the western Australian continent that resulted in increased terrigenous materials delivered to the Mentelle Basin. Our results reveal a 5 Myr-long (43–38 Ma) warming reversal in the southern mid-high latitudes, providing an exception to the generally short-lived (10–100 kyr-long) hyperthermals that interrupted the long-term global cooling throughout the middle to late Eocene. As for the late Eocene (38–37 Ma), tectonic processes related to the sudden acceleration in seafloor spreading in the Tasman Sea led to the exposure of shallower areas, resulting in rapid detritus accumulation at the study site. During the late Eocene (37–34 Ma), major sediment provenance shifted from distal source areas (e.g., the Yilgarn Craton) to relatively proximal sources (e.g., the Leeuwin Block and Perth Basin). We interpret that the regional uplift in southwestern Australia and coeval climate cooling resulted in the diversion and inactivation of large drainage systems, thus blocking the transportation of sediment from distant regions.

Mass characterisation of elemental toxicants in popular cigarettes sale in Pakistan using ICP-OES

ABSTRACT Environmental pollution and public health risks increase due to elevated metal levels in cigarettes throughout the globe especially in the developing countries. Herein, study is carried out to investigate the heavy metals and rare earth element contents in the popular cigarette brands (local and imported) in Pakistan. Twenty-six elements are measured in cigarette, tobacco, wrapping paper and filter (n = 168) sold in the Pakistan market in 14 brands of cigarettes using inductively coupled plasma-optical emission spectrometry (ICP-OES). The mean concentrations of Cr, V, Mo, Ni, Sn, As, Sb, Fe, Al, Mg, Ti and B (8.30, 0.22, 0.45, 1.85, 4.63, 1.32, 0.89, 378.01, 180.18, 2134.21, 6.53 & 22.20 μg/g), respectively, are slightly higher in local cigarette brands and the mean concentration of Co, Cd, Pb, Se, Sr, Mn, Cu, Zn, Ca, K, Na, Y, Zr and Ba (0.49, 0.69, 1.58, 1.47, 71.03, 68.23, 32.69, 32.33, 2906.82, 7601.73, 962.31, 0.10, 1.04 & 35.19 μg/g), respectively, are slightly higher in imported cigarette brands. The concentrations of Pb, Ni, Cd, Co, Fe and Zn in local tobacco cigarettes are approximately comparable to concentration levels of metals in imported tobacco cigarettes sold in other countries. While a strong positive correlation was observed in Cr, Sn, Mn, Ba, Ni, Co, As and Sr, while K, Mo, Ti, Ca and Mo were negatively associated with other elements. In addition, this study also provides an important information on the elemental levels such as alkali metals (Na & K), alkaline rare earth metals (Mg, Ca, Sr & Ba), transition metals (Ti, V, Mo, Y & Zr), post-transition metals (Sn), metalloids (B & As) and reactive non-metal (Se) for the very first time in Pakistan in different components of cigarettes. We believe that this study will be beneficial to the prevention of public health hazards and the reduction of human health risks through tobacco consumption.

Remarkable kinetics of novel Ni@CeO2–MgH2 hydrogen storage composite

Magnesium hydroxide (MgH2) has excellent reversibility and high capacity, and is one of the most promising materials for hydrogen storage in practical applications. However, it suffers from high dehydrogenation temperature and slow sorption kinetics. Rare earth hydrides and transition metals can both significantly improve the de/hydrogenation kinetics of MgH2. In this work, MgH2–Mg2NiH4–CeH2.73 is in-situ synthesized by introducing Ni@CeO2 into MgH2. The unique coating structure of Ni@CeO2 facilitates homogeneous distribution of synergetic CeH2.73 and Mg2NiH4 catalytic sites in subsequent ball milling process. The as-fabricated composite MgH2-10 wt% Ni@CeO2 powders possess superior hydrogenation/dehydrogenation characteristics, absorbing 4.1 wt% hydrogen within 60 min at 100 °C and releasing 5.44 wt% H2 within 10 min at 350 °C. The apparent activation energy of MgH2-10 wt% Ni@CeO2 is determined to be 84.8 kJ/mol and it has favorable hydrogen cycling stability with almost no decay in capacity after 10 cycles.

Enhancement of permittivity off-diagonal terms in rare earth transition metal / heavy metal hetero-structured films

The spin Hall effect, Dzyaloshinskii-Moriya interaction, Rashba effect, etc. are extremely important effects for the development of the conduction phenomenon of spin electronics due to the breaking of the spatial inversion symmetry of the hetero interface made of heavy metals such as Pt and W. These are due to SOI (spin-orbit interaction). Most of these studies have been conducted in the frequency domain below GHz, and there are few studies in the energy domain of light. Therefore, in the region of light energy, the magnetic optical Kerr effect spectra of the TbCo/Pt hetero-structured film with large SOI from the Pt interface and the TbCo/Cu hetero-structured film with small SOI from the Cu interface were measured, and the permittivity tensors were investigated respectively. As a result, in the TbCo/Pt hetero-structured film, the dielectric constant off-diagonal component real part of the thin TbCo layer increased about twice as much as that of bulk TbCo in the energy region smaller than 2.5 eV. However, this increase was not observed in the TbCo/Cu hetero-structured film. This result suggests that the influence of the Pt hetero interface where the spatial inversion symmetry is broken may appear even in the energy region of light. Furthermore, it has been confirmed that TbCo/W hetero-structured film using W with a large SOI has the same increasing effect as that of the TbCo/Pt.

Density functional theory study on hydrogen storage capacity of metal-embedded penta-octa-graphene

H2 storage capabilities of penta-octa-graphene (POG) adorned by lightweight alkali metals (Li, Na, K), alkali earth metals (Be, Mg, Ca) and transition metals (Sc, Ti, V, Cr, Mn) are studied by density functional theory. Metals considered, with the exception of Be and Mg, can be stably adsorbed to POG, effectively avoiding metal clustering. The average H2 adsorption energies are calculated in a range from 0.14 to 0.95 eV for Li (Na, K, Ca, Sc, Ti, V, Cr, Mn) decorated POG. Because the H2 adsorption energies for reversible physical adsorption lie in the range of 0.15–0.60 eV and the desorption temperatures fall in the range of 233–333 K under the delivery pressure, 4Li@POG and 2Ti@POG are found to be the most suitable for H2 storage at ambient temperature. By polarization and hybridization mechanisms, up to 3 and 5 hydrogen molecules are stably adsorbed around each Li and Ti, respectively. The H2 gravimetric densities can reach up to 9.9 wt% and 6.5 wt% for Li and Ti decorated POG, respectively. Our findings suggest that, with metal decoration, such a novel two-dimensional carbon-based structure could be a promising medium for H2 storage.

Moderate levels of oxygenation during the late stage of Earth's Great Oxidation Event

The later stages of Earth's transition to a permanently oxygenated atmosphere during the Great Oxidation Event (GOE; ∼2.43–2.06 Ga) is commonly linked with the suggestion of an “oxygen overshoot” during the ∼2.22–2.06 Ga Lomagundi Event (LE), which represents Earth's most pronounced and longest-lived positive carbon isotope excursion. However, the magnitude and extent of atmosphere-ocean oxygenation and implications for the biosphere during this critical period in Earth's history remain poorly constrained. Here, we present nitrogen (N), selenium (Se), and carbon (C) isotope data, as well as bio-essential element concentrations, for Paleoproterozoic marine shales deposited during the LE. The data provide evidence for a highly productive and well-oxygenated photic zone, with both inner and outer-shelf marine environments characterized by nitrate- and Se oxyanion-replete conditions. However, the redoxcline subsequently encroached back onto the inner shelf during global-scale deoxygenation of the atmosphere-ocean system at the end of the LE, leading to locally enhanced water column denitrification and quantitative reduction of selenium oxyanions. We propose that nitrate-replete conditions associated with fully oxygenated continental shelf settings were a common feature during the LE, but nitrification was not sufficiently widespread for the aerobic nitrogen cycle to impact the isotopic composition of the global ocean N inventory. Placed in the context of Earth's broader oxygenation history, our findings indicate that O2 levels in the atmosphere-ocean system were likely much lower than modern concentrations. Early Paleoproterozoic biogeochemical cycles were thus far less advanced than after Neoproterozoic oxygenation.

Elemental Profiling for Discrimination of Geographical Origin of Tea (Camellia sinensis) in north-east region of India by ICP-MS coupled with Chemometric techniques

The study aimed to discriminate the teas originated from eight north-east region of India using 67 elemental profiling through the use of ICP-MS and process the large data with chemometric software. Among the 67 elements, concentrations of 18 elements were significantly different in the eight regions (Darjeeling, Tripura, Upper Assam, South Bank, Terai, North Bank, Dooars and Cachar). Selected 18 elements belongs to alkali metal (Rb, Cs), alkaline earth metal (Mg, Sr, Ba), transition metal (V, Cr, Mn, Co, Ni, Zn, Mo), basic metal (Al), metalloid (B), non-metal (Se) and lanthanide (La, Ce, Nd). Multivariate chemometric analysis with PCA, LDA, SVM & OPLS DA were performed on the concentration of 18 elements on 307 authentic sample set. The correct classification rate for the training set (307) and test set (24) tea samples were 100% for SVM, LDA and OPLS DA model and confidence measure for SVM and LDA model were 99.4% and 88.97%, respectively. Variable importance in projection (VIP) values ranged between 1.04-1.51 for five elements (Cr, Mo, Rb, Mn and Ni), which can be considered as significant parameter for discrimination. The results demonstrated that ICP-MS with chemometric software could be used to discriminate the geographical origin of tea.

Formation of nanogratings driven by ultrafast laser irradiation in mid-IR heavy oxide glasses

This work demonstrates for the first time the formation of nanogratings inside Barium Gallo-Germanate (BGG) glasses using femtosecond laser direct writing. These heavy oxide glasses, with a characterized transparency window up to 6 μm, along with the polarization sensitive birefringent nanostructures induced by femtosecond laser, offer an excellent platform for the development of mid-Infrared photonic applications. The fabricated glasses, containing both rare earth elements (Gd, Y) and transition metals (Zn, Ta), are directly compared to amorphous GeO2 and commercial alumino-germanate (Corning-9754) glasses commonly used in this field. The nanogratings processing window in each glass was investigated by varying laser parameters (pulse duration, energy, repetition rate), and electron microscopy imaging directly evidenced the porous nanostructures. Among the results, a strong form birefringence in 8% ZnO containing BGG glass, e.g., up to −0.029 ± 0.001, was reported. Finally, birefringent embedded Fresnel GRIN plates were directly written in a BGG glass, to demonstrate the functionalization potential of these materials.

Metal element doping in Cs(Pb1 − xDEx)Br3 for solar cell materials

The structure, and the electronic properties, caused by alkaline earth metals and transition metals substituting for Pb in CsPbBr3 (CPB) are studied by the first principal calculations. Obtained results show that with increasing the dopants concentration, the substitution of Pb with alkali earth metals in CsPbBr3 induces an increase of the electronic band gap, and the direct band gap turns to be the indirect band gap; On the other hand, the substitution of Pb by transition metal elements in CsPbBr3 induces a decrease of the band gap, and the band gap becomes indirect band gap. Doping for Pb may adjust the bandgap of the CsPbBr3 to be 1.3∼1.5eV for fabricating the high efficiency solar cells. The calculated results also prove that the electronegativity of the metal is related the band gap of the doped CPB, which may be related to the outermost s-orbital electrons in the band. The average energy of the s-orbital electrons of the doped metal is highly consistent with the electronegativity of the metal and the change of the band gap after doping. This may open a new way to design the dopants for CPB.

Earth through the looking glass: how frequently are we detected by other civilizations through photometric microlensing?

ABSTRACT Microlensing is proving to be one of the best techniques to detect distant, low-mass planets around the most common stars in the Galaxy. In principle, Earth’s microlensing signal could offer the chance for other technological civilizations to find the Earth across Galactic distances. We consider the photometric microlensing signal of Earth to other potential technological civilizations and dub the regions of our Galaxy from which Earth’s photometric microlensing signal is most readily observable as the ‘Earth microlensing zone’ (EMZ). The EMZ can be thought of as the microlensing analogue of the Earth Transit Zone (ETZ) from where observers see Earth transit the Sun. Just as for the ETZ, the EMZ could represent a game-theoretic Schelling point for targeted searches for extra-terrestrial intelligence (SETI). To compute the EMZ, we use the Gaia DR2 catalogue with magnitude G < 20 to generate Earth microlensing probability and detection rate maps to other observers. While our Solar system is a multiplanet system, we show that Earth’s photometric microlensing signature is almost always well approximated by a binary lens assumption. We then show that the Earth is in fact well hidden to observers with technology comparable to our own. Specifically, even if observers are located around every Gaia DR2 star with G < 20, we expect photometric microlensing signatures from the Earth to be observable on average only tens per year by any of them. In addition, the EMZs overlap with the ETZ near the Galactic Centres which could be the main areas for future SETI searches.

Solvent-driven fractional crystallization for atom-efficient separation of metal salts from permanent magnet leachates

This work reports a dimethyl ether-driven fractional crystallization process for separating rare earth elements and transition metals. The process has been successfully applied in the treatment of rare earth element-bearing permanent magnet leachates as an atom-efficient, reagent-free separation method. Using ~5 bar pressure, the solvent was dissolved into the aqueous system to displace the contained metal salts as solid precipitates. Treatments at distinct temperatures ranging from 20–31 °C enable crystallization of either lanthanide-rich or transition metal-rich products, with single-stage solute recovery of up to 95.9% and a separation factor as high as 704. Separation factors increase with solution purity, suggesting feasibility for eco-friendly solution treatments in series and parallel to purify aqueous material streams. Staged treatments are demonstrated as capable of further improving the separation factor and purity of crystallized products. Upon completion of a crystallization, the solvent can be recovered with high efficiency at ambient pressure. This separation process involves low energy and reagent requirements and does not contribute to waste generation.

Towards a classification scheme for the rocky planets based on equilibrium thermodynamic considerations

ABSTRACT A classification scheme for rocky planets is proposed, based on a description of the Earth System in terms of the Landau–Ginzburg Theory of phase transitions. Three major equilibrium states can be identified and the associated planetary states or phases are: Earth-like Holocene state; hot Venus-like state; cold Mars-like state. The scheme is based on an approach proposed to understand the Earth transition from the Holocene to the Anthropocene, driven by the impact of the human action on the Earth System. In this work, we identity the natural conditions that cause transformations on the planets forcing them into one of the states identified above. We discuss how the parameters that describe these transformations can be related with exoplanets observables. In analysing the relevant physical parameters, we were stroke by the similarities between Earth and Venus, and how likely is that the Anthropocene transition may lead to hot-house Earth scenario.

In-situ infrared spectroscopic study of the mechanism of the low temperature selective catalytic reduction of NO surface by Mn/ bastnaesite concentrate

The Mn/bastnaesite concentrate and Mn/Al2O3 catalysts were prepared by impregnation method, and their NH3-SCR denitrification performance was tested. The results showed that the Mn/bastnaesite concentrate catalyst achieved up to 95% NO conversion rate at 150 °C, and the Mn/Al2O3 catalyst reached 76% at 300 °C. A series of characterisation results showed that the bastnaesite concentrate can better interact with MnOx species and promote mutual dispersion compared to Al2O3. The Mn/bastnaesite concentrate has a stronger redox capacity, and good NH3 and NO adsorption capacity at low temperatures. The multi-element coexistence system of bastnaesite concentrate itself is a significant advantage of its use as a carrier. In-situ Fourier transform infrared (FTIR) results showed that the Mn/bastnaesite concentrate catalyst follows an L-H mechanism throughout the reaction, with NH4+ species in the Brønsted acidic site on the catalyst surface being the main reactant species. Most of NO is converted to monodentate nitrite, which is formed by bonding with Mn3+ provided by the supported Mn species, rare earth elements and transition metal ions contained in the carrier itself to form O–N–O–Mn3+ intermediates, which participate in the reaction together, and then combined with the adsorbed NH4+/NH3 species to produce N2 and H2O. An E-R mechanism was also present on the catalyst surface, NO participates directly in the reaction in gaseous form, and the NO [NH2](ads) intermediate species produced by interaction with NH4+ species in the acidic position of Brønsted was further decomposed to N2 and H2O. By comparing the reaction mechanism with the commonly used catalyst carrier Al2O3 for NH3-SCR, it can be concluded that bastnaesite concentrate as a carrier not only has the performance of conventional carriers, but also has certain catalytic activity and can interact with the active components to give it excellent performance, which provides a theoretical basis for rare earth minerals as denitrification catalysts.

Impact of the No-Till technology on erosive degradation of soils in hollows

The present research is aimed at studying the impact of the modern no-till agricultural technology on the development of erosion processes on cultivated arable land in the subzone of the southern chernozems of the Volgograd region. Evaluation of the impact of this agricultural technology was based on the analysis and comparison of soil cover in hollows located in the fields cultivated using either the classic technology or the no-till technology. The research methodology is based on combination of remote, field and laboratory methods for studying the soil cover. Analysis and generalization of data obtained in the course of laboratory studies of selected soil samples made it possible to identify a high degree of erosion processes in the hollows located in the fields, which had been cultivated using the no-till technology for three years. Comparison of the values of the content of organic carbon in the zones of removal, transit and accumulation of fine earth indicates the development of water degradation processes in the middle part of the hollows. Thus, for soil samples taken from a depth of 0-10 cm, the value of organic carbon content in the variant of soil tilled using the new technology is 2.6%, while in the variant tilled using the classic technology, this value is equal to 3.1%. The revealed differences in the soil cover of the hollows can be explained by interaction of the patterns of development of erosion-accumulation processes and the features of the no-till technology in specific natural and climatic conditions.

Highly selective extraction of uranium from wastewater using amine-bridged diacetamide-functionalized silica

A major environmental concern related to nuclear energy is wastewater contaminated with uranium, thus necessitating the development of pollutant-reducing materials with efficiency and effectiveness. Herein, highly selective mesoporous silicas functionalized with amine-bridged diacetamide ligands SBA-15-ABDMA were prepared. Different spectroscopy techniques were used to probe the chemical environment and reactivity of the chelating ligands before and after sorption. The results showed that the functionalized SBA-15-ABDMA had a strong affinity for uranium at low pH (pH = 3) with desirable sorption capacity (68.82 mg/g) and good reusability (> 5). It showed excellent separation performance with a high distribution coefficient (Kd,U > 105 mL/g) and separation factors SFU/Ln > 1000 at a pH of 3.5 in the presence of lanthanide nuclides, alkaline earth metal and transition metal ions. In particular, SiO2spheres-ABDMA was used as a column material, which achieved excellent recovery of U(VI) (> 98%) and good reusability for samples of simulated mining and nuclear industries wastewater. XPS and crystallography studies clearly illustrated the tridentate coordination mode of U(VI)/PEABDMA and the mechanism and origin behind the high selectivity for U.

Zeolitic Imidazolate Framework 67-Derived Ce-Doped CoP@N-Doped Carbon Hollow Polyhedron as High-Performance Anodes for Lithium-Ion Batteries

Zeolitic Imidazolate Framework 67 (ZIF-67) and its derivates have attracted extensive interest for lithium-ion batteries (LIBs). Here, Cerium-doped cobalt phosphide@nitrogen-doped carbon (Ce-doped CoP@NC) with hollow polyhedron structure materials were successfully synthesized via ionic-exchange with Co and Ce ions using the ZIF-67 as a template followed with a facile low-temperature phosphorization treatment. Benefitting from the well-designed hollow polyhedron, steady carbon network, and Ce-doping structural merits, the as-synthesized Ce-doped CoP@NC electrode demonstrated superior performance as the anode in LIBs: a superior cyclability (400 mA h g−1 after 500 cycles) and outstanding rate-capability (590 mA h g−1, reverted to 100 mA g−1). These features not only produced more lithium-active sites for LIBs anode and a shorter Li-ion diffusion pathway to expedite the charge transfer, but also the better tolerance against volume variation of CoP during the repeated lithiation/delithiation process and greater electronic conductivity properties. These results provide a methodology for the design of well-organized ZIFs and rare earth element-doped transition metal phosphate with a hollow polyhedron structure.

Fire ecology for the 21st century: Conserving biodiversity in the age of megafire

Fire ecology for the 21st century: Conserving biodiversity in the age of megafire

Characteristics of trace elements in crude oil in the east section of the south slope of Dongying Sag and their application in crude oil classification

The east section of the south slope of the Dongying Sag is rich in oil and gas resources, with diverse reservoir types and complex physical properties of crude oil. It has typical characteristics of multi-source and multi-stage accumulation. The classification of crude oil types is the basis of petroleum geology research. By analyzing the content and distribution characteristics of trace elements in typical crude oil samples, combined with mathematical statistics, the effective classification of crude oil types in the study area is realized. The content of alkali metals, alkaline earth metals and transition metal elements in crude oil is significantly higher than that of rare earth elements, and the content of light rare earth elements is higher than that of heavy rare earth elements. There is a good correlation between the total amount of trace elements and the bulk composition of crude oil, while the correlation between the total amount of rare earth elements and the bulk composition of crude oil is relatively poor. The cluster analysis of multiple trace element-related parameters can classify the crude oil into three types, and the biomarker parameters of different type crude oils show obvious differences, indicating that the use of trace elements to classify crude oil types is effective and feasible in the study area. This study shows that the content, distribution characteristics and related parameters of trace elements in crude oil can be used as effective oil source correlation tools, reasonable selection of correlation parameters, and comprehensive analysis of cluster analysis methods can accurately classify the types of crude oil.

Thermodynamic calculation of phase equilibria of rare earth metals with boron binary systems

Abstract In order to develop novel materials based on rare earth (RE) boride and/or transition metals, phase equilibria and thermodynamic information of the RE–B based alloys are indispensable. On the basis of experimental phase equilibria and thermodynamic properties, thermodynamic assessments of the RE–B (RE = La, Sm, Gd and Tb) binary systems were carried out by the CALPHAD (Calculation of Phase Diagram) method. Self-consistent parameters of the RE–B (RE = La, Sm, Gd and Tb) binary systems were obtained, which can be used to reproduce well the experimental data. Furthermore, in combination with the previous assessments of the RE–B binary systems in the literature, phase equilibria and thermodynamic properties of the RE–B (RE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) binary systems are discussed systematically. The tendency of phase equilibria and thermodynamic information as a function of RE atomic number is demonstrated. In general, the enthalpy of mixing of liquid RE–B alloys and the enthalpy of formation of the RE–B intermetallic compounds become more and more negative with the increase in RE atomic number (except for La, Ce, Pr and Nd), while the phase transition temperatures for the RE–B intermetallic compounds increase gradually.

3-D synthetic modelling and observations of anisotropy effects on SS precursors: implications for mantle deformation in the transition zone

SUMMARY The Earth's mantle transition zone (MTZ) plays a key role in the thermal and compositional interactions between the upper and lower mantle. Seismic anisotropy provides useful information about mantle deformation and dynamics across the MTZ. However, seismic anisotropy in the MTZ is difficult to constrain from surface wave or shear wave splitting measurements. Here, we investigate the sensitivity to anisotropy of a body wave method, SS precursors, through 3-D synthetic modelling and apply it to real data. Our study shows that the SS precursors can distinguish the anisotropy originating from three depths: shallow upper mantle (80–220 km), deep upper mantle above 410 km, and MTZ (410–660 km). Synthetic resolution tests indicate that SS precursors can resolve $\ge $3 per cent azimuthal anisotropy where data have an average signal-to-noise ratio (SNR = 7) and sufficient azimuthal coverage. To investigate regional sensitivity, we apply the stacking and inversion methods to two densely sampled areas: the Japan subduction zone and a central Pacific region around the Hawaiian hotspot. We find evidence for significant VS anisotropy (15.3 ± 9.2 per cent) with a trench-perpendicular fast direction (93° ± 5°) in the MTZ near the Japan subduction zone. We attribute the azimuthal anisotropy to the grain-scale shape-preferred orientation of basaltic materials induced by the shear deformation within the subducting slab beneath NE China. In the central Pacific study region, there is a non-detection of MTZ anisotropy, although modelling suggests the data coverage should allow us to resolve at least 3 per cent anisotropy. Therefore, the Hawaiian mantle plume has not produced detectable azimuthal anisotropy in the MTZ.