Constraints on mantle heterogeneity

Compositional and structural variations within Earth’s lower mantle are a complex puzzle to which seismic data hold clues.

Advances in seismological observational and modelling techniques are needed to constrain complex lowermost mantle structures and understand their influence on the global dynamics and evolution of Earth’s interior.

Nature Geoscience spoke with Samantha Hansen, a geophysicist at the University of Alabama and Sebastian Rost, a global seismologist at the University of Leeds about the ultralow velocity zones in the lowermost mantle.

A record of lower mantle flow from 50 million years ago is preserved in the Pacific region and provides evidence for past lower mantle deformation, according to seismic anisotropy tomography.

Global detections of ultralow velocity zones in high-velocity lowermost mantle regions are associated with thermochemical anomalies linked to subducted slabs, according to analysis of SKKKP B-caustic diffractions with anomalous seismic structures in the mantle and outer core.

The presence of an ultralow velocity zone and seismic anisotropy in the lowermost mantle beneath the Himalayas is linked to subducted slab remnants and southwest mantle flow, according to analyses of seismic waves and mantle anisotropy measurements.

Computer simulations show that mantle material from Theia, a proto-planet theorized to have struck the proto-Earth in the Moon-forming giant impact, may be the source of Earth’s basal mantle anomalies.

An ultra-low seismic velocity region that may contain unstable mineral phases exists within the cold Pacific slab near the 410-km discontinuity at the Kuril subduction zone, according to analyzes of P-wave travel times and waveforms from dense seismic arrays.

A partially molten low-seismic-velocity zone in the asthenosphere is globally prevalent, but partial melting is not the primary control of low asthenospheric viscosity, according to analysis of seismic waves travelling through the mantle.

The seismic anomaly in the lowermost mantle beneath Africa is greater in height and less stable than its Pacific counterpart because of its lower density, according to numerical simulations of the anomalies as thermochemical piles.

Ultra-low velocity zones (ULVZs) are localized small-scale patches with extreme physical properties at the core-mantle boundary. Here, the authors discover a mega-sized ULVZ (1,500 × 900 km) at the northern edge of the Pacific Large Low Velocity Province.

The internal structures of ultralow-velocity zones at the base of the mantle are consistent with an origin from remnants of the early Earth’s differentiation, according to seismic data analysis and geodynamical modelling.

Dense Fe³⁺-rich bridgmanite can explain the seismic features of Large Low Shear Velocity Provinces, as it can form large-scale thermochemical piles in the deep mantle that remain stable throughout Earth’s history.

Earth’s deep-mantle domains are geochemically distinct. The African domain is enriched in subducted material, which suggests a different history from the Pacific domain and a dynamic relationship between plate tectonics and deep-mantle structures.

Unexpectedly low seismic velocities of CaSiO₃ perovskite in deeply subducted oceanic crust can explain the properties of anomalous continent-sized regions in Earth’s lower mantle.

Ultralow velocity zones are detected on the core-mantle boundary, but their origin is enigmatic. Here, the authors find that the global distribution and large variations of morphology of ultralow velocity zones are consistent with most having a compositionally-distinct origin.

PREMA, the highly fusible Prevalent Mantle now found throughout the mantle, may have been generated soon after Earth’s accretion with minimal subsequent modification, according to a combination of composition data from Cenozoic sodic basalts and mantle convection simulations

A low-viscosity layer atop the mantle transition zone may facilitate slab sinking and recurring intermediate-depth seismicity, according to an analysis of seismic observations and velocity models from the Indian-Eurasian collision zone.

Kimberlites are rare volcanic rocks with unusually deep origins. This Review explores the origin and evolution of kimberlite melts and their insights into mantle composition and dynamics.

The mantle of the Earth influences many dynamic processes such as crust formation, recycling and mantle convection. This Review describes modern isotopic methods used to characterize plume-derived basalts and gain insight into the composition of the mantle.

Experimental determination of how the post-garnet phase transition pressure varies with temperature suggests a downward-convex phase boundary with potential implications for mantle dynamics.

Geochemical zonation of the Tristan-Gough hotspot track has been demonstrated for the conjugate Rio Grande Rise on the South American Plate, suggesting geochemically distinct Tristan and Gough plumelets existed since the plume head/tail transition.

Correlation between large igneous province activity and iron formation ages suggests that subducted iron formations may have facilitated mantle plume upwelling in the Archaean and Proterozoic Earth.

This study suggests that the observed shear-velocity reduction beneath the southern side of the Southwest Sub-basin (SWSB) of the South China Sea (SCS) may be due to the presence of 150–300 ppm of water and 5–10% of lower continental crust.

Volatile-rich kimberlite magmas may be transported to the surface by broad mantle upwellings located above mobile basal mantle structures, according to global models of mantle convection over the past 200 million years.

Discovering ancient mantle plumes is challenging. By combining electrical conductivity with mineral physics modelling, this work finds a remnant of an ancient plume trapped in the mantle transition zone and sheds new light on mantle plume physics.

The paper reports the occurrence of quartz-bearing rhyolitic melt inclusions and interstitial glasses within peridotite xenoliths. Their O-isotope composition proves crustal derivation and cycling into the mantle at convergent plate margins.

Indo-African mantle upwellings are arranged in a tree-like structure, which might reflect linear staggered detachment of proto-plumes from the lowermost mantle, according to seismic tomographic imaging.

Mantle plumes are an integral aspect of Earth’s convection system, yet, difficulty in imaging mantle upwellings led to controversies surrounding their origin, dynamics and composition. This Review synthesizes geophysical, geodynamic and geochemical constraints on mantle plumes and their importance in the Earth system.

The lithosphere beneath the Ontong Java Plateau is thickened by up to 40 km relative to the surrounding ocean floor which suggests it formed through the ascent of a mantle plume, according to analyses of seafloor seismic observations.

Here, the authors compile a global geochemical database of Neogene-Quaternary intraplate volcanism. By comparing the distribution and composition of these rocks with tomographic models they show that intraplate volcanism can be used to constrain upper-mantle structure at the time of eruption.

Although it was assumed for decades that the Earth’s mantle could not be magnetic, recent evidence suggests that parts of the upper mantle have magnetic remanence. This Review critically revisits mantle magnetism, discusses recent magnetic data and identifies unresolved questions about the sources of this magnetism.

A large, deep reservoir of asthenosphere flows eastward from the Réunion hotspot and interacts with the Indian spreading ridge, suggests seismological imaging.

This study uses reverse-time migration full-waveform seismic imaging to reveal a thinned transition zone and a 1000-km mid-mantle discontinuity under the Pacific near Hawaii which they link to the upper boundary of upwelling plume material.

Phase transitions in the mantle transition zone could affect material and heat exchange between the upper and lower mantle. This Review discusses how compositional heterogeneity affects mantle convection based on seismic observations, plausible mantle compositions and model predictions.

A new study by @JinZhang_MP models the global distribution of wadsleyite proportion, temperature and water content in the upper mantle transition zone.

The mantle transition zone is poorly, mechanically mixed, and acts to impede mantle flow, according to seismic observations integrated with detailed mineral-physics models.

Data from ocean bottom seismometers show that the mantle transition zone beneath the equatorial Mid-Atlantic Ridge is thin and warm, which suggests more material transfer than previously thought.

Two seismic discontinuities in the mantle transition zone beneath the western Pacific represent subducted slab interfaces that could be the slab Moho and partially molten sub-slab asthenosphere, according to an analysis of seismic data.

The widespread intraplate volcanism in northeast China and the unusual ‘petit-spot’ volcanoes offshore Japan could have resulted from the interaction of the subducting Pacific slab with a hydrous mantle transition zone.