Earth’s deep interior remains one of the most enigmatic frontiers in geoscience, with vast expanses beneath our feet holding secrets about our planet’s early formation and dynamic evolution. A breakthrough study now sheds light on the nature of the lowermost mantle, particularly the intriguing seismic anomalies known as large low-velocity provinces (LLVPs) and ultralow-velocity zones (ULVZs). These enigmatic structures have baffled scientists for decades due to their distinct seismic signatures and proposed geochemical anomalies that suggest a complex origin story rooted deep within Earth’s history.
Traditionally, these deep mantle anomalies have been linked to the relics of an ancient basal magma ocean (BMO), a global layer of partially molten silicates thought to have existed during Earth’s formative years. The crystallization and differentiation of this primordial magma ocean have been hypothesized to create compositional heterogeneities retained to this day. However, the existing models face a critical challenge: the predicted thick layers of iron-rich ferropericlase—expected from a crystallized BMO—do not align with seismic observations. Instead, tomography suggests that the lowermost mantle’s composition must be more varied and less dominated by ferropericlase cumulates.
Addressing this paradox, researchers Deng, Miyazaki, Yuan, and colleagues harnessed an innovative approach combining thermodynamic and geodynamic modeling to explain how contamination from the Earth’s core could modify the basal magma ocean’s crystallization process. Their model introduces the concept of a basal exsolution contaminated magma ocean, wherein oxides exsolved from the Earth’s core percolate upward and contaminate the crystallizing mantle material. This interaction fundamentally alters the mineralogy and dynamics at the planet’s bottommost layer, challenging previously held assumptions about the mantle’s composition.
Thermodynamic modeling demonstrated a key result: the presence of core-derived oxides suppresses the crystallization of ferropericlase in the basal magma ocean. Instead of forming overly thick layers of this iron-rich mineral, the contamination encourages the crystallization of alternative phases that better fit seismic velocity profiles observed beneath large low-velocity provinces. This insight provides a reconciliatory bridge between geochemical theory and seismic data, offering a more coherent picture of Earth’s deep interior structure.
The researchers’ geodynamic simulations further elucidate how this contaminated, crystallized mantle material evolves. As the basal magma ocean solidifies under the influence of continuous core exsolution, the resulting solid mantle layer takes on distinct physical and chemical properties consistent with LLVPs and ULVZs observed by seismic tomography. The simulations indicate that this layer is compositionally dense and thermomechanically distinct, creating conduits for dynamic interactions between mantle convection, core-mantle boundary processes, and deep Earth’s layered structure.
One particularly fascinating outcome of this study is the potential explanation for small-scale seismic scattering phenomena detected near core-mantle boundaries. The geodynamic models suggest that diapirs—buoyant blobs—of oxide-rich material exsolved from the core can become entrained within the solid mantle matrix. These diapirs, possessing unique chemical signatures, could act as localized heterogeneities responsible for the complex scattering patterns seen in seismic data across deep mantle regions.
Furthermore, the contaminated basal magma ocean’s preserved chemical distinctiveness could explain geochemical anomalies found in ocean island basalts (OIBs), which are volcanic rocks sourced from deep within the mantle. In particular, isotopic signatures for silicon, tungsten, and helium extracted from OIBs may trace their origin back to this basal melting and contamination process. Such signatures highlight a unified mechanism, uniting seismic, geochemical, and geodynamic observations within the framework of basal magma ocean evolution influenced by core exsolution.
This new model injects fresh vigor into longstanding debates about the core-mantle boundary region, which plays a pivotal role in Earth’s thermal and chemical evolution. The concept of a magma ocean continuously contaminated by core-derived oxides not only solves inconsistencies in the predicted mineralogical layering but also enriches our understanding of how Earth’s internal reservoirs interact over geological time. This complex interplay influences surface volcanism and, ultimately, the planet’s habitability.
By integrating insights from thermodynamic calculations with high-resolution geodynamic simulations, the research highlights how subtle chemical interactions at the core-mantle boundary can dramatically alter the mantle’s physical state and compositional heterogeneity. These heterogeneous reservoirs beneath the tectonic plates are key players in Earth’s mantle convection system, which governs the recycling of materials and the generation of the geomagnetic field.
Beyond the immediate geological implications, this work hints at broader planetary processes. The mechanisms proposed could be extrapolated to interpret the internal structures of other terrestrial planets or exoplanets with differentiated cores and mantles. Understanding how core exsolution influences basal magma oceans could provide a benchmark for planetary formation and evolution models in the broader cosmos.
At the heart of this story is Earth’s basal magma ocean, a vast and ancient feature once thought to be homogenously crystallizing into predictable layers. Instead, this ocean emerges as a chemically dynamic and evolving system, shaped by ongoing contamination from the core. This revised perspective not only offers explanations for the seismic and geochemical riddles but also exemplifies the intricate coupling between Earth’s core and mantle.
The implications of this research challenge the paradigm that the mantle is chemically uniform beneath the seismic boundaries and that LLVPs simply represent large blobs of early-formed mantle. They embrace a more nuanced vision, where the mantle is a mosaic of interacting reservoirs, continuously sculpted by geochemical fluxes arising from the core. Such a setting naturally explains the complex signatures observed in deep mantle tomography and geochemical fingerprints on the surface.
Moreover, the study elevates the importance of core exsolution — the process by which light elements and oxides segregate from the core — as a dominant factor influencing mantle evolution. This finding shifts the scientific conversation away from treating the lower mantle and the core as isolated reservoirs to considering their continuous and intricate exchange influencing Earth’s long-term dynamics.
As the scientific community digests these findings, future research will likely seek to refine the model through complementary seismic imaging and high-pressure mineral physics experiments. This will help further constrain the mineral phases predicted by the contaminated basal magma ocean and elucidate how such phases influence seismic wave propagation.
In conclusion, this pioneering work marries cutting-edge thermodynamic theory with detailed geodynamic processes, illuminating a previously unrecognized liaison between Earth’s core exsolution and deep mantle heterogeneity. It rewrites our understanding of the basal magma ocean’s fate and illuminates the geological record inscribed deep beneath the Earth’s surface, all while providing a cohesive framework connecting seismic anomalies, geochemical signatures, and planetary dynamics.
Article Title:
Deep mantle heterogeneities formed through a basal magma ocean contaminated by core exsolution
Article References:
Deng, J., Miyazaki, Y., Yuan, Q. et al. Deep mantle heterogeneities formed through a basal magma ocean contaminated by core exsolution.
Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01797-y
Image Credits: AI Generated
