DFT simulations reveal seifertite’s high seismic velocities and anisotropy, explaining ultra-high-velocity zones and discontinuities near the core-mantle boundary, refining understanding of deep-Earth composition and mantle dynamics.
Study: Elasticity of seifertite under mantle conditions and its implications for velocity anomalies at the core-mantle boundary. Image Credit: rdonar/Shutterstock
In a recent article published in the journal Communications Earth and Environment, researchers investigated the elastic properties of seifertite under conditions relevant to Earth's lowermost mantle, emphasizing how these properties influence seismic velocity anomalies near the core-mantle boundary (CMB).
What Causes Unusual Seismic Signals Deep Inside Earth?
Seifertite, a high-pressure polymorph of silica, is central to explaining complex seismic features observed in this region, such as ultra-high-velocity zones (UHVZs) and velocity discontinuities. The Earth’s lowermost mantle exhibits notable seismic heterogeneities, including large low-velocity provinces (LLVPs) and sharp shear wave velocity discontinuities, which inform our understanding of mantle convection and chemical layering. Prior studies have proposed several mechanisms for these features, including thermal anomalies, phase transitions in mantle minerals, and chemical heterogeneities associated with slab subduction.
Among these, seifertite’s unique elasticity and phase transitions have sparked attention, but its high-pressure elastic behavior has remained inadequately characterized. The mineral’s orthorhombic structure and transition from CaCl2-type silica at depths around 2500 km affect the seismic wave speeds notably. Additionally, subducted materials such as mid-ocean ridge basalt (MORB) and oceanic crust offer distinctive compositional anomalies that could affect seismic velocities near the CMB, but their exact influence remains debated.
Simulating a Key Deep-Earth Mineral
The elasticity of seifertite was examined using density functional theory (DFT) calculations to derive its thermal elastic constants under various pressures and temperatures characteristic of the deep mantle. The study employed the Quantum ESPRESSO software to perform first-principles simulations that incorporate structural and vibrational contributions to elasticity.
Elastic tensors were calculated to obtain bulk and shear moduli, which were then used to compute compressional (VP) and shear (VS) wave velocities and anisotropy parameters. Phase transitions were assessed by integrating existing experimental data and computational phase diagrams.
To estimate the seismic properties of subducted oceanic crust, a compositional model of MORB was used with phase proportions adjusted for mantle depth effects, and aggregate velocities were computed by averaging the elastic moduli of constituent minerals weighted by volume fractions. This approach enabled comparisons of predicted seismic signatures of the oceanic crust versus ambient mantle materials.
Seifertite’s Role in Seismic Velocity and Mantle Heterogeneity
Seifertite exhibits exceptionally high seismic velocities relative to other mantle minerals, surpassing those of common phases such as bridgmanite and post-perovskite near the CMB. Notably, it exhibits strong elastic anisotropy, comparable to that of post-perovskite, underscoring its role in contributing to the observed seismic anisotropy in ultra-high-velocity zones.
A phase transition from CaCl2-type silica to seifertite at depths around 2500 km results in a marked reduction of about 3% in shear wave velocity, while compressional wave velocity remains largely unchanged. This finding offers a plausible explanation for the negative velocity discontinuities observed just above the D" region in seismic studies, which could not be satisfactorily accounted for by thermal effects alone.
The investigation also evaluated the seismic properties of the oceanic crust under mantle conditions, finding that MORB compositions yield higher compressional-wave velocities and steeper velocity gradients than those of surrounding mantle material. This outcome challenges hypotheses that attribute LLVP origins primarily to the accumulation of subducted oceanic crust. Even when incorporating recent experimental evidence pointing to lower velocities for davemaoite, a significant MORB component, the oceanic crust’s seismic signature remains inconsistent with the low-velocity anomalies characterizing LLVPs.
Moreover, core-derived silica phases, including seifertite, were identified as likely major contributors to the ultra-high-velocity zones near the CMB due to their elevated seismic velocities. However, pure silica phases are estimated to be metastable only over limited timescales at the base of the mantle, suggesting dynamic processes govern their distribution. The combined elastic and phase-transition data improve the interpretation of seismic discontinuities and anisotropies, offering better constraints on the composition and dynamics of the deep Earth.
Implications for Mantle Composition and Resource Insights
The study advances knowledge of seifertite’s elasticity at high pressure and temperature, highlighting its critical role in shaping seismic velocity anomalies at the core-mantle boundary. Its high seismic velocities and pronounced anisotropy substantiate seifertite as a key mineralogical contributor to UHVZs and complex anisotropic signals. The phase transition from CaCl2-type silica to seifertite produces a distinct shear velocity decrease, providing a compelling mechanism for the negative velocity discontinuities observed above the D" layer, which purely thermal models struggle to explain.
The findings also clarify that subducted oceanic crust, modeled through MORB compositions, exhibits seismic velocity characteristics inconsistent with the low-velocity LLVPs, suggesting that LLVPs arise from other compositional or thermal anomalies rather than the accumulation of oceanic crust. From a mining perspective, understanding the high-pressure mineral physics of silica phases like seifertite could inform exploration of deep-Earth mineralogy and the potential for locating mineral reservoirs shaped by extreme Earth processes. The work provides a foundation for future investigations into deep mantle mineral behavior that could impact resource assessment and modeling of mantle convection-driven geochemical cycles.
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Journal Reference
Duan L., Wang D., et al. (2026). Elasticity of seifertite under mantle conditions and its implications for velocity anomalies at the core-mantle boundary. Communications Earth and Environment. DOI: 10.1038/s43247-026-03454-7, https://www.nature.com/articles/s43247-026-03454-7