Elasticity of polycrystalline davemaoite constrains its grain size in the lower mantle
Abstract
Earth's lower mantle hosts large low shear-velocity provinces (LLSVPs) beneath Africa and the Pacific, but their origin remains debated. Davemaoite, a major lower-mantle mineral, has been proposed as a contributor to these anomalies; however, its experimentally measured shear modulus is approximately 30% lower than first-principles predictions, a longstanding discrepancy between theory and experiment. Here, using million-atom machine-learning molecular dynamics simulations, we show that nanoscale grain-boundary disorder, invisible to conventional x-ray diffraction, can reconcile this gap. Introducing 5.8 vol% disordered regions reduces the shear and bulk moduli by 37% and 12%, respectively. This shear-selective softening can reproduce LLSVP-like seismic anomalies in basalt-rich assemblages, but only at disorder levels corresponding to grain sizes smaller than those expected in the lower mantle. Combining the disorder-elasticity relationship with seismic constraints, we derive a minimum davemaoite grain size of approximately 100 nm. This limit is consistent with mantle grain growth models and with attenuation-based evidence for coarse-grained LLSVPs.
Related
- Temperature Mediated Balance of Singlet Fission and Symmetry-Breaking Charge-Transfer in a Polycrystalline Perylene Bisimide Thin Film
- Fluorine-Assisted Stabilization of Cubic Phase Boron Nitride Polycrystalline Solids.
- Precise molecular sieving in polycrystalline covalent organic framework membranes
- Resolving the Strength–Modulus–Elasticity Tradeoff in Elastomers Using Dual Phase‐Separated Nanodomains
- Flexoelectricity-driven softening of bend elasticity leads to spontaneous chiral symmetry breaking in a polar fluid
BibTeX
@misc{zhang2026elasticity,
title = {{Elasticity of polycrystalline davemaoite constrains its grain size in the lower mantle}},
author = {Peiyu Zhang and Liang Yuan and Rong Huang and Yu Ye and Xiang Wu and Junfeng Zhang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.39423},
eprint = {2609.39423},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.39423},
}
RIS
TY - UNPB
TI - Elasticity of polycrystalline davemaoite constrains its grain size in the lower mantle
AU - Peiyu Zhang
AU - Liang Yuan
AU - Rong Huang
AU - Yu Ye
AU - Xiang Wu
AU - Junfeng Zhang
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2609.39423
UR - https://arxiv.org/abs/2609.39423
AB - Earth's lower mantle hosts large low shear-velocity provinces (LLSVPs) beneath Africa and the Pacific, but their origin remains debated. Davemaoite, a major lower-mantle mineral, has been proposed as a contributor to these anomalies; however, its experimentally measured shear modulus is approximately 30% lower than first-principles predictions, a longstanding discrepancy between theory and experiment. Here, using million-atom machine-learning molecular dynamics simulations, we show that nanoscale grain-boundary disorder, invisible to conventional x-ray diffraction, can reconcile this gap. Introducing 5.8 vol% disordered regions reduces the shear and bulk moduli by 37% and 12%, respectively. This shear-selective softening can reproduce LLSVP-like seismic anomalies in basalt-rich assemblages, but only at disorder levels corresponding to grain sizes smaller than those expected in the lower mantle. Combining the disorder-elasticity relationship with seismic constraints, we derive a minimum davemaoite grain size of approximately 100 nm. This limit is consistent with mantle grain growth models and with attenuation-based evidence for coarse-grained LLSVPs.
ER -