发表机构
Columbia University（哥伦比亚大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过从头算热弹性计算，揭示利蛇纹石声速争议源于其取向状态，实验速度偏向慢方向，依赖VRH均值会高估蛇纹石化程度。
AI 中文摘要
蛇纹石矿物是上地幔中富含氢的相，在俯冲带的水输送中起着核心作用。利蛇纹石是冷板块和浅层蛇纹石化地幔中预期的低温多晶型。我们利用结合密度泛函理论与r2SCAN meta-GGA和准谐近似的从头算热弹性框架，计算了其在300 K下的压缩曲线、弹性张量和声速。r2SCAN再现了测量到的压缩曲线和平衡体积，误差在0.2%以内。弱层间氢键导致显著的轴向软化，在0 GPa时C33≃0.21C11，C44≃0.13C66。通过在所有传播方向上求解Christoffel方程，我们构建了速度态密度（VelDOS），它揭示了高密度的慢声学模式以及被Voigt-Reuss-Hill（VRH）聚合平均所掩盖的其他方向特征。报道的实验速度优先采样该分布的较慢部分，而不是聚集在VRH值附近，这种对应关系与实验未分辨的细微晶体织构或择优取向一致。因此，利蛇纹石合适的地震速度端元取决于其取向状态，当地震观测优先采样慢晶体方向时，仅依赖VRH速度可能导致对蛇纹石化程度的过高估计。方向分辨的单晶测量和具有独立量化织构的聚合测量将为这一解释提供直接检验。
英文摘要
Serpentine minerals are abundant H-bearing phases in the upper mantle and play a central role in water transport in subduction zones. Lizardite is the low-temperature polymorph expected in cold slabs and shallow serpentinized mantle. Using an ab initio thermoelastic framework combining density-functional theory with the r2SCAN meta-GGA and the quasiharmonic approximation, we calculate its compression curve, elastic tensor, and acoustic velocities at 300 K. r2SCAN reproduces the measured compression curve and equilibrium volume to within 0.2%. Weak interlayer hydrogen bonding gives rise to pronounced axial softening, with $C_{33} \simeq 0.21C_{11}$ and $C_{44} \simeq 0.13C_{66}$ at 0 GPa. Solving the Christoffel equation over all propagation directions, we construct the velocity density of states (VelDOS), which reveals a high density of slow acoustic modes and other directional features obscured by Voigt-Reuss-Hill (VRH) aggregate averages. Reported experimental velocities preferentially sample the slower portion of this distribution rather than clustering near the VRH values, a correspondence consistent with subtle crystallographic texture or preferential orientation not resolved experimentally. Thus, the appropriate seismic-velocity endmember for lizardite depends on its orientational state, and reliance on VRH velocities alone may lead to overestimation of the degree of serpentinization when seismic observations preferentially sample slow crystallographic directions. Direction-resolved single-crystal measurements and aggregate measurements with independently quantified texture would provide direct tests of this interpretation.
