Sound Velocities of Glaucophane at High Pressure and Temperature: Implications for the Low Velocity Layer in Subduction Zones

This is the authors' abstract. We don't add key points for this paper.

Geophysical observations reveal a low velocity layer atop the slab in the circum‐Pacific subduction zones at a depth of 100–250 km, whose origin is not well constrained. The presence of blueschist may potentially cause the low velocity layer. To test this hypothesis, we measured sound velocities in glaucophane‐the dominant mineral in blueschist‐using the ultrasonic interference method at pressures up to 9.9 GPa and temperatures up to 673 K. High‐temperature finite strain fitting of the data yielded the following elastic properties: . These results show that the elastic properties of glaucophane (e.g., its relatively low bulk‐to‐shear modulus ratio) differ significantly from those of most other minerals in subducting slabs. Combining the elastic properties of the subducting slab with our experimental data, we calculated the velocities of several blueschist mineral assemblages consisting of glaucophane and lawsonite. Our estimates indicate that an assemblage of 63.9% glaucophane and 36.1% lawsonite closely matches the seismic observations of the low‐velocity layer.