Laboratory measurements of seismic velocity and attenuation in antigorite serpentinite at a confining pressure of 2 kbar and temperatures up to 550 ◦C (i.e., in the antigorite stability field) provide new results relevant to the interpretation of geophysical data in subduction zones. A polycrystalline antigorite specimen was tested via forced-oscillations at small strain amplitudes and seismic frequencies (mHz-Hz). The shear modulus has a temperature sensitivity, ∂G/∂T, averaging −0.017 GPa K−1. Increasing temperature above 500 ◦C results in more intensive shear attenuation (Q−G1) and associated modulus dispersion, with Q−G1 increasing monotonically with increasing oscillation period and temperature. This “background” relaxation is adequately captured by a Burgers model for viscoelasticity and possibly results from intergranular mechanisms. Attenuation is higher in antigorite (log10 Q−G1 ≈ −1.5 at 550 ◦C and 0.01 Hz) than in olivine (log10 Q−G1 ≪ −2.0 below 800 ◦C), but such contrast does not appear to be strong enough to allow robust identification of antigorite from seismic models of attenuation only.
|Original language||English (US)|
|State||Published - Nov 16 2018|