Unusually large shear wave anisotropy for chlorite in subduction zone settings

Mainak Mookherjee (1) , David Mainprice (2)

1 Cornell University [New York]
2 Manteau et Interfaces

Using first principle simulations we calculated the elasticity of chlorite. At a density ρ~ 2.60 g cm−3, the elastic constant tensor reveals significant elastic anisotropy: VP ~27%, VS1 ~56%, and VS2 ~43%. The shear anisotropy is exceptionally large for chlorite and enhances upon compression. Upon compression, the shear elastic constant component C44 and C55 decreases, whereas C66 shear component stiffens. The softening in C44 and C55 is reflected in shear modulus, G, and the shear wave velocity, VS. Our results on elastic anisotropy at conditions relevant to the mantle wedge indicates that a 10-20 km layer of hydrated peridotite with serpentine and chlorite could account for the observed shear polarization anisotropy and associated large delay times of 1-2 s observed in some subduction zone settings. In addition, chlorite could also explain the low VP/VS ratios that have been observed in recent high-resolution seismological studies.

Mots clés: subduction zone; elasticity; anisotropy; chlorite; hydrous phases; high-pressure

Domaines: Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux

Mainak Mookherjee, David Mainprice. Unusually large shear wave anisotropy for chlorite in subduction zone settings. Geophysical Research Letters, 2014, 41 (5), pp.1506-1513. ⟨10.1002/2014GL059334⟩. ⟨hal-01053707⟩