Olivine Crystallographic Fabrics and Their P-wave Velocity Structures within Peridotites in the Uppermost Mantle

Abstract

 Olivine crystal grains have various crystallographic orientations within a peridotite, resulting in a crystallographic fabric as well as a texture. Six types of fabrics have been identified in mantle peridotites: A, B, C, D, E and AG types. These fabric types have unique seismic properties such as P-wave and S-wave velocity anisotropy. A new method is proposed to classify olivine fabrics based on P-wave velocity structure on a Vp-Flinn diagram. Three P-wave velocities (V₁, V₂, V₃) are used, two of which are the maximum (V₁) and minimum (V₃) velocities, and the third (V₂) is the velocity perpendicular to the orientations of these two velocities. Relationships between V₁/V₂ and V₂/V₃ classify fabrics into three types: A type (equivalent to B, C and E types), D type and AG type. Moreover, taking into account structural framework such as foliation and lineation, the Vp-Flinn diagram can be expanded to identify all types of fabrics. This method is successfully applied to fabrics previously studied in Oman ophiolite.