Magnetic fabric studies of samples from Hole 808C, Nankai Trough

Abstract

Measurements of magnetic susceptibility anisotropy, orientated using stable remanences, are presented for Hole 808C, over the depth range 200 to 150m below seafloor. Within the accretionary prism, magnetic fabric directions are remarkabley consistent, the maximum susceptibility axes lying horizontal and at right angles to the direction of underthrusting, with minimum susceptibility axes generally close to vertical. Steeper inclinations of the minimum susceptibility axes are observed in the fold below the frontal thrust and in a disturbed zone just above the decollement. Anisotropy parameters are scattered, possibly reflecting local inhomogeneity of deformation, but the broad pattern is consistent with the model for magnetic fabric modification put forward by Graham (1966). Below the decollement the magnetic fabric is strongly oblate, with no preferred azimuthal orientation. There is evidence of deformation of remanence in the zone immediately below the frontal thrust. -Author