Fractal vein distributions within a fault-fracture mesh in an exhumed accretionary melange, Chrystalls Beach Complex, New Zealand

A well developed fault-fracture mesh is observed in the Chrystalls Beach Complex, an accretionary mélange within the Otago Schist on the South Island of New Zealand. In this study, an analysis of vein thicknesses and clustering of veins is presented. Both shear and extension veins have a power-law thickness distribution. Measures of vein spacing best fit a power-law distribution, but a small data set limits this interpretation to a small fractal range. Vein clustering varies from random to moderately clustered between outcrops, and is the greatest where a large proportion of relatively competent blocks occurs within the mélange. Fractures are distributed within the mélange matrix, and this localized deformation requires heterogeneity in rheology and/or fluid pressure distribution, whereas pervasive, distributed deformation occurs in relatively homogeneous rock. The overall trend of this deformation being mainly accommodated by thin veins required that new fractures formed preferentially over refracturing existing veins, which highlights the distributed nature of deformation within a fault-fracture mesh. The predominance of new fractures may result from vein material being stronger than the cleaved wall rock, such that wall rock failure occurred instead of reopening of pre-existing shear and extension veins