Formation and evolution of the Solander Basin, southwestern South Island, New Zealand, controlled by a major fault in continental crust and upper mantle

Seismic reflection and refraction data from the Solander Basin, southern Ne w Zealand, show that its structural evolution has been controlled by a majo r fault, named here the Tauru Fault, that cuts the entire crust and splays into a diffuse zone in the upper mantle. The tectonic setting of the Soland er Basin has evolved from Eocene-Oligocene extension and transtension to Mi ocene-Quaternary transpression and subduction. The Tauru Fault is 100 km ea st of the active Puysegur subduction zone thrust and is part of the overrid ing plate. On the basis of lower crustal reflectivity, the base of the crus t beneath the adjacent Stewart Island shelf is at similar to 30 km depth (s imilar to 9 s two-way time (TWT)), and rises to similar to 20 km (similar t o 8 s TWT) beneath the Solander Basin. This is consistent with gravity data . Prominent dipping reflections show that the Tauru Fault can be traced to similar to 30 km depth (similar to 12 s TWT), where it merges with a zone o f subhorizontal reflectors in the upper mantle. The Tauru Fault dips simila r to 30 degrees northeast and appears to offset the Moho in a reverse sense . Stratigraphic relationships show that the Tauru Fault was active as a nor mal fault during Eocene extension, when Solander Basin crust was thinned an d ocean crust was generated farther south in the Solander Trough. It has be en reactivated as a reverse fault during at least two phases of Miocene-Qua ternary compression and is still active. The strike of the Tauru Fault, whi ch is parallel to Paleozoic-Mesozoic structures and was poorly oriented for the known Eocene extension direction, strongly suggests that it formed pri or to Eocene time. The Tauru Fault significantly influenced the geometry of Eocene basin formation, producing a strongly asymmetric basin dominated by east dipping normal faults, with a single eastern boundary fault. Our data demonstrate that Miocene-Quaternary simple shear associated with the Tauru Fault cuts the whole crust and continues into the upper mantle. We conclud e that variations in strength of the lithosphere, particularly associated w ith inherited structures in the crust and upper mantle, may control many as pects of basin development, passive margin formation, and the kinematics of continental deformation zones.