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Published 2007 | Accepted Version
Book Section - Chapter Open

Geophysical Structure of the Southern Alps Orogen, South Island, New Zealand


The central part of the South Island of New Zealand is a product of the transpressive continental collision of the Pacific and Australian plates during the past 5 million years, prior to which the plate boundary was largely transcurrent for over 10 My. Subduction occurs at the north (west dipping) and south (east dipping) of South Island. The deformation is largely accommodated by the ramping up of the Pacific plate over the Australian plate and near-symmetric mantle shortening. The initial asymmetric crustal deformation may be the result of an initial difference in lithospheric strength or an inherited suture resulting from earlier plate motions. Delamination of the Pacific plate occurs resulting in the uplift and exposure of mid-crustal rocks at the plate boundary fault (Alpine fault) to form a foreland mountain chain. In addition, an asymmetric crustal root (additional 8 - 17 km) is formed, with an underlying mantle downwarp. The crustal root, which thickens southwards, comprises the delaminated lower crust and a thickened overlying middle crust. Lower crust is variable in thickness along the orogen, which may arise from convergence in and lower lithosphere extrusion along the orogen. Low velocity zones in the crust occur adjacent to the plate boundary (Alpine fault) in the Australian and Pacific plates, where they are attributed to fracturing of the upper crust as a result of flexural bending for the Australian plate and to high pressure fluids in the crust derived from prograde metamorphism of the crustal rocks for the Pacific plate.

Additional Information

Copyright 2007 by the American Geophysical Union. We gratefully acknowledge the tremendous support of the people involved in the field work that provided the basis for this paper, in particularly in the SIGHT and SAPSE experiments. We also acknowledge funding support from NSF (grants EAR-9805224 (MDK)) and the NZ Foundation for Research Science and Technology. Reviews by Martin Reyners and Andrew Gorman were greatly appreciated.

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August 19, 2023
March 12, 2024