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Basin formation behind an active subduction zone: three‐dimensional flexural modelling of Wanganui Basin, New Zealand
Author(s) -
Stern T. A.,
Quinlan G. M.,
Holt W. E.
Publication year - 1992
Publication title -
basin research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.522
H-Index - 83
eISSN - 1365-2117
pISSN - 0950-091X
DOI - 10.1111/j.1365-2117.1992.tb00045.x
Subject(s) - geology , subduction , seismology , structural basin , pacific plate , thrust fault , plate tectonics , shear (geology) , tectonics , geomorphology , petrology
South Wanganui Basin is a Plio‐Pleistocene basin formed behind the Hikurangi subduction zone of the North Island, New Zealand. The active Benioffzone lies about 30–40 km beneath the centre of Wanganui Basin. We attribute the development of this basin primarily to frictional shear between the subducted Pacific plate and overriding Australian plate. This frictional interaction harnesses part of the ‘slab pull’ force of plate tectonics to deform the overriding plate and create the basin. The overall shape of the basin is modified to a lesser extent by the effects of uplift around the basin margin and by in‐plane compressional stress. A quantitative three‐dimensional model, based on flexure of a thin elastic sheet with spatially varying rigidity, is used to test the implications of our hypothesis. A maximum vertical loading stress of about 85 MPa is required to produce the vertical deformation in Wanganui Basin, and that in turn implies about 170 MPa of shear stress at the inclined subduction thrust. A vertical stress of 85 MPa applied over a 40‐km‐wide subduction thrust represents about 50% of the magnitude theoretically present in the ‘slab pull’ force. The effective elastic thickness ( T e ) of the flexed plate that provides the best fit to the observed deformation is 10 ± 5 km; such a low value of 7“ e is attributed to the high plate curvature and high strain rates associated with Wanganui Basin. Constraints on our analysis are provided by seismic reflection, seismicity, gravity, geodetic and geological data. A similar situation to Wanganui Basin, in which a high‐friction subduction thrust induces shortening and flexure of the overlying crust, may be found in the Puget Sound area of Washington State, USA.