Subduction, platform subsidence, and foreland thrust loading: The late Tertiary development of Taranaki Basin, New Zealand

Abstract

Borehole, seismic, and gravity data are used to investigate deformation of continental lithosphere at a Miocene collisional zone. Deformation is manifested in the three following principal forms: a long wavelength (>500 km) platform subsidence ascribed to mantle convection; flexural deformation on a scale of 100–200 km due to crustal thrusting at the eastern boundary of the Taranaki Basin; and a ductile thickening, evident on the deep seismic section of Taranaki Basin, that occurs on a scale of ∼10 km. Evidence for flexural deformation principally comes from the deep seismic section that shows a 150‐km wavelength bending of the Moho down toward the major zone of thrusting within the Taranaki Fault Zone. Paleowater depths, however, provide evidence for an initial early Miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading. Instead, we propose that this broad "platform subsidence" was driven by loading from a deep source, probably subduction‐induced flow in the mantle. By ∼22–19 Ma, 1–2 km of water existed over most of the area now occupied by South Taranaki Basin. By ∼19–17 Ma the water depth in the zone east of the Taranaki Basin, the Taranaki Fault Zone, had been replaced by rock due to submarine thrusting and crustal thickening. This build up of submarine topography in the Taranaki Fault Zone constitutes part of the load (25±8 MPa) that created and maintains South Taranaki Basin. Gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading, equivalent to 15±7 MPa over a 50‐km‐wide zone. This intracrustal load is explained as being due to thick‐skinned thrusting bringing denser, lower‐crustal rocks nearer to the surface in the thrust zone. The complete load on the Taranaki foreland is therefore in three parts; the submarine‐topographic load, the intracrustal load, and the loading of infilling sediments.

Retroarc foreland systems––evolution through time

“…One important difference between the proarc and retroarc foreland settings is that the retro-lithosphere is subject to the manifestation of additional mechanisms that create accommodation, related to sublithospheric forces. Sublithospheric ''loading'' of the overriding plate is primarily caused by the drag force generated by viscous mantle corner flow coupled to the subducting plate, especially where subduction is rapid and/or takes place at a shallow angle beneath the retroarc foreland basin (Mitrovica et al, 1989;Gurnis, 1992;Holt and Stern, 1994;Burgess et al, 1997). This corner flow-driven ''dynamic'' loading generates accommodation at continental scales, with subsidence rates decreasing exponentially with distance away from the orogen in a cratonward direction (Fig.…”

Tectonic reconstructions of New Zealand: 40 Ma to the Present

“…The pattern of subsidence and sedimentation indicates significant vertical displacement (westward downthrow) along the Taranaki Fault, but there is no evidence of contemporaneous faulting elsewhere within the Taranaki Basin. Stern & Holt (1994) and Holt & Stern (1984) ascribed a component of the subsidence in Taranaki to regional platform foundering, induced by mantle convection and hydrodynamic processes associated with the development of subduction east of the North Island. An implication of their premise is that a shallow-dipping slab (Pacific plate) extended a considerable distance beneath the North Island by c. 25 Ma.…”

Events in the Precambrian history of the Earth: Challenges in discriminating their global significance

“…For example, high-frequency stratigraphic sequences of 10 4 -10 5 years duration may be generated both by climatedriven eustasy and by tectonic processes such as periodic brittle failure of the crust in convergent plate-margin settings or periodic adjustments to the flexural load in foreland systems (Peper et al, 1992;Waschbusch and Royden, 1992;Miall, 2000). Lower frequency eustatic cycles induced by changes in the volume of mid-oceanic spreading centres (10 6 -10 8 y e a r s p e r i o d i c i ty ) a l s o c o m p e t e i n t e r m s of d u r a ti o n w i th c y c l e s generated by extensional downwarp and loading of the crust or by continental-scale mantle-thermal processes (i.e., dynamic topography; Mitrovica et al, 1989;Gurnis, 1992;Holt and Stern, 1994;Catuneanu et al, 1997;Miall, 2000).…”