Subduction initiation at a strike‐slip plate boundary: The Cenozoic Pacific‐Australian plate boundary, south of New Zealand

Abstract

[1] We first present a synthesis of the Macquarie Ridge Complex (MRC) tectonic structures as well as paleo-reconstruction models of the kinematic evolution of the Pacific-Australia plate boundary south of New Zealand, since the Eocene. We then ascertain the geodynamical conditions that preceded subduction initiation, and identify the nature and structures of the crust that first subducted, at the Puysegur subduction zone. This synthesis is used to produce a subduction initiation model for the Puysegur Region. Concomitant to inception of the Alpine Fault (ca. 23 Ma), a 150-km-wide transpressive relay zone developed along Puysegur Bank inherited structures, enabling localization of compressive deformation. Right-lateral motion at the relay zone has juxtaposed oceanic and continental crusts facilitating inception of subduction and controlling the subduction vergence. Subsequently, the Puysegur subduction zone initiated at the transpressive relay zone ca. 20 Ma. Upper and lower plate inherited structures guided and facilitated the lengthening of the subduction zone during the Neogene. The four individual segments of the MRC represent different stages of incipient subduction whose development depends on local geodynamical conditions and lithospheric heterogeneities. The example of the MRC demonstrates that subduction can initiate from an oceanic spreading center, through progressive changes in plate kinematics within a 10-15 Myr time frame.

Rapid conversion of an oceanic spreading center to a subduction zone inferred from high-precision geochronology

“…Intraoceanic subduction appears to be initiating along several sections of the Australian-Pacific plate boundary south of New Zealand, exploiting weaknesses associated with extinct spreading centers and/or fracture zones undergoing transpressional deformation (50)(51)(52). However, unlike the case in Palawan where deep underthrusting occurred within 1 My of oceanic crust formation, spreading at the boundary south of New Zealand had ceased and was followed by strike-slip deformation several million years before incipient subduction.…”

Crustal Velocity Structures Imaged from Four-Component OBS Data Across the Southern Gagua Ridge in the Western Philippine Sea

“…We suggest that the Huatung Basin is younger than the West Philippine Basin (Deschamps et al 1998) although the Huatung Basin did not over-thrust the West Philippine Basin as the west-dipping thrust below the Eastern Trough of the Gagua Ridge is not apparent in the OBS model. Therefore, the Gagua Ridge was formed by transpression and an incipient subduction may have occurred during the ridge formation, such as in the Puysegur Ridge formation in the South Ocean (Collot et al 1995;Lebrun et al 2003).…”

“…The crustal structures at the Puysegur Ridge and the surrounding basins off South New Zealand (Collot et al 1995), including thrust faults, fracture zones and igneous rocks, were otherwise similar to the crustal structures of the Gagua Ridge and surrounding the Huatung and Philippine basins. The Puysegur Ridge and the Gagua Ridge were formed by transforming to compression and an incipient subduction that might have occurred during ridge formation (Lebrun et al 2003).…”

“…This hypothesis posits that the Gagua Ridge may have formed due to strike-slip deformation of the West Philippine Basin from the geophysical data (Deschamps and Lallemand 2002). Similarly, the Puysegur Ridge, including over-thrusts and fractures, off south New Zealand in the South Ocean between the Australian and Pacific Plates was formed due to transpression by increasing transverse shortening during the southward migration of the Pacific-Australian pole of rotation and possible incipient subduction (Collot et al 1995;Lebrun et al 2003).…”

Lithosphere as a Nonlinear System: Geodynamic Consequences

“…The vortex-like opening of the spreading basin generated at the Pacific-Australian plates' boundary to the west from New Zealand since Eocene is an exceptionally demonstrative example. In accordance with the names of adjacent oceanic basins, the authors of investigations devoted to this region [24] call it Tasman-Emerald Basin (TEB). Its evolutional scheme is based on combined tectonic analysis of both marine geophysical data and geological structure of South New Zealand Island.…”