Cretaceous Evolution of Zealandia dictated by congested subduction

Betts, Peter1, Moresi, Louis2, Whittaker, Joanne3, Miller, Meghan2

1School of Earth Atmosphere and Environment, Monash University, Melbourne, Australia, 2Research School of Earth Sciences, Australian National University, Canberra, Australia, 3Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia

Congested subduction occurs when buoyant lithosphere within the downgoing plate interacts with the with the convergent margin trench and prevents the slab from subducting in the region of collision. This can trigger several dynamic behaviours in the slab including slab tearing beneath the congestion and roll back of the trench away from the collision zone.  Congested subduction also drives contemporaneous shortening and extension along different parts of the overriding plate, and has the potential to dismember and segment subducting slabs.

During the Cretaceous collision of the Hikurangi Plateau with the east Gondwana margin triggered a major re-organisation of the margin culminating in the opening of the Tasman Sea and separation of Zealandia from Gondwana.  Tectonic models for this plateau accretion have proposed collision between the plateau and Campbell Plateau (South Island of New Zealand) at ca. 100 Ma, which triggered the opening of the Tasman Sea at ca 84 Ma.   These models are appealing because they explain the present-day relationship between the Hikurangi Plateau and the New Zealand along the Pacific-Australia plate margin. 

In this abstract, we provide an alternative model for the collision of the Hikurangi Plateau and Gondwana that is informed by numerical modelling of congested subduction.  We present this alternative tectonic model as a series of G-plates reconstructions.  Our new model requires collision of the Hikurangi Plateau with the Gondwana along the North Island of New Zealand, rather than the South Island.  Suturing of the Hikurangi Plateau with the North Island resulted in crustal shortening in front of the collision zone and triggered collapse of the Gondwana margin to the south and north.  Initiation of asymmetric trench roll back to the south is evidenced by the ubiquitous extension in the overriding plate, affecting the Campbell Plateau and Chatham rise.  Asymmetric opening of Tasman Sea and opening of the Bounty Trough at 84 Ma.  Counter clockwise rotation of the Chatham and Campbell plateaus segmented the slab along the Gondwana margin.  Soft collision of southern Zealandia (Chatham and Campbell Plateau) along the southern margin of the Hikurangi Plateau occurred at ca 70 Ma and stable subduction was established outboard of this accreted margin.  In this model, the Alpine fault initiated as a sinistral fault at the transition between trench advance in the North Island and trench roll-back to the south. 


Biography

Peter Betts has a diverse portfolio of research that addresses tectonic problems through Earth history.  He is currently working on the Tectonic process related to congested subduction, the opening of new oceans, and the role of inherited structures on continental reactivation.

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