Development of arc curvature by asymmetric migration: Evidence from Permian–Triassic granitoids in the New England Orogen (eastern Australia)

Abstract

Magmatic arcs commonly display curved and segmented map-view geometry and their temporal evolution involves migration across strike and episodic magmatism. To investigate relationships between arc curvature and slab geometry in an evolving orogen, we studied the spatio-temporal evolution of a Permian–Triassic arc in eastern Australia. New and compiled U-Pb zircon dates reveal that arc magmatism was episodic, with peak activity at ∼252 Ma, followed by a ∼7 Myr magmatic lull. The onset of contractional deformation (Hunter-Bowen orogeny), at 269–252 Ma, was accompanied by landward arc migration, but the rates of arc advance varied along strike. This created a prominent curve in the arc. A subsequent phase of subduction rollback and/or slab steepening, at 240–235 Ma, was accompanied by trenchward arc migration and the development of a new non-curved arc. We suggest that arc curvature was likely the consequence of along-strike changes in the slab dip angle, with arc advance occurring in response to flattening of the subducting slab. The immobile portion of this arc coincides with an area where the underlying lithosphere is anomalously thick, indicating that arc migration was directly influenced by overriding-plate heterogeneities, whereby the presence of a thicker overriding lithosphere inhibited slab flattening. We conclude that interactions between slab geometry and overriding-plate thickness may control arc behaviour globally and may explain kinks and curvatures in other arc systems, such as in the Bolivian Orocline.