Rotation and offset of the Gondwana convergent margin in the New Zealand region following Cretaceous jamming of Hikurangi Plateau large igneous province subduction

Jamming of the Hikurangi Plateau (large igneous province) subduction, within the Chatham Rise convergent margin of Gondwana at circa 105Ma, led to offset and rotation of the convergent margin before subduction ceased in the New Zealand region at circa 100Ma. The southern limit of the plateau, following leading slab break off, is highlighted by a lineament of prominent horst blocks in the southern Bounty Trough. Subduction jamming of the Gondwana margin, and accompanying compression of the onshore margin and/or extension of the offshore margin, has led to two 60km left-lateral SSE offsets of the Chatham Rise convergent margin at the coast and in inland Canterbury. Recognition of the onshore Chatham Rise using the gravity data also highlights the correlation of the inland Chatham Rise and central South Island seismicity. In a similar manner to the rotation of Cretaceous spreading-ridge and transform-fault fabric adjacent to the Osbourn Trough spreading ridge, the convergence direction at the Gondwana margin was rotated anticlockwise to N-S between 105 and 100Ma. Most of this rotation has been accommodated by offshore extension and margin offset. The divergence between the anticlockwise rotation of offshore crustal structure and the jammed onshore margin led to the development of the Great South Basin at 105-100Ma. Further offshore in the Bounty Trough, extensional zones, formed between crustal blocks rotated to adjust to a changed Cretaceous direction of subduction, are evident in gravity and seismic profiles.