From Rifting to Subduction Initiation: Cenozoic Tectonics South of New Zealand

Abstract: New models for subduction initiation, and for the development of segmentation in nascent subduction zones, come from the tectonic history of the Pacific-Australia plate boundary south of New Zealand. The Pacific-Australia boundary in this area started as an orthogonal rift system that became oblique and then transpressive, linking to the Alpine fault system in New Zealand and to the Hikurangi Trench to the northeast. Seismic reflection profiles across the margins of this rift, and magnetic anomalies from Pacific-Australia seafloor spreading, and from adjacent plates, constrained the kinematics. However, the northern section of the rift system on the Pacific Plate lacked a conjugate on the Australian plate. Many previous models assumed that a missing conjugate area was subducted. The active source OBS and MCS studies on Marcus Langseth cruise 1802 in the Puysegur margin revealed a solution to this problem; the asymmetric part of the paleo rift system was found to be extended continental crust, and not oceanic crust. This extended continental crust has all been stranded in the Solander basin on the Pacific Plate side of the plate boundary. This new interpretation provides the geometric and structural setting for recent subduction initiation in the Puysegur segment. It also suggests a model for asymmetric evolution of other oceanic rift systems that continue along strike into regions of extended continental crust. A remaining major issue for this region is the complicated tectonics of the Macquarie Plate, which has a poorly defined northern boundary with the Australia plate, characterized by diffuse deformation. This may eventually lead to the development of another triple junction along this margin, isolating separate subduction zones, coinciding with the development of a discrete boundary between the Australia and Macquarie plates.

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I came here as an amateur volcano fan because I was always curious about how subduction zones were born and in googling the topic, I came across many scientific papers on the the Puysegur Trench and the Macquarie Tectonic Zone! This was a very informative presentation! I do wonder if some of the glitches in your presentation could have been prevented with a more thorough practice run-through. However the topic is fascinating to me, your information was very interesting and informative, and I suspect that many professional geologists and amateur geology enthusiasts would benefit from a good “plain English” presentation. I think of the Macquarie Zone as being to the topic of subduction zone initiation as similar to the East African Rift’s importance to the topic of spreading ridges.