Neotectonics of the Macquarie Ridge Complex, Australia‐Pacific plate boundary

Abstract

Abstract. New marine geophysical data along the Macquarie Ridge Complex, the AustraliaPacific plate boundary south of New Zealand, illuminate regional neotectonics. We identify tectonic spreading fabric and fracture zones and precisely locate the Australia-Pacific plate boundary along the Macquarie Ridge Complex. We interpret a-•5-10 km wide Macquarie Fault Zone between the two plates along a bathymetric high that extends nearly the entire length of the Australia-Pacific plate boundary south of New Zealand. We conclude that this is the active Australia-Pacific strike-slip plate boundary. Arcuate fracture zones become asymptotic as they approach the plate boundary. A broad zone of less intense deformation associated with the plate boundary extends -50 km on either side of the Macquarie Fault Zone. Marine geophysical data suggest that distinct segments of the plate boundary have experienced convergence and strike-slip deformation, although teleseismic evidence overwhelmingly indicates strike-slip motion along the entire surveyed boundary today. The McDougall and southernmost Puysegur segments show no evidence for past underthrusting, whereas data from the Macquarie and Hjort segments strongly suggest past convergence. The present-day strike-slip plate boundary along the Macquarie Ridge Complex coincides with the relict spreading center responsible for Australia-Pacific crest in the region. Our conceptual model for the transition from seafloor spreading to strike-slip motion along the Macquarie Ridge Complex addresses the decreasing length of spreading center segments and spacing between fracture zones, as well as the arcuate bend of the fracture zones that become asymptotic to the current transform plate boundary.

Geochemical fingerprint of hyaloclasts in glassy fragmental rocks of Macquarie Island (Southern Ocean): implications for volcanogenic sedimentary processes at a waning mid-ocean ridge

“…The island's crust formed near a ridge-transform intersection Daczko et al 2005) adjacent to a very long offset transform that linked the Proto-Macquarie Spreading Ridge to the Australian-Pacific-Antarctic triple junction ( Figure 1b) (Mosher & Massell-Symons 2008). Though extension and volcanism at the spreading ridge continued up until 6 Ma, transpression along adjacent transforms had initiated near the latitude of Macquarie Island by *27 Ma (Massell et al 2000;Goscombe & Everard 2001;Meckel et al 2005;Mosher & MassellSymons 2008).…”

Deformation from the convergence of oceanic lithosphere into Yap trench and its implications for early-stage subduction

“…Consequently, very little is known about the initial stage when two plates converge and one is bent and overthrusted. The difficulty of understanding the initial stages of subduction is compounded by the fact that only a handful of places exist on the Earth where such event can be observed, for example, at Macquarie Ridge Complex south of New Zealand (Collot et al, 1995;Massell et al, 2000) and Mussau Trench in the equatorial western Pacific (Hegarty et al, 1983). This paper provides a rare snapshot of early-stage subduction in the western Pacific, where a relatively young Caroline plate is being bent and thrust under the Philippine Sea plate along the Yap Trench.…”

Cenozoic reconstructions of the Australia-New Zealand-South Pacific sector of Antarctica

“…Starting around 31 Ma, spreading became more and more oblique until, around 12 Ma, motion along the boundary became essentially strike-slip [Lamarche et al, 1997]. Several recent studies have mapped the fracture zones and anomalies in these basins [Massell et al, 2000;Wood et al, 2000;Keller, 2003). We show isochrons for anomalies 8, 13 and 17 based on data presented in Keller [2003).…”