New constraints on plate tectonic puzzle of the SW Pacific

Abstract

A long‐standing problem in the tectonics of the southwest Pacific has been the lack of closure of the plate circuit linking the Antarctic, Australia, Lord Howe Rise, and Pacific plates in late Cretaceous and early Tertiary time [Molnar et al., 1975]. Avoiding unacceptable overlaps and underlaps in reconstructions of these plates requires invoking relative motion on one or more nebulous plate boundaries somewhere along the plate circuit, such as between East and West Antarctica, within West Antarctica [Stock and Molnar, 1987], or perhaps between the Lord Howe Rise and Challenger Plateau in the Tasman Sea [Lawverand Gahagan, 1994]. This problem is of more than mere local interestsince the motion of the Pacific plate relative to the rest of the globe is constrained through its connection with West Antarctica.

On the competing roles of fault reactivation and brittle failure in generating plate tectonics from mantle convection

“…Since the Permian, western orth America was a converging margin which has progressively evolved into a transform boundary [Atwater, 1970] ; at Cape Mendocino, California, the Cascade thrust is directly evolving into the San Andreas transform fault . Presently, the Macquarie ridge is primarily a strike-slip fault, but from at least 61 to 20 Ma it was an active spreading center on the Southeast Indian Ridge which evolved into a transform fault [ Cande et al , 1998]. Interestingly, as we have just described, this former spreading center (now a transform fault) is evolving into a zone of convergence with activation of thrust faults within the fault zone immediately south of the South Island of New Zealand [ Collot et al , 1995).…”

Mesozoic/Cenozoic tectonic events around Australia

“…Another tectonic event, the joining of the Bellinghausen plate to West Antarctica, was recorded at this time in the Pacific Ocean [Cande et al , 1998). The 61 Ma event also affected the Tasman Sea basin resulting in a counterclockwise change in the spreading direction, which initiated a period of transform motion along the central and northern parts of the eastern Australian margins [Gaina et al, 1998b].…”

“…Preliminary reconstructions that include relative motion between East and West Antarctica [Cande et al, 1998] based on recently collected geophysical data north of the Ross Sea and south of the Tasman Sea indicate that a B) IO tectonic event at 43 Ma may indeed mark the onset of renewed subduction east of Australia [Gaina, 1998] ( Figure 5b). There is abundant evidence that compression affected the eastern and northeastern Australian plate close to 43 Ma.…”

“…Satellite altimetry has revolutionized our knowledge of the tectonic structure of the ocean floor where ship data are sparse. Additional magnetic and seismic data have recently been collected off Antarctica [Ishihara et al, 1996;Mizukoshi et al, 1986;Saki et al, 1987;Tsumuraya et al, 1985], around the Macquarie Triple Junction and in the Tasman Sea [Cande et al, 1998] in the Tasman Sea and off West Australia [Symonds et al, 1996]. These data are being used to construct more detailed plate tectonic models.…”

“…These data are being used to construct more detailed plate tectonic models. We have combined some recently published work [ Cande et al, in press;Cande et al, 1998;Gaina et al, 1998a;Gaina et al, 1999;Gaina et al, 1998b;Mihut and Muller, 1998;Muller et al, 1998a;Muller et al, 1998b;Muller et al, 1997;Tikku, 1998;Tikku and Cande, 1999] with other work in progress to present digital grids of the age of the ocean floor ( Figure 1), spreading rates (Figure 2), asymmetries in crustal accretion ( Figure 3) and plate tectonic reconstructions to identify major plate tectonic events, evaluate their cause, and investigate their effect on anomalous intraplate subsidence or uplift and on the history of oceanic crustal accretion.…”