New constraints on the age and evolution of the Wishbone Ridge, southwest Pacific Cretaceous microplates, and Zealandia–West Antarctica breakup

Abstract

We present analytical results from four dredge locations across the eastern Zealandia continental margin and adjacent ocean crust. The 115 Ma dacites dredged from the West Wishbone Ridge (WWR) are isotopically primitive, weakly adakitic, slabderived lavas. The 97 Ma A-type granites and a basalt from the easternmost Chatham Rise enlarge the known area of postsubduction Gondwana magmatism. Amphibolite-grade schists from a fault block south of the Chatham Rise provide a critical bridge between the Zealandia and West Antarctica belts of Jurassic-Cretaceous accretionary prism rocks. The new recognition of the WWR as a remnant of a 115 Ma intraoceanic subduction system means that previous hypotheses of the WWR as a fracture zone or spreading ridge require modification. The dacite ages constrain the start of Osbourn Trough spreading, which caused breakup of the Hikurangi-Manihiki igneous plateau, to before 115 Ma. We speculate that, after 115 Ma, the WWR was rifted by an intraoceanic spreading center that developed along its southeast side. Impingement of this spreading center against the Gondwana margin led to widespread 95-100 Ma postsubduction magmatism, variable lithospheric stretching, and ultimately continental splitting of Zealandia and West Antarctica across basement trends.

Erratum to K. Hoernle, F. Hauff, P. van den Bogaard, R. Werner, N. Mortimer, J. Geldmacher, D. Garbe-Schönberg, B. Davy (2010) “Age and geochemistry of volcanic rocks from the Hikurangi and Manihiki oceanic Plateaus”, Geochimica et Cosmochimica Acta 74, 7196–7219

“…The elongation of the seamounts is interpreted to result from magmas rising along extensional faults (Hoernle et al, 2004), associated with the breakup of the Hikurangi and Manihiki Plateaus by ca. 115 Ma (Mortimer et al, 2006). The lack of erosional features, such as terraces or platforms, and the higher elevations of some compared to the guyots suggests that these seamounts had extensive late-stage volcanism, post-dating the formation of the flat-tops on the guyots.…”

Tectonics of the West Antarctic rift system: new light on the history and dynamics of distributed intracontinental extension

“…Remnants of the active margin are the submarine plateaus that border the Tasman Sea and provide a sparse geological record of the change in plate dynamics (Tulloch et al, 1991;Mortimer et al, 1999aMortimer et al, , 2006Mortimer, 2004).…”

Ultra‐fast early Miocene exhumation of Cavalli Seamount, Northland Plateau, Southwest Pacific Ocean

“…F, Strontium isochron diagram (no useful age information can be derived from the isochron lines, they are plotted for reference only). Reference data from Ruddock (1990), McCulloch et al (1994), Palmer et al (1995), Nicholson et al (2000), Nicholson & Black (2004), adams et al (2005, and Mortimer et al (1998Mortimer et al ( ,2003Mortimer et al ( ,2006.…”