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

Abstract

We present new photographic, petrological, geochronological, and isotopic data for gneissic and granitic rocks obtained from six sample stations on Cavalli Seamount during two cruises in 2002. These data lead to revision of earlier conclusions based on two dredges of schist in 1999. Based on c. 100 Ma ages of zircon cores, and whole rock petrochemistry and tracer isotopes, we interpret the protoliths of paragneisses and orthogneisses to probably have been sedimentary and plutonic correlatives of the Late Cretaceous Houhora Complex. U-Pb dating of low Th/U zircon rims confirms an earliest Miocene high-grade metamorphic episode. A cooling history based on Ar-Ar K-feldspar dating indicates ultra-rapid cooling (c. 2000°C/m.y.) and vertical exhumation (c. 100 mm/yr) of the rocks at 19.9 Ma. Our preferred tectonic model relates the amphibolite facies metamorphism to Northland Allochthon emplacement and the rapid exhumation to dextral transtension along the Vening Meinesz Fracture Zone system and/or a rapidly retreating Pacific trench.

New Caledonia Obducted Peridotite Nappe: Offshore Extent and Implications for Obduction and Postobduction Processes

“…Peridotite and/or serpentinite have been dredged at four localities south of the Cook Fracture Zone, along the western side of the Three Kings Ridge: at Southern Surveyor 237 voyage, dredges 28, 30, and 31, and at FAUST‐2 voyage dredge DR1 (Bernardel et al, ; Meffre et al, ; see also http://pet.gns.cri.nz; Figure ). Late Eocene HP/LT metamorphic rocks have been dredged as clasts in a conglomerate along the western side of the Three Kings Ridge (Meffre et al, ), and several dredges on Cavalli Seamount near Northland, New Zealand, have yielded in situ granite and amphibolite facies metamorphic rocks (Mortimer et al, , ) (blue circles in Figure ). In a general sense these metamorphic dredge sites present a relatively similar structural setting to the Félicité Ridge and the Mt.…”

Zealandia: Earth’s Hidden Continent

“…The elevation is a function of many features, fundamentally lithosphere density and Stagpoole (2002) based on data from Smith and Sandwell (1997). Continental basement samples from Suggate et al (1978), Beggs et al (1990), Tulloch et al (1991Tulloch et al ( , 2009, Gamble et al (1993), McDougall et al (1994, and Mortimer et al (1997and Mortimer et al ( , 1998and Mortimer et al ( , 2006and Mortimer et al ( , 2008aand Mortimer et al ( , 2008band Mortimer et al ( , 2015. NC-New Caledonia; WTP-West Torres Plateau; CT-Cato Trough; Cf-Chesterfield Islands; L-Lord Howe Island; N-Norfolk Island; K-Kermadec Islands; Ch-Chatham Islands; B-Bounty Islands; An-Antipodes Islands; Au-Auckland Islands; Ca-Campbell Island.…”

Lithosphere delamination with foundering of lower crust and mantle caused permanent subsidence of New Caledonia Trough and transient uplift of Lord Howe Rise during Eocene and Oligocene initiation of Tonga-Kermadec subduction, western Pacific

“…Slab rollback and extension followed delamination during Tonga‐Kermadec subduction initiation and led to the formation of basins between the modern Tonga‐Kermadec and Norfolk ridges [ Crawford et al , 2003; Davey , 1982; Herzer et al , 2009; Malahoff et al , 1982; Mortimer et al , 2007; Schellart et al , 2006]. There is evidence for Cenozoic metamorphic core complexes immediately north of New Zealand [ Mortimer et al , 2003, 2008] and within New Caledonia [ Baldwin et al , 2007; Schellart et al , 2006], as there is in Europe [ Jolivet et al , 2009]. We also see evidence for broad transient dynamic and/or thermal topography with an amplitude of 1100–1800 km across a region of 700 km width between Norfolk Ridge and western Lord Howe Rise.…”