Basement gabbro from the Lord Howe Rise

Abstract

In 1975 a French expedition dredged a seamount on the Lord Howe Rise and recovered basalt with gabbro xenoliths. New analytical work indicates that the basalt is a strongly alkaline lava, similar to Neogene intraplate basalts that are widespread across Zealandia. The gabbro is a cumulate leucogabbro containing augite, plagioclase, titanomagnetite and, in some parts, rare olivine (now entirely pseudomorphed by clay). Whole rock and clinopyroxene element concentrations and ratios indicate that the gabbro is weakly alkaline to transitional in composition and is not petrologically related to the basalt. Attempts to date the gabbro by the Rb-Sr method have been unsuccessful but clinopyroxene has an initial 87 Sr/ 86 Sr of c. 0.7036, that varies little with age. Whole rock and mineral chemistry, and Sr, Nd, and Pb isotopic ratios support an origin for the gabbro as part of an intraplate mafic pluton (of probable Late Cretaceous age), rather than as a continuation of the Devonian-Cretaceous convergent margin Median-New England Batholith.

Anomalous passive subsidence of deep‐water sedimentary basins: a prearc basin example, southern New Caledonia Trough and Taranaki Basin, New Zealand

“…Basement rocks in the southern part of the NCT represent a wide range of mostly continental rock types including, plutonic, metamorphic, meta‐sedimentary and sedimentary rocks that formed at or near the complex Paleozoic and Mesozoic subduction margin of the Gondwana continent (Mortimer et al ., ; Mortimer, ,b). Seismic refraction data indicates thin (10 km) crust with high (7.0–7.4 km/s) lower crustal seismic velocities in the northern part of the NCT that are consistent with highly thinned continental crust, underplated basalt, or oceanic crust that may postdate Gondwana subduction (Klingelhoefer et al ., ).…”

Cretaceous felsic volcanism in New Zealand and Lord Howe Rise (Zealandia) as a precursor to final Gondwana break-up

“…It represents one of only three pre-Cenozoic basement samples ever recovered from the Lord Howe Rise (Mortimer 2004b;Mortimer et al 2008). This Deep Sea Drilling Program hole penetrated 513 m below sea level and bottomed in 156 m of rhyolitic volcanic rocks (van der Lingen 1973).…”

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).…”