40Ar/39Ar geochronology and volume estimates of the Tasmantid Seamounts: Support for a change in the motion of the Australian plate

Abstract

New volume estimates and 40 Ar/ 39 Ar ages for the Tasmantid Seamounts are reported here to investigate the origin of volcanism and potential links between volcanism and changes in the speed and direction of migration of the Australian plate during the Cenozoic. The results show that the average extrusive volume of individual volcanoes along the seamount chain is 2587 km 3 (stdev. = 3078 km 3), and that volumes generally increase towards the south. An exception, the Britannia Guyot, located in the middle of the seamount chain, shows the largest eruptive volume (11374 km 3). Nineteen new 40 Ar/ 39 Ar ages, from Wreck to Gascoyne, show that the emplacement of the Tasmantid Seamounts occurred between 33.2 ± 1.5 to 6.5 ± 0.6 Ma. A single linear regression applied to the age versus latitude data, assuming volcanism to be caused by plate migration over a stationary hotspot, reveals a plate migration rate of 62 ± 2 km.Ma-1 (R 2 = 0.97, n = 27) between ~33 and 6 Ma. However, the bend in the seamount track, corresponding with the period of largest eruptive volumes, suggests three distinct segments in the Tasmantid age versus latitude data. The northern segment is consistent with a plate migration rate of 75 ± 10 km.Ma-1 (R 2 = 0.88, n = 10) and the southern segment reveals a plate migration rate of 64 ± 4 km.Ma-1 (R 2 = 0.94, n = 17). The period between these two segments, from ~25 to 19 Ma, overlaps with the period of slow migration and change in the direction of the Australian plate derived from the age versus latitude distribution of continental central volcanoes. The new Tasmantid Seamount results support the interpretation that Australia's northward trajectory involved a series of collisions and associated changes of direction and speed.

Geophysical and geological characterisation of dredge locations from RV Southern Surveyor voyage ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

“…4c). The age progression from the more highly sampled Tasmantid trail, and Australian onshore volcanism, is interpreted to show a transient deceleration in Australia's northward motion in the late Oligocene, lasting 3-6 Myrs (Crossingham et al, 2017;Knesel et al, 2008). The new age constraints from the Horsehead and Chesterfield sites support the view that the kinks in the Tasmantid and Lord Howe trails formed roughly contemporaneously.…”

“…Another alternative to explain the peak in magma flux is that it is associated with plume temperatures at the start-up phase of volcanism, as has been documented in Iceland (Spice et al, 2016). However, it is unknown whether the Horsehead and Chesterfield sites mark the start-up phase of volcanism along this trail and secondly, edifice volumes along the Tasmantid trail calculated by Crossingham et al (2017) also peak in the late Oligocene suggesting that the increase in magma flux may be more regional in nature.…”

“…The Tasmantid and Lord Howe Seamount chains are collinear, broadly north-south trending age-progressive volcanic trails that have been demonstrated to record the rapid northward motion of the Australian plate over a relatively slowly moving mantle source (Knesel et al, 2008;McDougall and Duncan, 1988). The Tasmantid Chain can be traced northward just south of the Louisiade Plateau with an oldest age of > 50 Ma based on recent 40 Ar/ 39 Ar dating of dredge samples collected during RV Southern Surveyor voyage ss2012_v07 (Crossingham et al, 2017;Kalnins et al, 2015). The northernmost identified extent of the Lord Howe seamount trail was previously limited to the Bellona Plateau at the northern end of the Lord Howe Rise (Fig.…”

Magma production along the Lord Howe Seamount Chain, northern Zealandia

“…M Seton et al ss5/2004and ss02/2005, 2006aKalnins et al 2015). The youngest dated seamount associated with this trail is the Gascoyne Seamount with an age of ∼7 Ma (McDougall & Duncan, 1988;Kalnins et al 2015;Crossingham et al 2017) and lies 250 km north of the presumed location of the Tasmantid hotspot (Fig. 2).…”

“…Fichtner et al 2010; Montelli et al 2004) and a poorly sampled tapestry of plateaus and ridges at the oldest end of the tracks whose relationship to hotspot volcanism remains enigmatic. Recent geochemical and 40 Ar-39 Ar dating of dredge samples from the Tasmantid seamounts (Kalnins et al 2015;Crossingham et al 2017) and two samples from the northern Lord Howe seamounts (Mortimer et al 2018) have redressed one of the major shortcomings, resulting in a more comprehensive dataset that can be used to evaluate the eruptive history of these volcanic edifices.…”