According to a study published in the journal Gondwana Research, researchers have solved a long-standing geological mystery by discovering that the Lord Howe Island and Tasmantid seamount chains in the Tasman Sea are connected by a single mantle plume. Located about 600 kilometres off the New South Wales coast, Lord Howe sits on a weathered volcanic remnant, while a second chain runs roughly 650 kilometres to the west, tracing the northward drift of the Australian tectonic plate over the past 40 million years.
How a Single Mantle Plume Splits Beneath the Tasman Sea
Most volcanoes form where tectonic plates meet, but hotspots like Hawaii are created when a plume of hot rock rises from deep inside the Earth to melt through a moving plate. In the Tasman Sea, two nearly identical chains run side by side. According to the study, a single deep-mantle plume rises and is deflected by a slab of old seafloor that sank at a subduction zone and stalled about 500 kilometres down.
Because the plume cannot push through the dense slab, it bends around the obstacle and escapes through gaps on either side, forming two separate branches of volcanoes at the surface. Researchers backed this discovery with three distinct lines of evidence: interior Earth simulations, tectonic plate reconstructions of the last 200 million years, and lead isotope chemistries from lavas carrying fingerprints over a billion years old.
Did You Know? Lead isotopes extracted from the lavas of both the Lord Howe and Tasmantid chains require more than a billion years to develop. This timeline proves the erupted material originates deep in the Earth’s mantle rather than from the nearby 60-million-year-old subducted slab.
Predicting the Future of the Lord Howe and Tasmantid Chains
Simulations of Earth’s interior reveal that branching mantle plumes do not last forever. As the obstructing slab sinks deeper into the mantle, one branch eventually becomes dominant while the other shuts down. Geological data shows that the Lord Howe seamount chain has produced smaller eruptions since about 23 million years ago, whereas the Tasmantid volcanoes have produced larger eruptions over the same timeframe.
Based on these findings, researchers predict that the Tasmantid chain will become the primary conduit, while the Lord Howe chain will eventually terminate many millions of years into the future. This dynamic behavior challenges the traditional view of mantle plumes as straight, unbending conduits from the deep Earth to the surface.
Implications for Global Plate Tectonic Reconstructions
Geoscientists rely on volcanic hotspots to track how continents move because plumes stay relatively fixed while plates slide above them. If a single plume can split and shift when encountering subducted slabs, existing models of absolute plate motion may require significant revision. The findings suggest that other closely spaced chains around the world—such as Yellowstone in the United States—might share a similar branching history.
Pro Tip for Researchers
While current seismic imaging beneath the Tasman Sea remains blurry, resolving these deep structures will require higher-resolution seismic data and fresh rock samples from underwater volcanoes to better constrain magma geochemistry.
Frequently Asked Questions
What is a seamount chain?
A seamount chain is a series of underwater volcanoes formed as a tectonic plate moves over a stationary hotspot of magma.
Why are there two chains side by side in the Tasman Sea?
According to the Gondwana Research study, a single mantle plume splits when it hits a stalled, subducted slab of seafloor, forcing the magma to rise through gaps on either side.
Will Lord Howe Island disappear soon?
While the Lord Howe chain has seen smaller eruptions over the last 23 million years, any future termination of the volcanic conduit will take many millions of years to occur.
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