Researchers have discovered that the Kerguelen hotspot, which created the 5,000-kilometer Ninetyeast Ridge in the Indian Ocean, moved several hundred kilometers within the Earth’s mantle. According to a study published in Nature Communications, this movement challenges the long-held geological assumption that mantle hotspots remain stationary while tectonic plates drift over them.
Why is the movement of the Kerguelen hotspot significant?
For decades, geologists operated under the assumption that mantle hotspots act as fixed, stationary points. As tectonic plates move over these plumes, they leave behind predictable trails of volcanic activity, such as the Hawaiian Islands. However, the new data regarding the Ninetyeast Ridge suggests these plumes can be mobile.
Dr. Hugo Olierook from Curtin’s School of Earth and Planetary Sciences, one of the study’s authors, stated that while hotspot movement is thought to be common, it is notoriously difficult to prove. Olierook noted that this research marks the first documented case of such movement in the Indian Ocean, having previously only been demonstrated for a few hotspots in the Pacific Ocean.
The study found that the Kerguelen hotspot moved due to interactions with the Indian–Antarctic spreading ridge. This movement means the hotspot is not a fixed anchor, but a dynamic feature influenced by regional mantle convection.
The Ninetyeast Ridge is a massive underwater mountain range. It stretches over 5,000 kilometers, maintains an average width of 200 km, and reaches heights of 3.5 km above the seafloor.
How did scientists map the volcanic progression?
To reconstruct the history of the ridge, the research team employed two primary advanced geophysical techniques: seismic tomography and high-precision geochronology.
Seismic Tomography
Scientists used seismic tomography to create three-dimensional images of the Earth’s interior. This method analyzes seismic waves generated by earthquakes. Because these waves change speed depending on the density and temperature of the material they pass through, researchers can map mantle structures like plumes and ponding zones.
Argon Dating
The team used 40Ar/39Ar dating to determine the ages of volcanic rocks along the ridge. This method measures the decay of radioactive isotopes in minerals to calculate how long ago the rock solidified. By combining these precise dates with seismic imaging, the researchers mapped the volcanic progression with unprecedented accuracy.
How does this change tectonic history models?
The discovery of a mobile hotspot necessitates a reevaluation of global plate motion models. If hotspots move, they cannot serve as reliable, fixed reference points for tracking how tectonic plates have shifted over millions of years.
Professor Fred Jourdan from Curtin’s School of Earth and Planetary Sciences and the John de Laeter Centre explained that previous models relied on rough age estimates of the Ninetyeast Ridge to understand how Earth’s plates reconfigured. According to Jourdan, the use of high-precision dating allows scientists to refine these models, providing better insights into ancient continental movements.
This shift suggests that localized mantle dynamics, rather than just global mantle flow, play a larger role in shaping the Earth’s surface than previously understood. This mirrors patterns observed in Pacific hotspots that form the Hawaiian Islands.
Can an underwater ridge act as a climate archive?
Beyond its tectonic significance, the Ninetyeast Ridge serves as a critical record of Earth’s environmental history. Because the ridge has remained near the equator for tens of millions of years, its sediments provide a relatively undisturbed window into the past.
At IODP Site U1443, located on the ridge’s crest, researchers have drilled sediments that preserve clues about:
- The history of the Indian monsoon
- Changes in ocean circulation
- Fluctuations in ocean salinity and sea levels
- The movement of materials from landmasses into the Bay of Bengal
Because the site is perched on the ridge rather than buried under heavy sediments from the Bengal Fan, it offers a cleaner data set for scientists studying long-term climate change.
Frequently Asked Questions
What is the Ninetyeast Ridge?
The Ninetyeast Ridge is the world’s longest preserved linear volcanic ridge. It is a 5,000-kilometer-long underwater mountain chain located in the Indian Ocean.
What is a mantle hotspot?
A hotspot is an area where plumes of hot, buoyant rock rise from deep within the Earth’s mantle to the crust, creating volcanic activity often independent of tectonic plate boundaries.
Why was the Kerguelen hotspot study important?
It proved that the Kerguelen hotspot moved several hundred kilometers within the mantle, challenging the idea that all hotspots are stationary.
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