The origins of the North Atlantic Ocean, a geological feature formed roughly , have long been a subject of debate among geoscientists. Was the massive volcanic activity that accompanied its formation driven by a deep mantle plume – a localized upwelling of abnormally hot rock from within the Earth – or primarily by the thinning of the Earth’s crust due to plate tectonics? New analysis of basalt cores extracted from the ocean floor off the coast of Norway suggests the latter may be the more significant factor.
For decades, scientists have been intrigued by the volcanic rifted margin between Norway and Greenland, a region that experienced one of the largest volcanic events in Earth’s history. This event is also linked to a period of intense global warming during the Eocene Epoch, making understanding its cause particularly crucial. The prevailing theories centered around a mantle plume rising and melting the crust, or significant stretching and thinning of the lithosphere – the rigid outer layer of Earth – due to the forces of plate tectonics.
Researchers from the University of Utah, led by associate professor of Geology & Geophysics Sarah Lambart, have now presented evidence supporting the plate tectonics hypothesis. Their findings, published in the journal Geochemistry Geophysics Geosystems (or “G-Cubed”), are based on detailed analyses of basalt cores recovered during an expedition facilitated by the International Ocean Discovery Program. The expedition, Expedition 396, utilized the research vessel JOIDES Resolution for an eight-week drilling operation.
“Both of them are involved for sure. It’s a chicken and egg situation,” Lambart explained. “We now have evidence for significant extension before you have this peak of magmatism.” This suggests that the stretching and thinning of the crust initiated the process, creating the conditions for increased magma production, rather than a plume directly causing the rifting.
The team’s analysis focused on the chemistry of the basalt cores. By examining the composition of the rock, they were able to reconstruct the conditions under which it formed. The data indicates that substantial extension of the lithosphere occurred *before* the peak of volcanic activity. This pre-existing thinning would have reduced the pressure on the underlying mantle, allowing it to melt more easily and generate magma.
The debate between mantle plume and plate tectonic drivers isn’t new. The MantlePlumes.org website details research into intraplate stress and deformation, linking changes in subduction zones to continental breakup and crustal fragmentation. However, the new core samples provide a more direct line of evidence regarding the specific conditions present during the North Atlantic’s formation.
The implications of this research extend beyond simply understanding the past. The processes that shaped the North Atlantic Ocean are relevant to other rifted margins around the world and to understanding the broader relationship between mantle dynamics and plate tectonics. Understanding the relative contributions of these forces is also important for understanding the associated climate changes. The Eocene Epoch, during which the North Atlantic formed, was a period of significant global warming, and the volcanic activity associated with the rifting likely played a role in that warming.
The research highlights the power of deep-sea drilling and core analysis in unraveling complex geological mysteries. The ability to retrieve and analyze rock samples directly from the ocean floor provides a unique window into Earth’s past, allowing scientists to test hypotheses and refine our understanding of the planet’s dynamic processes. The basalt and sediment cores recovered during the expedition represent a valuable resource for future research, and will undoubtedly continue to yield new insights into the formation of the North Atlantic and other rifted margins.
Further research will likely focus on refining the timeline of events and quantifying the relative contributions of plate tectonics and mantle processes. While the new data strongly suggests that lithospheric thinning was the primary driver of magmatism, the role of a mantle plume cannot be entirely ruled out. It’s possible that a plume contributed to the overall heat flow and magma production, but that its influence was secondary to the effects of plate tectonics.
