New research suggests the Hawaiian hotspot migrated southward between 50 and 60 million years ago.

Hotspots describe a concentration of molten tunnels, allowing magma from deep in the mantle a direct path through Earth's crust to the surface, where the molten rock forms volcanoes.

The concept of the volcanic hotspot has been used to account for the creation of the Hawaiian Islands, the youngest members of the Hawaiian-Emperor chain of volcanic islands. Most models that simulate the evolution of the Hawaiian-Emperor chain operate under the assumption that hotspots are stationary, and that the movement of tectonic plates drives the evolution of chains of volcanic islands.

But new research suggests a complicated scenario, one in which the hotspot is also on the move.

If the movement of the Pacific plate was the only driver of the Hawaiian-Emperor chain, then the string of islands should follow a fairly predictable path. But some 47 million years ago, the chain took a left turn as it shifted southward, creating a 60 degree bend.

"If you try to explain this bend with just a sudden change in the movement of the Pacific Plate, you would expect a significantly different direction of motion at that time relative to adjacent tectonic plates," Bernhard Steinberger, a researcher with the GFZ German Research Center for Geosciences, said in a news release. "But we have not found any evidence for that."

To put the evolution of the Hawaiian-Emperor chain in proper context, Steinberger and his colleagues used updated rock dating data from the Rurutu volcanic chain in the Western Pacific, as well as the Louisville chain in the Southern Pacific.

The new data helped scientists better understand how the positioning of the three hotspots have moved relative to each other over time. Their findings -- published in the journal Nature Communications -- suggest the Hawaiian hotspot moved relative to the other hotspots between 50 and 60 million years ago.

"This makes it very likely that mainly the Hawaii hotspot has moved," said Steinberger.

The updated models suggests the Hawaiian hotspot migrated southward at a rate of several dozen miles per million years.

"Our models for the motion of the Pacific Plate and the hotspots therein still have some inaccuracies," Steinberger said. "With more field data and information about the processes deep in the mantle, we hope to explain in more detail how the bend in the Hawaiian-Emperor chain has evolved."

The roots of modern volcanism can be traced to early Earth
Washington (UPI) Feb 28, 2018 - Modern volcanic hotspots may be linked to molten rock formed billions of years ago, just after Earth formed. According to new research, the study of hotspot lava could offer new insights into the geologic evolution of early Earth.

During Earth's formation, the planet divided into two material layers. Denser, iron metal sank, forming the core, while less-dense, silicate-rich rock rose to form the mantle. During Earth's early history, deep pockets of the mantle rose and separated, solidifying to form Earth's crust. Some portions sank back to the bottom as they solidified and gained density.

The convection-like cycle -- processes of rising and falling, melting and solidifying -- continues today. Over the course of Earth's geologic history, the cycle has created a mostly uniform chemical composition throughout the mantle.

Despite millions of years of churning, however, not all of the mantle has become thoroughly mixed.

In a new paper, published this week in the journal Nature, geologists argue that some parts of the mantle remain unblended, with a chemical composition and texture different from most of the molten rock found in the mantle.

New analysis of volcanic rocks collected from Reunion Island in the Indian Ocean suggest islands formed by volcanic hotspots are linked with these ancient pockets of unmixed mantle.

As part of their analysis, scientists developed a new method for identifying these unique portions of the mantle using radioactive isotopes.

Elemental isotopes with an unstable number of neutrons release energy during their radioactive decay. Over time, this process can change the number of protons and neutrons in the nucleus, causing the element to transform into a entirely new element.

Samarium-146, for example, boasts a half-life of 103 million years, after which it decays into neodymium-142. Samarium-146 was present when Earth first formed, but quickly went extinct, disappearing just 500 million years after Earth formed. As such, an abundance of neodymium-142 serves as a signature of ancient rocks.

Differences in the ratios between neodymium-142 and other isotopes can reveal whether a rock has been significantly altered during its time in the mantle, or remains mostly unchanged since its formation a few billion years ago.

The latest analysis of neodymium isotope ratios suggests plume magma on Réunion is sourced from a pocket of mantle that remains chemically unaltered.

"The mantle differentiation event preserved in these hotspot plumes can both teach us about early Earth geochemical processes and explain the mysterious seismic signatures created by these dense deep-mantle zones," Bradley Peters, a geologist with the Carnegie Institution for Science, said in a news release.

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