Hawaii: How the chain got its kink

New model clears decades of dispute among geo-researchers

The Hawaiian Emperor necklace has a kink - but why? © National Geophysical Data Center / USGS
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Abruptly turned down: For decades, researchers have been arguing over what gave the Hawaii-Emperor island chain in the Pacific its striking kink. Was it an abrupt change of direction of the Pacific Plate? Or a hike of the hotspot? A solution to the conflict is now being provided by scientists in the journal "Nature Communications". Their result: Both previously discussed explanations are correct.

The Hawaiian Emperor chain is one of the most spectacular geological features of the earth: more than 6, 000 kilometers long, this series of volcanic undersea mountains and islands in the Pacific. The Hawaiian Islands in particular are still considered a textbook example for the operation of a hotspot - a hot uprising of magma in the mantle. Like a cutting torch, this magma melts through the earth's crust - and as it moves, so do the volcanoes that are created.

The puzzle of the Knicks

One feature, however, does not fit into the scheme: The Hawaii Emperor chain has a kink. About half the length of the otherwise row of straight rows of islands make a bend of about 60 degrees. What causes this kink, geologists argue for several decades. Some researchers blamed a sudden change of direction on the Pacific Earth Plate 47 million years ago. Evidence could have found researchers in a neighboring group of underwater mountains.

Other scientists, however, see the cause in the hotspot itself. Because according to recent findings can also Mantelplumes move. In the case of Hawaii, the hotspot is said to have moved south relatively quickly before coming to a standstill some 47 million years ago. "This scenario had its charm, because on the adjacent tectonic plates so far there was no evidence that the Pacific plate then suddenly changed direction, " said Bernhard Steinberger from GeoForschungszentrum Potsdam (GFZ).

In order to create a kink of 60 degrees solely by hotspot migration, the hotspot would have to move to the south in an unrelaistically fast manner. GFZ (Torsvik et al.)

Too fast to be true

Which of these two scenarios could have actually produced the current form of the Hawaii-Emperor chain, Steinberger and his colleagues have now verified using a geophysical-tectonic model. In this they let the hotspot with constant plate movement wander or turn off the Pacific plate at a stationary hotspot. display

It turned out: Neither of the two processes can explain the unusual shape of the volcanic chain - at least not alone. If only the hotspot moves, then it would have to move unrealistically fast, as the simulation showed. The mantle plume would then have to cover 42 centimeters per year that is five times faster than the drift of the Pacific earth plate.

It will not work without a plate turn

In addition, the hotspot should not only have moved to the south, but also to the west but this is not possible due to the mantle currents at this location, as the researchers report. "There is simply no geodynamic basis for that, " they explain. In addition, then the entire Emperor chain should not be older than 52 million years the oldest Unterseeberg is already 80 million years old.

Real course of the chain (yellow) and course with bare change of direction of the earth plate (red). This chain is about 800 kilometers shorter than in reality. The missing piece can be explained by the movement of the hotspot (blue line). GFZ (Torsvik et al.)

"We do not come to the conclusion that the 60 degree bending was mainly caused by the change in the movement of the Pacific Plate, " says co-author Pavel Doubrovine of the University of Oslo. However, even this change of direction alone can not explain the current form of the Hawaii-Emperor chain. "In our model, the chain is shifted to the south and the Emperor chain would have to be around 800 kilometers shorter, " the researchers report.

Both are right

This means that only both processes together could create the unusual chain of islands. "While we need to change the direction of the Earth's plate to explain the geometry of the Knick, the 2, 000-kilometer Emperor chain would not have been created if the Hawaiian hotspot were not S "It would have moved, " say the scientists. The plume must have migrated eight times latitude in the time 80 to 10 million years ago.

"If we accept this solution, then we can finally stop spinning around and moving forward, " says first author Trond Torsvik from the GFZ. "Then we can focus on the next exciting question: what exactly did the Pacific Plate change its direction 47 million years ago?" (Nature Communications, 2017; doi: 10.1038 / ncomms15660)

(Helmholtz Center Potsdam GFZ German Research Center for Geosciences, 09.06.2017 - NPO)