Nav: Home

The mysterious bend in the Hawaiian-Emperor chain

June 08, 2017

The volcanic islands of Hawaii represent the youngest end of a 80 million years old and roughly 6,000 kilometres long mountain chain on the ground of the Pacific Ocean. The so-called Hawaiian-Emperor chain consisting of dozens of volcanoes is well known for its peculiar 60 degrees bend. The cause for this bend has been heavily debated for decades. One explanation is an abrupt change in the motion of the Pacific tectonic plate, the opposite model states southward drift of the mantle plume that has sourced the chain since its beginning 80 million years ago. Apparently both processes play an important role, shows a new study in Nature Communications, published by a group of scientists from the University of Oslo, German Research Centre for Geosciences GFZ Potsdam, and Utrecht University.

Many volcanic ocean islands are created by columnar shaped hot upwellings called mantle plumes that originate near the ~3000 km deep base of Earth's mantle. Mantle plumes are not much influenced by surface motions of the tectonic plates that slowly move over them. Hence, long linear chains of plume-sourced volcanoes that get older and older with increasing distance from active hotspots can be tracked for hundreds to thousands of kilometres. In the Hawaiian hotspot trail, the Hawaii islands are the youngest in the chain that stretches nearly 6,000 km to Detroit seamount in the northwest Pacific, where volcanism occurred about 80 million years ago. An unprecedented 60 degrees bend characterizes the Hawaiian-Emperor Chain, dividing it into the older Emperor Chain and the younger Hawaiian Chain. The bend has been dated to 47 Ma (Fig. 1).

"The ultimate cause for the formation of the Hawaiian-Emperor Bend (HEB) was a prominent change in the Pacific plate motion at 47 Ma", says the lead author of the new study, Trond Torsvik from the University of Oslo and visiting researcher at GFZ at the moment. The team affirms a hypothesis by the US-geophysicist Jason Morgan who proposed that already in the early 1970s. "But it is not that simple as it was suggested forty years ago", says Torsvik.

Jason Morgan was the first to use hotspots as a reference frame for global plate motions. In his model mantle plumes -- which are manifested by hotspots at the surface -- were considered fixed in the mantle, and the Hawaiian-Emperor Bend was attributed to a simple directional change of the Pacific plate motion (Fig. 1). But his plate model with fixed hotspots became challenged from the 1980s.

"Since the late 1990s it has become clear that hotspots are not totally fixed", says GFZ´s Bernhard Steinberger, one of the co-authors of the paper. That is now generally accepted, he adds, and mantle flow models predict that the Hawaiian hotspot has drifted slowly to the south. "But some recent studies have argued that rapid southward motion of the hotspot before 47 Ma can explain the formation of the bend without requiring Pacific plate motion change", he says. "Such a scenario has become attractive because the geology of the plates surrounding the Pacific shows no clear evidence for a Pacific plate motion change."

The new study shows clearly why this simply does not work. It would require an unrealistically high rate of hotspot motion of about 42 cm/year which would be much faster than the average speed of tectonic plates. Moreover, this would imply that the Emperor Chain was created in just five million years and Detroit Seamount should only be 52 million years old (Fig. 2a). This prediction is obviously falsified by the recorded Detroit Seamount island ages of about 80 Ma (Fig. 1).

"Alternatively, a slower hotspot motion towards the WSW could explain both geometry and ages of the Emperor chain", says Steinberger. However, such a direction of motion is inconsistent with mantle convection models.

"Our paper is a good example of how very simple simulations of plate and hotspot kinematics can be used to explore which geodynamic scenarios for the formation of the Hawaiian-Emperor Bend are possible, and which ones are not", says Pavel Doubrovine from the University of Oslo, another co-author on the paper. "We cannot avoid the conclusion that the 60 degrees bend is predominantly caused by a directional change in the Pacific plate motion." Yet, some southward plume motion is required (blue line in Fig. 2b), otherwise the Hawaiian-Emperor Chain would be around 800 kilometres shorter.

"Explaining the geometry, length and age progression of the Hawaiian-Emperor Chain, requires both: the change in the direction of plate motion and the movement of the hotspot", states Torsvik. "If, after more than two decades of debating the end-member scenarios of plate motion change versus hotspot drift, geophysicists will be able to agree that neither of the two is satisfactory - then we can move forward and address a more interesting question: what actually drove the Pacific plate motion to change at about 47 million years ago?" Hopefully, it will not take further 40 years to get an answer to this, he adds.
-end-
Title of the original study: Torsvik, T.H., Doubrovine, P.V., Steinberger, B, Gaina, C., Spakman, W., Domeier, M. (2017). Pacific plate motion change caused the Hawaiian-Emperor Bend. Nat. Commun. 8, 15660 doi: 10.1038/ncomms15660.

Link: https://www.nature.com/articles/ncomms15660

Detailed captions for the figures attached:

Fig. 1: The Hawaiian-Emperor Chain is an example of a hotspot track - a trail of volcanic islands and seamounts created on a lithospheric plate as the plate slowly shifts over a spot of localized melting sourced by a jet of hot material rising from the deep mantle (mantle plume). With the advent of the plate tectonics theory in the 1960s, it was quickly recognized that the bend at the junction between the older Emperor segment of the chain (~80 to 47 million-years-old) and the younger Hawaiian trail likely reflects a prominent change in the motion of the Pacific plate in middle Eocene time. This explanation was prevalent until the 1990s. But then new geophysical evidence came to light suggesting that the Hawaiian plume itself was drifting to the south during the formation of the Emperor seamounts. Some researchers dismissed the plate motion change, arguing that the southward hotspot drift that ceased at ~47 Ma was all that was needed to create the bend.

Fig. 2 a: Simulating the Hawaiian-Emperor Bend: A simulation that assumes that the Pacific plate moves with a constant angular velocity to the north-west (8 cm/year). To produce a 60o bend with the Pacific plate not changing its direction and velocity and purely southward hotspot drift (~19o of north-south motion) requires an extreme rate of hotspot motion (42 cm/year), which would imply that the Emperor Chain has been created in just five Myrs and Detroit Seamount is only 52 Myrs old.

Fig. 2 b: The yellow line represents the actual track of the Hawaiian-Emperor Chain (as in Fig. 1) and the red line shows a track that would be produced by the motion of the Pacific plate, that changes at 47 Ma, if the hotspot were fixed relative to the mantle. You see that the red line is displaced southward compared with the Hawaiian-Emperor Chain, and that is the effect of southward hotspot drift for the past 80 million years (blue line), which has lengthened the Emperor Chain by about 800 km.

GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre

Related Tectonic Plates Articles:

The birth and death of a tectonic plate
Geophysicist Zachary Eilon developed a new technique to investigate the underwater volcanoes that produce Earth's tectonic plates
From where will the next big earthquake hit the city of Istanbul?
Scientists reckon with an earthquake with a magnitude of 7 or greater in this region in the coming years.
Deep-seated tectonic genesis of large earthquakes in North China
In the 1960s-1970s, North China has undergone a series of strong earthquakes.
Tectonic shift?
A recent study by researchers at the University of Delaware, the University of Oxford and the University of Minnesota, Twin Cities, provides a new data set that scientists can use to better understand plate tectonics -- the movement of the earth's outer layer.
SLU geologists discover how a tectonic plate sank
Saint Louis University researchers report new information about conditions that can cause the Earth's tectonic plates to sink into the Earth.
Oceans may be large, overlooked source of hydrogen gas
Serpentinized rocks formed near fast-spreading tectonic plates under Earth's seafloor could be a large and previously overlooked source of free hydrogen gas, a Duke University study finds.
Young bowhead whales may cease growing lengthwise to grow head and baleen plates
Young bowhead whales may cease growing lengthwise and undergo severe bone loss to help grow their enormous head and baleen plates, according to a study published June 22, 2016 in the open-access journal PLOS ONE by John George from North Slope Borough Department of Wildlife Management, Alaska, and colleagues.
UNC-Chapel Hill scientists find likely cause for recent southeast US earthquakes
The southeastern United States should, by all means, be relatively quiet in terms of seismic activity.
Study: Ancient tectonic activity was trigger for ice ages
Continental shifting may have acted as a natural mechanism for extreme carbon sequestration.
Hi-tech opens up Earth's secrets
A JCU scientist has developed a hi-tech animation of millions of years of tectonic plate movements that could lead to new mineral discoveries and help predict volcanic eruptions.

Related Tectonic Plates Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...