Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Textbook case of tectonic movement is wrong, says new study

21.08.2003


Results from an expedition to the sea floor near the Hawaiian Islands show evidence that the deep Earth is more unsettled than geologists have long believed. A new University of Rochester study suggests that the long chain of islands and seamounts, which is deemed a "textbook" example of tectonic plate motion, was formed in part by a moving plume of magma, upsetting the prevailing theory that plumes have been unmoving fixtures in Earth’s history. The research will be published in the August 22 issue of Science.



"Mobile magma plumes force us to reassess some of our most basic assumptions about the way the mantle operates," says John Tarduno, professor of earth and environmental sciences at the University. "We’ve relied on them for a long time as unwavering markers, but now we’ll have to redefine our understanding of global geography."

Traditionally, the islands were thought to have formed as the massive Pacific plate, the largest single section of Earth’s crust, moved sluggishly between the Americas and Asia. A plume, or "hot spot," brought super-heated magma from deep in the Earth to close to the crust, resulting in concentrated areas of volcanic activity. As the Pacific plate moved across this hot spot, the plume created a long series of islands and subsurface mountains. Though this chain of seamounts seemed like a perfect record of Pacific plate movement, a strange bend in the chain, dated at about 47 million years ago, troubled some geologists. To most, however, this bend was taken as the classic example of how plates can change their motion. In fact, a figure of the bend can be found in nearly all introductory text books on geology and geophysics.


Tarduno and an international team spent two months aboard the ocean drilling ship JOIDES Resolution, retrieving samples of rock from the Emperor-Hawaiian seamount chain miles beneath the sea’s surface. Rocks retrieved in 1980 and 1992 hinted that the seamounts were not conforming to expectations. The team started at the northern end of the chain, near Japan, braving cold, foggy days and dodging the occasional typhoon to pull up several long cores of rock as they worked their way south. Using a highly sensitive magnetic device called a SQUID (Superconducting Quantum Interference Device), Tarduno’s team discovered that the magnetism of the cores did not fit with conventional wisdom of fixed hotspots.

The magnetization of the lavas recovered from the northern end of the Emperor-Hawaiian chain suggested these rocks were formed much farther north than the current hotspot, which is forming Hawaii today. As magma forms, magnetite, a magnetically sensitive mineral, records the Earth’s magnetic field just like a compass. As the magma cools and becomes solid rock, the compass is locked in place. Measuring the angle that this magnetism records relative to the Earth’s surface allows geophysicists to determine the latitude at which magma solidified: Near the equator the angle is very small while nearer the poles, the angle is near vertical. If the Hawaiian hot spot had always been fixed at its current location of 19 degrees north, then all the rocks of the entire chain should have formed and cooled there, preserving the magnetic signature of 19 degrees even as the plate dragged the new stones north-westward. Tarduno’s team, however, found that the more northern their samples, the higher their latitude. The northern-most lavas they recovered were formed at over 30 degrees north about 80 million years ago, nearly a thousand miles from where the hot spot currently lies.

"The only way to account for these findings is if the Pacific plate was almost stationary for a time while the magma plume was moving south," says Rory Cottrell, research scientist and coauthor of the paper. "At some point about 45 million years ago, it seems that the plume stopped moving and the plate began."

At the mysterious bend in the chain the magnetite latitude readings level off to 19 degrees, suggesting that for some reason the magma plume stopped dead in its tracks.

"Why the hot spot stopped moving south, and whether this is related to the Pacific plate suddenly moving, is something we’d all like to discover," says Tarduno. "There’s been a quiet controversy about hot-spot motion for 30 years because some people thought the accepted theory wasn’t adding up. This study answers a lot of questions."

Aside from shedding light on tectonic motion, the findings will likely prove a boon for climatologists studying the ancient Earth. Climate changes are recorded in rocks such as those on the Pacific ocean floor, but in order to accurately judge ancient climate, the scientists must know at what latitude the rocks were at a given time in the past. Measuring against the bent Hawaiian-Emperor chain would yield results that would misplace those rocks and so throw off scientists’ picture of early Earth’s climate. The study also vindicates the work of some mantle modelers who have never had a problem with moving hot spots and who did not like the idea that a crustal plate as large as the Pacific could make a nearly right-angle bend in just a million years or so.

A meeting this month in Iceland, beneath which a hot spot is thought to currently reside, will focus heavily on the state of knowledge about plumes including the new idea that they are not stationary. As Tarduno says, "We’re all just swaying around in the mantle wind."

This research was funded by the National Science Foundation.

Jonathan Sherwood | University of Rochester
Further information:
http://www.rochester.edu/pr/News/NewsReleases/latest/Tarduno-HotSpot.html

More articles from Earth Sciences:

nachricht Atmospheric scientists reveal the effect of sea-ice loss on Arctic warming
11.03.2019 | Institute of Atmospheric Physics, Chinese Academy of Sciences

nachricht Sensing shakes
11.03.2019 | University of Tokyo

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Revealing the secret of the vacuum for the first time

New research group at the University of Jena combines theory and experiment to demonstrate for the first time certain physical processes in a quantum vacuum

For most people, a vacuum is an empty space. Quantum physics, on the other hand, assumes that even in this lowest-energy state, particles and antiparticles...

Im Focus: Sussex scientists one step closer to a clock that could replace GPS and Galileo

Physicists in the EPic Lab at University of Sussex make crucial development in global race to develop a portable atomic clock

Scientists in the Emergent Photonics Lab (EPic Lab) at the University of Sussex have made a breakthrough to a crucial element of an atomic clock - devices...

Im Focus: Sensing shakes

A new way to sense earthquakes could help improve early warning systems

Every year earthquakes worldwide claim hundreds or even thousands of lives. Forewarning allows people to head for safety and a matter of seconds could spell...

Im Focus: A thermo-sensor for magnetic bits

New concept for energy-efficient data processing technology

Scientists of the Department of Physics at the University of Hamburg, Germany, detected the magnetic states of atoms on a surface using only heat. The...

Im Focus: The moiré patterns of three layers change the electronic properties of graphene

Combining an atomically thin graphene and a boron nitride layer at a slightly rotated angle changes their electrical properties. Physicists at the University of Basel have now shown for the first time the combination with a third layer can result in new material properties also in a three-layer sandwich of carbon and boron nitride. This significantly increases the number of potential synthetic materials, report the researchers in the scientific journal Nano Letters.

Last year, researchers in the US caused a big stir when they showed that rotating two stacked graphene layers by a “magical” angle of 1.1 degrees turns...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Researchers measure near-perfect performance in low-cost semiconductors

18.03.2019 | Power and Electrical Engineering

Nanocrystal 'factory' could revolutionize quantum dot manufacturing

18.03.2019 | Materials Sciences

Long-distance quantum information exchange -- success at the nanoscale

18.03.2019 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>