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 How much biomass grows in the savannah?
16.02.2017 | Friedrich-Schiller-Universität Jena

nachricht Canadian glaciers now major contributor to sea level change, UCI study shows
15.02.2017 | University of California - Irvine

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Tune your radio: galaxies sing while forming stars

21.02.2017 | Physics and Astronomy

Improved Speech Intelligibility and Automatic Speech-to-Text Conversion for Call Centers

21.02.2017 | Trade Fair News

36 big data research projects

21.02.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>