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 In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>