Featured Research

from universities, journals, and other organizations

Earth's Continental Land Masses Created In Short, Fast Bursts, Scientists Say

Date:
December 8, 2000
Source:
University Of Toronto
Summary:
Scientists believe they have unraveled one of geology's most enduring mysteries about how the Earth's continental crust was built, and they say it happened in a relative blink of an eye.

Scientists believe they have unraveled one of geology's most enduring mysteries about how the Earth's continental crust was built, and they say it happened in a relative blink of an eye.

According to Alexander Cruden, associate professor of geology at the University of Toronto and second author of the paper to appear in the Dec. 6 issue of Nature, the way that granite forms - a rock that makes up about 70 to 80 per cent of the Earth's continental crust - is not the sluggish, multi-million year process that scientists previously believed. In fact, Cruden and his co-authors argue that the process occurs in rapid, dynamic and possibly catastrophic events that take between 1,000 and 100,000 years, depending on the size of the granite intrusion. And that's changing how scientists look at the formation of the Earth's continents.

Cruden conducted the research with Nick Petford of Kingston University and Ken McCaffrey of the University of Durham, both in England, and Jean-Louis Vigneresse of the Centre National de la Recherche Scientifique in Nancy, France.

"In the past, we thought that granite magma - which cools and crystallizes to form very large granite intrusions - moved up through kilometres of crust as large, solid blobs at rates of about a metre per year. Because the continental crust is largely made up of these intrusions, the prevailing view was that the continents grew slowly and steadily over millions of years. But we've found that magma actually has quite low viscosity and is relatively runny," says Cruden. "Because it is runny, it's able to channel its way from the mantle and lower crust through fractures and cracks that are as small as one metre thick. This way, the magma can ascend 20 to 30 kilometres into the upper crust quite rapidly."

Therefore, says Cruden, a 50 km wide intrusion of granite, in say Greenland or the Canadian Shield, that geologists would have once estimated to have taken millions of years to form may have actually taken only 50,000 years. Smaller intrusions that are 10 km across may form in as little as 1,000 years. And from a geological point of view, that's extraordinarily fast, he adds.

The researchers used experimental studies that involved melting rock samples to understand how granite magma initially forms in the upper mantle and lower crust and how fast it can move. That data was then applied to theoretical models to determine its method and rate of ascension. New models for the emplacement stage - where the granite is intruded into older rock in the upper crust - are based on a combination of theoretical studies and fieldwork in areas such as the Canadian Shield, Sweden, the Sierra Nevada of California, Greenland and the Andes of South America. A unique aspect of the research is that the three main stages of granite formation - generation, ascent and emplacement - are regarded together as a system. Historically, these processes have been studied by different geological specialists in isolation from each other.

Cruden likens the granite formation process to subterranean volcanic eruptions. Like Lego blocks built on top of one another, large parts of the Earth's continental land masses were created by tens of thousands of quick eruptions or bursts of molten magma that were transferred rapidly from the mantle and lower-most crust and then injected as large horizontal sheets into the upper crust. These sheets then cooled and crystallized to form the large granite intrusions that we see exposed at the surface of all continents today, he says.

The Earth's continents began forming approximately four billion years ago, Cruden explains. "This research has important implications for how we understand the basic physics and chemistry of crust formation processes as well as the formation of economic ore deposits - gold and copper, for example - many of which are associated with granite intrusions."

This study was funded by Natural Environmental Research Council of the United Kingdom, the Natural Sciences and Engineering Research Council of Canada and the Centre National de la Recherche Scientifique of France.


Story Source:

The above story is based on materials provided by University Of Toronto. Note: Materials may be edited for content and length.


Cite This Page:

University Of Toronto. "Earth's Continental Land Masses Created In Short, Fast Bursts, Scientists Say." ScienceDaily. ScienceDaily, 8 December 2000. <www.sciencedaily.com/releases/2000/12/001207140240.htm>.
University Of Toronto. (2000, December 8). Earth's Continental Land Masses Created In Short, Fast Bursts, Scientists Say. ScienceDaily. Retrieved August 27, 2014 from www.sciencedaily.com/releases/2000/12/001207140240.htm
University Of Toronto. "Earth's Continental Land Masses Created In Short, Fast Bursts, Scientists Say." ScienceDaily. www.sciencedaily.com/releases/2000/12/001207140240.htm (accessed August 27, 2014).

Share This




More Earth & Climate News

Wednesday, August 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Calif. Quake Underscores Need for Early Warning

Calif. Quake Underscores Need for Early Warning

AP (Aug. 26, 2014) Researchers at UC Berkeley are testing a prototype of an earthquake early warning system that California is pursuing years after places like Mexico and Japan already have them up and running. (August 26) Video provided by AP
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Brazil Tries Genetically Modified Mosquitoes to Fight Dengue

Brazil Tries Genetically Modified Mosquitoes to Fight Dengue

AFP (Aug. 25, 2014) A factory in the industrial state of Sao Paulo produces genetically modified mosquitoes to fight dengue, a deadly tropical disease more prevalent in Brazil than anywhere else in the world. Duration: 00:57 Video provided by AFP
Powered by NewsLook.com
Raw: Prime Minister at Japan Landslide Site

Raw: Prime Minister at Japan Landslide Site

AP (Aug. 25, 2014) Japanese Prime Minister Shinzo Abe visited Hiroshima on Monday as rescuers expanded their search for dozens still missing from landslides around the western Japanese city that killed at least 50 people. (Aug. 25) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins