Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. 24/7 Space News .




TECTONICS
Constructive collisions
by Staff Writers
Munich, Germany (SPX) Apr 09, 2013


One popular model for the accretion process postulates that a huge oceanic plate - the Farallon Plate - acted as a conveyor belt to sweep crustal fragments eastwards to the margin of American Plate, to which they were attached as the denser Farallon Plate was subducted under it.

The mountain ranges of the North American Cordillera are made up of dozens of distinct crustal blocks. A new study clarifies their mode of origin and identifies a previously unknown oceanic plate that contributed to their assembly.

The extensive area of elevated topography that dominates the Western reaches of North America is exceptionally broad, encompassing the coastal ranges, the Rocky Mountains and the high plateaus in between.

In fact, this mountain belt consists of dozens of crustal blocks of varying age and origin, which have been welded onto the American continent over the past 200 million years.

"How these blocks arrived in North America has long been a puzzle," says LMU geophysicist Karin Sigloch, who has now taken a closer look at the problem, in collaboration with the Canadian geologist Mitchell Mihalynuk.

Collisions and continental growth
One popular model for the accretion process postulates that a huge oceanic plate - the Farallon Plate - acted as a conveyor belt to sweep crustal fragments eastwards to the margin of American Plate, to which they were attached as the denser Farallon Plate was subducted under it.

However, this scenario is at variance with several geological findings, and does not explain why the same phenomenon is not observed on the west coast of South America, the classical case of subduction of oceanic crust beneath a continental plate.

The precise source of the crustal blocks themselves has also remained enigmatic, although geological studies suggest that they derive from several groups of volcanic islands.

"The geological strata in North America have been highly deformed over the course of time, and are extremely difficult to interpret, so these findings have not been followed up," says Sigloch.

Sigloch and Mihalynuk have now succeeded in assembling a comprehensive picture of the accretion process by incorporating geophysical findings obtained by seismic tomography.

This technique makes it possible to probe the geophysical structure of the Earth's interior down to the level of the lower mantle by analyzing the propagation velocities of seismic waves. The method can image the remnants of ancient tectonic plates at great depths, ocean floor that subducted, i.e., disappeared from the surface and sank back into the mantle, long time ago.

Intra-oceanic subduction of the Farallon Plate
Most surprisingly, the new data suggest that the Farallon Plate was far smaller than had been assumed, and underwent subduction well to the west of what was then the continental margin of North America.

Instead it collided with, and subducted under, an intervening and previously unrecognized oceanic plate. Sigloch and Mihalynuk were able to locate the remnants of several deep-sea trenches that mark subduction sites at which oceanic plates plunge at a steep angle into the mantle and are drawn almost vertically into its depths.

"The volcanic activity that accompanies the subduction process will have generated lots of new crustal material, which emerged in the form of island arcs along the line of the trenches, and provided the material for the crustal blocks," Sigloch explains.

As these events were going on, the American Plate was advancing steadily westwards, as indicated by striped patterns of magnetized seafloor in the North Atlantic.

The first to get consumed was the previously unknown oceanic plate, which can be detected seismologically beneath today's east coast of North America. Only then did the continent begin to encounter the Farallon plate. On its westward journey, North America overrode one intervening island arc after another - annexing ever more of them for the construction of its wide mountains of the West.

(Nature, 4.4.2013)

.


Related Links
LMU
Tectonic Science and News






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECTONICS
Earth is 'Lazy' When Forming Faults Like Those Near San Andreas
Amherst MA (SPX) Apr 06, 2013
Geoscientist Michele Cooke and colleagues at the University of Massachusetts Amherst take an uncommon, "Earth is lazy" approach to modeling fault development in the crust that is providing new insights into how faults grow. In particular, they study irregularities along strike-slip faults, the active zones where plates slip past each other such as at the San Andreas Fault of southern California. ... read more


TECTONICS
Russia rekindles Moon exploration program, intends setting up first human outposts there

Pre-existing mineralogy may survive lunar impacts

Lunar cycle determines hunting behaviour of nocturnal gulls

Ultraviolet spectrograph observes mercury and hydrogen in GRAIL impact plumes

TECTONICS
Registration Opens for NASA Night Rover Energy Challenge

Final MAVEN Instrument Integrated to Spacecraft

Used Parachute on Mars Flaps in the Wind

BusinessCom Networks Connects Mars 2013

TECTONICS
NASA Celebrates Four Decades of Plucky Pioneer 11

Do Intellectual Property Rights on Existing Technologies Hinder Subsequent Innovation

Boeing Completes Preliminary Design Review for Connection Between CST-100 Spacecraft and Rocket

NASA Invests in Small Business Innovative Research and Technology Proposals to Enable Future Missions

TECTONICS
Shenzhou's Shadow Crew

Shenzhou 10 sent to launch site

China's Next Women Astronauts

Shenzhou 10 - Next Stop: Jiuquan

TECTONICS
Spooky action at a distance aboard the ISS

First data released from the Alpha Magnetic Spectrometer

Alpha Magnetic Spectrometer Team Publishes First Findings

New crew takes express ride to space station

TECTONICS
Future Looks Bright for Private US Space Ventures

Europe's next ATV resupply spacecraft enters final preparatio?ns for its Ariane 5 launch

ILS Proton Launches Satmex 8 Satellite for Satmex

When quality counts: Arianespace reaffirms its North American market presence

TECTONICS
The Great Exoplanet Debate

NASA Selects Explorer Investigations for Formulation

The Great Exoplanet Debate Part Four

Astronomers Anticipate 100 Billion Earth-Like Planets

TECTONICS
What's between a slip and a slide?

Light may recast copper as chemical industry 'holy grail'

New camera system creates high-resolution 3-D images from up to a kilometer away

Theory and practice key to optimized broadband, low-loss optical metamaterials




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement