Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. Earth Science News .




TECTONICS
Curvy Mountain Belts
by Staff Writers
Boulder CO (SPX) Jul 03, 2012


(A) Block diagram depicting the effect of lithospheric bending around a vertical axis and the resultant strain field (modified tangential longitudinal strain). Strain ellipses depict arc-parallel shortening in the inner arc and arc-parallel stretching in the outer arc. Note the different behavior of the mantle lithosphere in the inner and outer arcs and the increase in thickness of mantle lithosphere below the inner arc and thinning below the outer arc. (B) Snapshot illustration of arc development starting with a linear belt resulting from a Gondwana-Laurentia collision. (C) Second snapshot illustrating oroclinal bending, which causes lithospheric stretching in the outer arc and thickening beneath the inner arc (Gutierrez-Alonso et al., 2004). (D) The final stage of oroclinal bending, depicting delamination and collapse of thickened lithospheric root beneath the inner arc, replacement of sinking lithosphere by upwelling asthenospheric mantle, and associated magmatism in the inner and outer arc regions. (E) Two tomographic views of the analogue modeled mantle lithosphere geometry after buckling around a vertical axis where the lithospheric root is developed under the inner arc (top-frontal view from the concave part of the model; bottom-view from below); 3-D coordinate axes given. (F) Tomographic 3-D image of the delaminated lithospheric root obtained with analogue modeling; 3-D coordinate axes given. For a larger version of this image please go here.

Mountain belts on Earth are most commonly formed by collision of one or more tectonic plates. The process of collision, uplift, and subsequent erosion of long mountain belts often produces profound global effects, including changes in regional and global climates, as well as the formation of important economic resources, including oil and gas reservoirs and ore deposits.

Understanding the formation of mountain belts is thus a very important element of earth science research. One common but poorly understood aspect of mountain belts are the many examples of curved (arcuate) mountain ranges.

The Appalachian range in Pennsylvania, the Rocky Mountains in central Montana, the Blue Mountains in Oregon, the Bolivian Andes of South America, and the Cantabrian Arc in Spain and northern Africa are among many examples of noticeably curved mountain belts.

The cause of these curvy mountains is among the oldest topics of research in geology, and there is still extensive debate on what mechanisms are most important for making a curvy mountain range.

A common question is whether these presently curvy mountain ranges were originally straight and then later bent or whether they were uplifted in more or less their present shape.

Another important aspect of the origin of these curved mountain ranges is the thickness of the rock units involved in their formation. Some workers have proposed that these ranges are composed of relatively thin slices of crustal rocks (limited to several kilometers in thickness), while others have argued that at least some of these curvy ranges involve the entire thickness of the lithospheric plates (30 to 100 km thick).

One of the most promising ways to answer these questions utilizes comparisons of the orientation of structural features in rocks (fault planes and joints), records of the ancient magnetic field directions found in rocks, and the timing of deformation and uplift of the mountain belts.

An international group of researchers from Spain, Canada, and the United States, led by Dr. Gabriel Gutierrez-Alonso, have presented a compelling study of one of the best examples of curved mountain ranges: the Cantabrian Arc in Spain and northern Africa.

They have compiled an extensive collection of fault and joint orientation data and directions of the ancient geomagnetic field recorded by Paleozoic rocks collected in Spain.

The Cantabrian Arc was formed during the collision of a southern set of continents (Gondwanaland [present day Africa-South America-Australia-India-Antarctica]) with a northern set of continents (Laurentia [present day North America and Eurasia]) to produce the supercontinent Pangea.

In a nutshell, their combined study has found that the curved pattern of the Cantabrian Arc was produced by the bending of an originally straight mountain range.

The main line of evidence supporting this view is the patterns of rotation that are obtained from the directions of the ancient geomagnetic field recorded by the rocks of these mountain ranges.

Combined with an analysis of the faults and joints in the rocks, and the ages of rocks that have variations in the amount of rotation indicated by the magnetic directions, the age of the bending of the Cantabrian Arc is confined to a relatively narrow window of geological time between 315 and 300 million years ago.

Gutierrez-Alonso and colleagues compare the age range of this mountain bending event to the ages of igneous activity and uplift of the region and propose that widespread changes in the deeper (mantle) portion of the lithospheric plate in the area are coeval, and likely linked to, the rotation of the Cantabrian Arc to produce its characteristic sharp curviness.

Based on this linkage, they propose that this, and perhaps many other, curvy mountain ranges are produced by rotation of entire portions of the lithosphere of tectonic plates, rather than just thin slices of crustal rocks.

Buckling an orogen: The Cantabrian Orocline: G. Gutierrez-Alonso et al., Depto. de Geologia, Universidad de Salamanca, Plaza de los Caidos s/n, 37008 Salamanca, Spain. Posted online 27 June 2012; doi: 10.1130/GSATG141A.1.

.


Related Links
Geological Society of America
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
New observations on the San Andreas Fault in Santa Cruz Mountains, Seattle Fault Zone
Los Angeles CA (SPX) Jun 04, 2012
Recent paleoseismic work has documented four surface-rupturing earthquakes that occurred across the Santa Cruz Mountains section of the San Andreas Fault (SAF) in the past 500 years. The research, conducted by the U.S. Geological Survey, with assistance from the California Geological Survey, suggests an average recurrence rate of 125 years, indicating the seismic hazard for the area may be ... read more


TECTONICS
Jakarta, Canberra boost asylum cooperation

Google urges governments to share disaster data

20 killed as fuel truck crash in China sparks fire

Record radiation levels detected at Fukushima reactor

TECTONICS
Body scanner takes tailoring to the masses

H.K.'s SCMP editor under fire as press freedom 'shrinks'

Apple pays $60 mn to end China iPad trademark row

Now Everyone Can Build a Satellite Like NASA: Online!

TECTONICS
India's monsoon seen picking up after slow start

Saving the Baltic Sea

Dying trees in Southwest set stage for erosion, water loss in Colorado River

Research Vessel Winds Down Visit to Vietnam

TECTONICS
Study: Wrong diet doomed 1912 polar try

Scientists to produce first 3-D models of Arctic sea ice

Canada builds up arctic region defenses

Greenland ice may exaggerate magnitude of 13,000-year-old deep freeze

TECTONICS
Screening horticultural imports: New models assess plant risk through better analysis

Scientists urge new approaches to plant research

Want bigger plants? Get to the root of the matter

S. Korean farmers rally against China trade talks

TECTONICS
Northeast India floods kill 79, displace two million

Shallow 6.3-magnitude quake hits northwest China

Floods swamp eastern India, 1.3 million displaced

UCSB scientists compile first study of potential for tsunamis in northwestern California

TECTONICS
Chimpanzees cleared after mauling American in S.Africa: park

Rwanda gorillas prosper despite guerrillas next door

Kenyan army hunts kidnappers of four foreign aid workers

23,000 Angolans back home as refugee status ends

TECTONICS
Seabirds studied for clues to human aging

Hong Kong's land shortage forces bereaved to sea

Diet of early human relative Australopithecus shows surprises

Outside View: 18th-century words for today




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