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Scientists Study Earth's Missing Crust

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Brittany
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« on: April 14, 2007, 10:38:15 pm »

Scientists Study Earth's Missing Crust
By Juan Manuel Pardellas
March 7, 2007 7:41AM




"It is like a window into the interior of the Earth," Bramley Murton, a geophysicist who is taking part in the six-week mission, said Tuesday from the research ship RRS James Cook as it headed to the site, still five days away. 
 
 
British scientists have embarked on a mission to study a huge area on the Atlantic seabed where the Earth's crust is mysteriously missing and instead is covered with dark green rock from deep inside the planet.

The 12-member expedition to take an unprecedented peek at Earth's mantle left the Canary Islands on Monday with a new high-tech vessel and a robotic device named Toby that will dig up rock samples at the site and film what it sees.

The main site -- there is at least one other in roughly the same area and a third is suspected -- is about three miles below the surface of the Atlantic and located about 2,000 nautical miles southwest of the Canaries.

It is part of a globe-spanning ridge of undersea volcanos, the kind of structure that forms when Atlantic tectonic plates separate and lava surges upward to fill the gap in the Earth's crust.

But that apparently did not happen this time. Where there should be a four-mile-thick layer of crust, there is instead that much mantle -- the very dense, dark green rock that makes up the deep inner layer of the Earth.

Scientists have seen chunks of mantle that have been spewed up with lava, but never such a large, exposed stretch.

"It is like a window into the interior of the Earth," Bramley Murton, a geophysicist who is taking part in the six-week mission, said Tuesday from the research ship RRS James Cook as it headed to the site, still five days away.

This exposed layer is irregularly shaped, about 30 miles long and perhaps that distance or more at its widest. It was detected about five years ago with sonar from a surface vessel.

There are two main theories as to what happened, Murton said: A fault ripped away huge chunks of crust, or in an area of crust-forming volcanoes, this area was mysteriously devoid of that outer material, Murton said.


Roger Searle of Durham University, one of the lead researchers, said the study aims to provide insight on everything from the chemistry of oceans to the mechanisms of how the Earth behaves under so much water.

The robotic device will land on the exposed mantle, deploy a drill, and dig into the rock to bring back samples.

The project is being financed by Britain's National Environment Research Council and the Department of trade and Industry's Large Scientific Facilities Fund.
 



© 2007 Associated Press/AP Online. All rights reserved.
© 2007 Sci-Tech Today. All rights reserved.
 

http://www.sci-tech-today.com/story.xhtml?story_id=0110013AXUK9
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Brittany
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« Reply #1 on: April 14, 2007, 10:39:28 pm »

Can someone say, "Atlantis?"
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« Reply #2 on: April 14, 2007, 10:45:22 pm »

Geology & Geophysics Group
Iberia & Newfoundland margins
Contact: Dr Donna Shillington


The Iberia-Newfoundland conjugate margins constitute one of the best-studied nonvolcanic rifted margin systems in the world. Four Ocean Drilling Program (ODP) legs (103, 149, 173 and 210) and numerous geophysical studies have been dedicated to this rift system. Rifting of these margins was accompanied by very little synrift magmatism. As a result, key rifting structures are not obscured by synrift volcanic flows, making this margin pair an ideal natural laboratory in which to study the processes responsible for continental breakup and incipient seafloor spreading.




Drilling and geophysical studies of these margins have revealed that the late stages of rifting were partially accommodated by extension along detachment and/or rolling hinge faults and the exposure of subcontinental mantle at the seafloor. Many questions remain concerning the style of the early stages of rifting, the processes responsible for exposing subcontinental mantle, and how the transition from magma-starved rifting to initial seafloor spreading occurred. These topics are the motivation for additional proposed work on this margin system, including three Integrated Ocean Drilling Program (IODP) proposals.



Related publications

Chian, D., K. E. Louden, T. A. Minshull, and R. B. Whitmarsh, 1999, Deep structure of ocean-continent transition in the southern Iberia abyssal plain from seismic refraction profiles; Ocean Drilling Program (legs 149 and 173) transect: J. Geophys. Res., v. 104, p. 7443-7462.

Cole, P. B., T. A. Minshull, and R. B. Whitmarsh, 2002, Azimuthal seismic anisotropy in a zone of exhumed continental mantle, West Iberia margin: Geophys. J. Int., v. 151, p. 517-533.

Dean, S. M., T. A. Minshull, R. B. Whitmarsh, and K. E. Louden, 2000, Deep structure of the ocean-continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: The IAM-9 transect at 40o20'N: J. Geophys. Res., v. 105, p. 5859-5885.

Leythaeuser, T., T. J. Reston, and T. A. Minshull, 2005, Waveform inversion of the S reflector west of Spain: Fine structure of a detachment fault: Geophysical Research Letters, v. 32, Art No. L22304.

Minshull, T. A., 2002, The break-up of continents and the formation of new ocean basins: Phil. Trans. Royal Soc. London, v. 360, p. 2839-2852.

Manatschal,G., O. Müntener, L. Lavier, T. A. Minshull, and G. Peron-Pinvidic, Observations from the Alpine Tethys and Iberia/Newfoundland margins pertinent to the interpretation of continental break-up, in Extensional Deformation of the Lithosphere, Columbia University Press, in press.

Minshull, T. A., S. M. Dean, R. S. White, and R. B. Whitmarsh, 2001, Anomalous melt production after continental break-up in the southern Iberia Abyssal Plain, in R. C. L. Wilson, R. B. Whitmarsh, B. Taylor, and N. Froitzheim, eds., Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea, v. 187: London, Geological Society, p. 537-550.

Minshull, T. A., S. M. Dean, R. B. Whitmarsh, S. M. Russell, K. E. Louden, and D. Chian, 1998, Deep structure in the vicinity of the ocean-continent transition zone under the southern Iberia abyssal plain: Geology, v. 26, p. 743-746.

Pickup, S. L. B., R. B. Whitmarsh, C. M. R. Fowler, and T. J. Reston, 1996, Insight into the nature of the ocean-continent transition off West Iberia from a deep multichannel seismic reflection profile: Geology, v. 24, p. 1079-1082.

Pinheiro, L. M., R. B. Whitmarsh, and P. R. Miles, 1992, The ocean-continent boundary off the western continental margin of Iberia - II. Crustal structure in Tagus Abyssal Plain: Geophys. J. Int., v. 109, p. 106-124.

Russell, S. M., and R. B. Whitmarsh, 2003, Magmatism at the West Iberia non-volcanic rifted continental margin; evidence from analyses of magnetic anomalies: Geophys. J. Int., v. 154, p. 706-730.

Sawyer, D. S., R. B. Whitmarsh, A. Klaus, and e. al., 1994, Proc. ODP, Init. Repts, v. 149: College Station, TX, Ocean Drilling Program.

Shillington, D. J., W. S. Holbrook, B. E. Tucholke, J. R. Hopper, K. E. Louden, H. C. Larsen, H. J. A. Van Avendonk, S. Deemer, and H. J., 2004, Marine Geophysical Data on the Newfoundland Nonvolcanic Rifted Margin Around SCREECH Transect 2, in B. E. Tucholke, J.-C. Sibuet, and A. Klaus, eds., Proc. ODP, Init. Repts., v. 210: College Station, TX, Ocean Drilling Program, p. Available online at http://www-odp.tamu.edu/publications/210_IR/chap_05/chap_05.htm.

Shillington, D. J., W. S. Holbrook, H. J. A. Van Avendonk, B. E. Tucholke, J. R. Hopper, K. E. Louden, H. C. Larsen, G. T. Nunes, and O. L. S. S. Party, 2006, Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic reflection data on the Newfoundland margin: J. Geophys. Res., v. 111, p. doi:10.1029/2005JB003981.

Shillington, D. J., B. E. Tucholke, G. D. Karner, D. S. Sawyer, W. S. Holbrook, and H. Delius, in review, Linking core and seismic data without logs: Core-seismic correlation at Site 1276, in B. E. Tucholke, J.-C. Sibuet, and A. Klaus, eds., Proc. ODP Sci. Results, v. 210: College Station, TX, Ocean Drilling Program.

Tucholke, B. E., J.-C. Sibuet, A. Klaus, and et al., 2004, Proc. ODP, Init. Rept., v. 210: College Station, TX, Ocean Drilling Program.

Tucholke, B. E., and R. B. Whitmarsh, in press, The Newfoundland-Iberia conjugate rifted margins, in A. W. Bally, and D. G. Roberts, eds., Principles of Phanerozoic Regional Geology: Amsterdam, Elsevier.

Van Avendonk, H. J. A., W. S. Holbrook, G. T. Nunes, D. J. Shillington, B. E. Tucholke, K. E. Louden, H. C. Larsen, and J. R. Hopper, in press, Seismic velocity variations across the rifted margin of the eastern Grand Banks, Canada: J. Geophys. Res.

Peron-Pinvidic, G., G. Manatschal, S. M. Dean, and T. A. Minshull, Compressional structures on the West Iberia rifted margin: what controls their distribution? In: The Nature and Origin of Compression in Passive Margins, Geol. Soc. London Special Publication, London, Geological Society, submitted.

Peron-Pinvidic, G., G. Manatschal, T. A. Minshull, and D. Sawyer, The tectono-sedimentary and morpho-tectonic evolution recorded in the deep Iberia-Newfoundland margins: Evidence for a complex break-up history, Tectonics, submitted.

Whitmarsh, R. B., M.-O. Beslier, P. J. Wallace, and e. al., 1998, Proc. ODP Init. Rept., v. 173: College Station, TX, Ocean Drilling Program.

Whitmarsh, R. B., S. M. Dean, and T. A. Minshull, 2000, Tectonic Implications of exposure of lower continental curst beneath the Iberia Abyssal Plain, Northeast Atlantic Ocean: Geophysical evidence: Tectonics, v. 19, p. 919-942.

Whitmarsh, R. B., G. Manatschal, and T. A. Minshull, 2001a, Evolution of magma-poor continental margins from rifting to seafloor spreading: Nature, v. 413, p. 150-153.

Whitmarsh, R. B., and P. R. Miles, 1995, Models of the development of the West Iberia rifted continental margin at 40˚30'N deduced from surface and deep-tow magnetic anomalies: J. Geophys. Res., v. 100, p. 3789-3806.

Whitmarsh, R. B., P. R. Miles, and A. Mauffret, 1990, The ocean-continent boundary off the western continental margin of Iberia -- I. Crustal Structure at 40º30'N: Geophys. J. Int., v. 103, p. 509-531.

Whitmarsh, R. B., T. A. Minshull, S. M. Russell, S. M. Dean, K. E. Louden, and D. Chian, 2001b, The role of syn-rift magmatism in the rift-to-drift evolution of the West Iberia continental margin: geophysical observations, in R. C. L. Wilson, R. B. Whitmarsh, B. Taylor, and N. Froitzheim, eds., Non-volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea, v. 187: London, Geological Society, p. 107-124.

Whitmarsh, R. B., L. M. Pinheiro, P. R. Miles, M. Recq, and J.-C. Sibuet, 1993, Thin crust at the western Iberian ocean-continent transition and ophiolites: Tectonics, v. 12, p. 1230-1239.

Whitmarsh, R. B., R. S. White, S. J. Horsefield, J.-C. Sibuet, M. Recq, and V. Louvel, 1996, The ocean-continent boundary off the western continental margin of Iberia: Crustal structure west of Galicia Bank: J. Geophys. Res., v. 101, p. 28,291-28,314.

http://www.noc.soton.ac.uk/gg/research/rifts/newfoundland.php
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« Reply #3 on: April 23, 2007, 07:01:24 am »

Brittany,
I'd love to scream "Hey It's Atlantis"  but if you read Plato's stats you can clearly see that 30 miles isn't long enough to match Plato's descriptions.  30 miles only equals 260.42 stades.  Although it could be only a small portion of the missing continent, it seems like it'd be hard to explain why all the missing continent isn't showing up as this questionable mantle.  Gives us something more to speculate.   Grin
Blessed be,
Lynn
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Brittany
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« Reply #4 on: April 24, 2007, 03:38:58 am »

Hi Cleasterwood,

I'm fairly certain that those measurements are a little off. Take the measurements of Plato's flat plain, for instance - no large level place measures that big anywhere in the world.  I don't think that a continent could actually sink anyway (at least there is no evidence that one ever has), however, there is ample evidence that islands sink all the time. I'd say that Atlantis was a good-sized island that sank somewhere along the super volcanic Mid-Atlantic Ridge.
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