GeologyRocks"Deblobbing"
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"Deblobbing"
Mon, 01/30/2006 - 00:35IMHO it is rubbish - phrases like "liquid mantle" are a bit of a giveaway.
The Andean margin is complex and morphology is largely controlled by the nature of the subducted Nazca plate. Where there has been anomalously thick production of oceanic lithosphere at the spreading ridge local 'aseismic' ridges perpendicular to the spreading ridge are formed (I forget the exact names but Iqueque and Juan Fernandez are two of the three that spring to mind). Where these subduct, they are more buoyant that normal oceanic lithosphere and the overlying South American continent is uplifted.
The subduction of these aseismic ridges can be correlated not only with uplift on the Andean margin but the location of earthquakes in the subduction system and the presence / absence of volcanos in the high Andes
Hypocentre
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"Deblobbing"
Mon, 01/30/2006 - 15:33I'm inclined to agree about it being rubbish. I've had a look on the university's website for more info and found nothing but the same press release, which really doesn't present anything convincing. Thanks for the info about the Andes.
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Mon, 01/30/2006 - 16:49It may not be the best place to look, but I found the term deblobbing in This Abstract on the NASA Astrophysics Data System, and it does relate to the mantle, so it may be worth searching other journals you have access to.
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Mon, 01/30/2006 - 19:32I think I recall a similar theory on that programme with Aubrey Manning, was it "Journeys to the Centre of the Earth", or "Earth Story"? I can't remember but I think maybe the latter.
In it he was speaking to a scientist who said that the root of a mountain range could fall away, and he used it to explain the extremely rapid uplift of the Himalayas.
Definately Earth Story...just Googled it. It was "EPISODE 5: THE ROOF OF THE WORLD."
I think I got the same abstract as you from a different source:
http://www.brightsurf.com/news/headlines/view.article.php?ArticleID=22786
The research was carried out by Carmala N. Garzione at Rochester univeristy, if you want more information why not go straight to the horses mouth? E-mail: [email protected]
Ben.
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"Deblobbing"
Tue, 01/31/2006 - 04:53I don't believe it. but what do i know.
just seems like the energy from the rock "deblobbing" would travel very quickly, like an earthquake's waves. in which case the uplift would occur in seconds, not in millions of years. just like his bobber on the water analogy, if that's truly similar.
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Tue, 01/31/2006 - 08:22I kind of like the idea, although I'm not convinced by it. There's still a certain amount of debate about the formation of the Cornubian Batholith and its associated mountain range during the Variscan Orogeny. Deblobbing might propose an alternative theory, so I'm going to look into it a bit more. I have a feeling that it's going to create more problems than it solves, in which case I'll do what all good scientists do and ignore it.
Gus
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Tue, 01/31/2006 - 08:44I've done a bit of research and found some original papers by the actual researchers.
The press release was written by the Universty of Rochester science press release officer (who doesn't seem to write very scientifically in my opinion). Searching for the researcher "Carmala Garzione" came up with the following on Science Direct:
Carmala N. Garzione, Peter Molnar, Julie C. Libarkin and Bruce J. MacFadden, Rapid late Miocene rise of the Bolivian Altiplano: Evidence for removal of mantle lithosphere, Earth and Planetary Science Letters, Volume 241, Issues 3-4, 31 January 2006, Pages 543-556.
http://www.sciencedirect.com/science/article/B6V61-4HWXM3F-2/2/57f260f6706db9aa42f9a911d41a3bc2
Carmala N. Garzione, David L. Dettman and Brian K. Horton, Carbonate oxygen isotope paleoaltimetry: evaluating the effect of diagenesis on paleoelevation estimates for the Tibetan plateau, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 212, Issues 1-2, 15 September 2004, Pages 119-140.
http://www.sciencedirect.com/science/article/B6V6R-4CYNX5R-5/2/5fba7cd2402c4e1b1194c19aacc1be29
Aniki Saha , Asish R. Basu , Carmala N. Garzione , Pradyot K. Bandyopadhyay and Amitabha Chakrabarti, Geochemical and petrological evidence for subduction-accretion processes in the Archean Eastern Indian Craton, Earth and Planetary Science Letters, Volume 220, Issues 1-2, 30 March 2004, Pages 91-106.
http://www.sciencedirect.com/science/article/B6V61-4BSVSW3-9/2/c9297dd3a04b7abf4d870386e0578c39
David L. Dettman , Xiaomin Fang , Carmala N. Garzione and Jijun Li, Uplift-driven climate change at 12 Ma: a long [delta]18O record from the NE margin of the Tibetan plateau, Earth and Planetary Science Letters, Volume 214, Issues 1-2, 10 September 2003, Pages 267-277.
http://www.sciencedirect.com/science/article/B6V61-4997S6X-3/2/2a18747cc8c1ae121d2e9ceedb82e8fc
Xiaomin Fang, Carmala Garzione, Rob Van der Voo, Jijun Li and Majie Fan, Flexural subsidence by 29 Ma on the NE edge of Tibet from the magnetostratigraphy of Linxia Basin, China, Earth and Planetary Science Letters, Volume 210, Issues 3-4, 30 May 2003, Pages 545-560.
http://www.sciencedirect.com/science/article/B6V61-48GP6BB-2/2/3f34dd76a2c5de1bc51aed42589af455
Delores M. Robinson , Peter G. DeCelles , P. Jonathan Patchett and Carmala N. Garzione, The kinematic evolution of the Nepalese Himalaya interpreted from Nd isotopes, Earth and Planetary Science Letters, Volume 192, Issue 4, 15 November 2001, Pages 507-521.
http://www.sciencedirect.com/science/article/B6V61-44G8N33-4/2/d8be95c4097fda9056f8ee5d31d5ddd5
Carmala N. Garzione , Jay Quade , Peter G. DeCelles and Nathan B. English, Erratum to "Predicting paleoelevation of Tibet and the Himalaya from [delta]18O versus altitude gradients in meteoric water across the Nepal Himalaya": [Earth Planet. Sci. Lett. 183 (2000) 215-229], Earth and Planetary Science Letters, Volume 185, Issues 3-4, 28 February 2001, Page 397.
http://www.sciencedirect.com/science/article/B6V61-429XTF2-D/2/4ee51dded0b81343b603ca2c005d82d8
Carmala N. Garzione, Jay Quade, Peter G. DeCelles and Nathan B. English, Predicting paleoelevation of Tibet and the Himalaya from [delta]18O vs. altitude gradients in meteoric water across the Nepal Himalaya, Earth and Planetary Science Letters, Volume 183, Issues 1-2, 30 November 2000, Pages 215-229.
http://www.sciencedirect.com/science/article/B6V61-41NCXCS-M/2/655119ee823ff49489ad684d1965d4d9
N. B. English, J. Quade, P. G. DeCelles and C. N. Garzione, Geologic control of Sr and major element chemistry in Himalayan Rivers, Nepal, Geochimica et Cosmochimica Acta, Volume 64, Issue 15, August 2000, Pages 2549-2566.
http://www.sciencedirect.com/science/article/B6V66-40VT30V-1/2/dd758ba2dca7996fe6eca8aba8181a39
The links should take you to the abstract and if you have access via your university, a PDF version of the paper too 
Jon
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"Deblobbing"
Tue, 01/31/2006 - 19:10Thanks for all the input. I'll see if I can access those papers from University. I agree about the press release officer not writing very scientifically. It will probabably help to read explanations from the researchers themselves.
I don't believe it. but what do i know.
just seems like the energy from the rock "deblobbing" would travel very quickly, like an earthquake's waves. in which case the uplift would occur in seconds, not in millions of years. just like his bobber on the water analogy, if that's truly similar.
Isostatic rebound is a slow process, as is mantle movement. If this were to happen, it would be over a much longer scale.
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Tue, 01/31/2006 - 22:41I can understand it a bit more for a continental/continental plate boundary like the Himalaya - there are few other mechanisms than some form of delamination available to generate plateau uplift.
From the paper titles that Jon lists (thanks!) it looks like they are trying to apply the Himalayan theories to the Andes. Oceanic/Continental collisions are, in my view, very different beasts. I've not had a chance to read the papers but subduction may cause removal of part of the continental mantle lithosphere by "erosion" (but it's not really 'dropping' off the bottom). The Wadati-Benioff zone (and hence the subducted oceanic plate) in this area is shallow and underplates the continental lithosphere - if anything it would hold the continental lithosphere up rather than let it fall off under its own weight I think.
On a tangent - one of my best experiences was taking the train over the Andes from Chile to Bolivia
Hypocentre
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Submitted by Matt on Sun, 01/29/2006 - 21:52."Deblobbing" may not sound like a very scientific word, but it's the term given to a dense root beneath the Earth's crust--a blob--that becomes unstable and begins to flow downward into the earth's mantle under the force of its own mass, until it detaches. When two tectonic plates collide, such as the Nazca oceanic plate in the southeastern Pacific colliding with the South American continental plate, the continental plate usually begins to buckle. Floating on a liquid mantle, the plates press together and the buckling creates the first swell of a mountain range.
Below the crust, however, there also is a kind of buckling going on in the solid portion of the upper mantle. This dense mantle root clings to the underside of the crust, growing in step with the burgeoning mountains above. This dense root acts like an anchor, weighing down the whole range and preventing it from rising, much like a fishing weight on a small bobber holds the bobber low in the water. In the case of the Andes, they swelled to a height of about one kilometer before the mantle root beneath them disconnected and sunk into the liquid mantle. The effect was like cutting the line to the fishing weight--the mountains suddenly "bobbed" high above the surrounding crust, and in less than 3 million years, they had lifted from one kilometer to roughly four.
From: http://www.eurekalert.org/pub_releases/2006-01/uor-mrr012606.php
Does this theory hold any swing? It doesn't add up to me. Isn't the mountain root also composed of lower density material than the mantle, and thus a thicker section would float higher, rather than be weighted down? Any insight would be appreciated.