Deep Subduction of the Indian Continental Crust Beneath Asia

Geological investigations in the Himalayas have revealed evidence that when India and Asia collided some 90 million years ago, the continental crust of the Indian tectonic plate was forced down under the Asian plate, sinking down into the Earth's mantle to a depth of at least 200 km kilometres.

"The subduction of continental crust to this depth has never been reported in the Himalayas and is also extremely rare in the rest of world," said Dr Anju Pandey of the National Oceanography Centre in Southampton, who led the research.

[atsimg]http://files.abovetopsecret.com/images/member/bf07cb103c7d.jpg[/atsimg]

Pandey and her colleagues used sophisticated analytical techniques to demonstrate the occurrence of relict majorite, a variety of mineral garnet, in rocks collected from the Himalayas. Majorite is stable only under ultra-high pressure conditions, meaning that they must have been formed very deep down in the Earth's crust, before the subducted material was exhumed millions of years later.

"Our findings are significant because researchers have disagreed about the depth of subduction of the Indian plate beneath Asia," said Pandey. In fact, the previous depth estimates conflicted with estimates based on computer models. The new results suggest that the leading edge of the Indian plate sank to a depth around double that of previous estimates.

"Our results are backed up by computer modelling and will radically improve our understanding of the subduction of the Indian continental crust beneath the Himalayas," said Pandey. The new discovery is also set to modify several fundamental parameters of Himalayan tectonics, such as the rate of Himalayan uplift, angle, and subduction of the Indian plate.

www.sciencedaily.com...

Hello.

You should check into the "Growing Earth" theory. It will explain why we have the Himalayas and every other mountain range.

Peace





[edit on 29-5-2010 by letthereaderunderstand]

The expanding Earth hypothesis

I think you will find it to be an interesting read.

Thank you both!

Originally posted by sandri_90
Thank you both!

Thank you.

Peace

Leaving aside for the moment the fact that I have a problem with the source site and it's ability to tell the truth, the premise of the article is of interest.

Unfortunately however the reasoning that this material has come from deeply subducted zones has to be eroneous.

My reasoning for this is as follows.

The subduction of one plate under another firstly is a theory. When I was at school it was only just a theory, in other words it is fairly new and is a theory as it cannot be proven. If you accept that one plate subducts beneath the other then the subducting plate will eventually reach a point in the subduction where it's material is coalesced with the body of material into which it is 'falling'.

200km is peanuts! Since the last deep earthquake in Brazil (Acre) on the 24th for example was at 565 km, and the USGS explanation was that these deep subduction zone earthquakes are infrequent (see also Spain recently) one has to wonder how 200km is (and I quote the article)

extremely rare in the rest of world

Further they state

Majorite is stable only under ultra-high pressure conditions, meaning that they must have been formed very deep down in the Earth's crust, before the subducted material was exhumed millions of years later.

Must have been? There is no logic for that statement. The coming together of two continental plates would create immense pressures, and these do not have to be deep. Further more this is based on a computer model and we all know about those!!

So, a link from that article takes us to another on subduction under the Himalayas.

The researchers discovered that as the Indian and Eurasian tectonic plates collide, the Indian lower crust slides under the Tibetan crust, while the upper mantle peels away from the crust and drops down in a diffuse manner.

"The building of Tibet is not a simple process," said John Nabelek, an Oregon State University geophysicist and lead author on the Science study. "In part, the mountain building is similar to pushing dirt with a bulldozer except in this case, the Indian sediments pile up into a wedge that is the lesser Himalayan mountains.

OK, the bottom part slides downward and the top part crumples up. Now hold on that sort of destroys the theory that this deep crustal subduction is somehow later 'exhumed' as if it was a body. Source

A paragraph or two further on we have

In fact, the previous depth estimates conflicted with estimates based on computer models. The new results suggest that the leading edge of the Indian plate sank to a depth around double that of previous estimates.

Another nail in the coffin of the original theory? This is not me don't forget - this is other scientists. Now however we are getting closer to the sort of depths we should be talking about.

Again linking off the same article we have this:

About 55 million years ago, the Indian plate crashed into the Eurasian plate, forcing the land to slowly buckle and rise. Containing nearly one-tenth the area of the continental U.S., and averaging 16,000 feet in elevation, the Tibetan Plateau is the world's largest and highest plateau.

Tectonic models of Tibet vary greatly, including ideas such as subduction of the Eurasian plate, subduction of the Indian plate, and thickening of the Eurasian lithosphere. According to this last model, the thickened lithosphere became unstable, and a piece broke off and sank into the deep mantle.

"While attached, this immense piece of mantle lithosphere under Tibet acted as an anchor, holding the land above in place," said Wang-Ping Chen, a professor of geophysics at the U. of I. "Then, about 15 million years ago, the chain broke and the land rose, further raising the high plateau."

Source

So now we have a huge chunk sinking into the mantle - not being exhumed.

Since that latest study is the one referred to by the OP, it seems to me that their theory was already in tatters a year or more before they cooked it up.

One again the 'scientists' have ably demonstrated that actually they havet really got a clue what is happening but that they need to spout some sort of techno babble in order to keep the grant money flowing in.

As far as I am concerned 'subduction' remains a theory, and will continue to remain a theory unless they can come up with some better proof.

Finally a new theory about Pangea. Well I could hardly contain my laughter!! A snippet

These models suggest that plate tectonics is primarily driven by subduction and that supercontinents break up and migrate from sites of mantle upwelling to reassemble at sites of mantle downwelling where subduction zones exist.

Such models would predict that the young oceans created by the breakup of a supercontinent some 600 million years ago would have continued to expand as the continental fragments migrated toward sites of mantle downwelling that existed in the older ancestral Pacific Ocean. Instead, Pangea assembled as a result of the closure of the young oceans.

The geologic record suggests that there are geodynamic linkages between the younger and older oceans that deserve more detailed study; it also suggests that, in the case of Pangea, the reversal in continental motion may have coincided with emergence of a superplume 460–400 million years ago that produced mantle upwelling in the ancestral Pacific.

If so, the top-down geodynamics driven by subduction, which accounts for the assembly of the supercontinent that broke up 600 million years ago, may have been overpowered by bottom-up geodynamics involving large-scale mantle upwelling that led to the amalgamation of Pangea.

The titanic struggle between top-down subduction and bottom-up geodynamics! They should make a film. There is of course absolutely no suggestion of a reason as to WHY the mantle suddenly decided to have a large-scale upwelling.

Scientists :shk: :bnghd:

[edit on 30/5/2010 by PuterMan]