Reading about the recent earthquake, I’ve read statements that the India plate is being pushed under the Asian plate by tectonic processes.
Does that mean that the India plate will be destroyed by being submerged under the Asian plate? Would it pass all the way under the Asian plate and millions of years from now come out the other side? Or at some point will it stop being pushed under the Asian plate?
It’s actually colliding with the Eurasian plate, which extends all the way to the pole, then becomes the North American plate. Where would the “other side” be? What do you think would be propelling it, to keep it traveling perpetually, with no friction to stop it?
Nope, only oceanic crust subducts. Continental crust isn’t dense enough to sink into the mantle, so when you get a continent-continent collision the two continents just smash together but neither can sink below the other.
In the Himalayas, before the collision between India and Asia there was oceanic crust (from the old Tethys Sea) subducting under the Asian continent with India just being pulled along for the ride. It’s thought that the slab of oceanic crust is still down there somewhere continuing to pull India towards Asia and driving the continual uplift of the Himalayas, but India is never going to get pulled under.
It wasn’t destroyed when all the continents were smooshed together in Pangaea. It’s not going to be destroyed this time, either.
Did Everest just get a little taller?
Yeah, but one of these times … To the Moon Alice, to the Moon!! 
ETA: That’s a joke of course, but on second thought it got me thinking about which early Earth continents are currently in a 28-day orbit. Certainly some are, though there’s no way to rewind the clock accurately enough to ever know.
Yes. As it does every year by 5 cm. Use to be faster but the ol’ girl is slowing down.
Meanwhile, on the moon. . . .
I don’t know. That’s why I asked the question.
Thank you. So, when news articles say that the India plate is being forced under the Europe plate, they’re incorrect? (Not the first time that the news folks simplify…) So there’s a strong force pushing the India plate against the Europe plate, resulting in the Himalayas, but it’s not going under.
You mean the Eurasian plate, not the Europe plate.
Only oceanic crust gets subducted. Oceanic crust is denser and floats low on the mantle. Continental crust is less dense and floats higher. When oceanic crust meets continental crust, the oceanic crust will subduct under the continent. This is happening, for example, on the west coast of North America, where the Juan de Fuca Plate is subducting under North America.
But when continent meets continent, neither subducts. They just crash into one another and build high mountain ranges. The Appalachians, for example, are the result of such a crash some 300 million years ago. At the time, they were very high mountains, perhaps about as high as the Himalayans. But that orogeny is long over and the Appalachians are the eroded remnants of it.
Well, one other thing I didn’t mention is that the plate India is on is actually the Indo-Australian Plate. So even though the continent of India isn’t subducting for the reasons mentioned, if you want to get real pedantic about it the Indo-Australian Plate is in fact subducting under the Eurasian Plate, but only along the Sumatra and Java trenches (where the I-A Plate is oceanic crust) not in the Himalayas.
The Indo-Australian Plate probably is going to break up eventually because the Indian portion of it is moving a lot slower than the Australian portion. That’s because the force of the subducting oceanic crust pulling the plate along as it sinks (called “slab pull”) is really the major driver of plate motion. On the Australian side of the plate, they’ve got a nearly uninterrupted chain of subduction zones from Myanmar to Fiji, so it’s moving really fast but the Indian part of the plate is jammed into Eurasia so it’s kind of stuck.
The breakup of the plate might end uplift in the Himalayas, but it’s not really clear to what extent the uplift is being driven more by the slab pull from the ancient oceanic crust that’s currently under Tibet versus the rest of the plate kind of pulling it along. I suppose those of us who are around in a dozen million years or so might find out!
Well Australia propells it, and so …
it seems to me that Australia is big enough to push it completely under or obliterate it.
Australia may move over the top too.
But Asia is built from cratons, so they aren’t the deepest, while Australia is solid continent, so seems Australia should win there.
Yeah it would just go in under Asia and there it would sit…
But as to what would propell it ? What propels Australia ? Seems the relative density of the material in the earth suffers tides, and its being pushed around… perhaps enhanced by convection ;the explanation being that the tides ensure its continuously in one direction… not alternating randomly.
I’m kind of confused by this whole post, but maybe if we take it in chunks…
Maybe you’re misunderstanding what I said earlier. It’s not the continent of Australia that’s propelling it, it’s (primarilly) the force of the oceanic crust on the I-A plate subducting under Indonesia and under other oceanic crust on the Pacific Plate. Australia is just along for the ride. The other thing is that there still is slab pull from the ancient oceanic crust attached to India (now many kilometers under Tibet) so it may be that the Himalayan collision is self-sustaining even without the rest of the I-A plate.
Again, continental crust doesn’t subduct. Western North America is in large part made up of microcontinents that were much smaller than either India or Australia but got smashed into and incorporated into the continent instead of following the oceanic trench down into the mantle.
First off, do you have any idea what a craton actually is? Australia is one of the textbook examples! But none of that matters-- continental crust doesn’t subduct, regardless of whether it’s ancient continental core or relatively young sedimentary and igneous rocks. Nobody “wins” in a continent-continent collision. If North America didn’t “win” and force those Japan and New Zealand sized microcontinents to go down under it, India and Australia definitely aren’t going to be going down either!
No idea what you’re talking about. Read this: Plate tectonics - Wikipedia
(Granted, there is still some debate about whether the main driver of plate motion is mantle convection acting directly on the bottom of the plates or if it’s more gravity-based driven by the sinking cool oceanic crust. My impression is that the gravity-based view is the more accepted one these days, but maybe that’s just because the person I took tectonics from was pretty vocally in the “slab pull” camp.)
So in answer to panache45’s comment, is it correct that there is a mechanism that keeps a slab of crust moving under continental crust, but it’s only oceanic crust, which is denser and thus will go under a continental crust? but it can still survive, way, way down?
Confusing, I thought India was a separate plate from Australia’s. Is this under debate by geologists?
Here’s the quote from CNN which prompted my original question, by the way (it’s quoted in aldiboronti’s thread of Everest):
So CNN got it wrong, is that correct?
Yeah, the mechanism that keeps it moving is simply gravity pulling the cooler, denser oceanic crust down.
As for what happens to the slabs, that’s somewhat controversial. The best line of evidence has historically been the Benioff Zones which are earthquakes that persist along the subducting slab and then abruptly end at the 660 kilometer marker, which is the transition between the upper and lower mantle. It was originally thought that this meant that the slabs essentially broke up at that 660 KM marker. More recently, though, some high-resolution seismograph networks have been able to produce cool images like this. What the seismic tomography has shown is that sometimes the slabs do indeed get stuck at the 660 marker and basically pile up on it. Others, though, seem to continue down as identifiable anomalies all the way to the core-mantle boundary and pile up there, forming so-called slab graveyards. Diagram. At that point though, they’re certainly just compositional anomalies in the mantle as opposed to anything you’d really identify as crust.
It is a little bit of a “is Pluto a planet?” type situation. The fact that its velocity is so different from the Indo-Australian Plate is an argument for considering India its own plate, but on the other hand there isn’t a spreading center or transform fault zone or any other type of plate boundary to suggest a separate plate. Most maps that show the Indian Plate have a sort of arbitrary dividing line between it and the rest of the I-A Plate which isn’t very satisfying.
Ah, yes, that is definitely wrong.
Are you possibly mixing up the rate of progression of the Indian plate (which is about 5cm a year) with the rate of growth of Everest? It’s actually about 4mm per year, after erosion is taken into account.
http://www.nationalgeographic.com/features/99/everest/roof_start.html
As an aside, I’ve often wondered what happens to national boundaries when continental drift has gone on for long enough for it to be measured. Boundary disputes between India and both China and Pakistan are already fraught enough without 100 years of drift to account for.
