Thread: Plate Tectonics - an on again, off again affair?

Here is the abstract from an article published 4th January in Science:

Intermittent Plate Tectonics?
Paul G. Silver and Mark D. Behn
Although it is commonly assumed that subduction has operated continuously on Earth without interruption, subduction zones are routinely terminated by ocean closure and supercontinent assembly. Under certain circumstances, this could lead to a dramatic loss of subduction, globally. Closure of a Pacific-type basin, for example, would eliminate most subduction, unless this loss were compensated for by comparable subduction initiation elsewhere. Given the evidence for Pacific-type closure in Earth's past, the absence of a direct mechanism for termination/initiation compensation, and recent data supporting a minimum in subduction flux in the Mesoproterozoic, we hypothesize that dramatic reductions or temporary cessations of subduction have occurred in Earth's history. Such deviations in the continuity of plate tectonics have important consequences for Earth's thermal and continental evolution.

This would help to explain why the rate of cooling of the Earth is less than that predicted by models employing continuously active plate tectonics.

If plate tectonics does stop then erosion of the continents would, in theory, eventually remove all land from the globe. One wonders if the thinning of the continental bodies, along with isostatic uplift and heat build up might contribute to the eventual initiation of new rifting zones and forced subduction.

One wonders if the thinning of the continental bodies, along with isostatic uplift and heat build up might contribute to the eventual initiation of new rifting zones and forced subduction

Would this thinning occur in hot spots like Hawaii? There are some very old rock formations still visible in places with, I think, the average age of rock formations being around 200 MY? Is the presence of these old rocks the basis of your concurrence with the article?

Since the earth is very dynamic I would not be completely happy with a complete stop all over, maybe it stopped in some places and not in others ?? could large collisions (from space) result in new faults which then cause old lines to 'freeze' ?

the question is : what is the effect on the conveyor system in the mantle when the pull of a subduction zone stops ?
i expect that after some period of quiet the convection cells would rearrange themselves and subduction would resume elsewhere

in all that could mean a temporary slowdown of subduction activity followed by a resumption of normal service - on what timescale i don't know

what is the effect on the conveyor system in the mantle when the pull of a subduction zone stops

At the risk of exposing my near total ignorance of this topic, is it not rather the conveyor system that causes the subduction to occur?

This would help to explain why the rate of cooling of the Earth is less than that predicted by models employing continuously active plate tectonics.

Again from ignorance, is the earth still supposed to be cooling? I thought it cooled down to a certain level at which the heat produced by radioactivity and the rate of cooling reached a balance?

Originally Posted by KALSTER

what is the effect on the conveyor system in the mantle when the pull of a subduction zone stops

At the risk of exposing my near total ignorance of this topic, is it not rather the conveyor system that causes the subduction to occur?

not as far as i understand it : think of what would happen if you tried to push a large sheet of paper through a narrow gap, chances are it would start to bulge up somewhere - on the other hand, if you pull it through the gap, no such thing happens

Very interesting topic, I kind of wish I had done some geodynamics at uni now. I'm thinking out loud here, but if plate tectonics slowed down wouldn't it be very difficult for it to speed up again? I suppose a slow down in plate tectonics implies a kind of global stress equilibrium. To speed up again you'd need the stresses to build up or drop locally, but without plate tectonics how would this happen?

the way i understand it is that the overall strength of the convection remains more or less the same, but depending on the position of the continents, mid-ocean ridges and hot spots the apparent activity as seen by surface dwellers like us may vary over time

if the tectonic process seems to have slowed down, heat is probably building up somewhere prior to a major spreading event such as when pangaea broke up

I was wondering if anyone has heard of any studies comparing plate movements with the polar ice caps melting. It seems to me the movement of that amount of mass could affect the plates movement.

in what way do you see a resemblance between the two ?

Originally Posted by Howard

I was wondering if anyone has heard of any studies comparing plate movements with the polar ice caps melting. It seems to me the movement of that amount of mass could affect the plates movement.

It's called isostatic rebound. If you're feeling brave you could check out a study like this http://www.gps.caltech.edu/research/..._etal_2005.pdf

hang on - isostatic movement is something altogether different from the sideways movement in plate tectonics !?!