Plate Tectonics and New Geological Process:

[beecee]

https://phys.org/news/2021-05-discovery-geologic-plate-tectonic.html

Discovery of new geologic process calls for changes to plate tectonic cycle:

Geoscientists at the University of Toronto (U of T) and Istanbul Technical University have discovered a new process in plate tectonics which shows that tremendous damage occurs to areas of Earth's crust long before it should be geologically altered by known plate-boundary processes, highlighting the need to amend current understandings of the planet's tectonic cycle.

Plate tectonics, an accepted theory for over 60 years that explains the geologic processes occurring below the surface of Earth, holds that its outer shell is fragmented into continent-sized blocks of solid rock, called "plates," that slide over Earth's mantle, the rocky inner layer above the planet's core. As the plates drift around and collide with each other over million-years-long periods, they produce everything from volcanoes and earthquakes to mountain ranges and deep ocean trenches, at the boundaries where the plates collide.

Now, using supercomputer modelling, the researchers show that the plates on which Earth's oceans sit are being torn apart by massive tectonic forces even as they drift about the globe. The findings are reported in a study published this week in Nature Geoscience.

more at link................

 

the paper:

https://www.nature.com/articles/s41561-021-00746-9

Pre-collisional extension of microcontinental terranes by a subduction pulley:

 

Abstract:

Terrane accretion is a ubiquitous process of plate tectonics that delivers fragments of subduction-resistant lithosphere into a subduction zone, resulting in events such as ocean plateau docking or continental assembly and orogenesis. The post-collisional extension of continental terranes is a well-documented tectonic process linked with gravitational collapse and/or trench retreat. Here we propose that microcontinental terranes can also undergo a substantial extension before their collision with the upper plate, owing to pull from the trenchward part of the subducting plate. Forward geodynamic numerical experiments demonstrate that this pre-collisional extension can occur over a protracted phase on microcontinents that are drifting towards a subduction zone, which distinguishes the deformation from post-collisional extension on the overriding plate, as is traditionally postulated. The results show that the magnitude of pre-collisional extension is inversely correlated with the size of the microcontinental terrane and imposed convergence velocity. We find that locations along the Tethyan belts, namely, the Sesia zone and Eastern Anatolia, are evidence for this style of pre-collisional extension, as this mechanism reconciles with geothermobarometric data and kinematic analyses. The operation of this subduction pulley reveals that drifting lithospheric plates may undergo substantial tectonic events before the arrival and involvement with regular plate boundary processes.

[studiot]

Unfortunately this article is subscription only.

I would like to see at least a diagram in case something is lost in the translation from Turkish.

[beecee]

36 minutes ago, studiot said:

Unfortunately this article is subscription only.

I would like to see at least a diagram in case something is lost in the translation from Turkish.

Turkish? 😉  from the article.....   illustrative 

Elements of a newly discovered process in plate tectonics include a mass (rock slab weight), a pulley (trench), a dashpot (microcontinent), and a string (oceanic plate) that connects these elements to each other. In the initial state, the microcontinent drifts towards the subduction zone (Figure a). The microcontinent then extends during its journey to the subduction trench owing to the tensional force applied by the pull of the rock slab pull across the subduction zone (Figure b). Finally, the microcontinent accretes to the overriding plate and resists subduction due to its low density, causing the down-going slab to break off (Figure c). Credit: Erkan Gün/University of Toronto

There is also an illustrative video

Edited May 12, 2021 by beecee

[studiot]

Thank you @beecee that is enough to get the gist of it.

Turkish - When I tried to follow your link the first time I saw mention of the Univesity of Istambul and examples in Turkey.

 

The idea that the subducting plate is drawn ever more steeply downwards and eventually breks off has been around for quite some time.
Ted Nield details the evidence for this in his 2007 book Supercontinent.

The mechanical model of the dashpot, pulley and tension connections is new to me at least and interesting to consider.

I wonder how many such situations there are (were) around the globe ?

 

Thank you for a good response and an interesting article now I understand what it is all about. +1

[beecee]

1 hour ago, studiot said:

Thank you @beecee that is enough to get the gist of it.

Thank you for a good response and an interesting article now I understand what it is all about. +1

Thank you for a down to Earth explantion.

[Area54]

A handful of disparate thoughts on the topic:

I wonder @beecee if the words "tremendous damage occurs to areas of Earth's crust" are yours, or from the paper. I would not characterise deformation, whether folding, or faulting, as damage. Damage is something that happens to objects with a purpose that interferes with that purpose. Deformation is something that routinely happens to rock. In the context of this forum the casual "tremendous damage" is fine, but if those are the words of the authors I am rather surprised.

I agree with @studiot that the slab pull- break off is not new. Without seeing the paper in full I',m left thinking, are they arguing this mechanism, involving a micro continent, as the only, or the commonest cause for break off? Presumably not, as I can't see what evidence they could bring to supprt such a view.

The notion of stress within the oceanic plates does not seem new to me. The concept of rigid plates as a fundamental part of plate tectonics has long been understood to be a generalisation/approximation. I take the fundamental message of this paper to be that a portion of the structural deformation of obducted terranes occurs before they collide with the 'target' continent. That is new and very interesting. Thanks.

[studiot]

2 hours ago, Area54 said:

I wonder @beecee if the words "tremendous damage occurs to areas of Earth's crust" are yours, or from the paper. I would not characterise deformation, whether folding, or faulting, as damage. Damage is something that happens to objects with a purpose that interferes with that purpose. Deformation is something that routinely happens to rock. In the context of this forum the casual "tremendous damage" is fine, but if those are the words of the authors I am rather surprised.

Yes I wondered about some of the wording in the available extracts.
For instance the idea of plates 'drifting' around the globe harps back to the theory of continental drift.

 

As regards to 'damage', that may not be the best word but deformation does not tell the whole story either.
Crustal (and other) rocks can and do continually degrade by various natural processes as well as specific event such as plate boundary activity.

[Area54]

10 minutes ago, studiot said:

As regards to 'damage', that may not be the best word but deformation does not tell the whole story either.
Crustal (and other) rocks can and do continually degrade by various natural processes as well as specific event such as plate boundary activity.

While this is true I doubt that the natural processes of weathering will be significantly affected by the tensional forces discussed in the paper. I gave some though to mentioning metasomatic and metamorphic changes, but could based on the abstract the authors do not appear to directly suggest those. I should expect enhanced metasomatism via increased micropores in a tensional environment. Enhanced metamorphism seems unlikely - perhaps @beeceecould say if the paper offers examples of such in the Turkish locations referenced.

[studiot]

55 minutes ago, Area54 said:

While this is true I doubt that the natural processes of weathering will be significantly affected by the tensional forces discussed in the paper.

Well you should not doubt it. Tensional forces from any source always aid the degradation due to chemical weathering, for instance by causing joints which allow the acid solvents to penetrate deeply into the body of the rock.

 

Anyway as you say, your observations were side observations, and my comments were equally quick responses.

I propose to do some reading up on the mechanical models I dubbed interesting and will report back when I have found more out.

[beecee]

4 hours ago, Area54 said:

A handful of disparate thoughts on the topic:

I wonder @beecee if the words "tremendous damage occurs to areas of Earth's crust" are yours, or from the paper.

From the paper or article of course.

 

4 hours ago, Area54 said:

In the context of this forum the casual "tremendous damage" is fine, but if those are the words of the authors I am rather surprised.

OK, I see what you mean...it is from the physorg article and while it didn't really cause me any great concern, I would say it's just poor journalism by the physorg journalist, which is why with any interesting article I reproduce, I will also supply the scientific paper below that article. 

Otherwise I find yours and studiot's comments informative and adding more knowledge to my own scant geological knowledge.

Thanks.