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Push vs. Pull: What Drives Tectonics?


Doc Socks Junior

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Unsatisfied with upending continent-continent collision dynamics recently, Dr. Rowley is back at it again with a paper on the geodynamics of the East Pacific Rise (EPR).

The main thrust (heh) of it is that top-down plate tectonics fails to explain observations at the EPR. Plate tectonics has seen some interesting debate fairly recently most centering on plates vs. plumes - what controls it all?

And, indeed, the "textbook" explanation for the dominant mechanism is pull from subducting slabs.

However, Rowley and co-authors believe and provide evidence for mantle convection playing a larger role than currently given credit for.

Quote

Earth’s tectonic plates are generally considered to be driven largely by negative buoyancy associated with subduction of oceanic lithosphere. In this context, mid-ocean ridges (MORs) are passive plate boundaries whose divergence accommodates flow driven by subduction of oceanic slabs at trenches. We show that over the past 80 million years (My), the East Pacific Rise (EPR), Earth’s dominant MOR, has been characterized by limited ridge-perpendicular migration and persistent, asymmetric ridge accretion that are anomalous relative to other MORs. We reconstruct the subduction-related buoyancy fluxes of plates on either side of the EPR. The general expectation is that greater slab pull should correlate with faster plate motion and faster spreading at the EPR. Moreover, asymmetry in slab pull on either side of the EPR should correlate with either ridge migration or enhanced plate velocity in the direction of greater slab pull. Based on our analysis, none of the expected correlations are evident. This implies that other forces significantly contribute to EPR behavior. We explain these observations using mantle flow calculations based on globally integrated buoyancy distributions that require core-mantle boundary heat flux of up to 20 TW. The time-dependent mantle flow predictions yield a long-lived deep-seated upwelling that has its highest radial velocity under the EPR and is inferred to control its observed kinematics. The mantle-wide upwelling beneath the EPR drives horizontal components of asthenospheric flows beneath the plates that are similarly asymmetric but faster than the overlying surface plates, thereby contributing to plate motions through viscous tractions in the Pacific region.

Rowley et al., 2016, Kinematics and dynamics of the East Pacific Rise linked to a stable, deep-mantle upwelling, Science Advances.

 

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Well this is giving me flashbacks to undergrad. One of my lecturers was a leading proponent of the plate side of plates vs plumes. Can't remember her name now.

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It's still ongoing. I always liked this picture.

Image result for plates vs plumes

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1 hour ago, Socks Junior said:

It's still ongoing. I always liked this picture.

Image result for plates vs plumes

Never really got into it myself. Just one of those ones that would have the lecturers grumbling about each other. Nice diagram though.

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Reminds me of my college days...not that I remember much from that time...

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