Posted: Jan 02, 2019 12:10 pm
SkyMutt wrote:
At the risk of raising some ire for indulging you, I'm going to respond, indulging myself.
Finally! Someone genuinely interested.
SkyMutt wrote:
The illustration is confusing to me. It purports to depict "mantle flow" and "GPS horizontal vectors." Yet the mantle is not the surface; how could its movement be tracked by GPS? Why bring GPS into it at all? You write of "evolution of the surface" which would of course not necessarily be the same as the underlying movement of the mantle, let alone movement deeper in the mantle.
OK, let's simplify before discussing what could be at the origin of the lithosphere displacements. What is represented here are lithosphere displacements as measured by GPS stations.
SkyMutt wrote:
The vectors you depict appear to be chaotic outside of a "river" leading to the subduction zone. Can you produce anything from a reputable source that shows this is accurate?
Yes, this figure for example from Mattei et al (2004) doi:10.1029/2003JB002506 :
- a-A-velocity-field-for-the-Aegean-region-based-on-GPS-measurements-from-McClusky-et_W640.jpg (77.28 KiB) Viewed 2217 times
SkyMutt wrote:
If the illustration is meant to depict horizontal movement of the mantle, why would that result in reduction of surface area? As far as I know nobody is claiming that there's any appreciable reduction of the Earth's surface. Rather the idea is that the production of new oceanic crust is in equilibrium with subduction of old oceanic crust. As I understand it, the action of a subduction zone doesn't result in gross reduction of surface area, just as production of new oceanic crust at the spreading centers doesn't result in a gross increase of surface area.
Yes, the hypothesis is that there is destruction of lithosphere at subduction zones of equal amount of production of lithosphere at spreading ridges. So subduction = reduction of lithosphere surface.
This is what I'm questioning here.
SkyMutt wrote:
I suppose you're trying to make some point with this illustration--why don't you just go ahead and lay out the argument behind the illustration and the evidence that supports it?
In the illustration above there is a subduction zone and no spreading ridge. So the surface of the lithosphere in the rectangular area should decrease with time if the premise of subduction=reduction is satisfied. Yes there is obviously no reduction of surface of that rectangular area.. Because there's is sufficient lithosphere extension at the back of the subduction zone to balance the lithosphere that is consumed in the subduction zone. It is very clear from the GPS vectors. OK?