A Revolution in Plate Tectonics?

Driving mechanism and 3-D circulation of plate tectonics

A conceptual shift is overdue in geodynamics. Popular models that present plate tectonics as being driven by bottom-heated whole-mantle convection, with or without plumes, are based on obsolete assumptions, are contradicted by much evidence, and fail to account for observed plate interactions. Subduction-hinge rollback is the key to viable mechanisms. The Pacific spreads rapidly yet shrinks by rollback, whereas the subduction-free Atlantic widens by slow mid-ocean spreading. These and other first- order features of global tectonics cannot be explained by conventional models. The behavior of arcs and the common presence of forearc basins on the uncrumpled thin leading edges of advancing arcs and continents are among features indicating that subduction provides the primary drive for both upper and lower plates. Subduction rights the density inversion that is produced when asthenosphere is cooled to oceanic lithosphere: plate tectonics is driven by top-down cooling but is enabled by heat. Slabs sink more steeply than they dip and, if old and dense, are plated down on the 660 km discontinuity. Broadside-sinking slabs push all sublithosphere oceanic upper mantle inward, forcing rapid spreading in shrinking oceans. Down-plated slabs are overpassed by advancing arcs and plates, and thus transferred to enlarging oceans and backarc basins. Plate motions make sense in terms of this subduction drive in a global framework in which the ridge-bounded Antarctic plate is fixed: most subduc- tion hinges roll back in that frame, plates move toward subduction zones, and ridges migrate to tap fresh asthenosphere. This self-organizing kinematic system is driven from the top. Slabs probably do not subduct into, nor do plumes rise to the upper mantle from, the sluggish deep mantle.

So if this is the case the mag striping should get closer together as one gets farther from the spreading center, to accommodate the compression? Is this the case? Do you know if anyone has looked into this?

I don't understand this rollback reference.

The authors made the case that the bottom layer of this part of the Sierra simply broke off and sank, and the overlying continental crust was simply unbounded. They claimed to have seismic evidence of this sinking slab.

We can go back to at least 2004 for proof positive that the HEB is not tied to a fixed hot spot.

I've seen asteroid impact as a suggestion for the origins of the Yellowstone weak spot. :)

The conjecture for these zone of propagating weakness is as tenuous as it is for a long slender magma-pipe from the core/mantle boundary.

Although I am not yet brave enough to jump entirely off the hotspot bandwagon (it has been a good ride for 25 years and besides, if there was ever a hotspot, you would think that it would be Hawaii), I have to admit that the behavior of the hotspot seems unhotspotlike. It apparently zoomed southwest at high speeds, sometimes going fast and sometimes slower, and screeched to a halt at the time of the Hawaiian-Emperor bend. I suspect something is amiss. Either we are being misled by some of the tectonic or age data, or we do not understand how the Hawaiian-Emperor chain formed. Back to Saturday Night Live: What the hell is that? I don’t know what the hell that thing is!

However, a persuasive, alternative model for the Emperor and Hawaiian volcanic chains remains to be fully quantified.

Any satisfactory theory for Hawaiian volcanism must explain (or rationalize) the:

change in migration direction of the melting locus at the bend,
association of the great bend with the Mendocino fracture zone,
change in migration rate at the bend,
apparent commencement of the volcanic chain near a ridge,
absence of a “plume head”,
large variations in magmatic production, and a current magmatic rate about 3 times greater than the next most productive hotspots,
absence of a significant heat flow anomaly,
absence of lithospheric thinning,
absence of a strong high-temperature signal in the erupted basalts,
production of very large volumes of magma even though the depth to the top of the melting column is exceptionally large compared with MORs,
spatial and temporal variation in the composition of erupted lavas on a variety of scales,
remote location of Hawaii, near the center of a very large plate,
location of the oldest end of the chain with respect to the “Pacific pocket”,
unique rift zones,
paired Loa and Kea trends,
seismic whole-mantle mantle structure that is apparently normal compared with the Pacific ocean elsewhere, and
occurrence of a bathymetric swell (a moat and “arch”) along the eastern two-thirds of the Hawaiian chain and wrapping around its southeastern end, with alkalic basaltic volcanism occurring at some places along it.

In conclusion, Hawaii is not fully explained by any current hypothesis. It is impressive that a region of the Earth so extensively studied for so many years, by so many Earth scientists with so many techniques could remain so intransigent to full understanding. Many of the numerous features that are not yet fully understood, and the parameters of alternative hypotheses, are not currently being studied, but they offer exciting research opportunities.

I don't get the impression, however, that the (academic) geology community is firmly married to the "fixed core/mantle plume" origin for hotspots,

Various authorities advocate six plumes about the Earth now, or 5000, or some intermediate quantity. All this and more is merely rationalized from the physics-defying starting assumptions.

Let's look at the moon.

The near side is basaltic maria and lower than the highlands facing space.

Lunar volcanoes should be of great interest.

Bottom line, if you want to go to the moon, sooner is better than later.