The Theory of Global Wrench Tectonics

The paradigmatic problems of Plate Tectonics are not only confined to the brittle surface layer – the lithosphere. In view of modern seismological tomography studies, the inferred structure and composition of the planet’s interior are difficult to reconcile with the idea of mantle convection that is the main driver of PT processes.

The traditional image of an early-stage molten planet, having subsequently undergone chemical differentiation, resulting in an internal layering arranged according to density, has become questionable. The classical view that iron and nickel, at some early stage, settled in a central core while lighter constituents moved upward to form the silicate mantle and crust is still in vogue, and yet confusion and disagreement about the physical and chemical conditions of the deep Earth prevail. Aspects of particular concern may be listed as follows:

• The Earth’s core seems both inhomogeneous and anisotropic.
• The core has a somewhat lower density than is presumed; this density anomaly has been explained by the presence of lighter substances such as hydrogen, silicon, carbon, helium, sulphur etc.
• The core-mantle (C-M) transition zone is undoubtedly a very complex region suggesting that the core is not in thermo-chemical equilibrium with the mantle.
• The lower mantle is apparently very inhomogeneous, potentially storing considerable volumes of interstitial water.
• The continental mantle differs in constitution from the oceanic mantle, leading to the concept of:
• Deep continental roots – perhaps extending even to the core-mantle boundary.

In fact, it looks as if the Earth is in a state of chemical disequilibrium. Degassing of the core and lower mantle is apparently incomplete, probably implying that the temperature of the deeper parts of the planet has always been moderate – higher temperature and magma pockets being properties only of the outer few hundred kilometres.

When extended to the surface, upstanding segments of the C-M boundary tend to correspond to deep oceanic depressions, while ‘topographically’ lower C-M regions accord with the location of the continents and their mantle roots.

In other words, it seems a distinct possibility that chemical agents, released by processes in regions of the C-M transition zone (or deeper), continue to behave as reactive substances rising across the mantle – causing mineralogical changes en route. This irregularly distributed vertical mass flow could be expected to have produced significant chemical and structural transformations of an outer brittle carapace – including building up the underlying inhomogeneous fluid and gas infected asthenosphere.

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