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Published 2006 | public
Book Section - Chapter

Plate tectonics; the general theory: Complex Earth is simpler than you think


The standard model of mantle dynamics and chemistry involves complex interactions between rigid plates and hot plumes, and exchanges of material between a homogeneous upper mantle and a "primitive" lower mantle. This model requires many assumptions and produces many paradoxes. The problems and complexities can be traced to a series of unnecessary and unfruitful assumptions. Dropping these assumptions, or assuming the opposite, removes many of the paradoxes. A theory of plate tectonics can be developed that is free from assumptions about absolute plate rigidity, hotspot fixity, mantle homogeneity, and steady-state conditions. Here, a simpler and more general hypothesis is described that is based on convective systems that are cooled and organized from the top. Plate tectonics causes thermal and fertility variations in the mantle and stress variations in the plates, thus obviating the need for extraneous assumptions about the deep mantle. The general theory of plate tectonics is more powerful than the current restricted forms that exclude incipient plate-boundary (also known as volcanic chains and hotspot tracks) and athermal (e.g., melting point, fertility, and focusing) explanations of melting anomalies. Plate tectonics, geology, mantle dynamics, magmatism, and recycling are upper-mantle processes, largely independent of the deep mantle. These ideas came about by examining the paradoxes and assumptions in current models of mantle structure, evolution, and chemistry. By identifying the assumptions that generate the anomalies, one can have a zero-paradox hypothesis. Eventually, new paradoxes will be identified, and a new paradigm will be introduced. This is the way science progresses.

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© 2006 Geological Society of America. Manuscript accepted by the Society 21 March 2006.

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