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Book Chapter

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

By
Don L. Anderson
Don L. Anderson
Seismological Laboratory, Caltech, Pasadena, California 91125, USA
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Published:
January 01, 2006

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.

“…. In science, conventional wisdom is difficult to overturn. After more than 20 years some implications of plate tectonics have yet to be fully appreciated by isotope geochemists… and by geologists and geophysicists who have followed their lead.

“ A myth is an invented tale, often to explain some natural phenomenon… which sometimes acquires the status of dogma… without a sound logical foundation. It is a dogma that has distorted thinking about the Earth for decades. In science this is an old story, likely to be repeated again, as the defenders of conventional wisdom are seldom treated with the same scepticism as the challengers of the status quo… the dogma has been defended with false assertions, defective data, misconceptions and misunderstandings, and with strawman arguments… The justification … boils down to a statement of belief, an opinion, rather than a deduction from observations.

“… geochemists are reluctant to abandon cherished concepts they grew up with and have vigorously defended during their education and research careers.”

—Richard L. Armstrong, 2002, The Persistent Myth of Continental Growth: Australian Journal of Earth Science, v. 38, p. 613–630.

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Contents

GSA Special Papers

Earth and Mind: How Geologists Think and Learn about the Earth

Cathryn A. Manduca
Cathryn A. Manduca
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David W. Mogk
David W. Mogk
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Geological Society of America
Volume
413
ISBN print:
9780813724133
Publication date:
January 01, 2006

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