Why would you expect Precambrian tectonics to be any different from those of today?

• at 3600 Ma, given the exponential character of radioactive decay, one would expect the heat flow to be 3 times that of present day.
• at 2600 Ma heat flow still should have been twice that of present day rates.
• continental crust is a chemical differentiate, and at some time in the Precambrian there was a lot less of it, and this would obviously effect the type of tectonics at that time.
• other terrestrial planetary bodies show distinctly different tectonic style, so other possibilities clearly exist.

How might of those differences been specifically manifest?

• higher geothermal gradients with shallower ductile-brittle regime.
• different metamorphic signatures (perhaps crucial for eclogites and olivine to spinel mantle transformation).
• thinner lithosphere and crust (thickness and thermal structure should be significant in subduction mechanics).
• higher convection rates and associated higher rates of tectonism (e.g. perhaps more hotspots).
• smaller and more mobile plates (permobile regime) with a greater length of plate boundary.
• different or unique geologic associations (e.g. greenstone belts?).

What would you look for in the geologic record to indicate that plate tectonics was operating at that time?

• ophiolites.
• blueschists and/or eclogites and accretionary melanges.
• polar wander paths.
• significant horizontal shortening (thin-skinned tectonism).
• evidence of the 'surface' isotope recycling that includes mantle material.

Course materials for Plate Tectonics, GEOL 3700, University of Nebraska at Omaha. Instructor: H. D. Maher Jr., copyright. This material may be used for non-profit educational purposes with appropriate attribution of authorship. Otherwise please contact author.