A critical assessment of Neoarchean "plume only" geodynamics: Evidence from the Superior Province

Criticisms of Archean plate tectonic models rarely offer detailed descriptions of alternative paradigms. The catalytic delamination-driven model for the coupled genesis of Archean crust and sub-continental lithospheric mantle described by Bedard (2006) is an exception in that a relatively comprehensive, but essentially 2-D, model is described. Although this novel model is frequently cited as an example of the diversity in geodynamic thought for the Archean, it is rarely assessed with reference to events in a specific craton, such as the Superior Province or a particular greenstone belt, such as the Abitibi. When this type of assessment is undertaken it becomes clear that the apparent simplicity of the model, one of its supposed virtues, constitutes a critical weakness. Although Bedard (2006) developed the catalytic model to overcome the perceived "melt productivity deficit" of Archean plate tectonic models, the catalytic process at the heart of the model is likely to be inefficient and provides insignificant improvements to crustal generation rates associated with subduction and "non-catalytic" plume tectonics. The model implies a near global craton in the Mesoarchean to Neoarchean but fails to address that fate of this craton during and after "crustal rigidification". Seismic reflectors observed beneath Archean cratons are characterized as failed delamination features but their global abundance suggests that syn- to post-tectonic TTG suites could not have been generated as a result of crustal restite delamination. The brief descriptions of suggested mechanisms for the generation of minor rock types, such as sanukitoids, mask the complexity inherent in the overall model. When considered in terms of the evolution of the Superior Province as a whole, it is evident that many of these suggestions are not only implausible, they are inconsistent with the timing and distribution of geological criteria used to mark the onset of "crustal rigidification". (C) 2012 Elsevier B.V. All rights reserved.