FORMATION AND AMALGAMATION OF ARCHEAN CRATONS: FIVE OUTSTANDING QUESTIONS (Invited Presentation)

Cratons are tectonically quiescent, long-lived, stable continental regions that have not experienced penetrative deformation or calc-alkalic magmatism. They are characterized by low surface heat flow, which reflects their cold and thick (200-300km) lithospheric keel. The negative thermal buoyancy of old and cold cratonic lithosphere is offset by the removal of partial melt and water, leaving a residual lithospheric mantle that is less dense and more buoyant than the fertile mantle. This subcontinental lithospheric mantle keel is mechanically coupled to the crust, and its thickness and buoyancy contributes to the overall strength and survivability of the craton.

Laurentia was assembled around a dozen or more Archean cratonic nuclei during a protracted period from the Neoarchean and Proterozoic. In this talk we identify five outstanding questions regarding the formation and evolution of cratons:

1. What was the nature of the earliest crust? Could the earliest crust be characterized as cratonic?
2. When and how did cratons first form, and in what tectonic regime? What is the role of the tonalite-trondhjemite-granodiorite suite in craton formation?
3. Unlike Proterozoic sutures, Archean sutures are not marked by high-conductivity. How do we recognize sutures representing Archean collisional events between cratonic blocks?
4. When did cratons become subaerial? What is the evidence?
5. Is craton assembly related to supercontinent formation?

This talk suggests hypotheses and strategies for investigating these questions using evidence from the Wyoming province, one of Laurentia’s larger cratons. The Wyoming province is more accessible than many of Laurentia’s Archean cratons, and its Archean rocks are exposed in Laramide-age uplifts that expose kilometer-scale vertical, three-dimensional sections of Archean history. Future research suggested by information from Wyoming and other cratons promises to resolve these questions and illumine the processes by which the earliest components of Laurentia were constructed and amalgamated.