21. Application of Low-Temperature Thermochronology to Craton Evolution

The view that cratons are tectonically and geomorphologically inert continental fragments is at odds with a growing body of evidence partly based on low-temperature thermochronology (LTT) studies. These suggest that large areas of cratons may have undergone discrete episodes of regional-scale Neoproterozoic and/or Phanerozoic heating, and cooling from modestly elevated paleotemperatures. Cooling is often attributed to the km-scale erosion of overlying low-conductivity sediments, rather than to removal of large sections of crystalline basement. Independent evidence for sedimentary burial includes: preservation of outliers, the sedimentary record in intracratonic basins, and sedimentary xenoliths entrained within kimberlites periodically emplaced into cratons. Further, stratigraphic and isotopic data from basinal sediments proximal to some cratons carry a record of the detritus removed, which can be linked temporally to cooling episodes in their inferred cratonic source areas. Differences in denudation rates reported from cratonic basement reconstructed from LTT data (long-term) and cosmogenic isotope and chemical weathering studies (short-term) reflect the strong contrast in erodibility potential between cover sediments since removed and the preserved crystalline rocks. Underlying processes involved in cratonic heating and cooling may include one of, or a complex interplay between: proximity to sediment sources from elevated orogens forming extensive foreland basins, structural deformation transmitted by far-field horizontal stresses from active plate boundaries, and the development of dynamic topography driven by vertical mantle stresses. Dynamic topography may also explain elevation changes observed in some cratons, where no clear deformation is apparent. LTT studies from classic cratons in Fennoscandia, Western Australia, Southern Africa, and Canada are reviewed, with emphasis on different aspects of their more recent evolution.