Contrasting styles of proterozoic crustal evolution: A hot-plate tectonic model for Australian terranes

Proterozoic terranes in Australia record complex tectonic histories in the interval 1900-1400 Ma that have previously been interpreted by means of simple intracratonic or platetectonic models. However, these models do not fully account for (1) repeated tectonic reactivation (both orogenesis and rifting), (2) mainly high-temperature-low-pressure metamorphism, (3) rifting and sag creating thick sedimentary basins, (4) the nature and timing of voluminous felsic magmatism, (5) relatively large aspect ratio orogenic belts, and (6) a general paucity of diagnostic plate-boundary features. A key to understanding these histories is the observation that Australian Proterozoic terranes are characterized by an extraordinary, but heterogeneous, enrichment of the heat-producing elements. This enrichment must contribute to long-term lithospheric weakening, and thus we advocate a hybrid lithospheric evolution model with two tectonic switches: plate-boundary-derived stresses and heat-producing-element-related lithospheric weakening. The Australian Proterozoic crustal growth record is therefore a function of the magnitude of these stresses, the way in which the heat-producing elements are distributed, and how both of these change with time.