Cratons are the ancient cores of continents, characterized by tectonic inactivity, a thick mantle lithosphere and low heat flow. Although stable as tectonically independent units for at least the past 2 billion years, cratons have experienced episodic rejuvenation events throughout their history. The lower part of the lithosphere is first weakened and altered by impregnation of magma at a few locations, which produces local density anomalies that have a destabilizing effect. These altered zones coalesce to form linear incisions at the base of the craton. Lateral erosion of the lithosphere is further aided by small-scale convection resulting from variations in lithosphere thickness, proceeding eventually to large-scale sinking of lithospheric mantle. Oxidation of volatile-enriched mantle leads to a significant drop in melting temperature as redox processes dominate melting mechanisms in cratonic mantle. Reduced conditions dominate in the deepest lithosphere, in contrast to shallower levels where carbon-slowly accumulated as diamond-is remobilized by oxidation.
展开▼
