6533b861fe1ef96bd12c4c80

RESEARCH PRODUCT

Rejuvenation and erosion of the cratonic lithosphere

subject

description

Cratons are ancient continental nuclei that have resisted significant fragmentation for almost two billion years. Yet, many cratons also experience phases of instability in the form of erosion and rejuvenation of their thick lithospheric mantle keels. Melting governed by redox processes as well as small-scale convection play a key role in triggering such instability. 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.