HR: 08:30h
AN: V31F-03 INVITED     [Abstracts]
TI: The Role of Continental Lithospheric Mantle in Earth Evolution
AU: * Carlson, R W
EM: carlson@dtm.ciw.edu
AF: Carnegie Institution of Washington, 5241 Broad Branch Rd, NW, Washington, DC 20015
AU: Shirey, S B
EM: shirey@dtm.ciw.edu
AF: Carnegie Institution of Washington, 5241 Broad Branch Rd, NW, Washington, DC 20015
AU: Pearson, G
EM: d.g.pearson@durham.ac.uk
AF: Durham University, South Road, Durham, DH1 3LE United Kingdom
AB: Oceanic and continental mantle lithospheres play a decidedly different role in the evolution of the overlying crust. Oceanic lithospheric mantle grows downward by conductive cooling from above eventually becoming so dense as to cause subduction of the overlying crustal section. Continental lithospheric mantle appears to form largely as the mantle wedge above continental convergent margins and thickens to 200 km or more through compression during continent-continent collision. High degrees of melting caused by water fluxing from the underlying subducting plate results in a highly depleted mantle residue with a chemical buoyancy and stiffness that contributes to the long-term survival of continental crust. Most lithospheric mantle keels appear to remain firmly attached to their overlying crustal sections. A good example is a locality near the southeastern border of the Kaapvaal Craton of southern Africa where the Archean lithosphere beneath the Craton is greater than 200 km thick. Only 70 km to the east, the lithospheric mantle is no older than 2.2 Ga to depths of 140 km suggesting the preservation of a steep lithospheric suture for billions of years. Other cratons, for example the Slave in northern Canada, show evidence of reworking from the bottom where magmatic input has caused substantial metasomatism and the injection of broadly basaltic components into the base of the lithosphere. Taken further, magmatic reworking of continental lithosphere can lead to its refertilization and hence densification, that ultimately will cause it to detach from the overlying crust as appears to have happened in the Sino-Korean Craton. In the majority of cases, however, old continental crust is underlain by old mantle lithosphere that can be a barrier to shallow mantle flow and thereby serve to protect the crust from deformation, filter the thermal and magmatic input from the underlying convecting mantle, and isostatically elevate the crust.
DE: 1025 Composition of the mantle
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
DE: 8103 Continental cratons
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005