|Title||Archean lithospheric mantle inversion: key to diamond productivity of cratonic keels?|
|Author||Percival, J A; Pysklywec, R N|
|Source||GAC-MAC-CSPG-CSSS Halifax 2005, building bridges - across science, through time, around the world: abstracts/AGC-AMC-SCGP-SCSS Halifax 2005, Jeter des ponts entre les disciplines scientifiques, les
époques, et unifier le monde : recueil des résumés; GAC-MAC-CSPG-CSSS Joint Meeting, Abstracts vol. 30, 2005 p. 152 Open Access|
|Links||Online - En ligne (HTML)|
|Alt Series||Earth Sciences Sector, Contribution Series 2004317|
|Meeting||From Cratons to Carals (GAC Halifax Symposium); Halifax, Nova Scotia; CA; May 16-18, 2005|
|Media||paper; on-line; digital|
|Subjects||Archean; lithosphere; mantle; diamond; craton; metamorphism; orogenies; orogenesis; continental crust; Mohorovicic discontinuity|
|Abstract||The survival of Archean diamonds in lithosphere whose crust underwent high-temperature metamorphism and widespread melting|
can be explained by considering the fate of depleted, buoyant lithosphere
beneath a cooling orogen. Mafic lower crust converts to
eclogite within a few million years, establishing a gravitational instability with respect to underlying, less dense mantle lithosphere.
Asthenosphere flow provides tractive force on the
lithosphere base, prompting inversion of a buoyant but top-heavy, ca. 200 km thick cell.
Eclogite decoupled from the crust may subsequently sink into asthenosphere, leaving the most depleted and refractory, former upper
mantle rocks at the base
of the lithosphere in the garnet field. Parameterized numerical experiments of the lithospheric inversion
process show a >40 m.y. pulse of elevated temperature (maximum 1100 °C) in the lower crust when ca. 1350 °C basal lithosphere is
into juxtaposition with the new Moho. Calculated P-T paths for different domains within the mantle lithosphere cell show both
isothermal decompression and loading trajectories as garnet-bearing rocks enter the spinel field and vice-versa. Similar
paths have been discerned from disequilibrium textures in a small population of mantle xenoliths, but existing interpretations (plume and subduction drag, respectively) do not account for the lack of annealing at ambient mantle conditions. The
calculated paths show zones in the central part of the inverting cell that criss-cross the graphite-diamond boundary, perhaps promoting growth of large crystals through small growth increments. Although the model does not account for the presence of
carbon in Archean lithosphere keels, it does provide a mechanism for growth of large diamonds and long-term craton stability.