Abstract
Lithospheric yield stress is a key parameter in controlling tectonic
processes. We calculate yield stress for a range of conditions
appropriate to the Archean Earth, including hotter mantle potential
temperatures and a range of Moho temperatures using 2D high resolution
numerical geodynamic modelling techniques. This range of conditions are
evaluated for generating felsic, tonalite-trondhjemite-granodiorite
(TTG), crust with the results bench marked against the preserved rock
record. The model results indicate that lithospheric yield stress
slightly lower than the present-day Earth values (i.e. < 100
MPa) generates TTG melt volumes similar to those preserved in the rock
record. In particular, large volumes of TTG melts form in the tails of
lithospheric drips. Melting occurs profusely within the thinner portions
of the drips as these regions are more ef�ciently heated by the
enclosing hotter mantle. In contrast, only limited melting occurs in
regions of thickened crust, in part because the weaker lithosphere
cannot sustain crustal thickening for long time periods, resulting in
its removal through drips. Our models highlight the dominance of
non-plate tectonic mechanisms in producing TTGs under the conditions
that operated on the hotter Archean Earth.