Is the subcontinental lithosphere beneath Archean terranes different from that beneath Proterozoic terranes?
P-wave velocities in mantle minerals are inversely proportional to the density of minerals of the same family – more correctly P-wave velocities are related to the rigidity characteristics of minerals, and Forsterite has a high velocity than Fayalite even though Forsterite is less dense than Fayalite. However, between mineral species, P-wave velocities increase with density from quartz to feldspar to pyroxenes to olivine to garnet. Density versus Vp, upper mantle minerals and rocks – seismantvp.jpg On the assumption that the base of the crust is located at the depth at which the seismic velocity exceeds 7.6 km/s, it would seem, with the exception of Canada, that the Crust of Archean provinces is relatively thin compared to Phanerozoic provinces. In explanation (Durrheim and Mooney, 1991) it has been proposed that the material for the formation of Archean crust was derived directly from the mantle beneath the Archean crust, which is therefore relatively depleted in crust forming element
