Thickness of the lithosphere beneath Precambrian cratons and mechanisms of their neotectonic crustal uplift

Аннотация

Up to 70% of the area of continents is occupied by the Precambrian crust. Shortening of this crust finished 0.5 Ga ago or earlier, while Pliocene–Quaternary rises made up of 100–200 to 1000–1500 m. In order to support these uplifts in the absence of shortening, the density in the lithosphere layer had to be considerably decreased. This lower density can be attributed to the replacement of the lower part of the mantle lithosphere with asthenospheric material or to the expansion of the inner parts of the crust resulting from repeated metamorphism. As is shown by our calculations, a decrease in density at depths of 150–250 km beneath the Precambrian cratons can lead to uplifts only up to 100 m in amplitude. Hence, the neotectonic uplifts were caused by expansion at higher crustal levels. This situation required the supply of a large amount of mantle fluid into the crust, and the volume of this fluid should be comparable to that of the new-formed relief