Home – Home – Jornals – Russian Geology and Geophysics 2005 number 12

The Paleoproterozoic collisional system of the northeastern Siberian craton is compared with the underlying lithospheric mantle. This system appeared at about 1.9-1.8 Ga, by accreting microcontinents with an age of 3.1-2.5 Ga. Evidence comes from isotope dating of the formation of ancient terranes, their thermal transformation and melting of collisional granitoids. The crustal structure inferred from geological and geophysical data bear a relict signature of collisional systems, including deformations, up to 58 km thickened crust, and even slope of seismic surfaces along the predicted directions of collisional overriding.
The crustal structures are underlain by thick, up to 260-300 km, diamondiferous lithospheric mantle with higher seismic velocities, which thins out to ≤200 km toward the margins of the region. This local bulge may be identified as a lithospheric keel (root). The spatial relationship between this mantle keel and crustal collisional system of Proterozoic age is geometrically evident, and magmatic events are obviously coeval. But proportions of relevant processes are not clear. The simplest supposition is that the keel formed as a result of accretion of fragments of the Archean lithospheric mantle together with the crustal terranes attached on top. This supposition contradicts the existing ideas that only the crust participated in continental collision, whereas the underlying mantle slipped free and far away. It should be the subject of future studies.