Diamond‐bearing Occurrences of the Ural‐Timan Fold Belt (Russia): The Result of Ultra‐deep Subduction?

Abstract

AbstractLarge deposits of diamonds are associated mainly with kimberlites (and related rocks) of the cratons, but they are also known in the folded belts surrounding them. As an example is the Baltica craton and the surrounding its the Ural‐Timan (UT) folded belt. With the first object are associated diamonds of the Arkhangelsk (kimberlites and placers) provinces, and with the second one ‐ mostly placer deposits of the UT province, the probable source of which are also kimberlites. The structural position, composition and age of the potentially diamond‐bearing complexes of the Urals and Timan make it possible to propose a new petrological‐geodynamic interpretation of their formation. According to this model, during the Vendian‐Cambrian subduction of the Pechora Ocean crust, several different depth complexes have been formed, being changed in the western direction. At a shallow depth level the oceanic crust subduction is accompanied only by fluid processing, without the magmatism participation. As a result, this process leads to the formation of fluidizate‐explosive rocks of the Sertynya complex, which marks the outlet of the ancient subduction zone into the surface. At a moderately deep (up to 100–150 km) level melts are being produced, the derivatives of which are not diamond‐bearing depleted kimberlites of the Khartes (V‐Cm) complex. Apparently by the beginning of the Ordovician the active subduction of the Pechora Ocean stops. It occurs an opening of a new Ural paleoocean, and the earlier submerged the oceanic slab continues moving under the Baltica craton. At a deep (above 150 km) level the slab interaction with the mantle produces typical kimberlite magmas (from the Ordovician to the Middle Devonian) transporting diamonds to the surface of the Ural‐Timan province proper.