The diachronous (step-wise) arc–continent collision in the Urals

The arc–continent collision in the Southern Urals was a theme of quite a few publications, dealing with many details of the process, such as deformation and origin of an accretionary prism, exumation of HP/LT metamorphic complexes, and flysch accumulation. Here more attention is drawn to the fact that in the northern areas of the Urals the analogous processes were lagging behind by at least 20 Ma or more compared to the South. The new data discussed in the paper support also the early observation that the metamorphic rocks exhumed at the stage of collision may preserve isotopic dates for all the earlier processes that took place in the subduction zone. It is suggested that the closure of isotopic systems could be influenced by a cooling action of the subducted slab. It is also pointed out that the diachroneity of collision may not be necessarily a result of an oblique collision: an orthogonal collision may be changed by a scissor-like closure of a triangle oceanic gap left after the first stage of the process.