A synthesis of the stratigraphic and tectonic setting of the Uralian ophiolites

Abstract

The Ural Mountains mark a 2500 km long, linear mid-Palaeozoic orogenic zone representing the closure of an ocean basin-island arc system between the European Plate to the west and the Siberian Plate to the east. Within the orogenic belt there are over 150 ophiolitic masses displaying sections of oceanic lithosphere with both harzburgitic and lherzolitic restites. These occur as tectonic slices and allochthons within volcano-sedimentary sequences and melanges. The paper concentrates on the main lines of evidence which form the basis for the palaeo-reconstruction of the collision zone. In particular, it reviews the stratigraphic, sedimentological and structural evidence which is used to support a model in which the ophiolites were emplaced from the east onto the continental margin of the European Plate. In general the evidence is that as older oceanic crust was obducted, new arc and oceanic crust was being created to the east. As well as providing a general geological map which locates the major ophiolites, the paper presents cross sections across the major zones of the belt, showing current views on palaeo-reconstructions. A tectonic model is presented which attempts to integrate the volcanic-sedimentary history of the belt with the emplacement history of the ophiolites.

Late Precambrian to Triassic history of the East European Craton: dynamics of sedimentary basin evolution

“…Early Ordovician rifting is evident in the Pechora-Kolva Basin. In the Polar Ural-Pay-Khoy belt, rifting persisted during the Tremadoc-early Arenig and culminated in late Arenig separation of a continental terrane from Baltica, the onset of sea-floor spreading, and the opening of the Uralian Ocean (Belyaev, 1994;Savelieva and Nesbitt, 1996). Thereafter, the Pechora Basin formed part of a carbonate-dominated passive margin.…”

“…Secondly, at the latitude of the Pechora Basin, magmatic rocks within the Urals indicate, on the basis of geochemical criteria, a change to subduction-related magmatism at the Early to Middle Devonian boundary (Bochkarev, 1990) and, as such, suggest a change in subduction polarity at that time. Thirdly, conodont stratigraphy (Puchkov, 1993;Savelieva and Nesbitt, 1996;A.V. Maslov, pers.…”

Lower to Middle Ordovician trilobite faunas along the Ural border of Baltica

“…The alluvial deposits in the westernmost facies belt are replaced to the east by shelf sediments followed by deep oceanic and rift sediments, which are allochthonous (e.g. Varganov et al 1973, Savelieva & Nesbitt 1996, Bogolepova & Gee 2004. The shore-most facies, the Eletsk [Eletskaya] contains a cyclic succession of various sandstones alternating with conglomerates (Manitanyrd Formation) of mainly continental and coastal shallow-water deposits, mostly without trilobites (Bogolepova & Gee 2004).…”

U-Pb Silurian age for a gabbro of the Platinum-bearing belt of the Middle Urals (Russia): evidence for beginning of closure of the Uralian Ocean

“…The mafic-ultramafic bodies are associated with rocks of the Tagil Zone, which consists of Early Ordovician to Early Silurian volcanic and volcano-sedimentary units, tectonically associated with shelf-facies and continental-slope deposits. They commonly developed a thermal aureole in the volcanosedimentary sequences (Savelieva & Nesbitt 1996). The massifs are mainly composed of gabbros (olivine gabbros, gabbro-norites, clinopyroxene-hornblende gabbros), and also of clinopyroxenites, wehrlites, dunites, pegmatitic gabbros and plagiogranites (Fig.…”

“…Remnants of oceanic lithosphere that became trapped along the suture between the colliding continents provide important time markers for the pre-collisional history of the orogen. Ophiolite complexes are numerous in the Urals (Savelieva & Nesbitt 1996) and crop out in the hanging wall of the Main Uralian Fault (MUF), the main suture zone that runs the entire length of the mountain belt (Matte 1995). These massifs appear as lens-shaped bodies mainly of lherzolitic and harzburgitic composition elongated parallel to the MUF (Savelieva et al 1997).…”