Timanian orogenic deformation along the northeastern margin of Baltica, Northwest Russia and Northeast Norway, and Avalonian–Cadomian connections

Abstract

Predominantly terrigenous sedimentary successions of mainly Neoproterozoic age characterise the northeastern margin of Baltica, and extend over a strike distance of 1800 km from the Timans in Northwest Russia to the eastern part of Varanger Peninsula in Northeast Norway. Along this passive, extensional, faulted continental margin, pericratonic and proximal, basinal facies domains can be traced adjacent to a major, complex, NW–SE-trending fault zone. Deep drillholes through the Pechora Basin in Russia have penetrated the pre-Palaeozoic oceanic tholeiites, and subduction-related island arc volcanites and diverse plutonic bodies in the distal parts of the ocean basinal domain—part of a Paleoasian ocean of unknown magnitude. In Mid to Late Vendian time, these Neoproterozoic magmato-sedimentary assemblages were telescoped and accreted against this same northeastern margin of Baltica; a phase of orogenic deformation and metamorphism known as the Timanian (formerly, Baikalian). Descriptions are given of the fold structures and associated metamorphic fabrics encountered in different parts of the exposed Timan–Varanger Belt. These are mostly NW–SE-trending, SW-verging folds and NE-dipping cleavages or, locally, schistosities. The complete cycle of Riphean–Vendian rifting, basinal deposition, and more distal, oceanic to multiple-arc, subduction-related magmatism carries many of the hallmarks of comparable tectonomagmatic cycles in the now dispersed, Avalonian–Cadomian terranes of eastern North America and western and Central Europe. Adopting the palaeomagnetic reconstruction showing Baltica in inverted position during Vendian time, the Timan–Varanger Belt and adjacent Pechora/Ural areas show good alignment with the fragmented Avalonian–Cadomian terranes situated along the margins of Gondwana. As well as possible variations in subduction polarity with time, polarity changes may also be inferred in the lateral sense, along the Avalonian–Cadomian–Timanian axis, during and immediately following the Timanian orogenic accretionary event.