3.6.3. Subsidence history of the EEP

The occurrence of a thick sedimentary cover over most of the platform is not common for old cratons. The effect of different tectonic processes on the topography of the EEP is reflected in its >1 Gy long sedimentary record. A general lack of deep geophysical data has prevented, until now, a thorough examination of the role of different tectonic processes in the development of the depressed topography of much of the EEP. These processes include, but are not limited to, collision and suturing of continental blocks, intracratonic rifting, and orogeny and subduction at the craton margins.

Although it has been often asserted that development of the Pripyat-Dniepr-Donets rift was caused by a Late Devonian mantle plume, lithosphere scale tectonic modelling of such a process, including the near break-up of the Sarmatian and Archean terranes into the Ukrainian Shield and the Voronezh Massif has never been performed. 4D modelling, requiring acquisition of new geophysical data on the lithospheric structure of the region, could establish thermo-mechanical links between the postulated mantle plume, the opening and closure of Tethyan oceanic domains, and the regional tectonic evolution of the southern parts of the EEP, including the subsidence of the Peri-Caspian Basin (much of which is at present close to or below sea level). Meandering rivers on the EEP, which enhance the deposition of sediments, may lead to further platform subsidence, especially in the Volga delta.

The Baltic Basin is an area of anomalous subsidence within the EEP (e.g. Sliaupa et al., 2006), where it can be demonstrated that lithospheric rheology likely plays an important role in controlling Neogene-Quaternary vertical movements (Fig. 67). The Baltic Sea depression is actually confined to the weakest lithosphere, which has an elastic effective thickness (EET) of just 22-25 km increasing to 40-60 km at the basin periphery (Fig. 67). This may explain the shape of its present-day geometry that might be inherited from the Paleozoic Baltic Basin. Yet, the origin of the Baltic Sea depression is still uncertain with an alternative hypothesis proposing that the Baltic Sea is an erosional feature. Although this area remains a key area for understanding the development of neotectonic depressions on cratonic platforms, much basic information required for its consistent rheological modelling is not yet available. Nevertheless, the new large-scale passive seismic experiment PASSEQ (Grad et al., 2006) will yield important new information on the structure of its lithosphere. Yet, as control on the sub-lithospheric mantle structure of the Baltic Basin are insufficient to constrain subsidence models in the context of large-scale regional processes, acquisition of corresponding data relies on the EUROARRAY component of TOPO-EUROPE.

Process-orientated modelling based on the subsidence history of the basin combined with modern geophysical data is required to elucidate the role of different tectonic processes, including Proterozoic rifting and associated rapakivi-anorthosite magmatism, involving thermo-mechanical and probably compositional reworking of the lithosphere, Late Neoproterozoic rifting and passive margin development, followed by the Early Paleozoic Caledonian collision and foreland basin development.

Quaternary glacial processes largely shaped the relief of the northern half of the EEP. There is a strong interaction between glacial and geodynamic processes. Advancement and retreat by several kilometres thick ice sheets induced considerable isostatic movements of the lithosphere and also apparently activated and de-activated tectonic structures, particularly faults. Although isostatic processes are well studied in Scandinavia, related vertical movements of adjacent platform areas have received little attention. Recent very detailed studies on Baltic Sea terraces in Lithuania permitted to date precisely when post-glacial isostatic rebound ended and tectonic deformations controlled by far-field stresses started to prevail. A co-operative study involving all circum-Baltic countries could provide regional-scale reconstructions of these phenomena. Available data suggest that neotectonically uplifted areas played a greater role in glacial sedimentation than subsiding areas and that this duality considerably affected the present-day relief.

Data on the structure of the lithosphere are important for assessing the isostatic response of the EEP to deglaciation and what role isostatic rebound plays in the development of platform topography. Continental-scale studies demonstrate that borehole data can provide a unique record on Pliocene and Quaternary climate fluctuations and related glaciations and inter-glacial stages (Kukkonen and Joeleht, 2003; Lindner et al., 2006); however, detailed regional models for the entire EEP are still missing.