New data on the tectonics and structure of the sedimentary cover of the White Sea rift system

Abstract

The White Sea is an inner sea of Russia, and its geology and geophysics are poorly studied. According to current ideas, rift structures of the Mezen syneclise extend to the White and Barents seas and bend round the Kola Peninsula in the southwest and northeast [1, 2, 4, 7, 8, 13]. Until the present time, these ideas were based only on fragmentary data of the analysis of potential geophysical fields and mainly on materials of the geology of land framing. The analysis of new marine CMP SR, gravity and magnetic survey, and continuous seismic profiling data obtained in 2003 and 2004 (MAGE) in combination with the results of geological and geophysical works on land allowed us to characterize for the first time the inner structure of the White Sea rift system (Fig. 1). From the tectonic point of view, the White Sea region is located in the northeastern framing of the Baltic Shield overlain by the sedimentary cover of the Russian Plate. The region is composed of Riphean, Upper Vendian, and Upper Paleozoic rock complexes and Quaternary sediments. The Mezen rift system comprises the Mezen Graben and the Ponoi Trough distinguished in Mezen Bay and the White Sea Funnel. The White Sea rift system includes the Kandalaksha, Kerets, and Onega grabens spatially related to the White Sea basin (Fig. 1). The two graben systems are separated by the Terskii terrace mainly composed of Lower Archean gneiss‐ granites and granodiorites. The Terskii terrace has clear boundaries. The southwestern boundary with the Kerets graben extends over a large fault with a total amplitude of ~1 km, which is traced in the southeastern direction from the Terskii shore to the Zimnii shore. The northeastern boundary with the Ponoi Trough is represented by the Zolotitsa tectonic zone, which extends from the Zimnii shore via the White Sea Neck to the eponymous Funnel, and the system of the NWtrending stepwise faults that probably make up the southwestern slope of the Mezen graben as well. The amplitude of faults along the Zolotitsa zone reaches 2 km. The Terskii terrace plunges in the southeast direction along the fault system below the sedimentary cover of the Russian Plate. The terrace on the Zimnii shore is complicated by the Zolotitsa and Ruchei salients and troughs of the Leshukon rift system. The thickness of the sedimentary cover in the offshore area of the Terskii terrace does not exceed 1 km. The sequence is composed of Riphean, Vendian, and Quaternary sediments. Riphean rocks fill up pockets in the crystalline basement, whereas Vendian and Quaternary sediments overlap the deeply eroded surface of underlying rocks.