Models of the deep structure of the White Sea paleorift crust system based on a comprehensive analysis of deep seismic profiles

Research subject. Deep structure of the earth's consolidated crust of the paleorift system of the White Sea and the Mezen syneclise.

Materials and methods. Two-dimensional seismic density models of the earth's crust structure were constructed on the basis of the 3-AP (Kem–White Sea–peninsula Kanin), Agat-2, Agat-3, and Quartz 2 reference seismic profiles. The state of the deep layers of the earth's crust was interpreted using the distribution of the effective density of the substrate and a model of distribution of magnetic anomalies sources. The latter model was constructed using the technique of two-dimensional inversion of an anomalous magnetic field. The magnetic field was analyzed based on a schematic map of magnetic field anomalies (AMP), synthesized by the authors based on the materials of magnetic surveys carried out in the waters of the Barents and White Seas at different time points and provided for their further interpretation. The main objective of constructing geological and geophysical models of the deep structure of the earth's consolidated crust of the White Sea paleorift system and the Mezen syneclise was to establish genetic relationships between near-surface geological structures and deep elements of the earth's crust structure.

Results. The conducted analysis of the abovementioned materials, taking into account the data on the near-surface structure of the earth's crust, allowed geological and geophysical models of the earth's crust to be constructed to the crust-mantle level along four reference seismic profiles – 3-AP, Agat-2, Agat-3, and Quartz-2 – crossing the structure of the Mezen syneclise in different directions. In addition, in the eastern part of the Mezen syneclise, a series of magnetic profiles is presented, demonstrating the confinement of the AMF sources to two hypsometric levels in the territory where the Late Paleozoic Mezen trap-dyke field, located in the sedimentary cover, was previously described.

Conclusions. Joint interpretation of seismic density models and those of distribution of magnetic anomaly sources made it possible to establish connections between physical parameters of models and geological structures or bodies and to create generalized geological and geophysical models of the studied areas of the earth's crust. According to the constructed 2D models of the deep structure of the earth's crust of the Mezen syneclise, the earth's crust has a complex and heterogeneous structure. The complex mosaic picture presented in the obtained models reflects the layered-block structure of the lithosphere. The block structure of the Mezen syneclise basement is mainly formed by riftogenic faults that limit grabens and horsts of the paleorift system of the White Sea and separate blocks with different density properties. The main structure-forming faults are listric in nature and flatten out toward the base of the upper or middle crust, acquiring detachment properties at depth. A certain correlation of the Moho surface relief with the structures of the surface layer of the earth's crust is noted. The distribution of deep sources of the anomalous magnetic field in 2D format for the low-frequency component of the magnetic field also reflects the structure of the earth's crust in the western part of the Mezen syneclise. Intense long-period magnetic anomalies here most likely reflect the saturation of the products of basic-ultramafic magmatism in the upper granite-metamorphic layer of the earth's crust.

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