Why is the South Caspian Basin clockwise rotating?

The Iranian lithospheric plate (ILP), positioned at the boundary of Euro-Asia and Gondwana, is vital from a tectonic-geodynamic perspective. Its role in the evolution of the South Caspian Basin (SCB) and the Mesozoic Terrane Belt (MTB) (confined to the northern rim of the Arabian Plate) is undeniable. The boundary between Eurasia and Gondwana separates the western – Aegean-Anatolian Plate and the relatively young Neoproterozoic belt associated with the MTB and the eastern – ILP, which contains fragments of Arabian craton and terranes of Archean-Early Proterozoic age. The northwestern regional block of the ILP is influenced by the deep rotating mantle structure (DRMS) (Eppelbaum et al., 2021) and rotates counterclockwise. The central block of the ILP is in the marginal periclinal zone of the DRMS, and its movement is oriented mainly to the north. The ILP's eastern part is outside the DRMS's guidance and rotates NNE clockwise.

Immediately to the north of the MTB, already to the west of the discordant junction of the Mesozoic ophiolites and the Zagros terrane, an extensive collision-subduction belt is formed in the former development of the Neotethys Ocean. It occupies approximately half of the ILP in the meridional direction. The belt is composed of a complex of volcanic, metamorphic, and sedimentary rocks and hypsometrically forms a vast zone of the Iranian plateau (in the southern part of the ILP). This sublatitudinal zone of uplifts is closely adjacent to the SCB and the south boundary of the Eurasian Plate and is located near the Earth’s critical latitude of 35^o.

Combined tectonic-structural and geophysical analyses suggesting the Zagros suture imply that it might have been a piece of the MTB in the southern zone of the Neotethys Ocean. Since the post-Carboniferous, its uplift has been attested as an isolated tectonic feature of the Neotethys Ocean. The sharp divisions of the ILP on the western, central, and eastern fragments have a rational explanation – deep-seated geodynamics inspired by the impact of the DRMS, critical Earth’s latitude, and the Ural-African geoid anomaly. These factors overwhelmingly impact the mantle-lithospheric structure in the region.

This study generalized tectonic-structural, GPS, paleomagnetic, gravity, magnetic, and thermal data. The ILP is known to have high heat flow values along with a thickened Earth’s crust. Combined geophysical data analysis indicates that the ILP’s blocks press on the southwestern edge of the SCB, causing it to rotate clockwise.

Thus, we can conclude that the SCB is affected by three main geodynamic components: (1) the counterclockwise rotation of the DRMS, causing the complex movement of the ILP’s western and central lithospheric blocks; (2) the multipart direct pressure of the ILP on the SCB; and (3) the impact of the giant Ural-African step and critical Earth’s latitude. The current rapid reduction of the Caspian Sea level is associated, along with other factors, with the unevenness of the modern collision processes.

Eppelbaum, L.V., Ben-Avraham, Z., Katz, Y., Cloetingh, S. and Kaban, M., 2021. Giant quasi-ring mantle structure in the African-Arabian junction: Results derived from the geological-geophysical data integration. Geotectonics, 55, No.1, 67-93.