Isostatic and Dynamic Components of the Observed Topography in the Central Tethyan Realm

Abstract

The convergence of the Arabian and Eurasian plates formed the present-day elevation along the collision zone since the Late Cretaceous. Isolating the dynamic contribution of convecting mantle to the topography is complicated by various isostatic and non-isostatic components of elevation. An incremental approach is used to derive residual topography after removing isostatic and elastically supported components. Joint spectral analysis of elevation and Free-Air Gravity Anomaly (FAA) proves that the elastic strength of the lithosphere supports short wavelength (λ < ∼200 km) elevation. Therefore, only long-wavelength (λ > ∼200 km) elevation and FAA are used for later isostatic reductions. The FAA spatially correlates with trends of major tectonic features, implying that the major portion of the long-wavelength FAA is supported by horizontal tectonic forces. The thickness of the equivalent slab to long-wavelength FAA is reduced from long-wavelength elevation. We argue that the isostatic topography is equally affected by the crust-mantle discontinuity (Moho) and lithosphere-asthenosphere boundary (LAB). The Moho-reduced topography is calculated by subtracting the isostatic contribution of Moho. The residual or lithosphere-reduced topography is calculated by subtracting the main trend of the LAB variations from the Moho-reduced topography. The residual topography suggests that the majority of the elevation in Anatolia and the Arabian Plate is isostatically supported by LAB variations. In the Iranian Plateau, isostatic compensation at the Moho is dominant. The maximum residual topography along the Red Sea ranges from 1000 to 2000 m, indicating the non-isostatic heterogeneous lithosphere and asthenosphere contribution to the elevation. The negative residual topographies for certain regions of central Iran and southern Eurasia probably indicate a geodynamic subsidence mechanism. The estimated residual topography of ±800 m in the East Anatolian-Caucasus-Iranian Plateau is in the order of magnitude of the Moho and lithospheric uncertainties. Therefore, the available data is insufficient to confidently attribute the residual topography to the dynamic topography.