Localization of Arabia-Eurasia Convergence in the Kura Fold-Thrust Belt: The Effect of the East Anatolian Plateau and Pre-Existing Crustal Weaknesses?

The Kura fold-thrust belt (KFTB) at the southern margin of the Greater Caucasus (GC) is a first-order structure within the central portion (40°E-50°E) of the Arabia-Eurasia collision and likely the landward continuation of the Apsheron Sill, a marine fold-belt forming the northern boundary of the South Caspian basin. New neotectonic and geologic mapping and synthesis of published geologic, geodetic and earthquake data suggests that Arabia-Eurasia convergence is currently focused within the KFTB, nearly 550 km north of the plate boundary, and that the KFTB may have accommodated ~50-80% of Arabia-Eurasia convergence since 5 Ma. Localization of convergence here is anomalous, but even more so when the geology of the intervening East Anatolian plateau (EAP) is considered. The EAP is a peculiar region of elevated topography, lying ~200 km south of the GC and generally interpreted as a remnant accretionary complex, the surface geology of which is now dominated by mid-Miocene to Recent volcanism. Previously published seismic and magnetotelluric data indicate that the plateau crust is ~45 km thick, lacks a mantle lithosphere, and has elevated fluid content (consistent with a few percent partial melt). Although these observations suggest that the EAP should be weak, published geodetic data indicate the region currently behaves rigidly. The implication is that the hot and thin EAP has behaved rigidly for at least 5 Ma to transfer Arabia-Eurasia convergence north 200 km into the KFTB. To explore the implications of this apparent paradox, we used a simple 2D mechanical model to investigate the behavior of the collision. We hypothesize that the apparent strength of the EAP and location of the KFTB may result from the anomalous elevation of the EAP and the exploitation of pre-existing weaknesses in the GC region in the form of a relict subduction zone along the southern margin of the range.