Subduction evolution in the Anatolian region: the rise, demise, and fate of the Anadolu Plate

Abstract

A major ocean basin once intervened the African and Arabian continents in the south and the Eurasian continent in the north: the Neotethys Ocean. Unlike the present-day Atlantic Ocean, it was not a single, wide ocean with one mid-oceanic ridge, but consisted of several relatively narrow oceanic seaways separated by (micro)continents with multiple plates bound by ridges and subduction zones, much as the present-day southwest Pacific. The closure of the Neotethys Ocean through subduction was followed by the collisions of (micro)continents with Eurasia and led to the Alpine-Himalayan mountain belt. The geological record of Anatolia (present day Turkey) holds record of two subduction zones within the Neotethys Ocean. One subduction zone existed along the southern Eurasian margin, the second started intra-oceanically. During progressive subduction, parts of the overriding oceanic lithosphere were emplaced over the southern continents, forming a distinct rock record known as ‘ophiolites’ – pieces of oceanic crust. Because subduction is a destructive process the surface record of subduction-dominated systems is naturally incomplete, and more so backwards in time. Relics of subducted lithosphere are sometimes preserved in mountain belts, but most of the original plates now reside in the mantle. Nevertheless, the sparse geological record preserved holds valuable information to restore past plate motions and the dynamic evolution of subduction zones. This thesis reveals the evolution of a double subduction system from the geologic record of Anatolia, from its birth to its demise, over a period of tens of millions of years. The aim of this thesis is to provide a comprehensive reconstruction and understanding of the Anatolian double subduction system, its effect on past plate motion, and the dynamic evolution of such complex systems. This thesis establishes quantitative relationships of the two subduction zones within Anatolia, which consumed oceanic and continental crust and lithosphere. The study of such a complex three-dimensional tectonic setting demanded an integrative approach in which the link between shallow surface and deep mantle processes is important for relating deformation at different levels and scales in the crust and lithosphere to the underlying tectonic processes. This thesis in particular focusses on: (1) Quantifying structure and style of upper plate deformation through the field study and kinematic reconstruction of sedimentary basins forming on the overriding plate, from the onset of subduction some 90-100 million years ago, until the present. (2) Understanding the evolution of the subduction systems and associated accretionary wedges through the study of the rock record of the subducting plate which came back to the surface along the subduction interface. (3) 2D restoration of upper plate deformation through block rotations accommodated along discrete fault zones and identification of tectonically coherent blocks through paleomagnetic methods. (4) Assessing how much Africa-Eurasia convergence was accommodated in the Anatolian mountain belt based on kinematic constraints on extension and shortening and how this compares to plate motion models. (5) Assessing where the lithosphere that must have been lost to subduction according to the reconstructions may reside in the Earth's mantle, as imaged by seismic tomography, and compare the reconstructed timing of onset and arrest of double subduction with Africa-Eurasia plate motions to assess whether perceived major dynamic effects of double subduction systems are valid.