North Aegean core complexes, the gravity spreading of a thrust wedge

Abstract

The North Aegean core complexes developed in middle Eocene soon after the end of continental block convergence and piling up of the Hellenic Thrust Wedge. They formed during back-arc extension, driven by the Hellenic slab rollback, at the back of the thrust wedge. A series of scaled laboratory experiments was performed to test whether the gravity spreading of a thrust wedge is a suitable process for the development of the North Aegean core complexes during back-arc extension. Wedge-shaped sand-silicon models with variable boundary displacement velocities and different geometries of the upper sand layer were used to study the effects of variations in wedge rheology on the pattern of extension. The models exemplify that extension, either distributed (wide rift mode) or localized (core complex mode), is always located at the wedge rear. Core complex development was favored in models with thicker brittle layer (higher frictional strength) and low stretching rate (lower ductile strength). Both core complex location at the wedge rear and detachment location and dip are interdependent and intrinsically related to the initial wedge shape of the extending system. The experimental model displays striking similarities with the extensional pattern of the North Aegean in terms of (i) location, size, and shape of core complexes as well as their sequence of development and (ii) detachment location and dip. We conclude that it is the initial wedge geometry of the system and the weak nature of the crust at the onset of extension that controlled the extensional pattern of the North Aegean domain.