From hanging wall to footwall: a story of crustal-scale piracy during the exhumation of the South Rhodope complex (northern Greece).

Rocks occupying the back-arc areas in subduction zones present a structural complexity resulting from subduction and exhumation processes, the latter contemporaneous with hydrothermal fluid circulation and ore deposition along crustal-scale shear zones. In many cases, the exhumation starts while rocks are situated in the middle crust, where ductile deformation prevails and ends when these rocks are exposed to the surface, juxtaposed against hanging wall rocks with contrasting mechanical properties and deformation history. The interplay between high- and low-grade rocks often results in complex patterns and puzzling structural inventories.

The Rhodope crystalline complex (north Greece) comprises high-grade ortho-and paragneisses that were subducted in HP-UHP in the Mesozoic and exhumed in the Oligo-Miocene, through a complex network of ductile shear zones and low-angle normal faults constituting the Kechros Detachment. The high-grade footwall rocks belong to the Lower and Intermediate Rhodope Terranes, juxtaposed against the low-grade carbonates and phyllites of Makri Unit and the late-Eocene-Oligocene supra-detachment sediments and volcanic rocks.

We have conducted a detailed mapping and structural study of the Kallintiri area (SW Byala Reka-Kechros Dome, Rhodope, northern Greece) to define the tectonostratigraphy of the area and discriminate between early ductile, subsequent brittle-ductile, and late brittle structures. Our results established a continuum of large-scale structures that brought the high-grade rocks from the middle crust to the surface, accompanied by corresponding fault rocks and structures, revealing the acting deformation mechanisms. During the exhumation process, the deformation was localized at the lower structural level of the Makri Unit due to the significant competence contrast between the structurally lower amphibolite-facies gneisses and the overlying lower-greenschist facies carbonates. As a result, the carbonate rocks from the hanging wall Makri Unit were mechanically coupled to the footwall and served as the main lithology that experienced mylonitic deformation.