Exhumation through Relamination: A Modeling Study of the Rhodope Metamorphic Complex

We propose that relamination of subducted continental crust can occur at extreme scales during early collision and use numerical modeling to identify the factors controlling this process. We employ 2D thermomechanical modeling using visco-elasto-plastic rheology and force boundary conditions to converge plates.

In our models, upper crust of the passive continental margin is pulled to mantle depth during early collision. Depending on boundary conditions and lithologic architecture of the downgoing plate, large volumes of subducted buoyant crust can relaminate from the slab, rise through the upper plate, and split the lithosphere even for considerable compressive tectonic stress. At the surface, such an exhumation is expressed as a phase of intense horizontal extension and magmatism. The process can create hundreds of kilometers wide core complex, in which metamorphic continental crust derived from the subducting plate is exposed. Horizontal tectonic stress, the thickness of the downgoing upper crust, and its rheological properties are among the factors that control the width and topography of the resulting complexes.

We propose that the Rhodope Metamorphic Complex on the Balkan Peninsula represents a prime example for this kind of dramatic relamination. Structurally deep tectonic units in this domain internal of the oceanic suture zone at the surface exhibit Eocene high-pressure metamorphism and nappe stacking followed by massive magmatism and large-offset normal faulting. Despite more than 100 kilometers of extension in Cenozoic times, the area still shows thick crust and high mountains, and we propose that extension was driven by massive relamination. Our modeling results support schemes that attribute the lower units of the Rhodope Metamorphic Complex to the subducting Adriatic plate.