Effects of margin-parallel shortening and density contrasts on back-arc extension during subduction: Experimental insights and possible application to Anatolia

- Models consisted on oceanic and continental plates floating on asthenosphere.
- We tested deformation velocity and density ratio (oceanic vs continental plate).
- We examine the factors generating extension during subduction.
- The density ratio is a key factor to facilitate extension during subduction.
- We propose an application to the Anatolian system.

So as to investigate the parameters influencing subduction and back-arc extension, we have done three series of laboratory experiments (32 in all) on physical models. Each model consisted of adjacent oceanic and continental plates, floating on an asthenosphere. In experiments of Series A, a wide rigid piston, moving horizontally, controlled the rate of convergence of the oceanic and continental plates, whereas, in Series B or C, a wide or narrow piston produced lateral compression, parallel to the continent-ocean boundary (COB) and perpendicular to the subduction direction. The parameters that we tested were (1) the velocity of plate convergence (Series A), (2) the width of the compressing piston (Series B and C), and (3) the density ratio between oceanic and continental plates (Series B and C). This density ratio was a key factor. For a ratio of 1.4, the amount of extension in the continental plate increased regularly throughout time; for a ratio of 1.3, the extension remained small, until the piston stopped moving laterally; and for a ratio of 1.1, there was little or no extension. The width of the compressing piston had a smaller effect, although a narrow piston provided more space, into which the continental plate could extend.One possible application of our models is to Anatolia. Despite similar geological settings, the areas north of the Hellenic and Cyprus subduction zones differ, in that extension is large in the former and much smaller in the latter. We suggest that one of the main driving forces for Aegean extension may have been a high density ratio between subducting oceanic lithosphere and a Hellenic-Balkanic upper plate.