The Diffuse Plate boundary of Nubia and Iberia in the Western Mediterranean: Crustal deformation evidence for viscous coupling and fragmented lithosphere

A spatially dense GNSS-based crustal velocity field for the Iberian Peninsula and Northern Africa allows us to provide new insights into two main tectonic processes currently occurring in this area. In particular, we provide, for the first time, clear evidence for a large-scale clockwise rotation of the Iberian Peninsula with respect to stable Eurasia (Euler pole component: N42.612°, W1.833°, clockwise rotation rate of 0.07 deg/Myr). We favor the interpretation that this pattern reflects the quasi-continuous straining of the ductile lithosphere in some sectors of South and Western Iberia in response to viscous coupling of the NW Nubia and Iberian plate boundary in the Gulf of Cádiz. We furnish evidence for a fragmentation of the western Mediterranean basin into independent crustal tectonic blocks, which are delimited by inherited lithospheric shear structures. Among these blocks, an (oceanic-like western) Algerian one is currently transferring a significant fraction of the Nubia–Eurasia convergence rate into the Eastern Betics (SE Iberia) and likely causing the eastward motion of the Baleares Promontory. These processes can be mainly explained by spatially variable lithospheric plate forces imposed along the Nubia–Eurasia convergence boundary.