Thermal structure of the crust in the Gibraltar Arc: Influence on active tectonics in the western Mediterranean

We have modeled thermal structure of the crust in the western Mediterranean on the basis of inversion of heat flow and elevation in the context of Airy's isostatic equilibrium. Modeling results reveal dramatic variations in crustal temperatures within the Gibraltar Arc region. The steep gradients in crustal thickness, together with the regional heat flow pattern lie at the origin of temperature anomalies. Temperatures at the base of the crust range between < 500 degrees C in the West Alboran Basin, where sediment accumulations exceed 8 km, and > 700 degrees C in the eastern Betics and the connection between the Rif and Tell belts in North Africa, where a high heat flow anomaly occurs. High-temperature zones define a hotter region (> 650 degrees C) running SW-NE across the central part of the Alboran Sea. These results agree with other geophysical evidence (e. g., low deep-crust V-p and P-n values) suggesting the occurrence of high temperatures in the deepest crust. According to the estimated silicic composition of the deep crust in the area, temperatures in some regions are appropriate for partial melting under muscovite dehydration conditions (> 700 degrees C). We have estimated that average partial melting ranges from similar to 12% (maximum XL) in the western Tell region to similar to 6% in the eastern Betics. This process modifies physical and mechanical properties of the deep crust enhancing crust-mantle decoupling and deep crustal flow with concomitant surface uplift. These mechanisms explain why high topography and active E-W extension occur transecting the overall orogenic trend of the Gibraltar Arc.