High mountains in a zone of extended crust: Insights into the Neogene-Quaternary topographic development of northeastern Iberia

Topographic analysis combined with geological and geophysical observations indicate that much of the present configuration of the northeastern Iberian Peninsula derives from Neogene-Quaternary opening of the western Mediterra nean basins following the Pyrenean orogeny. Mountainous topography up to 20 00 m lines the Mediterranean coastal margin of Cataluna (Spain) despite a c rustal thickness of 22 km at the coast. Geometric analysis of topographic p rofiles indicates a strong link between topography and extensional tectonic s. Trends in maximum, mean and minimum elevations show marked regional incr eases in a SW-NE direction along the axis of the Ebro basin towards the act ive Amer-Brugent normal fault. From patterns of local relief, characteristi cs of the fluvial drainage network, location of drainage divides, and degre e of escarpment retreat, we distinguish two overlapping areas of mountainou s topography, a southern area related to late Oligocene to middle Miocene r ifting and a northern area related to late Miocene to Quaternary rifting. T he youthful topography in the northern area likely results from mechanical unloading of the footwall of the Amer-Brugent normal fault. In the southern area (encompassing the Catalan Coastal Ranges), erosion continuously renew s topography produced by rifting while causing headward erosion of coastal rivers into the Ebro basin. Elevated topography along the Catalan margin de rives principally from flexural isostatic rebound due to tectonic and erosi onal denudation, causing exhumation of the rifted margin. Nonetheless, the height of the mountains and the thinness of the crust suggest an additional component of dynamic or thermal support of mountainous topography, likely buoyancy forces from density differences in the mantle.