The topography of the Iberian Peninsula: integrated geophysical-petrological multi-data inversion for lithospheric temperature and composition

Abstract:

The topography of the Iberian Peninsula is characterized by the presence of Variscan and Alpine orogenic belts and foreland basins, but what sets it apart from the rest of Western Europe are the large elevated flat surfaces (700 m over the sea level on average) in its central parts. The origin and support of such high average topography in Iberia, whether of isostatic or dynamic source, is a matter of intense debate across different Earth science fields. A fundamental key in understanding the Iberian topography is to have a reliable image of the present-day lithospheric thermochemical structure that so far remains poorly constrained, particularly at mantle level. The goal of this paper is to derive robust estimations of the thermal, compositional and density structure of the lithosphere beneath the Iberian Peninsula from integrated geophysical-petrological probabilistic inversion of surface wave, elevation, geoid anomaly and heat flow data. Our inversion shows an average lithospheric thickness of 80-100 km in the Iberian Peninsula with only moderate lateral variations in general. The most prominent feature is the steep lithospheric thickness change extending from the central to the easternmost Pyrenees. The thinnest lithosphere in our models is found in the south-eastern Mediterranean margin (<80 km) overlapping with a Neogene Iberian volcanic province (Tallante-Cabo de Gata volcanic fields).The present-day thermochemical structure stemming from our inversion reveals a clear imprint of the geodynamic evolution of Iberia. The lithospheric thickness and, therefore, the mantle geotherm are to a large extent related to Alpine Cenozoic tectonics. In the Alpine domain the western Pyrenees and Iberian chain seem to have been affected by Mesozoic rifting processes that would have imprinted a fertile signature into the previously more refractory Variscan Iberian lithosphere. To the south in Betic domain, the lithospheric thermochemical structure is likely conditioned by the ongoing Alboran slab subduction under Iberia. Except for the Mediterranean margin, where we find evidence for moderate negative dynamic topography, most of the surface elevation in Iberia can be explained by lateral density contrasts associated with crustal and lithospheric thickness and lithology variations.