Crustal structure from gravity signatures in the Iberian Peninsula

Abstract

Through two-dimensional fi ltering and spectral analysis of gravity data, we infer the density structure of the Iberia Peninsula’s lithosphere (western Europe). The gravity anomaly map of the Iberian Peninsula displays long-wavelength anomaly minima related to Alpine ranges. These anomalies are primarily linked to a greater crustal thickness. Low-pass filtering of the anomaly map using a cutoff wavelength of 150 km was adequate for effective separation of shallow and deep sources used for computing the three-dimensional (3-D) Moho interface. Tsuboi’s technique (identical to the equivalent stratum theorem) is used here to map the 3-D Moho interface by selecting mean source depths from the results of the spectral analysis, and assuming a homogeneous density contrast of 350 kg/m3. The most characteristic feature of the 3-D Moho geometry was the presence of several lows associated with mountain ranges created by Alpine tectonics. In those areas, the gravity-derived Moho reaches a depth of up to 45 km in the Pyrenees and Cantabrian Mountains and close to 40 km under the betics, Central System, and Iberian Chain. Under the Iberian Massif, the western part of the Iberian Peninsula composed of a Variscan basement, the Moho was located at a depth of 30–36 km. These results are consistent with existing seismic data and indicate that gravity-based techniques can provide very good estimates of lithosphere structure.