In search for a relationship between harmonic resolutions of the geoid, convective stress patterns and tectonics in the lithosphere: a possible explanation for the Betic-Rif orocline

Convective stress fields implied by the Runcorn model have been integrated with geological structures in the overlying lithosphere. This is dangerous since small-scale convection patterns in the mantle might have remained stationary for at least 50 Ma while particular parts of the lithosphere are likely to have passed over distinct convective stress regimes in such periods. The mantle component of the stress history of lithospheric structures younger than 32 Ma is potentially tractable if a mean plate velocity of 5 cm y^-1 is assumed. This is because the satellite gravity data used here allow the detection of convection cells with horizontal length scales of the order of 1600 km (which the lithosphere may cross in 32 Ma). For example, the sublithospheric stress field might have accounted for the uplift and subsequent subsidence of the Alboran Sea basin (W. Mediterranean), between 25 and 20 Ma ago. An immature diapiric rise of the mantle due to upwelling is likely to have occurred beneath this region between 25 and 20 Ma ago. The resulting lithospheric swell caused extensive tectonic unroofing by nappe spreading with or without some sliding. The subsidence of the Alboran Sea after the rise of the dome seems an excellent example of the combined effects of lithospheric cooling connected with ceasing mantle diapirism and mechanical thinning of the lithosphere by nappe translations.