Publication: Spectral analysis of the gravity and elevation along the western Africa–Eurasia plate tectonic limit: Continental versus oceanic lithospheric folding signals
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Publication Date
2010-09-22
Authors
De Vicente Muñoz, Gerardo
Fernández Lozano, Javier
Cloetingh, Sierd
Willingshofer, Ernst
Sokoutis, Dimitrios
Beekman, Fred
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Publisher
Elsevier
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Abstract
Large-scale folding is a key mechanism of lithospheric deformation and has been described in many parts of
the Earth, both for the continental and oceanic lithospheres. Some aspects of this process such as the presence of coupling/decoupling between the crustal deformation and the mantle lithosphere, or between different
lithospheres, make it necessary to accurately control the periodic characteristics of the elevation and of the
gravity signal. 1D spectral analysis of gravity and topography profiles is sensitive to a series of factors: the
location, length and orientation of the profiles, as well as the number of samples taken. We carry out a
systematic analysis of the periodicities in the topography and gravity, both 1D and 2D, along the western
border of the Africa–Eurasia plate tectonic boundary. We analyze the sensitivity of the 1D and 2D spectral
analysis in order to compare the results along a plate boundary where oceanic and continental lithospheres
are in contact with different tectonic, kinematic and rheological aspects. Our 1D spectral results indicate that the greater the profile length, the longer the wavelength peaks that are found. Nevertheless there are some periodic signals that appear in almost all the analyzed profiles: 100–250 km for the N–S profiles across oceanic plate boundary and 150–250 km where the plate boundary is
developed over continental lithospheres. The 2D spectral analysis avoids the problems found in relation to the
particular location of the profile but the resulting wavelengths are slightly higher than those obtained from
the 1D spectral analysis. The wavelengths estimated for both oceanic and continental lithospheres at the
Africa–Eurasia boundary (N250 km) show low values of mean mantle strength (b1013 Pa m). he presence of lithospheric folds means that the continental and oceanic lithospheres are mechanically oupled. This had previously been suggested for Iberia but not for the limit between S Iberia and the Terceira riple Junction.
The orientation of the lithospheric folds is NW–SE at the contact between continental lithospheres and NNE–SSW at the contact between oceanic lithospheres. This difference is also reflected in the signal anisotropy and must be related to the rotation of the tectonic stresses in the same direction. A large periodic signal (wavelength N600 km) was also detected both in 1D and 2D spectral results. After drawing the filtered values, the resulting maps indicate that this signal is related to the transition between continental and oceanic lithospheres and to the significant changes in crustal and/or lithospheric thickness from the Mid-Atlantic Ridge to the continental margins of western Eurasia.