Lithosphere dynamics and tectono-stratigraphic evolution of the Mesozoic Betic rifted margin (southeastern Spain)

Abstract

Quantitative subsidence analysis demonstrates that Mesozoic sediments in the eastern Betic Cordilleras have been deposited on a thermally subsiding, rifted margin. The dynamics of rifting are related to regional trans-tension in the Atlantic realm. Modelling of this phase of rifting at the southern Iberian margin shows that the associated stretching of the lithosphere significantly altered its geometrical and mechanical structure and exerted a major control on subsequent convergence tectonics. The Mesozoic stretching led to the formation of a ramp at the margin due to strong lateral variations in the effective elastic thickness (EET) of the lithosphere and the thickness of the crust, in a direction perpendicular to the margin. The existence of a ramp structure in the Late Mesozoic at the Iberian margin, which is also supported by stratigraphic and structural data, is important for the style of subsequent deformation of the lithosphere in Late Cretaceous-Tertiary times. The lateral variations in EET inferred from forward modelling of rifted margin stratigraphy could explain the observed multiple collapse of the Betic margin and the partitioning of deformation between the converging units involved in the Betic orogeny. Modelling of depth-dependent palaeo-rheological profiles of the margin shows that the mechanical properties of the lithosphere after stretching differed distinctly from those before stretching. Lithospheric deformation in the Betic Cordilleras during the Tertiary orogeny seems, therefore, to be largely controlled by the previous rifting phase. A comparison of the palaeo and present-day rheologies in terms of estimates for EET during Late Cretaceous and present times indicates that the mechanical properties of the lithosphère underlying the Betic orogen were also affected by rifting during Late Oligocene-Aquitanian times. This phase of rifting is coeval with extension in the Valencia trough, the Gulf of Lions and the West European rift system, which supports a causal relation with regional lithospheric processes. The lateral and spatial variations in thermo-mechanical properties of the lithosphere underlying the Betics, therefore, reflect the dynamics of lithospheric extension on a larger scale.