Mechanical (de-)coupling of the lithosphere in the Valencia Through (NW Mediterranean): What does it mean?

We study the mechanics of lithospheric decoupling in continental extensional basins in relation to the distribution of (non-)competent mechanical layers within the lithosphere and the position of the isostatic compensation level. We specifically address the different modes of deformation taking place in crustal levels according to a self-consistent formulation of the concept of mechanical decoupling. Subsequently, we investigate the style of lithospheric decoupling in the Valencia Trough (NW Mediterranean), a prime example of a young continental rift basin. During its evolution, the lower crust (or at least part of it) acted as a weak, non-competent layer that eventually flowed laterally to accommodate deformation in the subcrustal lithosphere and overlying crust, which became mechanically decoupled. We use a numerical model to discern whether these two layers deformed fully independently (vertical decoupling), or maintaining a mechanical link (horizontal and partial decoupling). Results of our study, constrained by a high-quality database, exclude fully decoupled mode and favor isostatic compensation level in the asthenosphere. Interpretation of our results in light of geological and geophysical data suggests that the present Valencia Trough is best described by partial lithospheric decoupling. © 2003 Elsevier Science B.V. All rights reserved

Cenozoic vertical motions of the Catalan coastal ranges (NE Spain): the role of tectonics, isostasy and surface transport.

We analyze the Cenozoic topographic evolution of the Catalan Coastal Ranges (NE Spain) and the role of fault activity, erosion, sedimentation, and isostasy in controlling uplift and subsidence. A forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of Cenozoic vertical motions. We show that the effect of isostasy, erosion, and sedimentation is as important as the contribution of fault deformation to the topography of the Catalan Coastal Ranges. The model predicts that Paleogene topography generation by thrusting was compensated by erosion (up to 1.3 km) and isostatic subsidence (up to 1.2 km), resulting in a 1.2-1.9 km high mountain range by the end of compression (29 Ma). During the Neogene, strong tectonic subsidence related to normal faulting and the consequent flexural uplift (of 0.7-1.2 km), surface erosion (as much as 1.6-2.3 km), and sedimentation (up to 4.5 km) led to the present landscape configuration. Extension rates along the Barcelona fault controlled flexural uplift and, in combination with erosion and sedimentation processes, led to the migration of the topographic maximum of the Prelitoral Range toward the easternmost Ebro Basin. Copyright 2004 by the American Geophysical Union

3D flexural modeling of the Ebro Basin (NE Iberia).

The Ebro Basin, the southern foreland basin of the Pyrenees, has undergone a complex evolution in which, apart from the Pyrenees, the Iberian Range and the Catalan Coastal Ranges have played an important role, both as sediment sources and as basin confining structures. The deflected basement underlying the Ebro Basin dips north, suggesting a lithospheric-scale control on the structure of this basin. This is compatible with the results of subsidence analyses, which show that the study area is not in a local mode of isostatic compensation. In order better to understand the mechanisms that led to the present configuration of the Ebro Basin, and particularly the relevance of the various kinds of (un)loading (e.g. surrounding fold-and-thrust belts, basin topography, subsurface loads), we carried out a 3-D kinematic modelling study that accounts for the flexural state of the lithosphere, subjected to various loads applied at its lateral boundaries, and the sedimentary fill of the basin. We also included the effect of Neogene extensional tectonics along the eastern basin margin, which is related to the opening of the Valencia Trough. We show the suitability of the 3-D lithospheric-scale flexural modelling approach to the study of NE Iberia. Modelling results point to a relatively strong lithosphere in this area, with values of effective elastic thickness ranging from 10 to 35 km in the Ebro Basin, increasing towards the Pyrenees. We also find that the topographic (tectonic) load itself is insufficient to explain the observed basement deflection. Thus an extra sub-surface load beneath the Pyrenees, corresponding to the underthrusted Iberian lithosphere, is required. The effect of lithospheric stretching in the Valencia Trough on the Ebro Basin is appreciable only in its eastern part, where the lithosphere was uplifted. This had considerable repercussions on the sedimentary and erosional regime of the Ebro Basin. We have analysed the link between the stretching-related, tectonically uplifted areas and the erosional patterns observed onshore northeast Iberia