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Different models have been proposed to explain the formation of the Ibero-Armorican Arc, which require significant vertical axis rotations, at the end of the Variscan orogeny. Estimates of the amount of contraction (horizontal shortening) needed for these rotations range from 54 % to 91 % perpendicularly to the arc. These estimates are compared with coeval deformational structures developed in two areas of the orogen, one in the autochthonous hinterland underlying the Galicia-Trás-os-Montes Zone in the southern branch of the arc, and the other in the Cantabrian Zone foreland in the core of the arc. From this analysis it follows that the late Variscan deformation together with the subsequent Alpine contraction is not sufficient to explain the formation of the Ibero-Armorican Arc as a secondary structure by means of vertical axis rotations. Our analysis suggests this arc is mainly a primary, or non-rotational curve, slightly modified by ca. 10 % of superposed contraction during late Carboniferous and/or Alpine times. Moreover, we propose that the assumptions underlying the interpreted geometry of the arc be re-evaluated, and we discuss the role of late-Variscan regional strike-slip faults in the Iberian and in the Armorican massifs that probably acted consecutively before and during the contraction of the arc. [ABSTRACT FROM AUTHOR]

A high-resolution seismic tomography survey was acquired to obtain a full 3D P-wave seismic velocity image in the Zancara River Basin (east of Spain). The study area consists of lutites and gypsum from a Neogene sedimentary sequence. A regular and dense grid of 676 shots and 1200 receivers was used to image a 500x500m area of the shallow subsurface. A 240-channel system and a seismic source consisting of an accelerated weight drop, were used in the acquisition. Half million traveltime picks were inverted to provide the 3D velocity model that allowed to resolve the structure up to 120m depth. The project targeted the geometry of the underground structure with emphasis in defining the lithological contacts but also the presence of cavities and fault/fractures. An extensive drilling campaign provided uniquely tight constraints on the lithology; these included core samples and wireline-log geophysical measurements. The analysis of the well-log data enabled the accurate definition of the lithological boundaries and provided an estimate of the seismic velocity ranges associated to each lithology. The final joint interpreted image reveals a wedge shaped structure consisting of four different lithological units. This study features the necessary key elements to test the traveltime tomographic inversion approach in the high-resolution characterization of the shallow subsurface. In this methodological validation test, traveltime tomography demonstrates to be a powerful tool with a relatively high capacity for imaging in detail the lithological contrasts of evaporitic sequences located at very shallow depths, when integrated with additional geological and geophysical data. [ABSTRACT FROM AUTHOR]

The structure of the Africa-Anatolia plate boundary in the eastern Mediterranean is examined.