Messinian to Quaternary Shortening Structures in the Palomares Margin: Partitioning of Deformation in an Oblique Convergence Margin (Algero-Balearic basin, Western Mediterranean)
We present two deep seismic reflection lines together with 3.5 kHz multi parametric echo-sounder profiles and bathymetric data acquired during the TOPOMED-GASSIS seismic survey across the Palomares margin in order to redefine the tectonic regime of the margin. These profiles evidence both pure shortening and transpressional strike-slip structures. Anticlines and synclines occur obliquely along the margin with a N40-50E orientation affecting the volcanic igneous basement up to the Quaternary sediments. The main anticline (the Abubacer antiformal ridge) is cut by reverse faults indicating a fault propagation fold system. The excess-area graphical technique applied on the balanced cross section indicates a 10 km depth basal detachment probably coinciding with the brittle-ductile transition as confirmed by available data about crustal thickness and heat flow in the region. The present character of these structures is confirmed by submarine channels deflection and the focal mechanisms in the region. N10E transpressional strike-slip structures occur in the southern part of the margin affecting both the volcanic igneous basement and the late Tortonian – Quaternary sediments indicating that Palomares-type faults continue southward offshore. Both pure shortening and transpressional strike-slip structures show a global age between the late most Tortonian and the Quaternary and are congruent with the onshore tectonic regime, the present NW-SE shortening stress field, GPS geodetic displacement data and focal mechanisms in the region.
The data presented here highlight a transpressive shortening tectonic regime along the Palomares margin that fit in an oblique convergence model where the present NW-SE shortening affects a NNE-SSW margin. This stress field generates subperpendicular NE-SW thrusts and folds, NNE-SSW sinistral and WNW-ESE dextral strike-slip faults. During the oblique convergence the shortening is mainly accommodated by the pure shortening structures, meanwhile the strike-slip faults connect most of these structures allowing the shortening transfer and the partitioning of deformation.
AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013