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Ana Ruiz-Constán, Universidad de Granada (Spain)
Jesús Galindo-Zaldívar, Universidad de Granada (Spain)
Carlos Marín-Lechado, Instituto Geológico y Minero de España (Spain)
Farida Anahnah, Universidad de Granada (Spain)
Francisco Javier Roldán, Instituto Geológico y Minero de España (Spain)
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The Guadalquivir basin is a Neogene foreland basin, located in the southern part of the Iberian Peninsula, bounded to the north by the Iberian Massif and to the south by the External Zones of the Betic Cordilleras. Its northern part is mainly filled by autochthonous sediments of Tortonian to Quaternary age, meanwhile the southern part is formed by Mesozoic and Cenozoic chaotic olistostromes which come from the External Zones.
A N-S cross section of the central Betic Cordilleras acquiring different geophysical data (magnetotelluric, gravity and seismicity) has been performed in order to obtain information of the deep structure of the zone. Gravity and MT data determine the continuity in depth of the Iberian Massif below the foreland Guadalquivir Neogene basin and the External Zones of the Cordillera. The major relieves at the Betic Cordilleras front are constituted by limestone outcrops of several square kilometres. Geophysical data allow to determine the lack of continuity in depth of these limestones supporting that they are large olistoliths involved in a clay ductile matrix with foraminiferal fauna that extends up to Late Langhian-Early Serravallian age, and does not represent a frontal tectonic unit of the Betic Cordillera.
2D inversion of new MT soundings acquired along the N-S profile provides the first deep resistivity image of the zone that support the results obtained from gravity data. The heterogeneous initial few kilometers in depth of the profile, characterized by high variability on conductivity values, corroborate the distinctive chaotic structure of the upper part of the crust in the frontal part of the mountain range. Shallow levels are formed by large resistive bodies (Subbetic Mesozoic limestone blocks) included in a more conductive matrix (gypsum and clays).
Although the northern margin of the Guadalquivir Depression is passive, the presence of olistostromes in the southern boundary evidences a main stage of tectonic activity during early-middle Miocene. Anyway, the irregular mountain front suggests a later long inactivity period. However shallow seismicity in this region points to a recent reactivation of a major detachment dipping southwards, to the Internal Zones of the Cordilleras, as consequence of the recent Eurasian-African convergence.
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