Late Orogenic doming in the eastern Betic Cordilleras: Final exhumation of the Nevado-Filabride complex and its relation to basin genesis: LATE OROGENIC DOMING IN THE BETICS
The geometry, timing, and kinematics of late orogenic extension in the Betic Cordilleras pose the problem of a decoupling of upper crustal and lower crustal deformation regimes. Perpendicular directions of extension in metamorphic domes and nearby sedimentary basins remain unexplained. This paper puts kinematic constraints on the final exhumation of the Nevado-Filabride complex, focusing on the formation of metamorphic domes and their relations with the adjacent basins. Structural fabrics and kinematic indicators below the main shear zones as well as their relations with both published changing metamorphic P-T conditions and geochronological data were studied. Our approach describes (1) a consistent top-to-the-west shear parallel to dome axes of during D2 (i.e., during decompression) with distributed ductile flow and the onset of strain localization along major shear zones, (2) further strain localization along the major shear zones under greenschist facies conditions, during D3 leading to S-C′ mylonites formation accompanied with a rock strong thickness reduction, (3) the divergence of shear direction on either limbs of domes during D3 showing the appearance of the dome geometry, and (4) a local evolution toward N-S brittle extension (D4) in the upper plate and formation of sedimentary basins. Continuous ductile to brittle top-to-the-west shear is compatible with the slab retreat hypothesis from the Miocene; the formation of domes which adds gravitational forces responsible for the final stages of exhumation is thus characterized by important kinematics changes necessary to explain coeval N-S opened basins. Later, from the upper Tortonian, a contractional event (D5) amplified the earlier domal structures forming the present north vergent folds.