Extensional tectonics in the northeastern Betics (SE Spain): case study of extension in a multilayered upper crust with contrasting rheologies

摘要

Extension in the northeastern Betics took place along two main directions, corresponding to a minimum of two successive orthogonal extensional systems with N-NW and W-SW sense of shear, respectively. Strain was strongly localised within weaker mctapelites and gypsum, leading to the development of several extensional detachments, which accommodated the thinning produced by extensional ramps and listric faults within the stronger carbonate rocks. Extension along several detachments led to the preservation in a single thinned section of layers representative of different crustal depths of a previously thickened upper crust. The N- to NW-directed extensional system was formed by brittle to brittle-ductile detachments, which were active during the Upper Oligocene and Lower Miocene, coeval to vertical ductile thinning of underlying greenschist-facies metamorphic rocks. The W- to SW-directed extensional system, active during the Middle and Upper Miocene, shows multiple slip surfaces, which transferred displacement to a brittle detachment with a ramp-flat geometry that stepped down into the footwall of the previous NW-directed system. The geometry of both extensional systems was determined by the rheological heterogeneity of the studied crustal section. Further Upper Miocene extension was accommodated by radial extension with a dominant set of SW-directed listric faults, which tilted the aforementioned detachments and exhumed them in the core of km-scale elongated extensional domes.