Flexural to broken foreland basin evolution as a result of Variscan collisional events in northwestern Spain
M. Keller, H. Bahlburg, C.D. Reuther, A. Weh, 2007. "Flexural to broken foreland basin evolution as a result of Variscan collisional events in northwestern Spain", 4-D Framework of Continental Crust, Robert D. Hatcher, Jr., Marvin P. Carlson, John H. McBride, José R. Martínez Catalán
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The Variscan Cantabrian Zone of northern Spain records the transition from passive-margin sedimentation to foreland basin deposition during the Late Devonian. Initiation of the foreland basin system is reflected in the evolution of a hinge line that separated the foredeep from the adjacent peripheral bulge. Bulge erosion provided siliciclastic detritus that was deposited in the evolving foredeep. After cessation of sedimentary input, the foredeep achieved starved conditions during the earliest Tournaisian. These events were a long-distance effect of initial subduction of the Iberian continental margin prior to collision between northwestern Gondwana and North America. During the Namurian, propagation of the deformation front and the rise of the orogen led to increasing input of detritus that began to fill the foredeep.
During the late Namurian and the early Westphalian, deformation started to affect the Cantabrian Zone. The Palencian nappes were emplaced onto the Valsurvio Dome, after which thick wedge-top deposits formed (the Curavacas Conglomerate). When the Esla nappe and the Valsurvio Dome became involved in deformation and approached the rigid lithosphere of the Cantabrian Block, anticlinal stacks began to form, and the lithosphere broke. Two major faults developed, the León fault and the Ruesga fault, which dissected the lithosphere to accommodate further compression. The resulting topography led to the gravitationally induced gliding of the Palencian nappes into the Pisuerga Carrión unit, where sedimentation and deformation continued under broken foreland basin conditions. The Cantabrian Mountains preserve a foreland basin system that in its early stage was formed under flexural deformation of the lithosphere induced by subduction. When deformation affected the autochthonous continental lithosphere, the size of the flexurally induced basins changed from a single, large-scale depocenter to smaller-scale, interconnected basins. In its late stage of development, the Cantabrian foreland basin system records the transition to broken foreland conditions as the thrust front approached the rigid Cantabrian Block, a basement feature that has influenced the tectonostratigraphic evolution of the Cantabrian Zone since Silurian times. Incipient oroclinal bending during the main stage of thrusting might have been an additional factor triggering the failure of the lithosphere.