New approaches for the application of paleomagnetism to fold and thrust belts
2016. "New approaches for the application of paleomagnetism to fold and thrust belts", Palaeomagnetism in Fold and Thrust Belts: New Perspectives, E. L. Pueyo, F. Cifelli, A. J. Sussman, B. Oliva-Urcia
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The Cotiella thrust sheet in the South Central Pyrenees is a well-studied example of an extensional basin that formed at the northern Iberian rift margin during the Late Cretaceous, and was inverted in the Late Cretaceous and Cenozoic on top of the South Pyrenean Central Unit. A palaeomagnetic study of the thick sequence of shallow marine syn-extensional carbonates filling the Cotiella Basin reveals the presence of a widespread secondary magnetization of both normal and reversed polarities. Neither in situ nor bedding tilt correction provides a satisfactory grouping of the palaeomagnetic directions, thus suggesting syn-deformational magnetization. Best clustering of palaeomagnetic vectors is obtained after unfolding into a post-extensional pre-compressional stage, coherent with an acquisition age between Santonian and Paleocene. Strong magnetic enhancement and very distinct magnetic properties with depth suggest a link with burial diagenesis of organic matter, precipitation of iron sulphides and subsequent oxidation to SD fine-grained magnetite. The secondary magnetizations of the Cotiella record significant vertical axis rotations ranging from 14° to 52° clockwise, coherent with the scenario of the Cotiella thrust sheet transported piggy-back and bent during the emplacement of the lower Gavarnie–Sierras Exteriores thrust sheet.
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Palaeomagnetism is a technique used to understand complex deformation patterns in fold-and-thrust belts; it can be used to characterize the distribution, magnitude and timing of vertical axis rotations, an elusive variable using other methods. A combination of palaeomagnetic and structural geology analyses has helped to unravel the geometry and kinematics of fold-and-thrust belts around the world and of different geological ages for more than 50 years. This volume comprises three sections: the first shows thorough overviews of western Mediterranean arcs and the western Carpathians; the second depicts several examples from the Andes, the Alps, Anatolia, Pyrenees, Iberian Ranges and the Atlas; and the third shows the latest research on the use of palaeomagnetism to understand fold-and-thrust belts in 3D and 4D in a more quantitative way and it also includes some methodological proposals to avoid common errors. In the papers of the first two sections, the combination of palaeomagnetic analyses with structural data, AMS or magnetostratigraphic analyses demonstrate the usefulness of palaeomagnetism in deciphering complex deformation patterns in fold-and-thrust belts.