Palaeomagnetism of Mesozoic magmatic bodies of the Fuegian Cordillera: implications for the formation of the Patagonian Orocline
Augusto E. Rapalini, Javier Peroni, Tomás Luppo, Alejandro Tassone, María Elena Cerredo, Federico Esteban, Horacio Lippai, Juan Franciscovilas, 2016. "Palaeomagnetism of Mesozoic magmatic bodies of the Fuegian Cordillera: implications for the formation of the Patagonian Orocline", Palaeomagnetism in Fold and Thrust Belts: New Perspectives, E. L. Pueyo, F. Cifelli, A. J. Sussman, B. Oliva-Urcia
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It is not known whether the Patagonian Orocline, the major bend of the southern Andes at the southern tip of South America, is a primary or secondary feature. Palaeomagnetic data along the Patagonian Orocline are still too scarce to provide a reliable and unambiguous answer to this question. New palaeomagnetic results on Late Jurassic–Late Cretaceous magmatic units along the central segment of the Fuegian Cordillera are reported. Data from four Late Cretaceous small intrusions and three sites on Late Jurassic–Early Cretaceous metabasalts and metagabbros showed anticlockwise declination deviations between 21° and 46° with respect to South America. From these and previous data, a picture of a nearly homogeneous post-Late Cretaceous regional rotation of the central Fuegian Cordillera is suggested. This supports a model of nearly 30° of anticlockwise secondary bending of the Patagonian Orocline since the Late Cretaceous (72 Ma). Lack of rotation of post-50 Ma sedimentary rocks exposed to the north of our study region, and larger rotations (of c. 90°) reported to the south of it suggest that a geographical and/or temporal progression of rotation values from south to north in the Fuegian part of the Patagonian Orocline should be investigated.
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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.