A post Late Cretaceous partial bending of the Patagonian Orocline?.

RAPALINI, A.; PERONI J. I.; LUPPO, T.; TASSONE A.; CERREDO, M. E.; LIPPAI, H.; VILAS, J. F.

Viña del mar

Congreso; International Congress on the Southern hemisphere (GEOSUR); 2013

Geosur

The southern Andes show a major bending at the southern tip of South America, where the Fuegian Cordillera shows a nearly E-W trend. This curvature is widely known as the Patagonian Orocline and whether this is a primary or secondary feature remains controversial. Paleomagnetism is a powerful tool to determine the primary or secondary origin of curved orogens. Paleomagnetic data along the Patagonian Orocline are still scarce to provide a reliable and unambiguous answer to this question. In recent years several paleomagnetic studies, some of them still unpublished, have provided a better and enlarged database to test the origin of this major curvature. Paleomagnetic data from three Late Cretaceous intrusives in the Fuegian Cordillera (the Jeujepén, Krank and Santa Rosa plutons) and a dacite exposed neaar Ushuaia show consistent ccw rotations between 28° and 35°. Meanwhile, four sites on Late Jurassic-Early Cretaceous metabasalts and metagabbros of the Lemaire Formation exposed at different localities in this range also show significant counterclockwise rotations (26-50°). A small area of the Santa Rosa pluton, affected by an E?W sinistral strike-slip fault, however, presented a much larger declination anomaly indicating the presence of a local tectonic rotation. From these and previous data a picture of a nearly homogeneous post- Late Cretaceous regional rotation of the Fuegian Cordillera is suggested. This supports a model of nearly 30° of ccw secondary bending of the Patagonian Orocline since the latest Cretaceous (72 Ma). Occasional larger declination anomalies are likely related to local rotations associated to strike-slip tectonics.