An Updated Paleomagnetic Test of the Patagonian Orocline

RAPALINI, AUGUSTO E.; PERONI, JAVIER; LUPPO, TOMÁS; TASSONE, ALEJANDRO; LIPPAI, HORACIO; VILAS, JUAN F.

Puerto Vallarta

Congreso; Reunión Anual de la Unión Geofísica Mexicana 2012; 2012

Unión Geofísica Mexicana

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. New paleomagnetic results on Late Jurassic to Late Cretaceous magmatic units along the Fuegian Cordillera of Argentina and Chile are reported. Five sites on Late Jurassic-Early Cretaceous metabasalts and metagabbros of the Lemaire Formation showed a post-tectonic characteristic remanence with significant counterclockwise rotations (26-50°) in four of them. Paleomagnetic data from a Late Cretaceous dacite and three small intrusions (the Jeujepén, Krank and Santa Rosa plutons) also showed ccw declination anomalies between 28° and 35°. A small area of the latter, affected by an E–W sinistral strike-slip fault, presented much larger declination anomalies 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