Paleomagnetic reconnaissance study on igneous units of the Fuegian Cordillera, Tierra del Fuego, Argentina.

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

Viña del mar

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

Geosur

The Fuegian Cordillera represents the southernmost segment of the Patagonian Andes. It constitutes a curved orogen bended ca. 90o from the main north-south structural trend of the Andean Cordillera into a roughly east-west chain. Our reconnaissance study was performed on Mid Jurassic to Cretaceous metavolcanic and meta-sedimentary units exposed in the inner parts of the Cordillera. The geologic survey comprised the units belonging to the Rocas Verdes Basin (RVB) assemblages, i.e.: the mostly acid volcanic/ volcaniclastic rocks ot the Lemaire Formation, the basic rocks of the quasi oceanic floor of the basin and the Lower Cretaceous marine sedimentary infill of RVB represented by the Yahgán and Beauvoir formations. The Rocas Verdes marginal basin was closed and inverted in the Late Cretaceous by a main compressional orogenic event. Our study included remote and scarcely surveyed areas for which a reconnaissance structural and geological mapping was produced. The main lithologies sampled for paleomagnetic determinations were: a) highly vesiculated aphyiric andesitic lavas and sills, and b) rarely vesiculated porphyritic- aphyiric gabbroic rocks. Demagnetization behavior suggested pyrrhotite as the main magnetic carrier. Although several sites showed unstable magnetic behavior, consistent paleomagnetic directions were determined at six different sites which allowed us to recognize counterclockwise rotations, as determined by anomalous declinations, between 25o and 75o. Albeit a large range of rotation values, the declination anomalies are roughly consistent with determinations from previous studies on other units and localities of the Fuegian Cordillera.