Geophysical modeling and structure of Ushuaia Pluton, Fuegian Andes. Argentina

PERONI J. I,; TASSONE A.; MENICHETTI, M.; CERREDO, M. E.

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Año: 2009 vol. 476 p. 436 - 476

0040-1951

Within the area of Ushuaia Bay (Tierra del Fuego, southernmost South America) the deformed Lower Cretaceous sedimentary rocks of Yahgán Formation host the Ushuaia pluton. The intrusive body is oval in map view; it is compositionally varied with rocks ranging from the ultrabasic to the mesosiliceous realm. The emplacement time is constrained within the Albian-Cenomanian span by new amphibole K/Ar data. Meso- and microstructures of UP and its host indicate a synkynematic emplacement with a dominant extensional component. A set transcurrent and normal faults related to the sinistral strike-slip Beagle Channel Fault System affect the pluton and its host. On the basis of aeromagnetic data combined with field information, a new model is presented for the Ushuaia pluton. Modeling results fit well with a laccolithic body with an estimated volume of around 111 km3. The model pluton cross-section displays a central zone with average thickness off 2000 m which progressively thins toward the margins (~ 500 m) and a southern root which reaches 5000 m deep. The combined structural and geophysical model supports a transtensive scenario for the Ushuaia pluton emplacement at Early-Late Cretaceous boundary.