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Thirty-nine K-Ar and one Ar-Ar radiometric dates from the eastern central MesoCenozoic Patagonian Batholith and eastern satellite plutons of the Aysén Region, of southern Chile between latitudes 45°and 48°S, combined with previous dating of seven plutons, have yielded six age groups: (1) Middle to Late Jurassic, (2) Early Cretaceous, (3) mid-Cretaceous, (4) Late Cretaceous, (5) Oligocene and (6) Miocene. In general, the Cretaceous and younger ages correspond to previous reported ages for other parts of the main batholith, but for the satellite plutons to the east show a wider age spectrum than the previously accepted Late Miocene dates. These results indicate a relatively continuous Late Jurassic to mid-Cretaceous plutonism, known to have been coeval with volcanic activity, followed by intermittent magmatism. Biotite K-Ar dates of c. 143-151 and 106-109 Ma, from cataclastic granitoids, may be marking the time of deformation. A review of all radiometric data on magmatic rocks from the region between 45°and 48°S in Chile shows a gap in Palaeocene ages that may correlate with a period of low-angle (flat slab) subduction between 65-50 Ma.

Theropod dinosaurs were the dominant predators in most Mesozoic era terrestrial ecosystems. Early theropod evolution is currently interpreted as the diversification of various carnivorous and cursorial taxa, whereas the acquisition of herbivorism, together with the secondary loss of cursorial adaptations, occurred much later among advanced coelurosaurian theropods. A new, bizarre herbivorous basal tetanuran from the Upper Jurassic of Chile challenges this conception. The new dinosaur was discovered at Aysén, a fossil locality in the Upper Jurassic Toqui Formation of southern Chile (General Carrera Lake). The site yielded abundant and exquisitely preserved three-dimensional skeletons of small archosaurs. Several articulated individuals of Chilesaurus at different ontogenetic stages have been collected, as well as less abundant basal crocodyliforms, and fragmentary remains of sauropod dinosaurs (diplodocids and titanosaurians).

International audienceRecent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera-Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (~2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause-and-effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction