Pliocene extensional tectonics in Eastern Central Patagonian Cordillera: geochronological constraints and new field evidence

LAGABRIELLE, Y., M. SUÁREZ, J. MALAVIEILLE, D. MORATA, F. ESPINOZA, R. C. MAURY, B. SCALABRINO, L. BARBERO, R. DE LA CRUZ, E.A. ROSSELLO & H. BELLON

Terra Nova

Blackwell

Lugar: Londres, Reino Unido; Año: 2007 p. 413 - 424

ABSTRACTRecent 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 with 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 old 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, compared to 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, with strong base level variations in the studied area, suggests a causal-effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. Uplift is purely tectonics in origin and occurred prior to the subduction of the Chile Ridge. Extension should be a consequence of this subduction.