Active Spreading Ridge Subduction beneath Patagonia: What really happened since 30 Ma?

SCALABRINO B., Y. LAGABRIELLE, J. MALAVIEILLE, R.C. MAURY, M. POLVÉ, F. ESPINOZA, CH. GUIVEL, S. DOMÍNGUEZ, H. BELLON, M. SUÁREZ, D. MORATA Y E.A. ROSSELLO

Montpellier, Francia

Conferencia; Subduction Zone Geodynamics Conference; 2007

Subduction Zone Geodynamics Conference

The Chile-Argentina Patagonian Cordillera is an unique natural laboratory allowing to study the interactions between oceanic and continental lithospheres during the subduction of an active spreading ridge beneath a continent. Subduction of the South Chile spreading Ridge (SCR), which separates the Nazca plate from the Antarctic plate, started around 15-14 Ma at the southern tip of Patagonia. Presently, the SCR enters the Peru-Chile trench at 46°S,at the site of the Chile Triple Junction (CTJ). We discuss the main events which occurred onland and offshore in the CTJ region, in relation with the processes of ridge subduction. Tectonic, sedimentary, and magmatic features are summarized in a 30 Ma-to Present chronological table. The pre-ridge subduction stage, from 30 to 15 Ma, is characterized by the birth and the growing up of the Patagonian relieve and by the shift from marine to continental detrital sedimentation in the foreland. The change from pre-ridge subduction to ridge subduction configuration is marked on land by a transition from calc-alkaline to alkaline volcanism and by the onset of emplacement of very large basaltic plateaus (period 15-12 Ma) following rapid erosion of the frontal belt. Post-plateau basaltic volcanism (< 4 Ma) corresponds to a period of tectonic and morphological rejuvenation during which the frontal part of the Cordillera has been affected by transtensional tectonics. These events are replaced in the framework of a tectonomagmatic model involving opening of slab windows due to both slab tear and ridge axis subduction.