Late Oligocene?Early Miocene submarine volcanism and deep-marine sedimentation in an extensional basin of southern Chile. Implications on the tectonic development of the North Patagonian Andes.

ALFONSO ENCINAS; ANDRÉS FOLGUERA; VERÓNICA OLIVEROS; LIZET DE GIROLAMO; FRANCISCA TAPIA; RICARDO RIFFO; FRANCISCO HERVÉ; KENNETH L. FINGER; VICTOR A. VALENCIA; GUIDO GIANNI; ORLANDO ÁLVAREZ

La Serena

Congreso; XII congreso Geológico Chileno; 2015

The Andean Cordillera shows evidence of alternatingphases of compressional and extensional deformation.Volcano-sedimentary marine strata in the Aysén region ofsouthern Chile were investigated to better understand thecauses of extensional tectonics and crustal thinning thatoccurred in the Andean orogeny as these depositsconstitute the only reliable record of submarine suprasubductionvolcanism during the Cenozoic in southernSouth America. In order to discern the age and tectonosedimentarysetting of these strata, referred to as theTraiguén Formation, we integrate sedimentology, ichnology,petrography, geochemistry, structural geology, foraminiferalmicropaleontology, and U-Pb geochronology. Our resultsindicate that the Traiguén Formation was deposited in adeep-marine extensional basin during the Late Oligocene?earliest Miocene. The geochemistry and petrography of thepillow basalts suggest that they formed in a convergentmargin on a thinned crust rather than at an oceanicspreading center. We attribute the origin of the Traiguénbasin to a transient period of slab rollback and vigorousasthenospheric wedge circulation that was caused by anincrease in trench-normal convergence rate at ca. 26?28 Maand which resulted in a regional event of extension andwidespread volcanism.