Late Oligocene early Miocene submarine volcanism and deep-marine sedimentation in an extensional basin of southern Chile: Implications for the tectonic development of the North Patagonian Andes

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

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2016 vol. 128 p. 807 - 823

0016-7606

The Chilean margin has been used as themodel of an ocean-continent convergent systemdominated by compression and activemountain building as a consequence of thestrong mechanical coupling between the upperand the lower plates. The Andean Cordillera,however, shows evidence of alternatingphases of compressional and extensionaldeformation. Volcano-sedimentary marinestrata in the Aysén region of southern Chilecontribute to an understanding of the causesof extensional tectonics and crustal thinningthat occurred in the Andean orogeny becausethese deposits constitute the only reliablerecord of submarine suprasubductionvolcanism during the Cenozoic in southernSouth America. In order to discern the ageand tectono-sedimentary setting of thesestrata, referred to as the Traiguén Formation,we integrated sedimentology, ichnology,petrography, geochemistry, structuralgeology, foraminiferal micropaleontology,and U-Pb geochronology. Our results indicatethat the Traiguén Formation was depositedin a deep-marine extensional basinduring the late Oligocene?earliest Miocene.The geochemistry and petrography of thepillow basalts suggest that they formed in aconvergent margin on a thinned crust ratherthan at an oceanic spreading center. We attributethe origin of the Traiguén Basin to atransient period of slab rollback and vigorousasthenospheric wedge circulation thatwas caused by an increase in trench-normalconvergence rate at ca. 26?28 Ma and thatresulted in a regional event of extension andwidespread volcanism.