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The Central Andes in Peru: ‘Old’ valleys in a ‘young’ mountain range?

TitleThe Central Andes in Peru: ‘Old’ valleys in a ‘young’ mountain range?
Publication TypeConference Paper
Year of Publication2005
AuthorsThouret, J. - C., Singer B., & Finizola A.
Conference Name6th International Symposium on Andean Geodynamics (ISAG 2005)
Conference LocationBarcelona
AbstractIgnimbrites provide excellent regional markers for the tectonic and sedimentary evolution and the history ofvalley formation on the western slope of the Central Andes (Figs. 1 & 2). Rhyolitic ignimbrite sheets of severalhundreds of km2 in area and several tens to hundreds of km3 in volume are of Miocene, Pliocene, and earlyPleistocene age in southern Peru (Thouret et al., 2001, 2003; Paquereau et al., 2003; Sébrier et al., 1988).Our twenty Ar40-Ar39 ages apparently provide (1) four Miocene ignimbrite sheets: 22-24 Ma old ‘Nazca-Puquio’and ‘Carumas’ ignimbrites, 18-19 Ma old ‘Alpabamba’ ignimbrites, and a large age range of 13 to 16 Ma, and 9Ma for ‘Huaylillas’ ignimbrites; and (2) three Plio-Quaternary ‘Sencca’ ignimbrite sheets dated at ca. 4.9, ca. 2-3, and 1.6-1.4 Ma. Opposite to the general stratigraphic scheme for southern Peru, most of the Senccaignimbrites are in fact younger than the ‘Barroso’ lavas of the late Miocene and early Pliocene composite cones.Here we use ignimbrites and pyroclastic deposits as markers for the history and evolution of the deepest valleysin Americas.