A Middle Miocene (13.5–12 Ma) deformational event constrained by volcanism along the Puna-Eastern Cordillera border, NW Argentina

Abstract

The features of Middle Miocene deposits in the Puna-Eastern Cordillera transition (Valles Calchaquíes) indicate that Cenozoic deformation, sedimentation and volcanism follow a complex spatiotemporal relationship. The intense volcanic activity recorded in the eastern Puna border between 14 and 11.5Ma coincides with the occurrence of one of the most important deformation events of the Neogene tectonic evolution in the region.Studies performed across the Puna-Eastern Cordillera transition show different relationships between volcanic deposits of ca. 13.5–12.1Ma and the Oligocene-Miocene Angastaco Formation. In this paper we describe the ash-flow tuff deposits which are the first of this type found concordant in the sedimentary fill of Valles Calchaquíes. Several analyses performed on these pyroclastic deposits allow a correlation to be made with the Alto de Las Lagunas Ignimbrite (ca. 13.5Ma) of the Pucarilla-Cerro Tipillas Volcanic Complex located in the Puna. Outcrops of the ca. 13.5Ma pyroclastic deposits are recognised within the Puna and the Valle Calchaquí. However, in the southern prolongation of the Valle de Hualfín (Tiopampa-Pucarilla depression) that separates the Puna from the Valle Calchaquí at these latitudes, these deposits are partially eroded and buried, and thus their occurrence is recorded only by abundant volcanic clasts included in conglomerates of the Angastaco Formation. The sedimentation of the Angastaco Formation was aborted at ca. 12Ma in the Tiopampa-Pucarilla depression by the Pucarilla Ignimbrite, which unconformably covers the synorogenic units. On the contrary, in the Valle Calchaquí the sedimentation of the Angastaco Formation continued until the Late Miocene.The different relationships between the Miocene Angastaco Formation and the ignimbrites with ages of ca. 13.5 and ca. 12Ma reveal that in this short period (~1.5m.y.) a significant deformation event took place and resulted in marked palaeogeographic changes, as evidenced by stratigraphic-sedimentological and chronological records in the Angastaco Formation.