The Granada Ignimbrite: a compound pyroclastic unit and its relationship with Upper Miocene caldera volcanism in the northern Puna.

CAFFE, P.J., SOLER, M.M., COIRA, B., ONOE, A.T., & CORDANI, U.G.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Lugar: Amsterdam; Año: 2008 vol. 25 p. 464 - 484

0895-9811

The Granada ignimbrite, an Upper Miocene volcanic unit from the northern Puna, has been previously interpreted as an extensive ignimbrite (>2300 km2) associated with eruptions from the Vilama caldera (trap-door event). Based on new data, we have revised its correlation, and re-defined the unit as a compound, high aspect ratio ignimbrite, erupted at ~9.8 Ma. Calculated volumes (~100 km3) are only  moderate in comparison to other large volume (>1000 km3) ignimbrites that erupted ~2-6 Ma later in  the region (e.g. Vilama, Panizos, Atana).                                                                                                                                                  Six new volcanic units have been recognized from sequences previously correlated with Granada (of which only one was sourced from the same center). Consequently, the area ascribed to the Granada ignimbrite is substantially reduced (630 km2), and links to the Vilama caldera are not supported.  Transport polarities suggest that the volcanic source for the Granada ignimbrite corresponds to vents concealed under younger (¡Ý7.9-5 Ma) volcanic rocks of the Abra Granada volcanic complex.  Episode/s of caldera collapse at some stage of eruption are likely, although the nature and timing of these cannot be defined from available data. The eruption of the Granada ignimbrite marks the onset of a phase of large volume (caldera-sourced) volcanism in the northern Puna.