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.L., ONOE, A.T., CORDANI, U.G.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Año: 2008 vol. 25 p. 464 - 484

0895-9811

The Granada ignimbrite, an Upper Miocene volcanic unit from the northern Puna, previously has been interpreted as an extensive ignimbrite (>2300 km2) associated with eruptions from the Vilama caldera (trap-door event). On the basis of new data, we revise its correlation and redefine the unit as a compound, high aspect ratio ignimbrite, erupted at approximately 9.8 Ma. Calculated volumes (~100 km3) are only moderate in comparison with other large volume (>1000 km3) ignimbrites that erupted approximately 2?6 m.y. later in the region (e.g. Vilama, Panizos, Atana). Six new volcanic units are recognized from sequences previously correlated with Granada (only one 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 directions suggest the volcanic source for the Granada ignimbrite corresponds to vents buried under younger (³7.9?5 Ma) volcanic rocks of the Abra Granada volcanic complex. Episodes of caldera collapse at some stage of eruption are likely, though their nature and timing 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.