Neogene to Quaternary ash deposits in the Coastal Cordillera in northern Chile: Distal ashes from supereruptions in the Central Andes Christoph Breitkreuz a, ⁎, Shanaka L. de Silva b , Hans G. Wilke c , Jörg A. Pfänder a , Axel D. Renno d a Institut für Geologie und Paläontologie, Bernhard-von-Cotta-Str. 2, TU Bergakademie Freiberg, 09599 Freiberg, Germany b College of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Administration Building, Oregon State University, Corvallis, OR 97331-5503, USA c Departamento de Ciencias Geológicas, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile d Institut für Mineralogie, Brennhausgasse 4, TU Bergakademie Freiberg, 09599 Freiberg, Germany abstract article info Article history: Received 15 July 2013 Accepted 3 November 2013 Available online 15 November 2013 Keywords: Supereruptions Central Andes Co-ignimbrite ash clouds Correlation 40 Ar/ 39 Ar ages Biotite composition Granulometry Silicic volcanic ash deposits investigated at 14 localities between 22° and 25°S in the Chilean Coastal Cordillera are found to be the distal ash fall from supereruptions in the Central Andean cordillera several hundreds of kilometers to the east. Depositional textures, modal composition and granulometry of the ashes and tuffs (the latter lithified by halite and gypsum under ultra-arid conditions) allow for a distinction between primary fallout/aeolian deposits (mean 4–5 Φ, sorting 1.5–2 Φ) and secondary deposits that formed by down wash from hill slopes during local rain fall. Primary volcanic components comprise two types of glass shards (with small stretched vesicles and coarse-walled with rounded to elliptic vesicles), and biotite. Previously published studies on ash deposits in the north Chilean Coastal Cordillera reported 14 40 Ar/ 39 Ar and K/Ar ages on biotite or sanidine ranging between 6.66 ± 0.13 and 0.6 ± 0.4 Ma. In this project, three 40 Ar/ 39 Ar ages on biotite have been determined for samples from the Cuenca del Tiburón, the northern margin of Salar de Navidad and from the Quebrada de la Chimba (3.9 ± 0.1 Ma, 4.1 ± 0.1 Ma, 6.0 ± 0.1 Ma, respectively). The range of the 17 ages coincides with the Late Miocene to Quaternary ages of the major ignimbrite-forming erup- tions of the high Andes to the east such as the Altiplano Puna Volcanic Complex (APVC). Electron microprobe data of glass and biotite of the Coastal Cordillera ashes have been compared with data from major ignimbrites of the APVC, of other major Central Andean volcanic fields, and of marine ashes (ODP Leg 201). Additional new biotite microprobe data from three APVC ignimbrites (Pastos Grandes, Pujsa and Guacha) have been included in the present study. Biotite composition of the investigated Coastal Cordillera ashes is similar to those of ignimbrites from the APVC. In particular, based in Fe, Mg, Mn and Ti, distal equivalents of the 3.96 ± 0.08 Ma Atana and/or 4.09 ± 0.02 Ma Puripicar and of the 5.6 ± 0.2 Ma Pujsa and/or the 5.56 ± 0.01 Ma Guacha eruptions can be identified. In addition, based only on age relations, distal ash units of the Pastos Grandes, Tatio and Purico eruptions may be present in the Coastal Cordillera. Composition of glass is comparable to APVC ignimbrite matrix glass and to marine glass, however, significant alkali depletion and SiO 2 enrichment is attributed to in situ alteration. The identification of these ashes demonstrates for the first time that the supereruptions in the southern Central Andes gave rise to voluminous ash clouds, most likely co-ignimbrite. The present outcrops represent ash dis- persed by easterly winds, consistent with atmospheric models that show favorable westward-directed winds existing in the upper troposphere/stratosphere during the southern summer in the southern Central Andes. This requires that current volume estimates for the major eruptions to be considered minima with a significant augmentation likely. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The Neogene evolution of the Central Andes was dominated by an ignimbrite flare-up that is expressed as the Neogene Ignimbrite Province of the Central Andes (de Silva et al., 2006). The Late Miocene to late Quaternary volcanic stratigraphy is dominated by regionally ex- tensive ignimbrites (ash-flow tuffs), the products of supereruptions, that cover several thousand square kilometers and represent erupted magma volumes of several hundreds to two thousand km 3 each (Sparks et al., 1985; de Silva, 1989a; de Silva and Francis, 1989; Ort, 1993; Lindsay et al., 2001a; Soler et al., 2007; Folkes et al., 2011; Salisbury et al., 2011; Ort et al., 2013). This platform of ignimbrite forms the base upon which the volcanoes of the modern volcanic arc are built. The ignimbrites were deposited by ground-hugging pyroclastic density currents (pyroclastic flows). Commonly, ignimbrites are as- sociated with distal accumulations of crystal-depleted ash that orig- inate from the eruption column or from ash clouds associated with Journal of Volcanology and Geothermal Research 269 (2014) 68–82 ⁎ Corresponding author. Tel.: +49 3731 39 3126; fax: +49 3731 39 3599. E-mail address: cbreit@geo.tu-freiberg.de (C. Breitkreuz). 0377-0273/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jvolgeores.2013.11.001 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores