Neogene to Quaternary ash deposits in the Coastal Cordillera in northern Chile; distal ashes from supereruptions in the Central Andes

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doi: 10.1016/j.jvolgeores.2013.11.001
Author(s): Breitkreuz, Christoph; de Silva, Shanaka L.; Wilke, Hans G.; Pfänder, Jörg A.; Renno, Axel D.
Author Affiliation(s): Primary:
Technische Universität Bergakademie Freiberg, Institut für Geologie und Paläontologie, Freiberg, Germany
Oregon State University, United States
Universidad Católica del Norte, Chile
Volume Title: Journal of Volcanology and Geothermal Research
Source: Journal of Volcanology and Geothermal Research, Vol.269, p.68-82. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273 CODEN: JVGRDQ
Note: In English. 66 refs.; illus., incl. 4 tables, sketch maps
Summary: 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 40Ar/39Ar and K/Ar ages on biotite or sanidine ranging between 6.66±0.13 and 0.6±0.4 Ma. In this project, three 40Ar/39Ar ages on biotite have been determined for samples from the Cuenca del Tiburon, 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 eruptions 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 SiO2 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 dispersed 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. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; Absolute age; Acidic composition; Andes; Ar/Ar; Ash clouds; Biotite; Cenozoic; Central Andes; Chile; Cordillera de la Costa; Correlation; Cuenca del Tiburon; Dates; Electron probe data; Eruptions; Grain size; Igneous rocks; Ignimbrite; K/Ar; Leg 201; Major elements; Mica group; Mineral composition; Neogene; Ocean Drilling Program; Pyroclastic flows; Pyroclastics; Quaternary; Quebrada de la Chimba; Salar de Navidad; Sheet silicates; Silicates; South America; Supereruptions; Tertiary; Volcanic ash; Volcanic rocks
Coordinates: S240000 S230000 W0690000 W0710000
Record ID: 2014002411
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands