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Early Miocene large-volume ignimbrites of the Oxaya Formation, Central Andes

Research output: Contribution to journalArticle (Academic Journal)

Original languageEnglish
Pages (from-to)716-733
Number of pages18
JournalJournal of the Geological Society
Issue number5
Early online date19 Apr 2016
DateAccepted/In press - 10 Feb 2016
DateE-pub ahead of print - 19 Apr 2016
DatePublished (current) - Sep 2016


During the early Miocene ignimbrite flare-up, significant parts of the Central Andes (17–20°S) were covered by large-volume ignimbrites. High-precision 206Pb/238U zircon dates constrain the flare-up in northern Chile at c. 18°S to a 3 myr period, starting with the deposition of the Poconchile ignimbrite at 22.736 ± 0.021 Ma. Of four main pulses, the two largest occurred at 21.924 ± 0.017 and 19.711 ± 0.036 Ma, when the >1000 km3 in volume Cardones and Oxaya ignimbrites erupted, respectively. The ignimbrites are high-SiO2 rhyolites and show significant heterogeneities in crystal content, mineral proportions and trace-element compositions. The zoned Oxaya ignimbrite implies incremental extraction of a crystal-poor magma overlying a crystal-rich magma. In contrast, petrological and textural heterogeneities in pumice clasts are spread throughout the Cardones ignimbrite and we propose magma mixing caused by destabilization of multiple magma bodies within a magmatic mush system. Distal and medial deposits of the Cardones ignimbrite, with a maximum welded thickness of at least 1000 m, entirely covered the western flank of the Central Andes, which implies infill of a significant topographic relief. Both compaction and welding resulted in a maximum thickness reduction of around 30% for the Cardones ignimbrite.

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Accepted Date 10/02/2016 E-pub date 19/04/2016

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