Abstract
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.
Original language | English |
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Pages (from-to) | 716-733 |
Number of pages | 18 |
Journal | Journal of the Geological Society |
Volume | 173 |
Issue number | 5 |
Early online date | 19 Apr 2016 |
DOIs | |
Publication status | Published - Sept 2016 |
Bibliographical note
Accepted Date 10/02/2016E-pub date 19/04/2016