Bulletin of Volcanology

, 71:419

Compositional variations and magma mixing in the 1991 eruptions of Hudson volcano, Chile

  • David J Kratzmann
  • Steven Carey
  • Roberto Scasso
  • Jose-Antonio Naranjo
Research Article

DOI: 10.1007/s00445-008-0234-x

Cite this article as:
Kratzmann, D.J., Carey, S., Scasso, R. et al. Bull Volcanol (2009) 71: 419. doi:10.1007/s00445-008-0234-x

Abstract

The August 1991 eruptions of Hudson volcano produced ~2.7 km3 (dense rock equivalent, DRE) of basaltic to trachyandesitic pyroclastic deposits, making it one of the largest historical eruptions in South America. Phase 1 of the eruption (P1, April 8) involved both lava flows and a phreatomagmatic eruption from a fissure located in the NW corner of the caldera. The paroxysmal phase (P2) began several days later (April 12) with a Plinian-style eruption from a different vent 4 km to the south-southeast. Tephra from the 1991 eruption ranges in composition from basalt (phase 1) to trachyandesite (phase 2), with a distinct gap between the two erupted phases from 54–60 wt% SiO2. A trend of decreasing SiO2 is evident from the earliest part of the phase 2 eruption (unit A, 63–65 wt% SiO2) to the end (unit D, 60–63 wt% SiO2). Melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases. The basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes. A combination of observed phase assemblages, inferred water content, crystallinity, and geothermometry estimates suggest pre-eruptive storage of the phase 2 trachyandesite at pressures between ~50–100 megapascal (MPa) at 972 ± 26°C under water-saturated conditions (log fO2 –10.33 (±0.2)). It is proposed that rising P1 basaltic magma intersected the lower part of the P2 magma storage region between 2 and 3 km depth. Subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber. Basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the Hudson caldera. The presence of tachylite in the P1 products suggests that some of the magma was stalled close to the surface (<0.5 km) prior to eruption. Seismicity related to magma movement and the P1 eruption, combined with chamber overpressure associated with basalt injection, may have created a pathway to the surface for the trachyandesite magma and subsequent P2 eruption at a different vent 4 km to the south-southeast.

Keywords

Hudson volcano Magma mixing Calc-alkaline magmas Andean volcanism Explosive eruptions 

Supplementary material

445_2008_234_MOESM1_ESM.xls (28 kb)
Table S1Sample locations, date sampled, coordinates, eruption sampled (if applicable), and sample collection numbers. (XLS 28.0 KB)
445_2008_234_MOESM2_ESM.xls (21 kb)
Table S2Major element compositions of andesites used in experimental work and bulk rock analyses of 1991 Hudson trachyandesite. Data normalized to 100% and pre-recalculation LOI given where applicable. (XLS 21.0 KB)

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • David J Kratzmann
    • 1
    • 4
  • Steven Carey
    • 1
    • 4
  • Roberto Scasso
    • 2
  • Jose-Antonio Naranjo
    • 3
  1. 1.GSO/Univ. of Rhode IslandNarragansettUSA
  2. 2.Dpto. de Cs. Geologicas, FCENUniv. de Buenos Aires Cuidad Univ.Buenos AiresArgentina
  3. 3.Serv. Nacional Geol. y MineriaCasillaChile
  4. 4.Graduate School of OceanographyNarragansettUSA

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