uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Experimental constraints on dacite pre-eruptive magma storage conditions beneath Uturuncu Volcano
Univ Bristol, Dept Earth Sci, Bristol BS8 1RJ, Avon, England.
Univ Bristol, Dept Earth Sci, Bristol BS8 1RJ, Avon, England.
Univ Bristol, Dept Earth Sci, Bristol BS8 1RJ, Avon, England.
Univ Bristol, Dept Earth Sci, Bristol BS8 1RJ, Avon, England.
2014 (English)In: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 55, no 4, 749-767 p.Article in journal (Refereed) Published
Abstract [en]

Cerro Uturuncu is a long-dormant, compositionally monotonous, effusive dacitic volcano in the Altiplano–Puna Volcanic Complex (APVC) of SW Bolivia. The volcano recently gained attention following the discovery of an ∼70 km diameter Interferometric Synthetic Aperture Radar (InSAR) anomaly roughly centred on its edifice. Uturuncu dacites, erupted over the past ∼1 Myr, invariably have a phase assemblage of plagioclase–orthopyroxene–biotite–ilmenite–magnetite–apatite–zircon and rhyolite glass. To better constrain storage conditions of the dacite magmas and to help understand their relationship with the observed deformation, petrological experiments were performed in cold-seal hydrothermal vessels. Volatile-saturated (PH2O = PTOTAL and PH2O + PCO2 = PTOTAL) phase equilibria experiments were run between 50 and 250 MPa and 760 and 900°C at fO2 ∼ Ni–NiO. Two synthetic starting compositions were investigated based on a typical Uturuncu dacite whole-rock and its rhyolitic groundmass glass. Pre-eruptive magma storage conditions have been estimated by comparing results from the experiments with natural phase assemblages, modes, and mineral and glass compositions. H2O-saturated experiments constrain storage pressures to 100 ± 50 MPa, equivalent to 1·9–5·7 km below surface. In the dacite, natural phase assemblages are reproduced at 870°C, 100 MPa with both orthopyroxene and biotite stabilized concurrently. Natural glass chemistries are most closely replicated at 50 MPa at 870°C, reflecting the role of decompression crystallization prior to eruption. In H2O-saturated rhyolite experiments the natural phase assemblage is most closely replicated at 870°C, 50 MPa. Isothermal, mixed volatile dacite experiments at 870°C further constrain storage pressures to 110 ± 10 MPa. Assuming that there has been no dramatic change in the eruptive behaviour of Uturuncu in the last 270 kyr, pre-eruptive storage of dacite magmas at ∼100 MPa precludes their role in producing the large diameter deformation anomaly. If deformation is a result of magmatic intrusion, then intrusion of less evolved magmas into deeper, mid-crustal storage regions is a more probable explanation. Intrusion within the Altiplano–Puna Magma Body (APMB), the extent of which is roughly coincident with the APVC, is most likely. It is proposed that dacite magmas form from andesitic parents, via fractionation and/or assimilation, within the APMB. Dacites then rise buoyantly to shallow storage levels where they stall and crystallize prior to eruption. Microlites form during subsequent ascent from the storage region to the surface.

Place, publisher, year, edition, pages
2014. Vol. 55, no 4, 749-767 p.
Keyword [en]
Andes, Central Volcanic Zone, dacite, phase-equilibrium experiments, rhyolite
National Category
Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
URN: urn:nbn:se:uu:diva-241042DOI: 10.1093/petrology/egu005ISI: 000333086000003OAI: oai:DiVA.org:uu-241042DiVA: diva2:777528
Funder
EU, European Research Council
Available from: 2015-01-08 Created: 2015-01-08 Last updated: 2017-12-05Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Muir, Duncan

Search in DiVA

By author/editor
Muir, Duncan
In the same journal
Journal of Petrology
Geology

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 335 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf