Jessica F. Larsen
Michelle L. Coombs
James E. P. Utley
Andrew P. Dunn
Sarah H. De Angelis
2020
<p><span>Understanding the impact of magmatic plumbing systems on explosive volcanic activity is important for hazard management. This study describes phase equilibria experiments using a high-silica andesite (HSA; SiO</span><sub>2</sub><span> = 62.5 wt%) from the 2006 eruption of Augustine Volcano, Alaska. Experiments were conducted under H</span><sub>2</sub><span>O saturated conditions, </span><span class="mathjax-tex"><span id="MathJax-Element-5-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>f</mi><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><msub><mn>0</mn><mrow class="MJX-TeXAtom-ORD"><mn>2</mn></mrow></msub></mrow></mrow></msub></math>"><span id="MathJax-Span-53" class="math"><span><span id="MathJax-Span-54" class="mrow"><span id="MathJax-Span-55" class="msubsup"><span id="MathJax-Span-56" class="mi">f</span><span id="MathJax-Span-57" class="texatom"><span id="MathJax-Span-58" class="mrow"><span id="MathJax-Span-59" class="texatom"><span id="MathJax-Span-60" class="mrow"><span id="MathJax-Span-61" class="msubsup"><span id="MathJax-Span-62" class="mn">0</span><span id="MathJax-Span-63" class="texatom"><span id="MathJax-Span-64" class="mrow"><span id="MathJax-Span-65" class="mn">2</span></span></span></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML">f02</span></span></span><span> = RRO (Re–ReO</span><sub>2</sub><span> or ~ Ni–NiO + 2), at pressures of 50–200 MPa (</span><i>P</i><sub>Total</sub><span> = </span><i>P</i><sub>H2O</sub><span>), and at temperatures of 800–1060 </span><strong>°</strong><span>C. Run durations varied from 23 to 539 h, inversely scaled with temperature. The natural Augustine HSA phase assemblage (plagioclase, two pyroxenes, Fe–Ti oxides, magnesio-hornblende) was reproduced at 860–880 </span><strong>°</strong><span>C and 120–200 MPa. Comparing experimental and natural glass and plagioclase compositions further refined those conditions to ~ 870 °C and 120–170 MPa. Crystallization of euhedral quartz was accompanied by biotite and small amounts of cummingtonite at </span><i>T</i><span> ≤ 850 °C. The relatively high temperature appearance of these typically low-</span><i>T</i><span> phases indicates that higher </span><span class="mathjax-tex"><span id="MathJax-Element-6-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>f</mi><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><msub><mn>0</mn><mrow class="MJX-TeXAtom-ORD"><mn>2</mn></mrow></msub></mrow></mrow></msub></math>"><span id="MathJax-Span-66" class="math"><span><span id="MathJax-Span-67" class="mrow"><span id="MathJax-Span-68" class="msubsup"><span id="MathJax-Span-69" class="mi">f</span><span id="MathJax-Span-70" class="texatom"><span id="MathJax-Span-71" class="mrow"><span id="MathJax-Span-72" class="texatom"><span id="MathJax-Span-73" class="mrow"><span id="MathJax-Span-74" class="msubsup"><span id="MathJax-Span-75" class="mn">0</span><span id="MathJax-Span-76" class="texatom"><span id="MathJax-Span-77" class="mrow"><span id="MathJax-Span-78" class="mn">2</span></span></span></span></span></span></span></span></span></span></span></span><span class="MJX_Assistive_MathML">f02</span></span></span><span> could enhance their stability. The storage conditions estimated from our experiments compare well with previous magma plumbing system models for Augustine from geophysical and petrological data. The refined experimental pressure range suggests a storage depth of 4.6–6.6 km, assuming a crustal density of 2650 kg/m</span><sup>3</sup><span>. The strong petrological and geochemical similarities between the products of the 2006, 1986, and 1976 eruptions suggest that the Augustine magmatic system had generally consistent crystallization conditions for the HSA lithology during that > 30-year time interval. The experimental results broad implications for understanding higher </span><span class="mathjax-tex"><span id="MathJax-Element-7-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>f</mi><mrow class="MJX-TeXAtom-ORD"><mrow class="MJX-TeXAtom-ORD"><msub><mn>0</mn><mrow class="MJX-TeXAtom-ORD"><mn>2</mn></mrow></msub></mrow></mrow></msub></math>"><span id="MathJax-Span-79" class="math"><span><span id="MathJax-Span-80" class="mrow"><span id="MathJax-Span-81" class="msubsup"><span id="MathJax-Span-82" class="mi">f</span><sub><span id="MathJax-Span-83" class="texatom"><span id="MathJax-Span-84" class="mrow"><span id="MathJax-Span-85" class="texatom"><span id="MathJax-Span-86" class="mrow"><span id="MathJax-Span-87" class="msubsup"><span id="MathJax-Span-88" class="mn">0</span><span id="MathJax-Span-89" class="texatom"><span id="MathJax-Span-90" class="mrow"><span id="MathJax-Span-91" class="mn">2</span></span></span></span></span></span></span></span></sub></span></span></span></span></span></span><span> magmas at andesitic arc volcanoes.</span></p>
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10.1007/s00410-020-1663-6
en
Springer
Phase equilibrium of a high-SiO2, andesite at fO2 = RRO: Implications for Augustine volcano and other high-fO2 arc andesites
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