Evidence for magmatic vapor deposition of anhydrite prior to the 1991 climactic eruption of Mount Pinatubo, Philippines
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Ryan T. Jakubowski
,
John Fournelle
Abstract
Anhydrite (CaSO4) phenocrysts from Mount Pinatubo pumices show evidence of having responded dynamically to changing conditions prior to the June 15, 1991 climactic eruption. Micrometer-sized and smaller pyramidal surface growth features and lesser numbers of etch pits on anhydrite surfaces are documented by scanning electron microscopy. Chemical analyses indicate that the pyramids are a CaSO4 polymorph and electron backscatter diffraction patterns show conclusively that the pyramids are indeed orthorhombic anhydrite and not another Ca-sulfate phase. Unit-cell measurements of volcanic anhydrite are identical with evaporitic anhydrite, as determined from single-crystal X-ray diffraction patterns.
The computer program SOLVGAS was used to identify conditions under which the pyramids may have precipitated. Thermodynamic modeling of a cooling magmatic gas (H2O-CO2-SO2) at 500 bars (maximum model pressure) and NNO +1.7 was performed. Assuming that the gas contained >10-9 mol% Ca and 4 mol% SO2, the program indicates that anhydrite will precipitate homogeneously at approximately 780 °C, whereas an isothermal drop in pressure would likely lead to dissolution. Pyramids located between a phenocryst and adjacent glass provide physical evidence that at least a portion of the pyramids nucleated and grew before the melt quenched.
We propose a mechanism to account for these previously unrecognized surface growths, which is that the anhydrite pyramids precipitated from a fluid or vapor phase that had separated from the magma at depth. At least a portion of the Pinatubo anhydrite phenocrysts provided substrates for nucleation and epitaxial growth of anhydrite. Because the anhydrite pyramids resemble products of chemical vapor deposition of metals and ceramics, we propose that this previously unrecognized process be termed magmatic vapor deposition. Evidence of high-temperature, magmatic vapor deposition of anhydrite could be used as an indicator that a pre-eruptive gas phase was accumulating or stored at depth, especially at arc volcanoes where excess amounts of sulfur are vented into the atmosphere
© 2015 by Walter de Gruyter Berlin/Boston
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- Temperature-induced Al -zoning in hornblendes of the Fish Canyon magma, Colorado
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- Anomalous optical properties of fibrous tremolite, actinolite, and ferro-actinolite
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Articles in the same Issue
- Evidence for magmatic vapor deposition of anhydrite prior to the 1991 climactic eruption of Mount Pinatubo, Philippines
- Experimental and modeled solubilities of chlorine in aluminosilicate melts, consequences of magma evolution, and implications for exsolution of hydrous chloride melt at Mt. Somma-Vesuvius
- Temperature-induced Al -zoning in hornblendes of the Fish Canyon magma, Colorado
- Analytical techniques for volatiles: A case study using intermediate (andesitic) glasses
- Anomalous optical properties of fibrous tremolite, actinolite, and ferro-actinolite
- Protoanthophyllite from three metamorphosed serpentinites
- Synthesis of beryllian sapphirine in the system MgO-BeO-Al2O3-SiO2-H2O and comparison with naturally occurring beryllian sapphirine and khmaralite. Part 1: Experiments, TEM, and XRD
- Intersite distribution of Fe2+ and Mg in the spinel (sensu stricto)–hercynite series by singlecrystal X-ray diffraction
- Structural relationships in (Mn1–xZnx)Mn2O4 (0 ≤ x ≤ 0.26): The “dragging effect” of the tetrahedron on the octahedron
- The grid-work texture of authigenic microcrystalline quartz in siliceous crust-type (SCT) mineralized horizons
- The crystal structure of vicanite-(Ce), a borosilicate showing an unusual (Si3B3O18)15– polyanion
- Submicrometer optical characterization of the grain boundary of optically active Cr3+ doped polycrystalline Al2O3 by near-field spectroscopy
- High-temperature, high-pressure optical spectroscopic study of ferric-iron-bearing tourmaline
- Infrared and Mössbauer study of Brazilian tourmalines from different geological environments
- Isothermal compression of staurolite: A single-crystal study
- Equation of state measurements of chlorite, pyrophyllite, and talc
- Structure change of Ca1–xSrxTiO3 perovskite with composition and pressure
- Mechanism of 2/1- to 3/2-mullite transformation at 1650 °C
- High-pressure deformation mechanism in scolecite: A combined computationalexperimental study
- Far infrared spectra of K+ in dioctahedral and trioctahedral mixed-layer minerals
- Ab initio quantum mechanical modeling of infrared vibrational frequencies of the OH group in dioctahedral phyllosilicates. Part I: Methods, results and comparison to experimental data
- Ab initio quantum mechanical modeling of infrared vibrational frequencies of the OH group in dioctahedral phyllosilicates. Part II: Main physical factors governing the OH vibrations
- On geological interpretations of crystal size distributions: Constant vs. proportionate growth
- Allabogdanite, (Fe,Ni)2P, a new mineral from the Onello meteorite: The occurrence and crystal structure
- Cristobalite inclusions in the Tatahouine achondrite: Implications for shock conditions
- Letters. Natural occurrence of Fe2SiO4 -spinel in the shocked Umbarger L6 chondrite
- Structural refinements of magnesite at very high pressure
