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The origin and significance of crystal rich inclusions in pumices from two Chilean ignimbrites

Published online by Cambridge University Press:  01 May 2009

S. L. de Silva
S. L. de Silva
Affiliation:
Department of Earth Sciences, Open University, Milton Keynes, Bucks. MK7 6AA, U.K.*
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Abstract

Crystal rich (∼ 70–98% phenocrysts) magmatic inclusions in pumices for compositionally heterogeneous ignimbrites from the Central Andes of northern Chile are interpreted as the products of crystal accretion at the sidewalls of the magma chambers. The inclusions are typically andesitic in composition and are found as ‘peppery textured’ lenses and bands, or as discrete ovoid ‘blobs’ within dacitic pumices from the early erupted portions of the ignimbrites. The inclusions have a bimodal gain size with large phenocrysts (> 1 mm), typical of those of the host pumice, set in a dominant finegrained framework (< 0.5 mm) of plagioclase, with lesser amounts of hornblende and biotite in equal proportions, and ubiquitous titanomagnetite in a matrix of vesiculated high-Si rhyolite glass. An igneous microgranular texture is defined by this framework. The mineralogy of the inclusions, as well as the compositions of the phenocrysts and glass, are very similar to those of the host pumices. These characteristics, in addition to available major, trace and REE data, are best reconciled if the inclusions represented samples of fractionated crystals and glass from the same magma as the host pumice. The restricted occurrence of these inclusions in the early erupted portions of the ignimbrites suggests that these crystal accumulations occurred in the upper portions of the magma chambers, at the sidewall; the dominantly fine grain size and crystal rich nature of the inclusions are considered to be the result of the higher thermal gradient in the boundary layer.

These inclusions may be an important link between the experimental and geochemical models for the origin of compositional layering in magma chambers by sidewall crystallization. The presence of similar inclusions in other ignimbrites and volcanics, as well as plutonics, suggest that they may be a common feature of silicic magmas.

Type
Articles
Information
Geological Magazine , Volume 126 , Issue 2 , March 1989 , pp. 159 - 175
Copyright
Copyright © Cambridge University Press 1989

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References

Bacon, C. R. 1983. Eruptive history of Mt. Mazama and Crater Lake caldera, Cascade Range, U.S.A. Journal of volcanology and Geothermal Research 181, 57–115.CrossRefGoogle Scholar
Bacon, C. R. 1986. Magmatic inclusions in silicic and intermediate volcanic rocks. Journal of Geophysical Research 91B, 6091–112.CrossRefGoogle Scholar
Bacon, C. R. & Druitt, T. H. 1988. Compositional evolution of the zoned calcalkaline magma chamber of Mount Mazama, Crater Lake, Oregon. Contributions to Mineralogy and Petrology 98, 224–56.CrossRefGoogle Scholar
Bacon, C. R. & Metz, J. 1984. Magmatic inclusions in rhyolites, contaminated basalts and compositional zonation beneath the Coso volcanic field, California. Contributions to Mineralogy and Petrology 85, 346–65.CrossRefGoogle Scholar
Blake, S. 1981. Eruptions from zoned magma chambers. Journal of the Geological Society of London. 138, 281–7.CrossRefGoogle Scholar
Blake, S. & Ivey, G. N. 1986. Magma mixing and the dynamics of withdrawal from stratified reservoirs. Journal of Volcanology and Geothermal Research 27, 153–78.CrossRefGoogle Scholar
Brandeis, G. & Jaupart, C. 1986. On the interaction between convection and crystallization in cooling magma chambers. Earth & Planetary Science Letter 77, 345–61.CrossRefGoogle Scholar
Chen, C. F. & Turner, J. S. 1980. Crystallization in a double-diffusive system. Journal of Geophysical Research 85, 2573–93.CrossRefGoogle Scholar
de Silva, S. L. 1987. Microgranular enclaves in pumices – the products of crystal accretion at the sidewalls of silicic magma chambers (abstract) EOS 68(44), 1512–3.Google Scholar
Didier, J. 1973. Granites and their enclaves. Amsterdam: Elsevier, pp. 393.Google Scholar
Eichelberger, J. C. 1975. Origin of andesite and dacite: evidence of mixing at Glass Mountain and other circum-Pacific volcanoes. Geological Society of America Bulletin 86, 1381–91.2.0.CO;2>CrossRefGoogle Scholar
Francis, P. W., McDonough, W. F., Hammill, M., O'Callaghan, L. J, & Thorpe, R. S., 1984. The Cerro Purico volcanic complex, North Chile. In Andean Magmatism – Chemical & Isotopic constraints (eds Harmon, R. S., Barriero, B. A.) pp. 107–124.Orpington U.K.: Shiva publishing.Google Scholar
Grove, T. L. & Donnelly-Nolan, J. M. 1986. The evolution of young silicic lavas at Medicine Lake Volcano California: implications for the origin of compositional gaps in calc-alkaline series lavas. Contributions to Mineralogy Petrology 92, 281–302.CrossRefGoogle Scholar
Guest, J. E. 1968. Banded Pumice in a Chilean ignimbrite. Geological Magazine 105, 177–84.CrossRefGoogle Scholar
Guest, J. E. 1969. Upper Tertiary ignimbrites in the Andean Cordillera of part of the Antofagasta province of northern Chile. Bulletin of the Geological Society of America 80, 337–62.CrossRefGoogle Scholar
Hawkesworth, C. J., Hammill, M., Gledhill, A. R., Van Calsteren, P. & Rogers, G. 1982. Isotope and trace element evidence for late stage intra-crustal melting in the high Andes. Earth and Planetary Science Letters 58, 240–54.CrossRefGoogle Scholar
Hildreth, E. W. 1979. The Bishop Tuff: Evidence for the origin of compositional zonation in silicic magma chambers. In Ash flow tuffs (eds Chapin, C. E., Elston, W. E.). Geological Society of America Special Paper 180, 43–76.CrossRefGoogle Scholar
Katsui, Y. 1963. Evolution and magmatic history of some Krakatoan calderas in Hokkaido, Japan. Journal of the Faculty of Science Hokkaido University Series IV, 11, 1–58.Google Scholar
Lewis, J. F. 1973. Petrology of the ejected plutonic blocks of Soufriere Volcano, St Vincent, West Indies. Journal of Petrology 14, 81–112.CrossRefGoogle Scholar
Lipman, P. W. 1965. Chemical comparison of glassy and crystalline volcanic rocks. Geological Society of America Special Paper 82, 260–1.Google Scholar
Lipman, P. W. 1967. Mineral and chemical variations within an ash flow sheet from Aso Caldera, southwestern Japan. contributions to Mineralogy and Petrology 16, 300–27.CrossRefGoogle Scholar
Lofgren, G. 1972. Temperature induced zoning in synthetic plagioclase feldspars. In Dynamic crystallization and devitrification studies 1970–1978 (ed. Lofgren, G., 1979) pp. 35–50. Houston, Texas: NASA JSC.Google Scholar
McBirney, A. R. 1980. Mixing & unmixing of magmas. Journal of Volcanology and Geothermal Research 7, 357–71.CrossRefGoogle Scholar
McBirney, A. R. & Noyes, R. M. 1979. Crystallization and layering of the Skaergaard Intrusion. Journal of Petrology 20, 487–554.CrossRefGoogle Scholar
McBirney, A. R., Baker, B. H. & Nilson, R. H. 1985. Liquid fractionation: Part 1: Basic principles and experimental simulations. Journal of Volcanology and Geothermal Research 58, 51–64.Google Scholar
Michael, P. J. 1983. Chemical differentiation of the Bishop Tuff and other high-silica magmas through crystallization processes. Geology 11, 31–4.2.0.CO;2>CrossRefGoogle Scholar
Miller, C. F. & Mittlefehldt, D. W. 1984. Extreme fractionation in felsic magma chambers: a product of liquid state differentiation or fractional crystallization? Earth and Planetary Science Letters 68, 151–8.CrossRefGoogle Scholar
Nagasawa, H. & Schnetzler, C. C. 1971. Partitioning of rare earth, alkali, and alkaline earth elements between phenocrysts and acidic igneous magma. Geochimica et Cosmochimica Acta 35, 953–68.CrossRefGoogle Scholar
Nicholls, I. A. 1971. Petrology of the Santorini volcano, Cyclades, Greece. Journal of Petrology 12, 67–119.CrossRefGoogle Scholar
Ritchey, J. L. 1980. Divergent magmas at Crater Lake, Oregon: Products of fractional crystallization and vertical zoning in a shallow water-undersaturated chamber. Journal of Volcanology and Geothermal Research 7, 373–86.CrossRefGoogle Scholar
Shaw, H R. 1965. Comments on viscosity, crystal settling and convection in granitic magmas. American Journal of science 263, 120–52.CrossRefGoogle Scholar
Sparks, R. S. J., Huppert, H. E. & Turner, J. S. 1984. The fluid dynamics of evolving magma chambers. Philosophical Transactions of the Royal Society of London A310, 511–34.Google Scholar
Spera, F. Y., Yuen, D. A. & Kirschvink, S. J. 1982. Thermal boundary layer convection in silicic magma chambers: effects of temperature dependant rheology and implications for thermogravitational chemical fractionation. Journal of Geophysical Research 87, 8755–67.CrossRefGoogle Scholar
Tait, S. R. 1987. Convective fractionation as a mechanism of magma chamber zonation: Evidence from cumulate nodules (abstract). Terra Cognita 7, G11.24 357–8.Google Scholar
Thompson, M. E. & McBirney, A. R. 1985. Redistribution of phenocrysts by convective flow in viscous boundary layer. Journal of Volcanology and Geothermal Research 24, 83–94.CrossRefGoogle Scholar
Wager, L. R. 1962. Igneous cumulates from the 1902 eruption of Soufriere, St. Vincent. Bulletin Volcanologique 24, 93–4.CrossRefGoogle Scholar
Walker, G. P. L. & Skelhorn, R. R. 1966. Some associations of acid and basic igneous rocks. Earth Science Reviews 2, 93–109.CrossRefGoogle Scholar
Wolff, J. A. & Storey, M. 1984. Zoning in highly alkaline magma bodies. Geological Magazine 121, 563–75.CrossRefGoogle Scholar
Worner, G. & Schmincke, H-U. 1984. Mineralogical and chemical zonation of Laacher See Tephra (East Eifel, W. Germany). Journal of Petrology 25, 805–35.CrossRefGoogle Scholar