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Zonation, mixing and eruption of silica-undersaturated alkaline magma: a case study from Tenerife, Canary Islands

Published online by Cambridge University Press:  01 May 2009

John A. Wolff
John A. Wolff
Affiliation:
Department of Geology, Imperial College, Prince Consort Road, London SW7 2BP, U.K.
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Abstract

The mineralogy and petrology of banded pumice clasts from a mixed-magma non-welded ignimbrite on Tenerife, Canary Islands, is described. Phenocrysts, which frequently show signs of resorption, are grouped into three assemblages in mutual disequilibrium; these assemblages were originally precipitated by alkali basalt magma (assemblage 1, titanaugite + olivine + calcic plagioclase + high-Mg Fe–Ti oxides), trachyandesitic magma (assemblage 2, salite + kaersutite + sodic plagioclase + hauyne + medium-Mg Fe–Ti oxides) and phonolitic magma (assemblage 3, aegirine-augite + biotite + sodic sanidine + sodalite + nepheline + sphene + low-Mg magnetite) respectively. Phenocryst types (e.g. clinopyroxene, feldspar) which are common to two or all assemblages are compositionally distinctive in each. The excess silica content of nepheline in assemblage 3 indicates a temperature of 770 °C for phonolitic magma, while Fe–Ti oxides and clinopyroxene-ilmenite give temperatures of 915 °C and 907 °C respectively for the trachyandesite. Assemblage 1 and 2 phenocrysts are set in mafic glass; assemblage 3 phenocrysts are only found in a matrix of salic (phonolitic) glass. Analyses of the volumetrically dominant phonolitic glass define a compositional trend consistent with fractionation of assemblage 3 phenocrysts. Analyses of the mafic glass scatter about a straight-line trend produced by mixing of phonolitic liquid with homogeneous intermediate (trachyandesitic) magma. These relations are interpreted as the result of two distinct magma mixing events, consequent on the invasion of a stably zoned magma chamber containing phonolitic liquid stratified above denser trachyandesitic magma, by intruding basaltic magma. High Ca content of assemblage 1 plagioclase suggests precipitation of the basaltic phenocrysts under locally high partial pressure of water. The preferred model involves, in chronological sequence: (i) generation of a differentiated phonolitic cap above trachyandesitic magma, through wall crystallization and boundary-layer uprise of phonolite; (ii) pooling, convective heat loss, and partial crystallization of dense, hydrous alkali basalt magma injected into the chamber and forming a liquid layer beneath the trachyandesitic magma; (iii) volatile saturation of the residual basalt liquid through crystallization, consequent buoyant uprise into, and efficient mixing with, trachyandesite; (iv) eruption of chamber contents and partial mixing of the mixed basalt–trachyandesite with phonolite, although the precise relative timing of eruption and the second mixing event is not known.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 6 , November 1985 , pp. 623 - 640
Copyright
Copyright © Cambridge University Press 1985

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References

Anderson, A. T. 1976. Magma mixing: petrological process and volcanological tool. Journal of Volcanology and Geothermal Research 1, 3–33.Google Scholar
Bishop, F. R. 1980. The distribution of Fe2+ and Mg between coexisting ilmenite and pyroxene with applications to geothermometry. American Journal of Science 280, 46–77.CrossRefGoogle Scholar
Blake, S. 1981. Eruptions from zoned magma chambers. Journal of the Geological Society of London 138, 281–7.Google Scholar
Blake, S. & Ivey, G. N. 1984. Magma mixing and the dynamics of withdrawal from stratified reservoirs. In Proceedings of ISEM Field Conference on Open Magmatic Systems (ed. Dungan, M. A., Grove, T. L. and Hildreth, W.), pp. 13–15. Institute for the Study of Earth and Man, Southern Methodist University, Dallas.Google Scholar
Booth, B. 1973. The Granadilla Pumice Deposit of southern Tenerife, Canary Islands. Proceedings of the Geologists' Association 84, 353–70.CrossRefGoogle Scholar
Borley, G. D. 1974. Aspects of the volcanic history and petrology of the island of Tenerife. Proceedings of the Geologists' Association 85, 259–79.CrossRefGoogle Scholar
Bottinga, Y. & Weill, D. F. 1970. Densities of liquid silicate systems calculated from partial molar volumes of oxide components. American Journal of Science 269, 169–82.CrossRefGoogle Scholar
Brooks, C. K. & Printzlau, I. 1978. Magma mixing in mafic alkaline volcanic rocks: the evidence from relict phenocryst phases and other inclusions. Journal of Volcanology and Geothermal Research 4, 315–31.Google Scholar
Burnham, C. W. 1975. Water and magmas: a mixing model. Geochimica et Cosmochimica Acta 39, 1077–84.CrossRefGoogle Scholar
Carmichael, I. S. E. 1967. The iron–titanium oxides of salic volcanic rocks and their associated ferromagnesian silicates. Contributions to Mineralogy and Petrology 14, 36–64.Google Scholar
Carmichael, I. S. E., Nicholls, J. & Smith, A. L. 1970. Silica activity in igneous rocks. American Mineralogist 55, 246–63.Google Scholar
Carmichael, I. S. E., Turner, F. J. & Verhoogen, J. 1974. Igneous Petrology. McGraw-Hill. 739 pp.Google Scholar
Dungan, M. A. & Rhodes, J. M. 1978. Residual glass and melt inclusions in basalts from DSDP Legs 45 and 46: evidence for magma mixing. Contributions to Mineralogy and Petrology 67, 417–31.CrossRefGoogle Scholar
Hamilton, D. L. 1961. Nephelines as crystallisation temperature indicators. Journal of Geology 69, 321–9.Google Scholar
Hibbard, M. J. 1981. The magma mixing origin of mantled feldspars. Contributions to Mineralogy and Petrology 76, 158–70.CrossRefGoogle Scholar
Huppert, H. E. & Sparks, R. S. J. 1980. The fluid dynamics of a basaltic magma chamber replenished by influx of hot, dense ultrabasic magma. Contributions to Mineralogy and Petrology 75, 279–89.CrossRefGoogle Scholar
Huppert, H. E., Sparks, R. S. J. & Turner, J. S. 1982. Effects of volatiles on mixing in calc-alkaline magma systems. Nature 297, 554–7.CrossRefGoogle Scholar
Huppert, H. E., Sparks, R. S. J. & Turner, J. S. 1984. Some effects of viscosity on the dynamics of replenished magma chambers. Journal of Geophysical Research 89, 6857–77.CrossRefGoogle Scholar
Kuo, L. C. & Kirkpatrick, R. J. 1982. Pre-eruption history of phyric basalts from DSDP Legs 45 and 46: evidence from morphology and zoning patterns in plagioclase. Contributions to Mineralogy and Petrology 79, 13–27.CrossRefGoogle Scholar
Luhr, J. F., Carmichael, I. S. E. & Varekamp, J. C. 1984. The 1982 eruptions of El Chichon volcano, Chiapas, Mexico: mineralogy and petrology of the anhydrite-bearing pumices. Journal of Volcanology and Geothermal Research 23, 69–108.CrossRefGoogle Scholar
Nelson, S. A. & Carmichael, I. S. E. 1980. Partial molar volumes of oxide components in silicate liquids. Contributions to Mineralogy and Petrology 71, 117–24.CrossRefGoogle Scholar
Ridley, W. I. 1970. The petrology of the Las Cañadas volcanoes, Tenerife, Canary Islands. Contributions to Mineralogy and Petrology 26, 124–60.CrossRefGoogle Scholar
Roeder, P. L., Campbell, I. H. & Jamieson, H. E. 1979. A re-evaluation of the olivine–spinel geothermometer. Contributions to Mineralogy and Petrology 68, 325–34.CrossRefGoogle Scholar
Roeder, P. L. & Emslie, R. F. 1970. Olivine–liquid equilibrium. Contributions to Mineralogy and Petrology 29, 275–89.Google Scholar
Scott, P. W. 1976. Crystallisation trends of pyroxenes from the alkaline volcanic rocks of Tenerife, Canary Islands. Mineralogical Magazine 40, 805–16.CrossRefGoogle Scholar
Scott, R. B. 1971. Alkali exchange during devitrification and hydration of glasses in ignimbrite cooling units. Journal of Geology 79, 100–10.CrossRefGoogle Scholar
Sigurdsson, H. & Sparks, R. S. J. 1981. Petrology of rhyolitic and mixed-magma ejecta from the 1875 eruption of Askja, Iceland. Journal of Petrology 22, 41–84.CrossRefGoogle Scholar
Sparks, R. S. J., Sigurdsson, H. & Wilson, L. 1977. Magma mixing: a mechanism for triggering acid explosive eruptions. Nature 267, 315–18.CrossRefGoogle Scholar
Sparks, R. S. J. & Walker, G. P. L. 1977. The significance of vitric-enriched air-fall ashes associated with crystal-enriched ignimbrites. Journal of Volcanology and Geothermal Research 2, 329–41.CrossRefGoogle Scholar
Storey, M. 1981. Trachytic pyroclastics from Agua de Pau volcano, São Miguel, Azores: evolution of a magma body over 4,000 years. Contributions to Mineralogy and Petrology 78, 423–32.CrossRefGoogle Scholar
Thompson, R. N. & Humphris, S. E. 1980. Silicate mineralogy of basalts from the East Pacific Rise, OCP Ridge, and Siqueiros fracture zone: Deep Sea Drilling Project Leg 54. Initial Reports of the Deep Sea Drilling Project Leg 54, 651–69.Google Scholar
Walker, G. P. L. 1972. Crystal concentration in ignimbrites. Contributions to Mineralogy and Petrology 36, 135–46.CrossRefGoogle Scholar
Walker, G. P. L. Ignimbrite types and ignimbrite problems. Journal of Volcanology and Geothermal Research 17, 65–88.CrossRefGoogle Scholar
Walker, G. P. L., Heming, R. F. & Wilson, C. J. N. 1980. Low-aspect ratio ignimbrites. Nature 283, 286–7.CrossRefGoogle Scholar
Walker, G. P. L., Wilson, C. J. N. & Froggat, P. C. 1981. An ignimbrite veneer deposit: the trail-marker of a pyroclastic flow. Journal of Volcanology and Geothermal Research 9, 409–22.CrossRefGoogle Scholar
Wellman, T. R. 1970. The stability of sodalite in a synthetic and aqueous chloride fluid system. Journal of Petrology 11,48–71.CrossRefGoogle Scholar
Wilson, L. 1980. Relationships between pressure, volatile content and ejecta velocity in three types of volcanic explosion. Journal of Volcanology and Geothermal Research 8, 297–313.CrossRefGoogle Scholar
Wilson, L., Sparks, R. S. J. & Walker, G. P. L. 1980. Explosive volcanic eruptions. IV. The control of magma properties and conduit geometry on eruption column behaviour. Geophysical Journal of the Royal Astronomical Society 63, 117–48.CrossRefGoogle Scholar
Wolff, J. A. 1984. Variation in Nb/Ta during differentiation of phonolitic magma, Tenerife, Canary Islands. Geochimica et Cosmochimica Acta 48, 1345–8.Google Scholar
Wolff, J. A. & Storey, M. 1983 a. The volatile component of some pumice-forming alkaline magmas from the Azores and Canary Islands. Contributions to Mineralogy and Petrology 82, 66–74.Google Scholar
Wolff, J. A. & Storey, M. 1983 b. The use of tephra studies to determine volatile release during large explosive volcanic eruptions. In Conference on Planetary Volatiles (ed. Pepin, R. O. and O'Connell, R.), pp. 194–8. Lunar & Planetary Institute Technical Report no. 83-01.Google Scholar
Wolff, J. A. & Storey, M. 1984. Zoning in highly alkaline magma bodies. Geological Magazine 121, 563–75.Google Scholar
Wolff, J. A., Wright, J. V., Smith, A. L., Clough, B. J., Roobol, M. J. & Self, S. 1980. Mixed pumice eruptions: field characteristics. Transactions of the 9th Carribean Conference 1, 355–65.Google Scholar
Wörner, G. & Schmincke, H.-U. 1984 a. Mineralogical and chemical zonation of the Laacher See tephra sequence. Journal of Petrology 25, 805–35.CrossRefGoogle Scholar
Wörner, G. & Schmincke, H.-U. 1984 b. Petrogenesis of the zoned Laacher See tephra. Journal of Petrology 25, 836–51.CrossRefGoogle Scholar
Wörner, G. & Wright, T. L. 1984. Evidence for magma mixing within the Laacher See magma chamber (East Eifel, Germany). Journal of Volcanology and Geothermal Research 22, 301–27.CrossRefGoogle Scholar