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Evolutionary stages of crystallization of weakly peralkaline syenites: evidence from ejecta in the plinian deposits of Agua de Pau volcano (São Miguel, Azores Islands)

  • F. Ridolfi (a1), A. Renzulli (a1), P. Santi (a1) and B. G. J. Upton (a2)

Abstract

Weakly peralkaline syenite ejecta within the plinian fall deposits of Agua de Pau volcano (São Miguel, Azores Islands) are divisible into (1) silica-undersaturated and (2) silica-saturated/oversaturated groups. The first group occurs in the pre-Fogo-A pyroclastic falls (15.2 ka) whereas the second occurs in the Fogo-A pumices (5 ka). The petrography indicates that the syenites of both groups crystallized at shallow depths and whole-rock geochemistry shows that they have compositions reflecting those of the Agua de Pau trachyte magmas. The syenites are inferred to be derived from solidification zones around the margins of the parental magma chamber. Mineral parageneses in both syenite groups permit distinction of three magmatic stages of crystallization: (1) an early crystallization stage; (2) a main crystallization stage during which most of the feldspar growth occurred; and (3) a late interstitial stage. Crystallization of the trachytic magmas yielded peralkaline residuals, highly enriched in volatiles, alkalis, HFSE and REE. In the silica-undersaturated syenites, the complex Zr-Ti silicate minerals, eudialyte and a låvenite-like mineral, crystallized interstitially from the residual magmas. In contrast, the zircono-silicate dalyite, and REE-rich minerals (chevkinite-(Ce), britholite-(Ce) and pyrochlore), together with thorite, were late-stage interstitial products of the silica-saturated/oversaturated syenites.

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Abdel-Monem, A.A., Fernandez, L.A., Boone, G.M. (1975 K-Ar ages from the eastern Azores groups (Santa Maria, São Miguel and the Formigas Islands). Lithos, 8, 247254.
Booth, B., Croasdale, R. and Walker, G.G.P. (1978 A quantitati ve study of . ve thousand years of volcanism of São Miguel, Azores. Philosophical Transactions of the Royal Society , 288A, 271319.
Burke, K.C. and Wilson, J.T. (1976 Hot spots on the Earth's surface. Pp. 3142 in: Volcanoes and the Earth's interior (Decker, R. and Decker, B.E. editors), Freeman, New York.
Cann, J.R. (1967 A second occurrence of dalyite and the petrology of some ejected syenite blocks from Sao Miguel, Azores. Mineralogical Magazine, 36, 227232.
Chakhmouradian, A.R. and Mitchell, R.H. (1999 Primary, agpaitic and deuteric stages in the evolution of accessory Sr. REE, Ba and Nb-mineralization in nepheline-syenite pegmatites at Pegmatite Peak, Bearpaw Mts, Montana. Mineralogy and Petrology, 67, 85110.
Chakhmouradian, A.R. and Mitchell, R.H. (2002 The mineralogy of Ba- and Zr-alkaline pegmatites from Gordon Butte, Crazy Mountains (Montana, USA): comparisons between potassic and sodic agpaitic pegmatite s. Contributi ons to Mineralogy and Petrology, 143, 93114.
Coulson, I.M. (1997 Post-magmatic alteration in eudialyte from the North Qo�roq centre, South Greenland. Mineralogical Magazine, 61, 99109.
Fernandez, L.A. (1980 Geology and petrology of the Nordeste volcanic complex, São Miguel, Azores. Geological Society of American Bulletin,, 91, 675680.
Fletcher, C.C.J. and Beddoe-Stephens, B. (1987 The petrology, chemistry and crystallization history of the Velasco alkaline province, eastern Bolivia. Pp. 403413 in: Alkaline Igneous Rocks (Fitton, J.G. and Upton, B.G.J., editors). Special Publication, 30. Geological Society, London.
Gandino, A., Guidi, M., Merlo, C., Mete, L., Rossi, R. and Zan, L. (1985 Preliminary model of the Ribeira Grande geothermal Field (Azores Islands) . Geothermics , 14, 1, 91105.
Gibb, F.F.G. (1973 The zoned clinopyroxenes of the Shiant Isles Sill, Scotland. Journal of Petrology, 14, 203230.
Harris, C., Cressey, G., Bell, J.D., Atkins, F.B. and Beswetherick, S. (1982 An occurrence of rare-earthrich eudialyte from Ascension Island, South Atlantic. Mineralogical Magazine, 46, 421425.
Hunter, R.H. (1996 Texture and development in cumulate rocks. Pp 77101 in: Layered Intrusions (Cawthorn, R.G., editor). Elsevier Science, Oxford, UK.
Johnsen, O. and Gault, R.A. (1997 Chemical variation in eudialyte. Neues Jahrbuch für Mineralogie Abhandlungen, 171, 215237.
Johnsen, O. and Grice, J.D. (1999 The crystal chemistry of the eudialyte group. The Canadian Mineralogist, 37, 865891.
Khomyakov, A.P. (1995 Mineralogy of Hyperagpaitic Alkaline Rocks . Oxford Science Publications, Oxford, UK, 222 pp.
Krause, D.C. and Watkins, N.D. (1970 North Atlantic crustal genesis in the vicinity of the Azores. Geophysical Journal, Royal Astronomical Society, 19, 261283.
Larsen, L.M. (1976 Clinopyroxenes and coexisting mafic minerals from the alkaline Ilímaussaq Intrusion, South Greenland. Journal of Petrology, 17, 258290.
Larsen, L.M. (1977 Aenigmatites from the Ilímaussaq intrusion, south Greenland: Chemistry and petrological implications. Lithos, 10, 257270.
Leake, B.E., Woolley, A.R., Arps, C., Birch, W.D., Gilbert, M.C., Grice, J.D., Hawthorne, F.C., Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Mandarino, J.A., Maresch, W.V., Nickel, E.H., Rock, N.N.M., Schumacher, J.C., Smith, D.C., Stephenson, N.N.C., Ungaretti, L.,Whittaker, E.E.J. and Youzhi, G. (1997 Nomenc la ture of Amphiboles: Report of the Subcommit tee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names. Mineralogica l Magazine, 61, 295321.
Le Maitre, R.W. (editor) (1989 A Classification of Igneous Rocks and Glossary of Terms . Blackwell, Oxford, UK 193 pp.
Macdonald, R. and Belkin, H.E. (2002 Compositional variation in minerals of the chevkinite group. Mineralogical Magazine, 66, 10751098.
Macdonald, R., Marshall, A.S., Dawson, J.B., Hinton, R.W. and Hill, P.G. (2002 Chevkinite-gro up minerals from salic rocks of the East African Rift. Mineralogical Magazine, 66, 287299.
Merlino, S. and Perchiazzi, N. (1988 Modular mineralogy in the cuspidine group of minerals. The Canadian Mineralogist, 26, 933943.
Middlemost, E.E.A. (1989 Iron oxidation ratios, norms and classification of volcanic rocks. Chemical Geology, 77, 1926.
Moore, R.B. (1990 Volcanic geology and eruption frequency, São Miguel, Azores. Bulletin of Volcanology, 52, 602614.
Moore, R.B. (1991 Geology of Three Late Quaternary Stratovolcanoes on São Miguel, Azores. US Geological Survey Bulletin , 1900, 46 pp.
Moreau, C., Ohnenstetter, D., Demaiffe, D. and Robineau, B. (1996 The Los archipelago nepheline syenite ring-structure: A magmatic marker of the evolution of the central and equatorial Atlantic. The Canadian Mineralogist, 34, 281299.
Nakamura, N. (1974 Determination o. REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary condrites. Geochimica et Cosmochimica Acta, 38, 757775.
Nash, W.P. and Wilkinson, J.J.F. (1970 Shonkin Sag laccolith, Montana. I. Mafic minerals and estimates of temperature, pressure, oxygen fugacity and silica activity. Contributions to Mineralogy and Petrology, 25, 241269.
Nicholls, J. and Carmichael, I.I.S. (1969 Peralkaline acid liquids: a petrological study. Contributions to Mineralogy and Petrology, 20, 268294.
Oberti, R., Ottolini, L., Della Ventura, G. and Parodi, G.N. (2001 On the symmetry and crystal chemistry of britholite: New structural and microanalytical data. American Mineralogist, 86, 10661075.
Osann, A. (1888 Ueber sanidinite von São Miguel. Neues Jahrbuch für Mineralogie, 1, 117130.
Papike, J.J., Cameron, K.L. and Boldwin, K. (1974 Amphiboles and pyroxenes: characterization of other than quadrilateral components and estimates of ferric iron from microprobe data. Geological Society of America, Program Abstracts, 6, 10531054.
Perchiazzi, N., McDonald, A.M., Gault, R.A., Johnsen, O. and Merlino, S. (2000 The crystal structure of normandite and its crystal-chemical relationships with laÊ venite. The Canadian Mineralogist, 38, 641648.
Powell, M. (1978 The crystallization history of the Igdlerfigssalik neph eline syen ite intrusion, Greenland. Lithos, 11, 99120.
Ridol., F. (2000 Studio petrografico e geochimico dei clasti sienitici inclusi nei prodotti vulcanici di São Miguel (Azzorre) e Tenerife (Canarie). Unpublished degree thesis, 108 pp.
Robinson, P., Spear, F.S., Schumacher, J.C., Laird, J., Klein, C., Evans, B.W. and Doolan, B.L. (1981 Phase relations of metamorphic amphiboles: Natural occurrence and theory. Pp. 1228 in: Amphiboles: Petrology and Experimental Phase Relations (Veblen, D.R. and Ribbe, P.H., editors). Reviews in Mineralogy, 9B. Mineralogical Society of America, Washington, D.C.
Rock, N.N.M. (1990 The International Mineralogical Association (IMA/CNMMN) Pyroxene Nomenclature Scheme: Computerization and its Consequences. Mineralogy and Petrology, 43, 99119.
Rønsbo, J.G. (1989 Coupled substitutions involvin. REEs and Na and Si in apatites in alkaline rocks from Ilímaussaq intrusion, South Greenland, and the petrological implications. American Mineralogist, 74, 896901.
Scott, P.W. (1976 Crystallization trends of pyroxenes from the alkaline volcanic rocks of Tenerife, Canary Islands. Mineralogical Magazine , 40, 316, 805816.
Searle, R. (1980 Tectonic pattern of the Azores spreading centre and triple junction. Earth and Planetary Science Letters, 51, 415434.
Shelley, D. (1992 Igneous and Metamorphic Rocks under the Microscope . Chapman & Hall, London, 445 pp.
Smith, J.V. and Brown, W.L. (1988 Feldspar Minerals 2nd edition (Vol. I). Springer-Verlag, Berlin, 824 pp.
Storey, M. (1981 Trachytic pyroclastics from Agua de Pau Volcano, São Miguel, Azores: Evolution of a Magma Body over 4000 Years. Contributions to Mineralogy and Petrology, 78, 423432.
Sørensen, H. (1997 The agpaitic rocks – an overview. Mineralogical Magazine, 61, 485498.
Storey, M., Wolff, J.A., Norry, M.J. and Marriner, G.F. (1989 Origin of hybrid lavas from Agua de Pau volcano, São Miguel, Azores. Pp. 161180 in: Magmatism in the Ocean Basins (Saunders, A. and Norry, M.J., editors). Special Publication, 42. Geological Society, London.
Walker, G.G.P. and Croasdale, R. (1970 Two pliniantype eruptions in the Azores. Journal of the Geological Society, London, 127, 1755.
Widom, E., Schmincke, H.U. and Gill, J.B. (1992 Processes and timescales in the evolution of a chemical zoned trachyte: Fogo-A, São Miguel, Azores. Contribut ions to Mineralogy and Petrology, 111, 311328.
Widom, E., Gill, J.B. and Schmincke, H.U. (1993 Syenite nodules as a long-term record of magmatic activity in Agua de Pau Volcano, São Miguel, Azores. Journal of Petrology, 34, 929953.
Wolff, J.A. (1987 Cristallisation of nepheline syenite in a subvolcanic magma system: Tenerife, Canary Islands. Lithos, 20, 207223.
Wolff, J.A. and Toney, J.B. (1993 Trapped liquid from a nepheline syenite: a re-evaluation of Na-, Zr-, Frich interstitial glass in a xenolith from Tenerife, Canary Islands. Lithos, 29, 285293.

Keywords

Evolutionary stages of crystallization of weakly peralkaline syenites: evidence from ejecta in the plinian deposits of Agua de Pau volcano (São Miguel, Azores Islands)

  • F. Ridolfi (a1), A. Renzulli (a1), P. Santi (a1) and B. G. J. Upton (a2)

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