Feldspar-liquid equilibria in pantellerites; an experimental study

Carmichael, I. S. E.; MacKenzie, W. S.

doi:10.2475/ajs.261.4.382

Cited by 85 publications

(23 citation statements)

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“…In the rhyolites the progression from comendite to pantellerite is marked by an increase in peralkalinity, and since, during normal fractionation processes more evolved liquids are usually increasingly peralkaline (Carmichael and MacKenzie, 1963;Bailey and Schairer, 1964), the most useful representation of the chemical variation between the two groups is in terms of increasing peralkalinity, of which the simplest measure is the agpaitic index (Na20+K20)/Al203. In the series peralkaline trachyte to rhyolite, the variation in q is more marked than change in agpaitic 40 index.…”

Section: Petrochemistrymentioning

confidence: 99%

“…For petrogenetic purposes it might have been instructive to include analyses of these metaluminous types in the compilation, but this inclusion would have widened the scope of the work far beyond our original intentions. In view of the importance of trachytes in the study of peralkaline rhyolites (Carmichael and MacKenzie, 1963;Bailey and Schairer, 1964), we prefer merely to stress the paucity of data on peralkaline trachytic glasses and to single out this field of research as requiring immediate attention. Of the three analyses plotting in the comenditic trachyte field ( fig.…”

Section: Trachyte Obsidiansmentioning

confidence: 99%

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Chemistry of igneous rocks; Part 1, The chemistry of the peralkaline oversaturated obsidians

Macdonald¹,

Bailey²

1972

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Section: Petrochemistrymentioning

confidence: 99%

Section: Trachyte Obsidiansmentioning

confidence: 99%

Chemistry of igneous rocks; Part 1, The chemistry of the peralkaline oversaturated obsidians

Macdonald¹,

Bailey²

1972

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“…The normal trend in a magmatic series is Po2 decay, but the net result of all the above conditions may be a different trend. WEBSTER • BRIGHT (1961) andCARMICHAEL &NICHOLLS (1967) have demonstrated that different solid solutions of Ti-Fe may coexist. Phases of a and to series equilibrate, at similar oxygen fugacities, to a andfi phases, and it is the Fe/Ti ratio or the fo2 that determines the presence or abundance of an w phase-if the oxygen fugacity is high or the Fe/Ti ratio is low, an to phase may precipitate.…”

Section: Geochemistry Of Facho Peralkaline Rhyolitesmentioning

confidence: 99%

Petrogenesis of early paleozoic peralkaline rhyolites from the Macedo de Cavaleiros region (NE Portugal)

Ribeiro¹

1987

Geol Rundsch

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ZusammenfassungPetrologie und Geochemie variszischer peralkaliner Gneisse aus Nordostpormgal, 1962 AbstractThe petrology and geochemistry of Variscan peralkaline gneisses from NE Portugal, discovered in 1962, is presented. Major and trace element data for the oversaturated sequence of the Macedo de Cavaleiros area depict some specific geochemical patterns: high Fe2OJ tl (even higher than in the Ethiopian Main Rift), high REE concentrations and small Eu anomalies. Field and petrographical observations also suggest that liquid immiscibility has played an important petrogenetic role in the crystallization trends. The alternating pyroxene-feldspar-hematite-rich bands observed in outcrop are interpreted as resulting from fluctuating fO2 conditions, petrological and geochemical data show that these pantelleritic and comenditic rocks are the end members of an alkaline-transitional basaltic sequence, by *) Author's address: M. L. RII3EII~O, Serviqos Geol6gicos de Portugal, R. Academia Ci~ncias, 19, 1200 Lisboa, Portugal.which they are overlain. An uppermost sequence of oceanic tholeiitic basalts completes the picture of an evolving rift environment, where mantle processes generate crustal thinning and eventually oceanic crust. R6sum6L'auteur pr6sente la p&rologie et la g6ochimie des gneiss varisques peralcalins du nord-est du Portugal, d~couverts en 1962. Les analyses des 616ments majeurs et en traces dans ces roches sursatur6es montrent quelques caract6fistiques sp6ciales comme la haute teneur en Fe203 (t) (sup6rieure m~me ~t celles de l',,Ethiopian Main Rifts,), la halite concentration en terres rares et la faible anomalie n6gative de Eu. La g4ologie de terrain et les observations p6trographiques sugg6rent aussi que l'imiscibilit6 entre liquides a jou6 un r61e p6trog6n6tique important au cours de la cristallisation. Les alternances de bandes alternativement riches en pyrox6ne-feldspath et en h6matite, observ4es sur les affleurements, sont interpr6t6es comme le r6sultat de la fluctuation de fO2. Les donn4es p6trologiques et g6ochimiques montrent que les roches pant616ritiques et comenditiques repr6-sentent les derniers termes d'une s6quence du type alcalintransitionel qui les surmonte. La s6quence volcanique dans le secteur de Macedo de Calvaleiros se termine par des basaltes thoi6iitiques qui compl&ent le cadre d'une environnement d'un zone de ,,rift,, dans laquelle les processus mant61iques ont d&ermin6 l'amincissement crustal et la formation d'une croOte oc4anique. KpaTKOe eo~ep~KaHne

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“…The concentration of these minor elements in the liquid portion of the pantellerite mag1na, shown by the whole-rock spectrographic analyses (table 2, columns 2, 3), is consistent with such an origin. Carmichael and MacKenzie (1963) believe that pantellerite liquids form by the separation of sodium-rich alkali feldspar ( Ab 60 to Ab 70 ) , sadie plagioclase, and pyroxene phenocrysts from melts of trachytic composition. To develop a high N a20 to K20 ratio as well as a high alkali to alumina ratio in a residual liquid by the separation of feldspar, the feldspar must be more potassic than the liquid from which it crystallizes.…”

Section: Genesismentioning

confidence: 99%

Geological Survey research 1965, Chapter B

1965

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Feldspar-liquid equilibria in pantellerites; an experimental study

Cited by 85 publications

References 0 publications

Chemistry of igneous rocks; Part 1, The chemistry of the peralkaline oversaturated obsidians

Chemistry of igneous rocks; Part 1, The chemistry of the peralkaline oversaturated obsidians

Petrogenesis of early paleozoic peralkaline rhyolites from the Macedo de Cavaleiros region (NE Portugal)

Geological Survey research 1965, Chapter B

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