Large glass inclusions in plagioclase phenocrysts and their bearing on the origin of mixed andesitic lavas at Tolim�n volcano, Guatemala

Halsor, Sid P.

doi:10.1007/bf01073516

Cited by 12 publications

(2 citation statements)

References 24 publications

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“…-não detectado i) mistura de magmas: as diferentes populações de fenocristais decorrem da mistura de magmas composicionalmente contrastantes, sendo nestes casos observadas variações significativas nos teores de An entre os cristais ou mesmo no fenocristal isolado (Dungan & Rhodes 1978;Tsuchiyama 1985;Halsor 1989). A presença de outras fases minerais deveria também indicar o fenómeno de mistura, como p. ex, piroxênios ou fenocristais de quartzo, se presentes (Kontak et al 1986).…”

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Química Mineral Das Rochas Vulcânicas E Lamprófiros Espessartíticos Da Associação Shoshonítica De Lavras Do Sul-Rs

Lima¹,

Nardi²

1998

RBG

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MINERAL CHEMISTRY OF VOLCANIC ROCKS AND LAMPROPHYRES OF LAVRAS DO SUL SHOSHONITIC ASSOCIATION, SOUTHERNMOST BRAZIL The Lavras do Sul Shoshonitic Association, situated in the southernmost Brazil, is composed of basic to acid volcanic and plutonic rocks, related to the late stages of Brasiliano Cycle. Spessartitic lamprophyres are associated to the late stages of shoshonitic magmatism. Major and some trace elements (Ba, Sr, Ni, Cr, Ti), were obtained by microprobe determinations, in major mineral phases of basic to intermediate volcanic rocks and lamprophyres of Lavras do Sul Shoshonitic Association. The composition of plagioclases is sodium enriched in relation to calc-alkaline rocks, varying from labradorite to andesine. The relatively low An-content is ascribed mainly to the alkali-calcic character of shoshonitic magmatism. The presence of albite in the lamprophyres is a result of late hydrothermal activity. The relatively high Ba content of plagioclases suggest that the mineral/liquid partition coefficient for this element in shoshonitic liquids is close to l. Olivine (Fo 67 ), with relatively low Mg/Fe ratios, and clinopyroxene, with composition close to diopside, are the main ferromagnesian phases, whose compositions are typical of basic and intermediate shoshonitic rocks. Magnesiohastingsite is the amphibole present in the lamprophyres, associated with clinopyroxene relicts which are diopside enriched relative to those oberved in trachybasalts. The coherence between mineral phases and whole-rock chemical compositions is consistem with differentiation processes dominated by fractional crystallisation, except for the lamprophyric liquids, whose evolution may have involved the assimilation of crustal components.RESUMO A Associação Shoshonítica de Lavras do Sul, situada no extremo sul do Brasil é constituída por rochas vulcânicas básicas até ácidas e rochas plutônicas relacionadas ao final do Ciclo Brasiliano. Lamprófiros espessartíticos são as manifestações mais tardias desde magmatismo shoshonítico. Neste trabalho são apresentados os resultados de elementos maiores e alguns elementos-traço (Ba,Sr, Ni, Cr, Ti), obtidos por microssonda eletrônica, nas principais fases minerais das rochas vulcânicas básicas, intermediárias e lamprófiros da Associação Shoshonítica de Lavras do Sul. A composição do plagioclásio é mais sódica do que as normalmente observadas nas rochas cálcico-alcalinas, variando de labradorita a andesina. O cárater álcali-cálcico possivelmente deternina este enriquecimento no componente albita. Os conteúdos elevados de Ba dos plagioclásios indicam um coeficiente de partição mineral/líquido em torno da unidade. A olivina (Fo 67 ), com razões Mg/Fe relativamente baixas e clinopiroxênio com composição próxima do diopsído, representam as principais fases ferromagnesianas, sendo estas típicas das rochas shoshoníticas básicas a intermediárias. Magnesiohastingsita é o anfibólio nos lamprófiros, além de relíctos de clinopiroxênio cuja composição aproxima-se daquelas observadas nos traquibasaltos. A combina...

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Química Mineral Das Rochas Vulcânicas E Lamprófiros Espessartíticos Da Associação Shoshonítica De Lavras Do Sul-Rs

Lima¹,

Nardi²

1998

RBG

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“…In the PMVF, there are also other disequilibrium textures, which are not interpreted as the result of magma mixing. These are (1) coarse sieved plagioclases, a result of adiabatic decompression (Nelson and Montana, 1992), the morphology of these plagioclase inclusions in T pre and TA pos rocks are different from those reported by Halsor (1989) which are explained as a consequence of rapid growth due to magma mixing processes; (2) amphibole with a rim of opaque and anhydrous minerals and biotite with an opaque rim, formed by decompression and volatile loss (Fig. 12; Rutherford and Hill, 1993;Browne and Gardner, 2006); (3) patchy zoning in feldspars, formed by dissolution of the crystal core by decompression, followed by crystallization of feldspar in equilibrium with the new conditions (Vernon, 2004); (4) embayed and non-rounded olivine phenocrysts (formed by crystal growth in equilibrium, Faure and Schiano, 2005); (5) feldspars with relatively large holes which are controlled by its crystal structure (skeletal growth, Lofgren, 1974).…”

Section: Textural and Mineralogical Evidence For Magma Mixing And Minglingmentioning

confidence: 94%

The role of magma mixing and mafic recharge in the evolution of a back-arc quaternary caldera: The case of Payún Matrú, Western Argentina

Hernando

Petrinovic

Llambías

et al. 2016

Journal of Volcanology and Geothermal Research

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Magmatic Processes

Cashman

Bergantz

1991

Reviews of Geophysics

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Large glass inclusions in plagioclase phenocrysts and their bearing on the origin of mixed andesitic lavas at Tolim�n volcano, Guatemala

Cited by 12 publications

References 24 publications

Química Mineral Das Rochas Vulcânicas E Lamprófiros Espessartíticos Da Associação Shoshonítica De Lavras Do Sul-Rs

Química Mineral Das Rochas Vulcânicas E Lamprófiros Espessartíticos Da Associação Shoshonítica De Lavras Do Sul-Rs

The role of magma mixing and mafic recharge in the evolution of a back-arc quaternary caldera: The case of Payún Matrú, Western Argentina

Magmatic Processes

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