Coronas from the Thessaloniki gabbros (North Greece)

Sapountzis, E.

doi:10.1007/bf00372079

Cited by 12 publications

(4 citation statements)

References 8 publications

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“…Although coronal reaction textures can involve a wide variety of minerals and bulk compositions, the reaction between olivine and plagioclase in metagabbroic rocks is by far the most common and most intensely studied type of corona (Shand, 1945; Gjelsvik, 1952; Murthy, 1958; Bose, 1%1; Reynolds & Frederickson, 1962; Mason. 1967; Frodesen, 1968;Starmer, 1969; Griffen, 1971Griffen, , 1972; Griffen & Heier, 1973; Whitney & McLelland, 1973; England, 1974; Gardner & Robins, 1974;Miller, 1974; Grieve & Gittins, 1975; Sapountzis, 1975;Esbensen, 1978; van Lamoen, 1979; Emslie, 1983; Mongkoltip & Ashworth, 1983; Nishiyama, 1983; Otten, 1984; Mork, 1985; Joesten, 1986a; Grant, 1988). Despite these numerous studies, the origin of coronas in metagabbroic rocks remains controversial.…”

Section: Previousty Proposed Origins For Divineplagioclase Coronasmentioning

confidence: 99%

The origin of olivine‐plagioclase coronas in metagabbros from the Adirondack Mountains, New York

Johnson

Carlson

1990

Journal Metamorphic Geology

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Olivine-plagioclase coronas in metagabbros from the Adirondack Mountains, New York (USA) are spatially well-organized reaction textures consisting most commonly of sequential layers of orthopyroxene, clinopyroxene, fplagioclase, and garnet; the textures are characteristic of diffusioncontrolled reaction kinetics. Although similar coronas have been interpreted by previous workers in terms of an isochemical steady-state diffusion model, petrographical relations and material-balance calculations establish that coronas in the Adirondack metagabbros cannot be treated as isochemical and do not form in a single-stage steady-state process; instead they evolve through time in a complex open-system reaction.In this study, the isochemical diffusion model is modified to account for elemental fluxes across the outer boundaries of the coronal reaction band, thereby approximating the open-system behaviour of the coronas. The sequence and relative proportions of product minerals calculated by the open-system steady-state model correspond closely to those observed in coronas of the Adirondacks, over a wide range of values for the relative diffusivities of chemical components involved in the reaction, regardless of the particular method used to determine material balance in the reaction texture.Despite this correspondence, petrographical evidence for successive replacement of coronal product layers reveals that the Adirondack coronas evolved through one or more transient states, rather than forming in a single-stage steady-state process. There is no evidence that the successive replacement of coronal product layers resulted from changes in pressure or temperature, but there is petrographical evidence that these changes resulted from modification of the composition of reactant plagioclase as the corona-forming reaction proceeded. This is confirmed by the fact that the evolution of the coronas over time can be replicated with the open-system diffusion model by simulating the effect of the gradual exhaustion of plagioclase as a source of the Ca and Si components required for reaction. These simulations suggest that successive stages in the evolution of the coronas are characterized by these product sequences: (i) orthopyroxene-clinopyroxene-plagioclase-garnet; (ii) orthopyroxeneclinopyroxene-garnet; and (iii) orthopyroxene-garnet. All of these stages, and the transitions between them, are observed petrographically. Coronas in Adirondack metagabbros appear, therefore, to have originated in a complex, open-system, diffusioncontrolled reaction in which the product assemblages changed as the reaction progressed.

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Section: Previousty Proposed Origins For Divineplagioclase Coronasmentioning

confidence: 99%

The origin of olivine‐plagioclase coronas in metagabbros from the Adirondack Mountains, New York

Johnson

Carlson

1990

Journal Metamorphic Geology

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“…Entretanto, não há evidências estruturais e texturais nos corpos e nas rochas encaixantes que sustentem a hipótese de dois eventos térmicos. As evidências texturais registradas nas rochas coroníticas excluem, ao mesmo tempo, a possibilidade de sua formação estar vinculada aos estágios finais de processos magmáticos (Sapountzis 1975, Lamoen 1979, Emmett 1982. Nas amostras analisadas, não se constatou a presença de feições de deformação nas coronas, mesmo naquelas nas quais os plagioclásios originais mostram sinais de deformação (cristais quebrados, com extinção ondulante, com lamelas de geminação encurvadas etc).…”

Section: Condições De Metamorfismo Das Rochas Dos Complexosunclassified

“…INTRODUÇÃO A presença de coronas entre olivina e plagioclásio, constituídas por ortopiroxênio, anfibólio e espinélio simplectítico, é freqüentemente descrita em rochas gabróicas, em terrenos de fácies granulito e anfibolito, tendo sido objeto de estudo de diversos pesquisadores como Murthy (1958), Griffin & Heier (1973), , Miller (1974), Grieve & Gittins (1975), Sapountzis (1975), Esbensen (1978), Lamoen (1979), Hamlyn (1980), Emmett (1982), Mongkoltip & Ashworth (1983), entre outros.…”

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FORMAÇÃO METAMÓRFICA DE CORONAS EM ROCHAS DOS COMPLEXOS MÁFICO-ULTRAMÁFICOS DE MANGABAL l E II, GOIÁS

Cândia¹,

SCHULTZ-GÜTLLER²,

Gaspar³

1990

RBG

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Coronas of orthopyroxene, pargasitic amphibole and spinel occur between olivine and plagioclase in metaperidotites, feldspathic metaharzburgites and meta-olivine gabbronorites of the two small ultramafic complexes Mangabal I e Mangabal II Geological, textural and phase petrological evidence indicate that corona formation was contemporaneous with a thermal event producing more hydrated paragenesis in other parts of the complex pointing to a metamorphic overprint under high grade conditions. The different stages of corona formation and the development of the more hydrated paragenesis (clinochlore, orthopyroxene, magnesium hornblende) could be explained by changes in the composition of the fluid phase under virtually similar P-T conditions. Thermochemical calculations for chemically closed systems and isochores of CO 2 , as determined from fluid inclusions, point to about 750°C and 6 to 7 kbar as P-T conditions of metamorphism.

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“…A partial list includes Shand (1945), Herz (1951), Gjelsvik (1952), Murthy (1958), Frodesen (1968), and Sapountzis (1975). In most cases, the reaction is thought to occur at high pressures and appears to be characteristic of gabbroids emplaced in a high-grade (upper amphibolite to granulite) metamorphic terrain.…”

Section: Emplacementmentioning

confidence: 96%

Petrology and emplacement of the Los Pinos pluton, southern California

Walawender¹

1976

Can. J. Earth Sci.

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The Los Pinos gabhrtj is located on the e;istern margin of the gabbro sub-helt of the Peninsular R;~nges bathrrlilh . Ttvc) lithrrlogic sequences are recognized in this pluton. The outer group consiht\ or hirntlrlal asserntrli~ge.; of hnr-nblcnde and pfagioclaqe in several te.uti~ral varieties. whereas the inner group contains a variety of olivine-plagioclase rocks. Symplectitic interyl~uwths ti!' spinel. an~phibole. ancl orthopyroxene have developed wherever rhe olivine and plirgicrcluse were in contact. The outer proup isgenerdlly the older of the two, although there is evidence suggesting that their rmplacemen~ overlapped in time. The contacl between the two groups i~ vhalacterizetl locally hy sequences of comb layers up to 65 m thick. Ma-jor-element chemical i~n;ilyse'i en1ph:rsizr [he differences between the two groups. The outer gmup is gcnel-ally richer in total al killis, titanium. and silica. Variation diagrams suggest (ha! different differeniia~icm mechanisms operaled within each group.Textural and published experimenral dapa suggesl that the t wogroups are derived from n parent magma hy ciinopyroxene fracrionatiun at P7 > 5 kbar. The more silicic differentiates were ernplaced nt sh:illower levels inlo a series of regionally metamorphopyiroxene a ...

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Coronas from the Thessaloniki gabbros (North Greece)

Cited by 12 publications

References 8 publications

The origin of olivine‐plagioclase coronas in metagabbros from the Adirondack Mountains, New York

The origin of olivine‐plagioclase coronas in metagabbros from the Adirondack Mountains, New York

FORMAÇÃO METAMÓRFICA DE CORONAS EM ROCHAS DOS COMPLEXOS MÁFICO-ULTRAMÁFICOS DE MANGABAL l E II, GOIÁS

Petrology and emplacement of the Los Pinos pluton, southern California

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