Nomenclature of Amphiboles

Leake, Bernard Elgey

doi:10.1180/minmag.1978.042.324.21

Cited by 1,002 publications

(468 citation statements)

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“…Generally, magmatic textures were preserved and gabbros have not acquired a visible metamorphic fabric, though actinolite in the matrix is not completely randomly oriented. The wide compositional variety of the amphiboles suggests multi-stage metamorphism, though the fact that composition never exceeds the limit of calcic amphiboles as defined by Leake (1978) indicates relatively low pressure conditions during all stages of metamorphism. The matrix assemblage is typical of mafic rocks metamorphosed at the greenschist facies, but the high modal abundance of hornblende, pseudomorphic after pyroxene, indicates higher degree of metamorphism at temperatures above 600°C (Spear, 1981).…”

Section: A2 Metagabbrosmentioning

confidence: 99%

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The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

et al. 1996

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-The six exposures of the Upper tectonic Unit of the Cycladic Massif occurring on the island of Tinos are shown to comprise a metamorphosed dismembered ophiolite complex. The common stratigraphic section consisting of tens-of-metres-thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low-angle normal faults. All rock types show evidence of a phase of regional greenschistfacies metamorphism, which in the case of the phyllites is accompanied by penetrative deformation. The greenschist-facies metamorphism in gabbros is preceded by high temperature sea-floor amphibolite-facies alteration, whereas in the serpentinites, the antigorite + forsterite greenschist-facies assemblage overprinted an earlier low temperature lizardite serpentinite. Trace element patterns of the mafic phyllites and a harzburgitic origin of meta-serpentinites suggest a supra subduction zone (SSZ) affinity for the ophiolitic suite. 5"O values of phyllites, gabbros and serpentinites range from 6 to 15%o. Model calculations indicate that such values are consistent with low temperature (50-200 °C) alteration of parent rocks by sea-water at varying water/rock ratios. This would agree with the early low temperature mineralogy of the serpentinites, but the early high temperature alteration of the gabbros would require the presence of "O-enriched sea-water.The following overall history is suggested for Tinos ophiolitic slices.(1) Oceanic crust was generated at a supra-subduction zone spreading centre with high temperature alteration of gabbros. (2) Tectonic disturbance (its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites) brought the already cooled ultramafics into direct contact with sea-water and caused low-7* serpentinization. (3) Tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite. (4) Regional metamorphism of all the ophiolite components at greenschist-facies conditions (~450 °C) overprinted the early alteration mineralogy. It was probably induced by continued thrusting and piling up of nappes. The Tinos ophiolite, dated as late Cretaceous and genetically related to other low pressure rock-units of the same age in the Aegean, differs in age and degree of dismemberment and metamorphism from ophiolites in mainland Greece.

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Section: A2 Metagabbrosmentioning

confidence: 99%

“…These shreds, together with clinozoisite (15-50%), chlorite (5-20%) Figure 4. Electron microprobe analyses of amphiboles, classified according to Leake (1978). All amphiboles are calcic: (Ca+Na) B ;> 1.34 and Na B < 0.67.…”

Section: A2 Metagabbrosmentioning

confidence: 99%

The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

et al. 1996

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“…The continent -continent convergence led to thickening of the crust followed by collapse of the subducted, predominantly igneous, crust that was involved in the formation of melt giving rise to MH granitoids. (Leake 1978). Symbols shown are common for all ensuing diagrams in the manuscript Maniar and Piccoli (1989).…”

Section: Resultsmentioning

confidence: 99%

Genesis of Ferropotassic A-Type Granitoids of Mühlig-Hofmannfjella, Central Dronning Maud Land, East Antarctica

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Abstract. Ferrosilite-fayalite bearing charnockite and biotite-hornblende bearing granite are exposed in Mühlig-Hofmannfjella, central Dronning Maud Land of East Antarctica. Both are interpreted as essentially parts of a single pluton in spite of their contrasting mineral assemblages. Based on petrologic and geochemical studies, it is proposed that H2O-undersaturated parent magma with igneous crustal component that fractionated under different oxygen fugacity conditions resulted in the Mühlig-Hofmannfjella granitoids.

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“…Amphibole (15% of the pluton by mode) is a brownish-or bluish-green ferroan pargasitic hornblende (Leake 1978). The amphibole is weakly zoned, with rims enriched in K, Al, and Fe.…”

Section: Igneous Mineralogymentioning

confidence: 99%

Using Incongruent Equilibrium Hydration Reactions to Model Latter‐Stage Crystallization in Plutons: Examples from the Bell Island Tonalite, Alaska

Beard¹,

Ragland²,

Crawford³

2005

The Journal of Geology

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(2005) Using incongruent equilibrium hydration reactions to model latter-stage crystallization in plutons: Examples from the Bell Island Tonalite, Alaska, J. Geol., 133,[589][590][591][592][593][594][595][596][597][598][599] [ A B S T R A C TModels using hydration crystallization reactions (the reverse of dehydration melting reactions such as amph ϩ ) for the Bell Island pluton define incongruent equilibrium crystallization paths from hydrous qtz p px ϩ melt -Ti andesine (30%-50% solid) to a solid tonalite consisting mostly of hornblende, melt ϩ pyroxene ϩ Fe oxides ϩ calcic biotite, epidote, sodic andesine, and quartz. In essence, hydration crystallization is a way to quantify and modify the lower temperature end of Bowen's discontinuous reaction series and apply it to natural samples. Hydration crystallization provides an alternative to crystal fractionation for explaining variations in pluton chemistry, especially the compositions of late plutonic melts. Another characteristic of hydration crystallization is that the reactions have the potential to buffer the water content of the melt during crystallization. Two closed-system models, representing different sets of starting conditions and phases, are considered, based on least squares, mass-balance calculations of reactions and constrained by the petrography of the rocks. Model 1 starts with an average modified Bell Island leucotonalite melt coexisting with two pyroxenes, two Fe-Ti oxides, and plagioclase at the beginning of hydration crystallization. The starting assemblage of model 2 omits orthopyroxene and magnetite, includes amphibole, and uses a calculated melt composition. Both models generally predict, via different series of hydration crystallization reactions, the observed subsolidus mode. Model 2, however, is preferred based on petrographic observations of the Bell Island rocks, specifically the lack of magnetite and orthopyroxene, as well as certain textural features.

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Nomenclature of Amphiboles

Cited by 1,002 publications

References 0 publications

The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

Genesis of Ferropotassic A-Type Granitoids of Mühlig-Hofmannfjella, Central Dronning Maud Land, East Antarctica

Using Incongruent Equilibrium Hydration Reactions to Model Latter‐Stage Crystallization in Plutons: Examples from the Bell Island Tonalite, Alaska

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