Paragenetic types of calciferous amphiboles of metamorphic rocks

Kostyuk, E.A.; Sobolev, V. S.

doi:10.1016/s0024-4937(69)80006-x

Cited by 31 publications

(11 citation statements)

References 5 publications

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“…Na 2 0 contents for Shirataki Ca-amphiboles exceed those of the more Ca-rich clinoamphiboles from non-blueschist areas, presumably because the relatively high pressures and low temperatures accompanying the production of glaucophane schists and related rocks favor coupled substitutions in amphiboles such as Na+Al VI for Ca+(Mg,Fe 2+ ). A similar generalization has been presented by Kostyuk and Sobolev (1969). Potash contents and Fe 2+ /Mg ratios of the Ca-amphiboles seemingly do not show significant contrasts in the different types of metamorphic terranes.…”

Section: Discussionsupporting

confidence: 82%

Ca-Amphibole Paragenesis in the Shirataki District, Central Shikoku, Japan

Ernst¹

1972

Geological Society of America Memoirs

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Calcic amphibole and coexisting albite 4-white mica + chlorite -I-epidote from 11 metabasaltic and 2 metasedimentary schists have been investigated from a portion of the relatively high pressure, low temperature (blueschist type) Sanbagawa terrane. The host rocks are representative of two adjacent and intergradational parts of a progressive metamorphic series.Although Ca-amphibole, white mica, and, to some extent, chlorite show enrichments in A1 with progressive metamorphism, the plagioclases change only from an average of An (l0 3 to An 017 . The Ca/Na ratios of calcic amphiboles do not appear to be related simply to metamorphic grade or to the An contents of coexisting plagioclases. The Ti0 2 contents of the mafic phases and white micas increase with grade. The distributions of the large Mn 2+ and small Ti 4+ ions between coexisting phases are: for manganese, chlorite > Ca-amphibole > epidote > white mica; and for titanium, Ca-amphibole = white mica > epidote > chlorite. These fractionations reflect in part the different sizes of the structural sites in the competing minerals. Although the paragenesis is roughly similar to those of other, higher temperature type terranes, there is a slight tendency for Shirataki Ca-amphibole (Si0 2 +Al 2 0 3 ) sums and soda contents to be higher and (total iron + magnesia) sums, as well as titania and lime contents, to be lower than values for calcic amphiboles from non-blueschist terranes.In contrast to higher temperature terranes elsewhere, the continuous change in composition of Shirataki Ca-amphiboles from actinolite at lower metamorphic grade through barroisitic amphibole to hornblende at higher grade argues against the presence of a solvus in this series under relatively high pressure, low temperature (glaucophane schist type) conditions. 73 on June 23, 2015 memoirs.gsapubs.org Downloaded from 74 W. G. ERNST CONTENTS

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Section: Discussionsupporting

confidence: 82%

Ca-Amphibole Paragenesis in the Shirataki District, Central Shikoku, Japan

Ernst¹

1972

Geological Society of America Memoirs

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“…Comparison of recalculation schemes using amphiboles of known Fe'+/FeZ+ (determined from wet chemical and Mossbauer analyses) indicates that no one recalculation scheme.is even near to being reliable (Graham, unpublished data). A detailed survey of analytical data on Fe3'/FeZ+ of hornblendes in a wide range of amphibolites (Wiseman, 1934; Pantin, 1956;Shido & Miyashiro, 1959; Leake, 1968;Kostyuk & Sobolev, 1969;Grapes et al, 1977) demonstrates that recalculation schemes (referenced above) may very significantly overestimate the Fe3 + content of metamorphic hornblendes (e.g. Graham, 1974), and that Fe3+/Fe2+ is invariably significantly lower in hornblendes coexisting with garnet than in hornblendes from garnet-free assemblages.…”

Section: (Ii) Amphibole Chemistrymentioning

confidence: 99%

A garnet–hornblende geothermometer: calibration, testing, and application to the Pelona Schist, Southern California

Graham

Powell

1984

Journal Metamorphic Geology

693

370

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A garnet-hornblende Fe-Mg exchange geothermometer has been calibrated against the garnet-clinopyroxene geothermometer of Ellis & Green (1979) using data on coexisting garnet + hornblende + clinopyroxene in amphibolite and granulite facies metamorphic assemblages. Data for the Fe-Mg exchange reaction between garnet and hornblende have been fitted to the equation.where K, is the Fe-Mg distribution coefficient, using a robust regression approach, giving a thermometer of the form:with very satisfactory agreement between garnet-hornblende and garnet-clinopyroxene temperatures. The thermometer is applicable below about 850 "C to rocks with Mn-poor garnet and common hornblende of widely varying chemistry metamorphosed at low sol.Application of the garnet-hornblende geothermometer to Dalradian garnet amphibolites gives temperatures in good agreement with those predicted by pelite petrogenetic grids, ranging from 520°C for the lower garnet zone to 565-610°C for the staurolite to kyanite zones. These results suggest that systematic errors introduced by closure temperature problems in the application of the garnet4nopyroxene geothermometer to the 'calibration' data set are not serious. Application to 'eclogitic' garnet amphibolites suggests that garnet and hornblende seldom attain Fe-Mg exchange equilibrium in these rocks.Quartzo-feldspathic and mafic schists of the Pelona Schist on Sierra Pelona, Southern California, were metamorphosed under high Present address:

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“…In the hypabyssal and subvolcanic horn blendes, in addition to those indicated, Fe 2 +, Ti:Mg= Fe2+, and probably, Si ** Ti, partici pate in the isomorphism. The change in the nature of the isomorphism in the amphiboles from formations of metamorphic rocks differing in conditions has been recorded by Kostyuk (1970) and Nikitina et al (1972).…”

Section: International Geology Reviewmentioning

confidence: 78%