Petrology of some Glaucophane Schist and Related Rocks from Taiwan

Tsung-Siang Chiu

Abstract

The study of glaucophane schists, garnet-epidote amphibolite, and epidote amphibolite in the eastern slope of Central Mountain Range, Taiwan indicate these assemblages are considered to exotic tectonic blocks emplaced into the feebly metamorphosed in situ graphite quartz schists of the Yuli belt. Thin lenses of Mn-rich metamorphosed tuff are intercalated into the metabasalts. Such high MnO and law MgO tuffaceous rocks are similar in bulk composition to some volcanic clays collected from deep ocean basin.

Microprobe analyses of coexisting minerals in glaucophane schist, garnet-epidote amphibolite, and epidote amphibolite have following results：(1) Garnet, consisting of almandine, spessartine, pyrope, and grossular. The components are less than Mn and Mg-rich compared to these in metabasalts of the Franciscan; (2) rim epidotes of the glaucophane schists are much higher in Fe than that of the garnet-epidote amphibolite meaning when glaucophanization was in an oxidized condition and probably at lower temperature than the metamorphism of the garnet-epidote amphibolite.; (3) phengite of the glaucophane schists have less Al2O3 content than those of the garnet-epidote amphibolite whereas micas of the epidote amphibolite are paragonite; (4) zoned amphiboles show the component in glaucophane schists core is sodic-calcic amphibole and the rim is glaucophane and in garnet-epidote amphibole are all calcic amphibole.

The garnet-epidote-rutile bearing glaucophane schists in taiwan probably recrystallized at temperatures above 350℃whereas the lawsonite-sphene glaucophane schists of the Franciscan equilibrated blew 350 ℃. The Mn-rich basaltic tuffs and their associated flows seem to have been metamorphosed at deep depths and at the temperature of the epidote amphibolite facies, then later by glaucophane schist facies metamorphism at lower temperature.

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Liou, J. G., Ho, C. O., and Yen, T. P. (1975) Petrology of some glaucophane schists and related rocks from Taiwan: J. Petrol., 16, pp. 80-109.

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