Greenschist-amphibolite transition equilibria at low pressures.

S. Maruyama, K. Suzuki, J. G. Liou

Research output: Contribution to journalArticle

114 Citations (Scopus)

Abstract

In low P-T progressive metamorphism of basaltic rocks in the Yap Islands, W Pacific, and in Kasuga, Japan, quartz-bearing assemblages change from albite + actinolite + epidote + chlorite (greenschist) to plagioclase + hornblende (amphibolite). This transition can be divided into three subzones characterized, respectively, by two Ca-amphiboles + two sodic plagioclases (B1), one Ca- amphibole + two sodic plagioclases (B2), and hornblende + plagioclase An12-50 (B3) together with epidote, chlorite and quartz. The B1-B2 boundary is sensitive to host-rock Fe/Mg ratio; hornblende and oligoclase appear simultaneously at the onset of zone B1 corresponding with the greenschist-epidote amphibolite facies boundary. With increasing metamorphic grade, plagioclase changes from albite (An0-7) through two Na-plagioclases to andesine (An12-50), epidote grades Ps35-17 and Ca-amphibole passes from actinolite through actinolite-hornblende pairs to hornblende; concurrently, the Al content of chlorite increases. The compositional range shown by amphiboles through this progressive sequence indicates that the so-called immiscibility between actinolite and hornblende may be a transition loop rather than a solvus; polymorphic transformation of actinolite is estimated to be at 420oC, 2 kbar and 450oC, 3 kbar Pfluid. The results subdivide the transition zone into a high-P albite-epidote amphibolite facies and a lower-P actinolite-calcic plagioclase hornfels facies (M.A. 15-483). Experimental data yield much higher T and a wider T range for the transition zone due to the equality of PH2O and Ptotal and possible lower fO2 compared to natural metamorphic conditions. -R.A.H.

Original languageEnglish
Pages (from-to)583-604
Number of pages22
JournalJournal of Petrology
Volume24
Issue number4
Publication statusPublished - 1983
Externally publishedYes

Fingerprint

greenschist
plagioclase
amphibolite
low pressure
Amphibole Asbestos
hornblende
epidote
amphiboles
amphibole
albite
chlorite
Quartz
amphibolite facies
transition zone
grade
Bearings (structural)
quartz
Rocks
rocks
hornfels

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Maruyama, S., Suzuki, K., & Liou, J. G. (1983). Greenschist-amphibolite transition equilibria at low pressures. Journal of Petrology, 24(4), 583-604.

Greenschist-amphibolite transition equilibria at low pressures. / Maruyama, S.; Suzuki, K.; Liou, J. G.

In: Journal of Petrology, Vol. 24, No. 4, 1983, p. 583-604.

Research output: Contribution to journalArticle

Maruyama, S, Suzuki, K & Liou, JG 1983, 'Greenschist-amphibolite transition equilibria at low pressures.', Journal of Petrology, vol. 24, no. 4, pp. 583-604.
Maruyama, S. ; Suzuki, K. ; Liou, J. G. / Greenschist-amphibolite transition equilibria at low pressures. In: Journal of Petrology. 1983 ; Vol. 24, No. 4. pp. 583-604.
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