ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Actinolite-actinolitic hornblende and actinolitic hornblende-hornblende pairs are described from gabbroic amphibolites and epidote amphibolites formed by dynamic metamorphism during uplift of gabbroic rooks in the Hidaka Metamorphic Belt, Hokkaido. Electron microprobe analyses indicate that coupled substitutions involved in the transition from actinolite to hornblende are essentially those of edenite and tschermakite-ferritschermakite together with smaller amounts of glaucophane-riebeckite, i.e. AlIV, AlVI, Fe3+, A-site occupancy and NaM4 increase with replacement of Mg by Fe2++ Mn and Si by AlIV. During metamorphism the amount of deformation due to shearing has affected the degree of compositional discontinuity in the actinolite-hornblende series and the compositional gap is most pronounced in the epidote amphibolite. The coexisting actinolite-hornblende do not represent an equilibrium pair as textural relations indicate that the actinolitic amphiboles are relics. It is suggested that shearing deformation during uplift has caused an overstepping of the changing physico-chemical conditions of metamorphism so that compositional readjustment of amphiboles was not achieved. Equilibrium-disequilibrium actinolite-hornblende pairs are discussed from other localities where rocks of basaltic composition have been metamorphosed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00373856
