Health & Environmental Research Online (HERO)


Print Feedback Export to File
6902089 
Journal Article 
Contrasting textural record of two distinct metamorphic events of similar P-T conditions and different durations 
Lexa, O; Stipska, P; Schulmann, K; Baratoux, L; Kroner, A; , 
2005 
Yes 
Journal of Metamorphic Geology
ISSN: 0263-4929
EISSN: 1525-1314 
WILEY 
HOBOKEN 
23 
8 
649-666 
English 
WOS:000232440300002 
A structural, metamorphic and geochronological study of the Stare Mesto belt implies the existence of two distinct metamorphic events of similar peak P-T conditions (700-800 degrees C, 8-10 kbar) during the Cambro-Ordovician and the Carboniferous tectonometamorphic events. The hypothesis of two distinct periods of metamorphism was suggested on the basis of structural discordance between an undoubtedly Carboniferous granodiorite sill intrusion and earlier Cambro-Ordovician fabrics of a banded amphibolite complex. The analysis of crystal size distribution (CSD) shows high nucleation density (N-0) and low average growth rate (Gt) for Carboniferous mylonitic metagabbros and mylonitic granodiorites. The parameter N-0 decreases whereas the quantity Gt increases towards higher temperatures progressively approaching the values obtained from the Cambro-Ordovician banded amphibolite complex. The spatial distribution of amphibole and plagioclase shows intense mechanical mixing for lower-temperature mylonitic metagabbros. In high-temperature mylonites a strong aggregate distribution is developed. Cambro-Ordovician amphibolites unaffected by Carboniferous deformation show a regular to anticlustered spatial distribution resulting from heterogeneous nucleation of individual phases. This pattern, together with CSD, was subsequently modified by the grain growth and textural equilibration controlled by diffusive mass transfer during Carboniferous metamorphism. The differences between the observed textures of the amphibolites are interpreted to be a consequence of the different durations of the Carboniferous and Cambro-Ordovician thermal events. 
Cambro-Ordovician and Carboniferous metamorphism; quantitative textural analysis; crystal size distributions; grain contact frequencies