Prograde metamorphism of metapelites, garnet-biotite thermometry and prograde changes of biotite chemistry in high-grade rocks of West Uusimaa, southwest Finland
1985; Elsevier BV; Volume: 18; Linguagem: Inglês
10.1016/0024-4937(85)90011-8
ISSN1872-6143
Autores Tópico(s)Paleontology and Stratigraphy of Fossils
ResumoThe metamorphic grade in west Uusimaa, SW Finland, increases from low- to intermediate-amphibolite facies in the west (Island of Kemiö) up to granulite facies in the middle and eastern parts. Mineral assemblages in metapelitic rocks indicate metamorphic conditions of 700–825°C, 3–5 kbar for the high-amphibolite and granulite facies region, which is in agreement with independent estimates. These metamorphic conditions are used to evaluate garnet-biotite thermometry. Zoning in garnet, Fe enrichment and Mg depletion towards rims bordered by biotite or cordierite, and a distinct Fe depletion/Mg enrichment of biotites in contact with garnet are caused by FeMg exchange of these minerals during retrogression (550°C). The general prograde metamorphic trend from medium- to high-grade in West Uusimaa is reflected by a systematic change in the composition of biotites. Thermometry and biotite chemistry are used to indicate that the granulite facies metamorphism in West Uusimaa is probably caused by a thermal event.
Referência(s)