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- Title
THE GRANODIORITES WITH BIOTITE NODULES IN THE NORTHERN SEBEȘ MOUNTAINS (SOUTH CARPATHIANS).
- Authors
Ion, STELEA; Monica, GHENCIU
- Abstract
A large swarm of rhyodacite dykes and some granodiorite bodies outcrop along the Rășinari Shear Zone in the northern Sebeș-Cibin Massif. The rhyodacites are Cretaceous in age and the granodiorites are older (Liasic probably) since they frequently occur as lithic restites in rhyodacites. Two granodiorite bodies on the central sector of the shear zone contain spheroidal biotite nodules, a rare petrographic feature found only in granitoid rocks. The typical internal structure of the nodules is quasi-concentric, with thick shells of biotite arranged around a central core consisting of intergrowth of biotite-quartz and biotite-plagioclase. The large nodules of 3-5 cm are polycentric, with two or three secondary centers around the core. According to Van Diever (1970), the biotite nodules in the granite of Craftsbury (Vermont, US) were formed by adhering of biotite sheets around some gas bubbles to which additional gas bubbles were attached during the ascending migration through a low viscosity, volatile-rich magma. The nodules float until the collapse of the gas bubble and the nodules with uncollapsed bubbles agglomerate in the ceiling of the magmatic chamber. The pegmatitic segregations in the granodiorites with biotite nodules from the north of the Sebeș Mountains corroborated with our microscopic observations support this hypothesis.
- Subjects
ROMANIA; VERMONT; BIOTITE; SHEAR zones; GRANODIORITE
- Publication
Oltenia, Studii si Comunicari Seria Stiintele Naturii, 2021, Vol 37, Issue 1, p7
- ISSN
1454-6914
- Publication type
Article