<abstract xml:lang="en" xmlns="http://www.w3.org/1999/xhtml"><p>The Strzegom-Sobótka Variscan Massif (Fore-Sudetic Block, NE Bohemian Massif) consists of various post-kinematic Variscan granitoids emplaced into Palaeozoic low grade metamorphic rocks. Biotite from five samples representing the hornblende-biotite monzogranite, biotite monzogranite and biotite granodiorite has been dated using the K-Ar method for two size-fractions (0.25-0.35 and 0.35-0.5 mm). Finer fractions show more intense chloritization and therefore the results for them were rejected in further discussion. Coarser fractions with higher potassium content were accepted as yielding a maximum estimate approaching the true K-Ar biotite cooling ages. The results are clustered in two groups. The older age group (308.8±4.6 Ma and 305.5±4.3 Ma) comprises results obtained from the biotite granodiorites. They are generally consistent with the zircon crystallization age of 308.4±1.7 Ma reported by Turniak <italic>et al.</italic> (2005) and imply rapid cooling of the biotite granodiorite from magmatic temperatures down to the closure temperature of K-Ar isotopic system in biotite. The younger group is defined by 291.0±4.4 Ma and 298.7±5.2 Ma ages for the hornblende-biotite monzogranite and 294.2±4.3 Ma age for the biotite monzogranite. In the absence of precise U-Pb or Pb-Pb zircon data further geochronological studies are needed to decipher precisely the cooling history of the monzogranites.</p></abstract>

The Strzegom-Sobótka Variscan Massif (Fore-Sudetic Block, NE Bohemian Massif) consists of various post-kinematic Variscan granitoids emplaced into Palaeozoic low grade metamorphic rocks. Biotite from five samples representing the hornblende-biotite monzogranite, biotite monzogranite and biotite granodiorite has been dated using the K-Ar method for two size-fractions (0.25-0.35 and 0.35-0.5 mm). Finer fractions show more intense chloritization and therefore the results for them were rejected in further discussion. Coarser fractions with higher potassium content were accepted as yielding a maximum estimate approaching the true K-Ar biotite cooling ages. The results are clustered in two groups. The older age group (308.8±4.6 Ma and 305.5±4.3 Ma) comprises results obtained from the biotite granodiorites. They are generally consistent with the zircon crystallization age of 308.4±1.7 Ma reported by Turniak et al. (2005) and imply rapid cooling of the biotite granodiorite from magmatic temperatures down to the closure temperature of K-Ar isotopic system in biotite. The younger group is defined by 291.0±4.4 Ma and 298.7±5.2 Ma ages for the hornblende-biotite monzogranite and 294.2±4.3 Ma age for the biotite monzogranite. In the absence of precise U-Pb or Pb-Pb zircon data further geochronological studies are needed to decipher precisely the cooling history of the monzogranites.

New K-Ar Cooling Ages of Granitoids from the Strzegom-Sobótka Massif, SW Poland

Institute of Geological Sciences, Wrocław University, M. Borna 9, 50-205 Wrocław

Institute of Physics, Maria Curie-Sklodowska University, Plac Marii Curie-Skłodowskiej 1, 20-031 Lublin, Poland

Geochronometria

{"article-title":"New K-Ar Cooling Ages of Granitoids from the Strzegom-Sobótka Massif, SW Poland"}

The Strzegom-Sobótka Variscan Massif (Fore-Sudetic Block, NE Bohemian Massif) consists of various post-kinematic Variscan granitoids emplaced into Palaeozoic...

New K-Ar Cooling Ages of Granitoids from the Strzegom-Sobótka Massif, SW Poland

Published Online: Jul 04, 2007

Page range: 5 - 9

DOI: https://doi.org/10.2478/v10003-007-0019-9

Keywords
Variscan granitoids, biotite, cooling age, K-Ar dating, Strzegom-Sobótka Massif

This content is open access.

New K-Ar Cooling Ages of Granitoids from the Strzegom-Sobótka Massif, SW Poland

Published Online: Jul 04, 2007

Page range: 5 - 9

DOI: https://doi.org/10.2478/v10003-007-0019-9

KeywordsVariscan granitoids, biotite, cooling age, K-Ar dating, Strzegom-Sobótka Massif

This content is open access.

Keywords
Variscan granitoids, biotite, cooling age, K-Ar dating, Strzegom-Sobótka Massif