New K-Ar cooling ages of granitoids from the Strzegom Sobótka Massif, SW Poland

• Autorzy: Turniak K. , Halas S. , Wójtowicz A.
• Języki publikacji: EN

Abstrakty

EN

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.

• Wydawca: De Gruyter
• Czasopismo: Geochronometria
• Rocznik: 2007
• Tom: Vol. 27
• Strony: 5--9
• Opis fizyczny: Bibliogr. 23 poz., rys., tab.

Twórcy

autor

Turniak K.

autor

Halas S.

autor

Wójtowicz A.

• 1Institute of Geological Sciences, Wrocław University, M. Borna 9, 50-205 Wrocław,

Bibliografia

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