%0 Journal Article
%T New K-Ar Cooling Ages of Granitoids from the Strzegom-Sob¨®tka Massif, SW Poland
%A Krzysztof Turniak
%A Stanislaw Halas
%A Artur W¨®jtowicz
%J Geochronometria
%@ 1897-1695
%D 2007
%I 
%R 10.2478/v10003-007-0019-9
%X The Strzegom-Sob¨®tka 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¡À4.6 Ma and 305.5¡À4.3 Ma) comprises results obtained from the biotite granodiorites. They are generally consistent with the zircon crystallization age of 308.4¡À1.7 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¡À4.4 Ma and 298.7¡À5.2 Ma ages for the hornblende-biotite monzogranite and 294.2¡À4.3 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.
%K Variscan granitoids
%K biotite
%K cooling age
%K K-Ar dating
%K Strzegom-Sob¨®tka Massif
%U http://versita.metapress.com/content/37h13415l645g253/?p=afc027f03dab499c92489dee5d7a7199&pi=1