Nowe dane o wieku skał cieszynitowych (Karpaty zewnętrzne, jednostka śląska) — rezultaty datowań metodą K–Ar

Jacek Grabowski, Leszek Krzemiński, Piotr Nescieruk, Mariusz Paszkowski, Andrzej Szydło, Zoltán Pécskay, Artur Wójtowicz


New data on the age of teschenitic rocks (Outer Carpathians, Silesian Unit)—results of the K–Ar dating.
Summary. New 40K/40Ar datings for intrusive teschenitic rocks in the Silesian Unit of the Outer Western Carpathians in Poland are presented. Several petrological varieties of the intrusions were studied at 5 localities. Dating was performed on monomineral separates of biotites and amphiboles, as well as on whole rock samples. Biotite ages (137.9–133.1Ma: Valanginian) are significantly older than those of amphiboles (112.5–89.9 Ma: Albian–Turonian). Whole rock ages are considerably spread between these two clusters, being concordant either with “biotite” or with“amphibole” dates, or much younger. Interpretation of data poses some problems because evidence exists for hydrothermal alterations what might influence Ar content  in both minerals. Older, biotite ages, are interpreted as more reliable crystallization ages since they are close to the age of surrounding sediments and are concordant with field observations that intrusions in some cases are almost surficial. Amphibole ages are probably affected by Ar loss due to hydrothermal activity. Comparison with recently published 40Ar/39Ar datings implies that duration of teschenitic and related magmatism in the Silesian Basin was probably from Valanginian up to Barremian–Aptian (ca. 15 Ma).

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