International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

GEOCHRONOLOGY OF TESCHENITIC INTRUSIONS IN THE OUTER WESTERN CARPATHIANS OF POLAND — CONSTRAINTS FROM 40K /40Ar AGES AND BIOSTRATIGRAPHY

Pages: 385 - 393

Authors: JACEK GRABOWSKI, LESZEK KRZEMINSKI, PIOTR NESCIERUK, ANDRZEJ SZYDLO, MARIUSZ PASZKOWSKI, ZOLTAN PECSKAY, ARTUR WOJTOWICZ

Abstract: New 40K/40Ar datings for teschenitic rocks in the Silesian Unit of the Outer Western Carpathians in Poland are presented. Several petrological varieties of intrusions were studied in 5 localities. Dating was performed on monomineral separates of biotites and amphiboles as well as on whole rock samples. The biotite ages (137.9–133.1 Ma — Valanginian) are significantly older than those of amphiboles (112.5–89.9 Ma — Albian–Turonian). Whole rock ages are considerably spread between those two clusters, being concordant either with ”biotite” or ”amphibole” dates or much younger. Interpretation of data poses some problems because evidence exists for hydrothermal alterations, which 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 the duration of the teschenitic and related magmatism in the Silesian Basin was probably from Valanginian up to Barremian–Aptian (ca. 15 Ma).

Keywords: Cretaceous, Outer Western Carpathians, Silesian Unit, teschenitic rocks, 40K/40Ar geochronology

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