Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

First found of proved pre-Variscan monazite in Moldanubicum


Václav Procházka, Petr Rajlich, Zuzana Korbelová, Viktor Goliáš

Geoscience Research Reports 43, 2010 (GRR for 2009), pages 240–244
Map sheets: Tábor (23-13)

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A deformed leucogranite at Sudoměřice near Tábor contains monazite rich in uranium (2.2-7.1 wt. % UO2) and therefore suitable for electron microprobe dating. In several grains, cores of Cambrian/Ordovocian age were found and verified by control analyses at another laboratory. The pre-Variscan chemical ages range mostly from 474 to 514 Ma (n = 5) and the ages of Variscan overgrowths and small grains prevalently from 294.4 to 319.2 Ma (n = 9); two outlying values (341 and 419 Ma) probably represent mixed ages. The leucogranite contains angular inclusions of a common Moldanubian well foliated biotite paragneiss, in which only Variscan and U-poor monazite was found. Thus the leucogranite cannot be interpreted as a Variscan intrusion contaminated with older monazite, and the Cambroordovician monazite ages most likely represent the younger limit of granite formation.