SROVNÁNÍ CHEMISMU TŘEBÍČSKÉHO DURBACHITU A JINÝCH DURBACHITŮ

Vol.7,(2000)

Petr Sulovsky

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Abstract
The Třebíč massif, composed mostly of ultrapotassic igneous rocks known as durbachites (melanogranite to melanosyenite), is the third most radioactive batholith in Czechia. The heavy mineral concentrates panned from bottom sediments of streams flowing across the massif, however, do not show a corresponding regional anomaly. The paper presents results of the first year research project focused on the explanation of this discrepancy. Based on large-scale sampling (117 samples taken at 49 sites), the distribution of U and Th follows the blocky pattern revealed by Bubeníček in 1968. The bulk rock chemistry of Třebíč durbachites confirmed their close similarity with other ultrapotassic rocks of the world and the "mixed" nature of their magma (matle / crustal sources). Both major and trace element concentrations indicate their association with collisional (syn- and post-) tectonic settings.

Keywords:
durbachite; radioactivity; trace elements; ultrapotassic rocks; Třebíč massif
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