Publication details

Distribuce a klasifikace intragranitických NYF pegmatitů třebíčského plutonu

Title in English Distribution and classification of intragranitic NYF pegmatites of the Třebíč Pluton
Authors

ZACHAŘ Adam

Year of publication 2015
Type Conference abstract
MU Faculty or unit

Faculty of Science

Citation
Description The Třebíč Pluton (TP) is a flat durbachite body (K, Mg-rich melamonzogranites to melaquartzsyenites), which intruded Moldanubian gneisses during Variscan orogenesis. TP is parental granite of abundant NYF pegmatites, from most of them are situated in the pluton itself and could be classificated as allanite-monazite and euxenite subtypes of REL-REE class, NYF family (Škoda et al. 2006). TP is divided by several fault systems into the mosaic of differently denudated rafts. Some of them contain many pegmatites, in the other hand in some of them pegmatites are scarce. The Třebíč Fault divides the pluton into two geophysically contrasting parts (radioactivity, gravity anomalies, density of rocks). The northern part is formed by Zhoř, Hroznatín and Tasov tectonic segments, southern part by Boňov and Ohrazenice part (Bubeníček 1968). Pegmatites are abundant in Hroznatín and Boňov segments, in the others are rare. In the Hroznatín segment, mainly in the vicinity of city Velké Meziříčí, are characteristic short, rod-like zonal pegmatites with significantly large primal cavities, often with albitisation a showing primitive mineralogy (allanite, titanite, ilmenite, zircon, more rare aeschynite, pyrite and tourmaline). These pegmatites mostly belong to allanite-monazite subtype. From the Boňov segment in the Třebíč-Vladislav area the abundant lense-like euxenite pegmatites with amazonite, Y+REE-Nb-Ta-Ti-oxides, in places altered beryl, tourmaline and rare Sn-minerals are known. Pegmatites contain small primal cavities. Isolated occurence of amazonite pegmatites is in vicinity of Boňov village (Škoda et al. 2006, Zachař a Novák 2013). Assuming that pegmatites in apical parts of pluton are, is possible these rafts rich in pegmatites are subsided, while some other rafts, namely Tasov segment, where the acid core of pluton encovered is, represent elevated and much denudated parts of pluton (Bubeníček 1968). This is fit with new geophysical datas (Leichmann et al., in print), where the areas of abundant occurences of pegmatites overlap with areas of hightened radioactivity, positive gravity anomalies and higher density of durbachites. Hence, pegmatites show the distribution of themselves in the parental granitic pluton and their mineralogical composition, which documents the level of fractionation, could serve for geological implication, too.

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