GRANITIC MAGMATISM ASSOCIATED WITH THE VARISCAN-AGE MOLDANUBIAN BATHOLITH, CZECH REPUBLIC: A GEOCHEMICAL COMPARISON BETWEEN THE MRÁKOTÍN AND KLENOV PLUTONS

The Moldanubian Unit represents deeply-eroded middle to lower crust that experienced pervasive high-T/P metamorphism and voluminous granitic magmatism during the Variscan orogeny. The Moldanubian batholith is a NNE-SSW striking composite batholith of Eisgarn-type granite that was emplaced shortly after regional uplift of the eastern margin of the Moldanubian Unit and migmatization of the host metapelitic rocks (the Pehløimov complex). It has been proposed (Žák et al., 2010) that the Moldanubian granites were produced by partial melting of the Pehløimov rocks during rapid uplift. We focus here on the 327 Ma Mrákotín pluton (within the main body of the batholith) and the 328 Ma Klenov pluton, which was emplaced ~30 km west of the Mrákotín pluton. Both plutons comprise equigranular to porphyritic andalusite two-mica granite. In addition, both plutons are strongly peraluminous and alkali-calcic (after Frost et al., 2001), characteristic of magmas generated from melting of overthickened metapelitic crust. However, most samples from the Mrákotín pluton are magnesian (Fe#=0.60-0.71), whereas most of the Klenov samples are ferroan (Fe#=0.91-0.94). The main bodies of both granites exhibit broadly similar chondrite-normalized REE patterns; Mrákotín rocks show slightly more REE fractionation (La_N/Yb_N=21.8-61.4) than Klenov samples (La_N/Yb_N=4.9-27.6), and less pronounced Eu-anomalies (Eu/Eu*=0.23-0.34 versus 0.38-0.68 in Klenov rocks). Metapelitic rocks of the Pehløimov complex are less fractionated than the granites (La_N/Yb_N=6.3-7.5) and have less-pronounced Eu-anomalies. Overall, the compositions of the plutons are consistent with an origin by partial melting of metapelitic rocks. Differences in composition between the Mrákotín and Klenov plutons probably reflect heterogeneity in the source, or slight differences in the conditions of partial melting.