Zachovalova, and 2 co-authors, reported in 2002 that the major-element chemistry as well as mineralogy indicate that the Aulova Batholith could be classified as a fractionated I-type granite. The interpretation of gravity data indicates a fair homogeneity of the batholith. The less fractionated amphibole − biotite tonalites and granodiorites form enclaves with remarkable cumulate textures. They are enriched in HFSE and REE as a consequence of crystal accumulation of allanite, apatite, ilmenite and titanite, their feldspar shows a rather simple internal fabric in CL. The more fractionated biotite granites constitute substantial part of the batholith. The enrichment in LILE and depletion in HFSE and REE corresponds to higher content of K-feldspar and lower amount of accessory phases.
Feldspars exhibit complex internal fabric in CL, indicating a major role for feldspar fractionation in the evolution of the batholith, as does the pronounced negative Eu anomaly and higher K/Ba ratio. The emplacement of the batholith was probably related to the Westphalian extensional tectonics. The Upper Carboniferous and lower Permian extension seems to have been generally of great importance for magmatic history of the eastern margin of Bohemian Massif, as manifested in the Boskovice Furrow, where the extensional tectonics connected with magmatic activity could be also documented.
The authors concluded that the negative correlation between SiO2 and xMg, and Sr/Rb ratio, but positive correlation SiO2 − K/Ba, as well as increase in the magnitude of negative Eu anomaly with SiO2 indicate a substantial role of fractionation processes in the evolution of the Aulova Batholith. The whole-rock geochemical data are supported by the compositional evolution of individual minerals: Biotites from granites have much lower xMg, compared to those from tonalites. K-feldspar from tonalities is richer in Ba, and contemporaneously K-feldspars from granites exhibit much more complex internal structure, documenting a role of fractionation (Shore − Fowler 1996). Plagioclase from granites has a similar complex structure and is more albitic in composition than plagioclase from tonalities. But the observed cumulate structures affecting the mafic minerals and some accessory minerals eg. apatite, biotite, titanite, zircon, allanite and xenotime indicate that processes of crystal accumulation played an important role in the earliest stages of the evolution.
Therefore, the authors concluded that the mafic enclaves are cumulates (Didier − Barbarin 1991, Best − Christians- en 2001), or orthocumulates (Shelley 1997), which were trapped and disrupted by granitic melt. The accumulation of accessory minerals controlled the distribution of REE and HFS elements. Cumulates are strongly enriched on REE, Y, Zr, Nb, Ti and P, and granites are depleted in these elements. The genetic interpretations of tectonic diagrams like the Y/Nb plot (Pearce et al. 1984) seem to be misleading because Y and Nb were preferably concentrated in the cumulates and later granites are therefore strongly depleted in these elements.
The major-element chemistry and mineralogy indicate strong I- type affinity of the batholith (Chappele − White 1992) dominated by accumulation and fractional crystallization. The high amount of allanite and low abundance of monazite are typical for I-type granites as well (Broska − Uher 1991, 2001). The high content of ilmenite and decrease of xMg in biotite with increasing total silica content are typical attributes of an ilmenite series batholith (Ishihara 1981). The presence of ilmenite instead of magnetite, which is normally more common in I-type granites, could be explained by in graphite- and carbonate-bearing rocks (Branná or Velké Vrbno groups) serving as a reducing agent (Ishihara 1981).
The composition of parental magma was probably granodioritic, because it must have allowed formation of mafic tonalite cumulates together with fractionated granites. Since the ratio between cumulate and fractionated products could not have been established in the field due to a possible influence of erosion, the precise composition of parental magma remains uncertain. However, because the both cumulates and fractionates are metaluminous, the parental melt was very likely metaluminous as well. Consequently, the protolith could be seen in the even strongly metaluminous rocks such as amphibolites or chemically related rocks (Johannes − Holtz 1996). The comparatively high contents of RE and HFS elements in the granites indicate that their relatively refractory carrier-phases (O’Hara et al. 2001) eg. zircon and apatite were involved in the melting. Therefore, it was likely a high-degree melting.
The emplacement of the batholith was likely related to the Westphalian extensional tectonic event (Maluski et al. 1995) which affected the northeastern margin of the Bohemian Massif. The late Carboniferous and early Permian extensional tectonics seems to be generally of great importance for magmatic history of the eastern margin of Bohemian Massif. Further manifestation of the extensional tectonics, followed by magmatic activity, could be documented in the Boskovice Furrow, where relatively primitive low-K, high-Na basaltic trachyande- sites, intruded lower Permian sediments (Leichmann 1996) and volcanoclastic material from effusive rocks forms a substantial proportion of the basin fill (Jelínek 2001).
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