**4.6 Titanite composition**

The composition of titanite ranges from 83 to 92 mol.% titanite end-member (**Table 4**). The Al and Fe3+ contents range from 0.06 to 0.16 apfu and from 0.01 to

**Figure 6.** *BSE image of zoned zircon from the Červená granodiorite.*

**Figure 7.**

*BSE image of titanite (Ttn) from the Červená granodiorite.*

0.04 apfu, respectively. Analyzed titanites show Al + Fe3+ excess over F. This excess indicates the occurrence of the coupled substitution of Al + Fe<sup>3</sup> (**Figure 11**). The content of (Al + Fe3+)-F component ranges from 6 to 13 mol.%. The content of (Al + Fe3+)-OH component is lower and ranges from 0 to 5 mol.%. The content of REE in analyzed titanites is usually low, however the content of Ce2O3 ranges from 0.11 to 0.33 wt.% and content of Nd2 O3 ranges from 0.02 to 0.30 wt.%.

*Investigation of Accessory Minerals from the Blatná Granodiorite Suite, Bohemian… DOI: http://dx.doi.org/10.5772/intechopen.102628*

**Figure 8.** *BSE image of allanite from the Blatná granodiorite (Aln, allanite; Bt, biotite; Kfs, K-feldspar; Qz, quartz).*

### **Figure 9.**

*BSE image of altered allanite from the Blatná granodiorite (Aln, allanite; Bt, biotite; Py, pyrite).*

### **4.7 Allanite composition**

The originally magmatic allanite contains 31.4–32.4 wt.% SiO2, 10.3–13.3 wt.% CaO, 9.8–15.1 wt.% FeO, 0.1–2.7 wt.% ThO2, and 17.5–23.2 wt.% REE2O3 (**Table 5**). Analyzed allanites are relatively enriched by Mn, containing 0.23–0.65 wt.% MnO. All analyzed allanites display variable distribution of REE, with the preference of Ce over

### *Mineralogy*


### **Table 2.**

*Representative microprobe analyses of apatite.*

La. Cerium is thus the predominant lanthanide, thus these allanites could be classified as allanite-(Ce). On the plot proposed by Petrík et al. [12], the analyzed allanites are located between allanite and ferriallanite (**Figure 12**). The Al values range between 1.44 and 2.12 apfu. It can be also observed, that the individual points are located between isolines 0.2 and 0.5 Feox. = Fe3+/(Fe3+ + Fe2+). The values of these points calculated by the method Armbruster et al. [13] are partly lower (0.18–0.43).


*Investigation of Accessory Minerals from the Blatná Granodiorite Suite, Bohemian… DOI: http://dx.doi.org/10.5772/intechopen.102628*

### **Table 3.**

*Representative microprobe analyses of zircon.*

**Figure 10.** *Chemical composition of zircon from granodiorites of the Blatná suite.*

The altered allanites are enriched in Si (40.6–42.0 wt.% SiO2 and Th (3.1–6.4 wt.% ThO2), depleted in Fe (2.2–4.2 wt.% FeO) and Ca (5.8–8.6 wt.% CaO). The altered allanites display also a lower total analytical sum, which indicate postmagmatic alterations.

## **5. Discussion**

### **5.1 Fractionation of the Blatná suite**

The high-K calc-alkaline to shoshonitic granitic rocks of the Blatná suite could be classified as hybrid H-granites in the sense of granite classification proposed by Castro et al. [14]. According to the primary Rb/Sr. ratio and the Nd-isotope ratios, the origin of this suite could be coupled either by mixing of different magmas with distinct isotopic features and/or by crustal contamination of more basic magmas. According to some other interpretation, granitic rocks of the Blatná suite are products of fractionation mantle-derived magmas and their mixing with relatively heated metamorphic rocks of the Moldanubian Zone [15]. The recently preferred explanation of the Blatná suite origin is coupled with remelting of a heterogeneous earth crust composed of immature greywackes rich in the Cambrian volcanogenic detritus [2]. An additional important process was variable mixing with slightly enriched mantle-derived monzonitic magmas, which also may have supplied the extra heat needed for the crustal anatexis [1].

### **5.2 Substitution in apatite**

There are systematic and distinctive differences in Fe, Mn, REE, F, and Cl contents in apatites from I- and S-type granitic rocks [7, 16]. For I-type, granitic rocks are



### *Mineralogy*


### **Table 4.**

*Representative microprobe analyses of titanite.*

### **Figure 11.**

*Chemical composition of titanite from granodiorites of the Blatná suite.*

significant a lower content of Fe and Mn, higher contents of LREE, and lower content of Y [17]. The content of Fe in analyzed apatites is 0.02–0.27 wt.% FeO and content of Mn in these apatites is 0.03–0.12 wt.% MnO. The increase of Mn content in apatites


*Investigation of Accessory Minerals from the Blatná Granodiorite Suite, Bohemian… DOI: http://dx.doi.org/10.5772/intechopen.102628*

### *Mineralogy*


### **Table 5.**

*Representative microprobe analyses of allanite.*

### **Figure 12.**

*The plot of total REE + Y + Th + Mn vs. Al contoured with isolines of the ratio Fox. = Fe3+/(Fe2+ + Fe3+) illustrating the chemical relationships in the system allanite-ferriallanite-epidote-clinozoisite according Petrík et al. [12].*

from S-type granitic rocks is a function of an increase of Mn/Fe and Mn/Ca ratios with fractionation [16]. The La/Y ratio in analyzed apatites is 0.01–0.40. This ratio is partly comparable with the La/Y ratio for I-type granitic rocks (0.2–3.25) according to Sha and Chappell [17].

### **5.3 Substitution in zircon**

The most common trace element in zircon is hafnium. The HfO2 contents in granitic rocks usually range from 0.5 to 9.9 wt.%, with a median of 1.5 wt.% [18]. In *Investigation of Accessory Minerals from the Blatná Granodiorite Suite, Bohemian… DOI: http://dx.doi.org/10.5772/intechopen.102628*

similar granitic rocks from the Bohemian Massif, their contents usually range between 0.8 and 2.2 wt.% HfO2 [19, 20]. The content of Y in zircon from granitic rocks is usually 0.2–0.7 wt.% Y2O3 [21]. In similar, biotite granites that form the Moldanubian batholith zircon contains 0.1–0.9 wt.% Y2O3 [19]. The content of ThO2 in F-low biotite granites from the Krušné Hory/Erzgebirge batholith is partly higher (up to 1.3 wt.% ThO2) [20], whereas its content in zircon from two-mica granites of the Moldanubian batholith is similar (0.01–0.2 wt.% ThO2) [19].

### **5.4 Substitution in titanite**

Titanite is, according to the variability of its chemical composition, suggested as a highly sensitive indicator of oxygen and water fugacity [22–24]. The chemical composition of analyzed titanite shows that the substitution (Al, Fe3+) + F = Ti4+ O2 is the most significant in analyzed titanites. According to their F, Al, and Fe3+ concentrations, the analyzed titanites could be considered as low-Al titanites, according to Oberti et al. [25]. Their low F and Al content could be well compared with the contents of both elements in similar magmatic titanites [26].

### **5.5 Substitution in allanite**

For allanite, two main substitutions occur, namely the epidote-allanite and the allanite-ferriallanite substitutions [27, 28]. For analyzed allanites from granodiorites of the Blatná suite, the allanite-ferriallanite substitution is significant. In the other Variscan granitic rocks from the Bohemian Massif allanite was found in some granites and granodiorites of the Moldanubian batholith [29] and from lamprophyres of the Krkonoše-Jizera composite pluton [30]. Allanites from both magmatic bodies display similar chemical compositions and also similar values of Feox. = 0.3–0.5.

## **6. Conclusions**

The granodiorites of the Blatná suite contain 12–18 vol.% of biotite, 28–42 vol.% plagioclase, 22–28 vol.% quartz, 9–19 vol.% K-feldspar, and 0.2–1.2 vol.% hornblende. These granodiorites are high-K, calc-alkaline to shoshonitic rocks.

The REE-, Zr-, and Y-bearing accessories in granodiorites of the Blatná suite are represented by apatite, zircon, and relatively rare occurred titanite and allanite. All analyzed apatites contain more F (3.0–4.5 wt.%) and less Cl (0.0–0.2 wt.%). Apatite zonation is very rare and coupled with different concentrations of Y and REE. The analyzed zircons contain low Hf concentrations (1.1–1.7 wt.% HfO2). The composition of analyzed titanite ranges from 83 to 92 mol.% titanite end-member. The analyzed allanites display variable distribution of REE, with the preference of Ce over La. Allanite is relatively Al-poor and displays Feox. ratio 0.2–0.5.

## **Acknowledgements**

This study was carried out thanks to the support of the long-term conceptual development research organization RVO 67985891. I am grateful to R. Škoda, R. Čopjaková, and J. Haifler from the Department of geological sciences of Masaryk University for technical assistance by electron microprobe analyses of selected minerals (allanite, apatite, titanite, and zircon).
