Printer Friendly

Sekaninaite and fingerprint hercynite in South Bohemian granulites.

INTRODUCTION

Granulite, mostly in its light acidic variety, belongs among the most typical lithologies of the south Bohemian part of Moldanubicum. It occurs in five main bodies shown in Fig. 1. In the order of decreasing areal extent these are as follows: Blansky les, Krist'anov, Prachatice and Lisov massifs, Krasejovka stock and Vcelnice, Ratibor and Zd'arske Chalupy lenses (comp. Vrana and Sramek 1999). The appurtenance of some further bodies to the granulite family remains still a subject to discussion but this is already beyond the scope of the present contribution. Special petrographic character of typical and unquestionable granulites, contrasting with the ambient crystalline schists, has been attracting the attention of geologists for more than one century, and the number of papers on these granulites is countless.

Also granulite minerals have been studied in detail, especially with the aid of electron microprobe techniques. For cordierite and spinel minerals occurring in the South Bohemian granulites not frequently but also not scarcely, however analytical determinations have been still missing. Also their position in the granulite evolution remained obscure. Some extreme and hitherto unknown structures merit more attention as well. The aim of the present paper is to reveal new facts in this respect and to contribute to the solution of the above mentioned, hitherto unanswered questions.

SAMPLES AND THEIR GEOLOGICAL POSITION

The material for our study comes from two localities: 1--from the abandoned two-bench quarry ,,Pod Libinem" known more likely under the name Bernkopf, in the SE outskirts of Prachatice, and 2 from a small granulite body at Zd'arske Chalupy settlement near Protivin SE of Pisek. In the Bernkopf guarry, sufficient fresh material is available, and the granulite body of Zd'arske Chalupy offers several small natural outcrops and boulders dispersed on a forested ridge. No problem was connected with the acquisition of suitable samples containing a cordierite mineral because its presence is macroscopically easily distinguishable in the rock. More complicated was the situation with spinel minerals as they are almost not visible by naked eye and are not present everywhere; therefore, several randomly collected rock specimens have to be taken. Our methodical approach consisted of a field study with rock sampling at both localities followed by microscopic examination of thin sections, chemical wet analyses of rocks and electron microprobe analyses of minerals in polished thin sections.

The Bernkopf locality, briefly described as an excursion stop by Vrana (1992), is situated in the marginal part of the Prachatice massif. Geological and petrographic characteristics of this large granulite body can be found e.g. in the papers of Hejtman (1977) or Fiala et al. (1987). The body is 12 km long and 7 km wide, surrounded by paragneisses and migmatites with amphibolite and quartzite layers and minor lenses of serpentinite and orthogneiss. The massif itself is composed mainly of slightly banded biotite-garnet granulite locally passing into very light facies almost devoid of biotite. Kyanite is a typical minor constituent and subsidiary amounts of further high-alumina minerals such as sillimanite, spinel, corundum and sapphirine, sometimes cordierite, have been reported (Slaby 1992a). Small granitic dykes (porphyries, pegmatites, aplites) cut the whole crystalline complex at several places.

[FIGURE 1 OMITTED]

The Zd'arske Chalupy granulite body, known from the paper of Fediukova and Fediuk (1971) and Fiala et al. (1987), is substantially smaller: slightly over 2 km long but only 150 m wide. It has the shape of a platy lens elongated along E-W strike, covered with Quaternary sediments at both ends It is incorporated between monotonous migmatites and a varied sequence of amphibolites, paragneisses, kinzigites and pyroxene gneisses penetrated by two-mica granite dykes. A minute serpentinite body is located at the margin of the granulite. The main granulite rock type is banded kyanite-bearing biotite granulite. Sillimanite, cordierite and scarce spinel occur in subordinate local parts of the body.

ROCKS

Our interest was not focused on common granulites occurring at both localities examined. For the characteristics of such rocks we refer to the descriptions of Fiala et al. (1987) or Vrana (1992) in the case of Bernkopf locality and Fediukova and Fediuk (1971) and Fiala et al. (1987) in the case of Zd'arske Chalupy site. The following mineral assemblage is typical for both of them: microperthitic feldspar > quartz > acid plagioclase > biotite > garnet [much greater than] kyanite > sillimanite ([+ or -]) > accessories. High Si[O.sub.2] content (often exceeding 70 %), predominance of [K.sub.2]O over [Na.sub.2]O and peraluminous chemistry, reflected in the presence of high-alumina minerals and in normative (sometimes even modal) corundum, can be presented as most typical geochemical features.

In degraded granulites, ferromagnesian silicates (garnet and biotite) and kyanite were partly or entirely transformed into new minerals phases--spinel and/or cordierite mineral. Such transformation is usually well visible macroscopically by the decreasing colour-ratio of the rock and by gradual loss of banded structure. In addition to that, grains of cordierite minerals, due to their partial pinitisation, are easily discernible by their grey-greenish tint. None of the previous papers reporting the presence of cordierite minerals in South Bohemian granulites quantificated their proportion in the bodies of common granulites. The following rough estimations attempt to eliminate this failure: Zd'arske Chalupy 1/2 %, Blansky les 3/4 %, Prachatice 2 %, Krist'anov 4 %. In the remaining South Bohemian granulite bodies (Krasejovka, Ratibor and Vcelnice) cordierite-bearing rock type is unknown. This observation leads to the conclusion that the proportion of cordierite minerals in South Bohemian granulites increasis westwards. As for the distribution of "cordierite" within the individual granulite bodies, the opinion of previous authors on its maximal concentration in peripheral parts of the bodies and along internal shear zones can be considered correct. Minerals of the spinel group are more frequent than "cordierite". They were found, i.g., also in the Krasejovka granulite stock, where cordierite minerals are absent (Slaby 1992). Anyway, their content in samples is mostly substantially lower than that of cordierite minerals and never exceeds 1 % of the total rock volume. Their contents show a rising trend in western direction, much like those of cordierite minerals. This phenomenon is apparently connected with the westerly accentuating peraluminous character of South Bohemian granulite bodies stressed by Vrana (1988).

"Cordieritized" granulites from both localities examined were chemically analysed. The results are given in Table 1. Compared to the analyses of unaffected granulites (Fediukova and Fediuk 1971, Slaby 1992b), no significant shift in the composition is perceptible. Therefore, the transformation can be considered as quasi-isochemical, operating in a practically closed system. All material needed for the growth of newly formed minerals, mainly Al, Fe and Mg, was taken from the immediate proximity without any substantial transport. The trigger for this nearly-isochemical process consisted in the abrupt change in physical conditions, especially pressure.

GARNET AND BIOTITE

These two ferromagnesian minerals, typical and widely distributed members of common granulites, are absent or substantially reduced in degraded "cordieritized" and/or "spinelitized" facies. Therefore they stand beyond the main scope of studies performed within this paper. Nevertheless, as the disintegration of both of them provided the starting material for the growth of cordierite and spinel minerals, their average chemical compositions according to a set of new EMPA data are summarized in Tables 2 and 3. The data show characteristic predominance of FeO over MgO in both minerals, more markedly for garnet than for biotite, and in both cases more distinctly for the Zd'arske Chalupy granulite than for the analogous rock from the Bernkopf Quarry. Garnet, folowed by kyanite (and by feldspar), is a more important supplier of aluminium than biotite for newly formed minerals.

SEKANINAITE

In Bohemian Massif, the following ten lithologies containing cordierite minerals have been recognized, ordered by their decreasing abundance: migmatized gneisses, contact metamorphosed pelites, contact-metamorphosed phyllites and mica-schists, high-alumina granites, retromorphosed granulites, pegmatites, high-Mg gneisses, porcellanites, contact metamorphosed sulphidic graphite schists and buchites on burning coal-heaps. Most minerals of these rock sare rich in magnesium, and--as well as in global scale specimens containing more than 50 % Fe/(Fe+Mg) (= sekaninaite) are relatively rare. Deer et al. (1986) stressed that such Fe-rich members of the cordierite group tend to be restricted to pegmatite occurrences, with a few exceptions of metamorphic rocks: hornfelses in Bavaria (Okrusch 1971) and granulites in Canada (Berg 1977). Reinhardt and Kleeman (1992) reported closely unspecified "Fe-cordierite" also from the Saxonian granulite massif. Sekaninaite as a new mineral of the cordierite series approved by IMA was discovered in pegmatite from Dolni Bory in Moravia by Stanek and Miskovsky (1975) and later studied by Cerny et al. (1997). Recently, specimens with up to 58 mol % of Fe-component were found in hornfelses of the thermal aureole of the Central Bohemian pluton (Fediuk 2001).

The presence of a mineral of the cordierite series in south Bohemian granulites was mentioned many times (i.e. Frejvald 1974, Vrana 1988, Kroner et al. 2000 a.o.) but in general as "cordierite" without any analytical data and specification. Only Fediukova, Fediuk (1971) reported the content of Fe-component of 71,5 % of this mineral from the granulite of Zd'arske Chalupy. However, they designated it--according to the practice of that time--with the collective name cordierite because sekaninaite was introduced four years later as the IMA-approved specific mineral species (Stanek and Miskovsky 1975). Besides that, their EMPA data were incomplete, giving FeO and MgO values only. Anyway, these data indicated that South Bohemian granulite "cordierites" probably belong in fact to the sekaninaite species in the sense of modern mineralogical systematics. New analyses performed for the present paper and shown in Table 4 and Fig. 2 confirmed this presumption unequivocally.

The Fe-content in sekaninaites from both localities examined clearly exceeds 50 %. Values for the Bernkopf locality are somewhat lower (54.7 to 56.6 %) than for the Zd'arske Chalupy body (65.6 to 72.5 %). The latter represent the most ferrous sekaninaite hitherto known from metamorphic rocks of the Bohemian Massif (sekaninaites from pegmatites are of course richer in Fe). The differences in Fe contents of sekaninaite between the two granulites studied mimic the chemistry of their parent rocks: the FeO/MgO ratio in the Bernkopf granulite equals 2.96 while the analogous value in the Zd'arske Chalupy granulite is almost twice higher (5.09). Cordierite minerals from Moravian granulites of the Bor-massif have their [X.sub.Mg] values below 0.5 (Stankova 1982, Povondra et al. 1992).

Sekaninaite grains are almost isometric in form and always xenoblastic in outline. Their amount in the rock varies considerably from zero to 20 % in the hand specimen. Their origin is directly connected with the state of the consumption of primary granulite ferromagnesian minerals, garnet and biotite. It was evidenced already in the paper of Fediukova and Fediuk (1971) that the crystalloblastic growth of sekaninaite in the Zd'arske Chalupy granulite is clearly younger than the origin of the rock foliation (banding and schistosity). The same holds for the Bernkopf granulite as shown in Fig. 3. From this fact it can be therefore concluded that a simplified model of the development in one continual metamorphic event along a dropping retrogressive path cannot be accepted. Obviously correct is the opinion that the change of the HT/HP regime producing the primary granulite assemblage with the rock foliation into a HT/LP blastic growth of sekaninaite is near-isothermal and connected with rapid decompressional exhumation of granulite bodies. Anyway, a clear gap in time as well as in metamorphic style between these two records is evident.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The cancer-like metastatic growth of sekaninaite poikiloblasts already mentioned in the Zd'arske Chalupy granulite is well developed in the Bernkopf granulite, too (Fig. 4). Formation of sekaninaite in granulites starts with fine pseudo-graphic intergrowth with quartz. In the course of further evolution, the grains become poikilitic and finally autonomous and almost free of inclusions.

HERCYNITE

Minerals of the spinel group have been reported many times from the south Bohemian granulites in previous papers. They were usually classified as either pleonast or hercynite; however always exclusively on the basis of visual microscopic evaluation. None chemical analysis have been published yet. For new data see Table 5. The Mg/Fe ratio is 0.68 for sample No. 1 (Bernkopf) and 0.59 for sample No. 2 (Zd'arske Chalupy), in both cases far below the ratio of 1.00 usually given as the limit between pleonaste (>) and hercynite (<). Its origin at both localities is analogical with other South Bohemian granulites (Stark 1928), in close connection with kyanite. It grows together with quartz, replacing kyanite according to the simplified equation: [Al.sub.2]Si[O.sub.5] + (Fe,Mg)O from garnet and biotite = Fe,Mg[Al.sub.2][O.sub.4] + Si[O.sub.2]. The slight surplus of FeO was bound mainly to subordinate amounts of ilmenite and magnetite. The timing of this process was connected with the decompression of granulites but it is definitely older than the blastic growth of sekaninaite. The reversal succession of both minerals, as claimed by Behr (1961) for Saxonian granulites, must be refused. These two minerals, hercynite and sekaninaite, never occur together: as soon as sekaninaite appears in the rock, hercynite disappears (is consumed).

Even though hercynite is a comparatively rare mineral in granulites, not its presence but its form merits a special attention in the case of the rock examined. This concerns especially the Bernkopf granulite because in the granulite of Zd'arske Chalupy hercynite usually occurs in minute individualized grains. Un the other hand, thin sections from the Bernkopf locality show a curious texture in some places--fingerprint hercynite + quartz symplectitic intergrowths as shown in Figs. 5 to 7. Such dactylitic texture is not unknown among minerals of the spinel group (see, e.g., Dowson and Smith 1975 for Mg-chromite, with references to previous authors and with 5 ways of genesis) but has not been observed in the Bohemian granulites. Fiala et al. (1987) mentioned a worm-like form of hercynite which could perhaps represent an incipient stage towards a dactylite but anyway it remains still far from a typical fingerprint form. Photos in Fig. 5 to 7 characterize the habitus of fingerprint intergrowths sufficiently and better than any verbal description. They are elongated following the columnar habitus of the replaced kyanite but are not strictly confined to it, and trend to affect also its closest neighbourhood continuing to build up a rather rounded form. Anyway, there is no doubt that the growth started with the replacement of original kyanite the relics of which are preserved in some symplectitic units. If the sum of volumes of both newly crystallized minerals in the symplectite (hercynite + quartz) was equal to the volume of the host mineral (kyanite), the resulting symplectite would copy the form of kyanite porphyroblasts; it would be a simple columnar pseudomorph. But this is not the case. Assuming the density of 3.6 for kyanite, 3.9 for hercynite and 2.65 for quartz, the sum of hercynite + quartz volume (in the ratio 40.4 : 59.6 vol.%) amounts to 114 % of the kyanite volume, due to the substantially larger volume of comparatively light quartz. The growth of this voluminous mineral pushes hercynite grains outsides thus increasing the size of the symplectitic unit along large crystal faces of the original kyanite column. The origin of crystaloblastic quartz grains causes the expansion and tendency towards rounding in the style of a yeast-effect.

Hercynite grains of the symplectite, mostly hundredths of mm in site, are isometric and almost xenoblastic. Their shape relation to the quartz grains reflects much higher values of surface energy (-1800 ergs/[cm.sup.2]) than for quartz (~ 500) (Spry 1969). Fingerprint texture of hercynite does not remain stable during further development of the rock. Its minute grains gradually recrystallize into bigger ones which finally cause the destruction of the dactylitic texture and replace it by an irregular aggregate. Photo in Fig. 7 illustrates the beginning of such recrystallization.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

DISCUSSION AND CONCLUSIONS

Most authors dealing with South Bohemian granulites repeatedly stated their retrogressive decompressional and quasi-isothermal development accompanying the gradual exhumation process of these bodies from the lower crust to the surface (latest Kroner et al. 2000, Svojtka et al. 2002). This process caused the instability of the primary granulitic mineral assemblage, especially of garnet, biotite and kyanite. Step by step, new minerals originated to substitute them: sillimanite (scarcely even andalusite--Fediukova 1971), muscovite, minerals of the spinel group, minerals of the cordierite series. The two last mentioned phases have been studied in two granulite bodies, the Prachatice massif and the Zd'arske Chalupy lens, within the present paper. The results can be summarized in the following three points:

* The direct connection of spinelids with the breakdown of kyanite under the import of Fe and Mg from garnet and biotite was confirmed. A hitherto unknown symplectitic fingerprint spinelid + quartz texture was discovered. Its origin under conditions of a pressure drop from original ca. 15 kbar to approximately one-half of this value is explained mainly by the yeast-effect of the volume increase of the crystalloblastic growth of quartz in the symplectite, the total volume of which exceeds the volume of the host kyanite by 15 %. The EMPA data for the spinelid have shown a composition corresponding to hercynite.

* The mineral of the cordierite group, although being also a minor and locally occurring constituent in granulites of both bodies examined, is much more frequent than hercynite. Its composition does not demand such extreme amount of Al, Fe and Mg. The proportion of these elements, released by the decomposition of garnet, biotite and kyanite (as well as that of hercynite) is sufficient for its larger quantity. Although built up principally from the same starting material and having also a retrogressive character, its origin differs from that of hercynite substantially. Hercynite is a product of continuous decompressional retromorphism linked directly with the primary granulitic metamorphism. The origin of the mineral of the cordierite series, on the other hand, is abruptly discontinuous with regard to this metamorphism not only as for the metamorphic parameters with pressure sunk below 4 kbar (Kroner 1992) but also in time. Supposing that the temperature remained almost constant also in such LP conditions, the concept of another heat source must be admitted, probably derived from magmatic chambers of Variscan granitoids. The new EMPA data proved the predominance of Fe over Mg. This ranges this mineral to sekaninaite within the cordierite-series. Its crystallization started with the origin of fine sekaninaite-quartz intergrowths (see Cerny et al. 1967, Fediukova and Fediuk 1971), but later the two minerals grew separately in autonomous grains. Finally, this process gained a metastatic, cancer-like character.

* Compositions of all Fe,Mg-minerals, primary as well as retrogressive, reflect the bulk rock chemistry, characterized by the predominance of iron. In the more acid granulite of Zd'arske Chalupy these minerals are Fe-richer than in the slightly more basic granulite of the Bernkopf locality. Diagrams in Figs. 8 and 9 express these relations diagrammatically. The transformational recrystallization occurred in the regime of a closed system.

[FIGURE 8 OMITTED]

[FIGURE 9 OMITTED]

REFERENCES

Behr, H. J.: 1961, Beitrage zur petrographischen und tektonischen Analyse des sachsischen Granulitgebirges (mit Anlagenmasse), Freiberger Forsch.-H., C 119. Freiberg.

Berg, J. H.: 1977, Regional geobarometry in the contact aureoles of the anorthositic Nain Complex, Labrador, Jour. Petrol. 18, 399-430.

Cerny, P., Jakes, P. and Cerna, I.: 1967, Pseudographic cordierite-quartz intergrowths in pegmatites and metamorphic rocks, Acta Univ. Carol., Geol., 2, 133-151, Prague.

Cerny, P., Chapman, R., Schreyer, W., Uttolini, L., Bottazzi, P. and McCammon, C.A.: 1997, Lithium sekaninaite from the type locality, Dolni Bory, Czech Republic, Canad. Mineral. 35/1, 167-173, Uttawa.

Deer, W. A., Howie, R. A. and Zussman, J.: 1986, Rock-forming minerals, 1B, disilicates and ring silicates, Longman, UK.

Dawson, J. B. and Smith, J. V.: 1975, Chromite-silicate intergrowths in Upper mantle peridotites, Physics and Chemistry of the Earths, 9, 339-350, Pergamon, Oxford etc.

Fediuk, F.: 1971, Cordierite in the Moldanubian gneisses, Krystalinikum 7, 183-204. Praha.

Fediuk, F.: 2001, Sekaninaite/cordierite compositional oscillation in some Bohemian hornfelses, Krysta linikum 27, 51-66, Brno.

Fediukova, E.: 1971, Andalusite in granulites of the Bohemian Massif, Tscherm. Min. petr. Mitt. 15, 249-257.

Fediukova, E. and Fediuk, F.: 1971, Moldanubian granulites of the Pisek--Tyn area, Acta Univ. Carol., Geol., Hejtman Vol., 25-47. Praha.

Fiala, J., Lang, M., Obrda, J., Pivec, E. and Ulrych, J.: 1982, Petrology of some garnet-kyanite-K-felspar leptynites of the Czech Moldanubicum (Czechoslovakia), Rozpr. Cs. Akad. Ved, R. mat. prir. Ved, 92/5, 1-85, Prague.

Fiala, J., Matejovska, U. and Vankova, V.: 1987, Moldanubian granulites and related rocks: petrology, geochemistry and radioactivity, Rozpr. Cs. Akad. Ved, R. mat. prir. Ved, 97/1, 1-102, Prague.

Frejvald, M.: 1974, Low-pressure re-metamorphism of granulite and orthogneiss complexes in the Krist'anov and Prachatice massifs (southern Bohemia), Mineral. Mag. 39/305, 612-613, London.

Hejtman, B.: 1977, Prachaticke granulitove teleso a jeho okoli, Exkurze do jihoceske casti moldanubika. Cs. Spol. Mineral. Geol., 15-26. Praha. (In Czech).

Kroner, U.: 1992, The deformation path of saxonian granulite complex--the change from compressional to extensional tectonic, Inter. Workshop High-pressure granulites--lower crustal metamorphism, abstracts. Czech. Geol. Survey, 13. Prague.

Kroner, A., O'Brien, P.J., Nemchin, A.A. and Pidgeon, R.T.: 2000, Zircon ages for high pressure granulites from South Bohemia, Czech Republic, and their connection to Carboniferous high temperature processes.--Contr. Mineral. Petrol. 138/2, 127-142.

Okrusch, M.: 1971, Garnet-cordierite-biotite equilibria in the Steinach aureole, Bavaria, Contr. Mineral. Petrol. 32, 1-23.

Povondra, P., Stankova, J. and Stanek, J.: 1992, C[O.sub.2]--bearing cordierite of Moldanubian leptynite rock series from Horni Bory, Czech Reopublic, Acta Univ. Carol., 3-4, 331-349.

Reinhardt, J. and Kleemann, U.: 1992, Exhumation of saxonian granulites: Petrological and structural evidence for crustal-scale extension, Inter. Workshop High-pressure granulites--lower crustal metamorphism, abstracts. Czech. Geol. Survey, 18,. Prague.

Slaby, J.: 1992a, Contrasting petrological and geochemical features of orthogneisses and granulites in South Bohemia, Inter. Workshop High-pressure granulites--lower crustal metamorphism, abstracts. Czech. Geol. Survey, 21. Prague.

Slaby, J.: 1992b, Kobyli hora, quarry 2 km NE of Prachatice, High-pressure granulites--lower crustal metamorphism, excursion guide. Czech geol. Survey, 4-6. Prague.

Spry, A.: 1969, Metamorphic textures, Pergamon Press, Oxford etc.

Stanek, J. and Miskovsky, J.: 1964, Zelezem bohaty cordierit z pegmatitu od Dolnich Boru, Cas. Mineral. Geol., 9, 191-192, Praha. (In Czech).

Stanek, J. and Miskovsky, J.: 1975, Sekaninaite, a new mineral of the cordierite series, from Dolni Bory, Czechoslovakia, Scripta prir. Fak. UJEP, 1/5, 21-30. Brno.

Stankova, J.: 1982, "Dist-sillimanite": its importance for assessment of polyphase metamorphism in the leptynite body near Bory, Czechoslovakia.--Krystalinikum 16, 53-66, Prague.

Stark, M.: 1928, Umwandlungsvorgange in Gesteinen des Bohmerwaldes, Lotos 7, 1-77, Prag.

Svojtka, M., Kosler, J. and Venera, Z. (2002): Dating granulite-facies structures and their exhumation of lower crust in thew Moldanubian Zone of Bohemian Massif, Int. J. Earth Sci (Geol. Rdssch.) 91, 373-385.

Vrana, S.: 1988, The Moldanubian zone in Southern Bohemia: polyphase evolution of imbricated crustal and Upper mantle segments, Proceed. 1st Int. Conf. Bohemian Massif, Czech geol. Survey, 331-336. Prague.

Vrana, S.: 1992, Lom pod Libinem--quarry, High-pressure granulites--lower crustal metamorphism, excursion guide.--Czech geol. Survey, 7-8, Prague.

Vrana, S. and Sramek, J.: 1999, Geological interpretation of detailed gravity survey of the granulite complex in southern Bohemia and its structure, Bull. Czech geol. Survey, 74/3, 261-277, Prague.

Ferry FEDIUK and Eva FEDIUKOVA

Geohelp, Na Petrinach 1897, 162 00 Prague, Czech Republic, e-mail: fediukgeo@atlas.cz
Table 1 Whole rock analyses and their
C.I.P.W. recalculations

                           1        2

Si[O.sub.2]            71.37    74.01
Ti[O.sub.2]             0.39     0.20
[Al.sub.2]
  [O.sub.3]            14.62    12.94
[Fe.sub.2]
  [O.sub.3]             0.31     0.51
FeO                     2.49     1.17
MnO                     0.05     0.03
MgO                     0.84     0.23
CaO                     1.68     0.86
[Na.sub.2]O             3.17     2.87
[K.sub.2]O              4.31     5.41
[P.sub.2][O.sub.5]      0.19     0.18
[H.sub.2][O.sup.+]      0.52     0.65
[H.sub.2][O.sup.-]      0.13     0.13
C[O.sub.2]              0.06     0.10
Total                 100.13    99.29
Qz                     28.76    32.92
Cr                      2.38     1.39
Or                     25.91    32.97
Ab                     28.96    26.58
An                      7.22     3.19
Hy                      5.37     1.55
H                       0.44     0.73
T                       0.55     0.29
Ap                      0.41     0.39

(1) Sekaninaite-bearing granulite, abandoned
quarry Bernkopf S of Prachatice. Analyzed by
Geoindustria Labs, Cernosice.

(2) Sekaninaite-bearing granulite, outcrop
in the forest 0.5 km ENE of Zdarske Chalupy.
Analysis taken over from Fediukova, Fediuk (1971).

Table 2 Averaged (from n = 15) microprobe analyses of
granulite garnets of Bernkopf and Zdarske Chalupy
localities, normalized to 24 oxygen equivalents.

                       1                     2

Si[O.sub.2]   39.83 [+ or -] 0.27   39.32 [+ or -] 0.33
Ti[O.sub.2]    0.21 [+ or -] 0.03    0.13 [+ or -] 0.02
[Al.sub.2]
  [O.sub.3]   21.94 [+ or -] 0.46   19.84 [+ or -] 0.27
FeO           23.73 [+ or -] 0.55   28.96 [+ or -] 0.37
MnO            0.61 [+ or -] 0.06    0.52 [+ or -] 0.02
MgO            7.54 [+ or -] 0.31    6.39 [+ or -] 0.14
CaO            5.83 [+ or -] 0.22    5.00 [+ or -] 0.19
Total                99.69                100.16
[Si.sup.IV]          6.104                 6.150
[Al.sup.VI]          3.963                 3.657
[Ti.sup.VI]          0.024                 0.015
[Fe.sup.+2]          3.041                 3.788
Mn                   0.079                 0.069
Mg                   1.723                 1.490
Ca                   0.957                 0.838
Alm                  52.32                 61.17
Spes                 1.362                 1.112
Pyr                 29.636                24.061
Gros                16.053                13.284
Ti-Gros              0.624                 0.370

Analyses: Czech geol. Survey Prague, Cam Scan 4 + Link Isis,
operator Z. Kotrba. For location 1 and 2 see Table 1.

Table 3 Averaged (from n = 10) microprobe analyses of granulite
botites of Bernkopf and Zdarske Chalupy localities, normalized
to 22 oxygen equivalents.

                               1                     2

Si[O.sub.2]           37.58 [+ or -] 0.29   38.19 [+ or -] 0.25
Ti[O.sub.2]            2.54 [+ or -] 0.07    1.94 [+ or -] 0.10
[Al.sub.2][0.sub.3]   18.34 [+ or -] 0.20   18.84 [+ or -] 0.19
FeO                   20.84 [+ or -] 0.29   22.22 [+ or -] 0.18
MnO                    0.11 [+ or -] 0.01    0.14 [+ or -] 0.02
MgO                    7.24 [+ or -] 0.16    6.03 [+ or -] 0.16
CaO                    0.48 [+ or -] 0.11    0.26 [+ or -] 0.09
[Na.sub.2]O            0.26 [+ or -] 0.05    0.23 [+ or -] 0.06
[K.sub.2]O             9.25 [+ or -] 0.13    9.18 [+ or -] 0.20
total                        96.64                 97.03
[Si.sup.IV]                  5.648                 5.729
[Al.sup.IV]                  2.352                 2.271
[Al.sup.VI]                  0.896                 1.060
[Ti.sup.VI]                  0.287                 0.219
[Fe.sup.2+]                  2.619                 2.788
Mn                           0.014                 0.018
Mg                           1.622                 1.249
Ca                           0.077                 0.042
Na                           0.076                 0.067
K                            1.773                 1.757
OH (calc.)                   4.000                 4.000

Analyses: Czech geol. Survey Prague, Cam Scan 4 +
Link Isis, operator Z. Kotrba. For location 1 and
2 see Table 1.

Table 4 Compositions of EMPA-analyzed cordierite minerals
(sekaninaites) from two S-Bohemian granulites and their
crystal-chemical formulae, normalized

                      1a      1b      2

Si[O.sub.2]           46.24   45.94   44.96
Ti[O.sub.2]           0.07    0.08    0.05
[Al.sub.2][O.sub.3]   31.72   31.47   30.48
FeO                   13.13   13.64   16.67
MnO                   0.30    0.33    0.33
MgO                   6.11    5.88    4.91
CaO                   0.18    0.20    0.20
[Na.sub.2]O           0.46    0.45    0.34
[K.sub.2]O            0.12    0.15    0.14
Total                 98.33   98.14   98.08
[Si.sup.IV]           4.904   4.897   4.874
[Al.sup.IV]           1.096   1.101   1.126
[Ti.sup.VI]           2.869   2.852   2.768
Ti                    0.006   0.006   0.004
[Fe.sup.2+]           1.165   1.216   1.511
Mn                    0.027   0.029   0.030
Mg                    0.966   0.935   0.793
Ca                    0.020   0.023   0.023
Na                    0.095   0.093   0.071
K                     0.016   0.020   0.019
100Fe/Fe+Mg           54.67   56.55   65.61

1a--individualized grain of sekaninaite
1b--poikilitic ("metastasized") sekaninaite
2--porphyroblastic sekaninaite

Analyses: Czech geol. Survey Prague, Cam Scan 4 +
Link Isis, operator Z. Kotrba. For location 1 (a,b)
and 2 see Table 1.

Table 5 Compositions  of EMPA-analyzed  spinelids
from two S-Bohemian granulites and their
crystal-chemical formulae, normalized to 24 cations

                      1        2

Si[O.sub.2]           0.03     0.04
Ti[O.sub.2]           0.07     0.05
[Al.sub.2][O.sub.3]   59.16    58.31
[Cr.sub.2][O.sup.3]   0.05     0.04
FeO                   28.42    30.57
MnO                   0.06     0.10
MgO                   11.85    10.18
CaO                   0.06     0.04
ZnO                   0.18     0.23
Total                 99.88    99.56
Si                    0.007    0.009
Ti                    0.011    0.008
Al                    15.208   15.012
Cr                    0.009    0.007
[Fe.sup.3+]           0.748    0.947
[Fe.sup.2+]           4.436    4.637
Mn                    0.011    0.019
Mg                    3.528    3.315
Ca                    0.014    0.009
Zn                    0.029    0.037

Analyses: Czech geol. Survey Prague, Cam Scan
4 + Link Isis, operator Z. Kotrba. Partitioning
of ferrous/ferric iron by charge balance. For
location 1 and 2 see Table 1.
COPYRIGHT 2003 Akademie Ved Ceske Republiky, Ustav Struktury a Mechaniky Hornin
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2003 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Fediuk, Ferry; Fediukova, Eva
Publication:Acta Montana. Serie A: Geodynamics
Article Type:Report
Date:Jul 1, 2003
Words:4916
Previous Article:Ti-rich granodiorite porphyries from the northeastern margin of the Klenov massif (Moldanubian Zone of the Bohemian Massif).
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters