Kotsis, T.

English

At the Eastern termination of the Alps there are various greenstones of basaltic origin, ullramafitites and a meta-ultrabasic rocks exposed in the tectonic windows of the Eisenberg-Group. The paper gives detailed description of the mineralogy and mineral chemistry of this rock suite

Kotsis T.

University of Szeged

Acta Mineralogica-Petrographica, Szeged, XXVIII, 5—9, 1986 PENNINIC OPfflOLITES AT THE EASTERN MARGIN OF THE EINSENBERG-GROUP (FELSŐCSATÁR, W-HUNGARY) T . KOTSIS Department of Petrology and Geochemistry, Loránd Eötvös University ABSTRACT At the Eastern termination of the Alps there are various greenstones of basaltic origin, ullra-mafitites and a meta-ultrabasic rocks exposed in the tectonic windows of the Eisenberg-Group. The paper gives detailed description of the mineralogy and mineral chemistry of this rock suite. INTRODUCTION In the "Rechnitzer Penninikum" (PAHR, 1977, 1980a, 19805) there is ample evi-dence of an igneous activity, the age of wich apparently coincides with the early stage of the Cretaceous sedimentation. Predominant products of this activity are lavas and tuffs of basaltic composition with gabbros and various ultramafics. The magmat-ic centers were found in Austrian territory, whereas in Hungary mainly pyroclastics were detected by mapping in the areas adjoining the Austro-Hungarian frontier. The original depth and character of the igneous activity is not yet fully disclosed and need more detailed research the first result of wich are presented here. GEOLOGICAL SETTING The Eisenberg-Window is built up by Mesosoic metasediments (i.e. quartz -phyllites, phyllites, carbonate-phyllites and calcareous shales) with some metamor-phic ophiolites (metabasalts, ultramafitites, meta-ultrabasics). Their lithostatigraphic setting was established on the basis of information supplied by outcrops, exploration-drifts and bore holes (SZEBENYI, 1948, VARR6K, 1953, KOTSIS, 1957, 1982, VENDEL andKisHAZi, 1967, KUBOVICS, 1983) . The deepest known members of the sequence are organic-rich graphite-bearing phyllites and quartzphyllites overlain by carbonate phyllites at places with a characteristic conglomerate (the Cak-conglomerate) wich are covered by carbonate phyllites, calcareous phyllites, calcareous shales and crys-talline limestone. The uppermost member of the sequence is a thick series of green-schist. The phyllite series contains large complexes of serpentinite to have been in-truded in solid state. Along the margins of the serpentinite mass there are meta-ultrabasics of various composition. . . . . . H-1088 Budapest, Muzeum krt 4/A, Hungary •5 PETROLOGY OF OPHIOLITES The ophiolites are represented by 1. greenstones, 2 ultramafics (serpentinized), 3. meta-ultrabasites. 1. Greenstones of basaltic origin. These rocks are usually of pale-green color, compact and — at places — exhibit more or less pronounced schistosity. Their major constituents are albite, epidote, tremolite-actinolite and chlorite. The mafic minerals are characteristically poor in iron: both the clinozoizite-epidote and tremolite-acti-nolite series are represented by their iron-poor members. It is the amount of chlorites wich fluctuates most, also it never exceeds the amount of the afore-mentioned two other components. The only felsic mineral is albite, occurring as large porphyroblasts. Minor components: quartz, titanite as common constituents of sedimentary origin, pyrite slightly altered to limonite and secondary vermiculite, rare carbonate. On the basis of 28 modal analyses of the basaltic greenstones the mineralogical composition is as follows: albite 3 0 % (19—37) , chlorite 18% ( 6 — 3 3 ) , epidote-clino-zoizite 2 3 % ( 5 — 3 5 ) , tremolite-actinolite 2 7 % ( 1 6 — 3 6 ) , titanite 5% ( 3 — 6 ) . Detailed mineralogical data (after LORENZ, 1976) are shown Fig. 1. Fig. 1. Mineral composition of basaltic greenstones. The possible pyroclastic origin of greenstones is reflected also by the relative high fluctuations of some elements from the chemical analyses (e.g. SiO,, NasO). Their whole rock chemical composition is shown in Table 1. 2. SERPENTINITES Serpentinites are medium green, blackish-green rocks with Al-bearing antigorite and' lizardite as major constituents. Monomineralic serpentinites are rare. They usually contain minor components as talc or fibrous silica minerals (lussatite, chal-cedony). At places relict aggregates of olivin, grains of ilmenite, magnetite and chro-mite also occur. There were no relict pyroxenes in any of the Hungarian rocks, whereas in Aus-tria W . POLLAK (1962) identified ones in the Badersdorf serpentinite. The antigorite-lizardite aggregates, however, nicely preserve the shape of the olivine grains. Chemical analyses of some selected samples are shown in Table 2. That clearly 6 TABLE 1 Chemical composition of the greenschists of the Eisenberg Group 1 2 3 • 4 5 6 7 8 9 10 11 12 13* SiO, 47.25 48.76 49.85 51-80 42.40 53.60 53.11 48.26 45.73 48.67 50-57 48.84 38.75 TiO, 1.52 1.57 1.57 2.33 0.92 0.95 0.69 1.57 1.12 1.60 1.20 1.13 6.23 Al.O, 16.23 « 13.77 17.40 14.02 17.26 19-58 16.55 16.77 17.04 15.75 13.83 17.68 13.55 Fe ,0 3 10.36 7.80 9.94 8.23 10.55 9.61 2.33 7.80 7.13 1.00 0.90 2.24. 8.83 Fe0 3 — 3.32 — — — 6-02 3.72 3.38 — 7.09 4.65 8.50 MgO 6.55 7.60 7.55 10-45 11.30 3.15 7.60 7.60 8.50 9.84 5.58 6.45 5.29 MnO 0.32 — 0.29 0-12 0.28 0.34 — - 0.27 0.15 — 0.15 0.12 0.19 CaO 9.30 7.57 6.60 9.46 7.95 6.10 9.54 7.57 11.95 7.84 12.16 12.56 11.25 N a , 0 3.11 3-42 2.41 0.18 1.34 2.56 0.22 3.42 2.70 2.94 4.49 2.77 1.95 K , 0 0.65 0.75 0.28 0.37 0.47 0.55 0.14 0.65 0.18 0.57 0.13 0.05 0.26 H s O 4.95 3.23 4.32 3.36 7.27 3.67 0.45 2.73 2.20 2.77 2.61 1.43 5.03 ¿Talk 3.76 4.17 2.69 0-55 1.81 3.11 0.36 4.07 2.88 3.51 4.62 2.82 2.21 1—9 Felsőcsatár; 10 Badersdorf; 11 Pinkatal-Burg; 12 Woppendorf; 13* crossit-greenschist Felsőcsatár TABLE 2 Chemical composition of the Felsőcsatár serpentinites 1 2 3 4 5 6 7 8 9 10 SiO, 39.30 37.85 TiO, . , 0.19 0.06 Al.O, 4.58 6.05 Fe,O s 10.28 10.98 FeO — — MgO 29.45 30.91 MnO 0.10 0.09 CaO 1.32 0.90 Na.O . _ 0.38 K.O — :; 0.26 tt.O ' . 13.41- • 12.32 39-28 36.31 39.05 36.45 0.01 0.01 0.02 0.01 1.52 1.63 1.69 1.28 8.52 7.45 7.19 4.50 36.83 35.45 36.45 33.62 0.08 0.14 0.08 0.25 091 1.06 0.91 3.54 0.14 — 0.39 0.64 0.32 — 0.12 0.43 12.32 17.02. 14.10 17.02 36.86 38.80 46.00 56.3 0.01 2.67 0.10 0.1 1.28 1.53 2.52 1.0 6.86 12.32 1.40 1.9 — — 4.40 3.5 32-85 27.90 32.30 26.3 0.19 0.13 0.10 — : 1.84 4.41 — 0:8 0.24 0.14 — 0.30 0.53 0.05 — 19.10 11.15 12.90 9.8 indicate the peridotitic pyroxenitic character of the parent rock: sample No. 9 is unusually low in CaO, wich calls for orthorhombic pyroxenes and olivine to be sup-posed as parent minerals (neither monocliriic pyroxenes nor Ca-amphiboles could provide for such a Ca-poor mineral assemblage when metamorphosed). The norma-tiv composition of their protolith rock (calculated on dry basis) probably comprises forsterite-rich olivine (cca 30 percent) and bronzitic pyroxene (cca 70 percent). The formation of the major constituents of these ultrabasic rocks (/. e. antigorite, lizardite and secondary magnetite) and the alteration of the serpentine minerals into talc and local silification of the serpentinite can be reconstructed and deduced from the equation (KUBOVICS, 1983) : 12 (Mg, Fe)2Si04+12 H 2 0+0 2 -~3 Mg6Si4O10OH8+2 FeFe204 Talc occurs mainly along the margins of the serpentinite bodies, thus reflecting the late metamorphic-metasomatic character of talc formation. It is accompanied by silica minerals and carbonates indicating that talc itself was formed by metamor-phic-metasomatic alteration also of serpentinites of ultramafic origin. It seems to be highly probable, however, that the reaction producing talc took place at a temper-ature somewhat higher than that of serpentinization (KUBOVICS, 1983): 12 M g ^ F e O ^ S i A + e H 2 0 + 0 2 ~ 6 Mg3Si4O10(OH)2+FeFe2O4 It can be supposed that the proportion of ferrous iron in the original pyroxene was somewhat higher than indicated by the equation above and thus the alteration may have resulted in the release of silica, which then contributed to the formation of talc and to silification. During serpentinization of the ultrabasites also some chlo-rites (chloritites, chlorite-schists) were formed in the marginal parts, the character of which is a sensitive indicator of the varying nature of the metamorphism. The chlorite schists consist mainly of Mg-rich chlorite minerals of various iron content, part of which.can be deduced from the original material of the parent ultra-basics (particularly when locally within the ultramafic suite the presence of some Al-rich rocks, such as hornblendites, can be supposed). Hornblendites often forming the marginal facies of peridotite-pyroxenite com-plexes offer an attractive explanation for the formation of the chlorite-schists by their metamorphic alteration. This idea seems to be supported by the presence of titanite-chlorite, a peculiar variety of chlorite-schists in the area concerned (see also below). 3. META-ULTRAB ASICS According to the latest results of mapping in the Felsőcsatár area there are titanium- and iron-bearing meta-ultrabasics of various origin in the scree covering the SE slopes of the Nagyvilágos-hill. As to petrology they are titanite-crossitites (1, 2, 3) titanite-chloritites (4) and crossite-epidote-greenstones (5). The titanite-crossitites consist of alkali-amphiboles of centimeter size with tita-nite-pseudomorphs after ilmenite. There is an inverse relationship between crossite, epidote, chlorite and albite: the less the percentage of crossite the higher the percent-ages of epidote-f chlorite-I-albite. It is remarkable that as to composition most crossite crystals are inhomogeneous and along their cleavage planes sometimes even glaucophane may occur. The titanite-chloritite consist of titanite and rhipidolithe with accessory magnetite and apatite in certain varieties (Table 3). 8 Modal analysis of meta-ultrabasic rocks TABLE 3 1 2 3 4 5 Crossite Albite Epidote Titanite 70 40 33 5 12 7 3 13 13 21 21 35 1 10 54 55 18 6 Magnetite 2 10 1 2 Chlorite Ilmenite Leucoxenc Calcite 29 36 1 Mineralogical and chemical variations of the above described mteamorphics are supposed to be due to the inhomogeneous nature of metamorphism on the one hand and to the differences between the equilibrium states of the parent mineral assemblages on the other. This means that chemical changes of metamorphic origin did most probably not affect the studied igneous complex as a whole. Unlike normal ultrabasics all the investigated titanite-crossitites are of a definite tholeiitic character wich suggest a hornblendite or some similar ultramafic rock as the parent material. All evidences point to the fact that the formation of the ultrabasics in the Hungarian part of the Rechnitzer Penninikum must have taken place under rather unusual conditions. HERITSCH, H . ( 1 9 5 6 ) : Der Natrium-Amphibol aus dem Glasbachgraben bei Schlaining, Burgenland. Tschermaks Min. Petr. Mitt., 10. p, 209—217. KOLLER, F . ( 1 9 7 9 ) : Die Zusammensetzung der Amphibole in Penninikum des Ostalpenrandes. Fortschr. Min., 5 7 , Bh. 1, p. 7 0 — 7 1 . KOLLER, F. and PAHR, A. ( 1 9 8 0 ) : The Penninic ophiolites on the Eastern End of the Alps. Ofioliti 5 , p.65—72 KOTSIS, T. (1957): Minerals of the Vashegy. Dissertation, (in KOCH, S: Minerals of Hungary. Buda- • pest, 1966) KOTSIS, T. ( 1 9 8 2 ) : Gesieinswelt und Bau der Eisenberggruppe. Vasi Szemle 3 6 , p. 8 3 — 8 8 . KuBOvics, I. ( 1 9 8 3 ) : Peírological characteristics and genetic features of crossit from Western Hun-gary. Földt. Közi., 113, p. 207—224. LELKES-FELVÁRY, G Y . ( 1 9 8 2 ) : A contribution to the knowledge of the Alpine metamorphism in the Kőszeg-Vashegy area (Western Hungary). Neues Jb. Geo!- Paleont. Mh., 5, p. 297—305. PAHR, A. (1977): Ein neuer Beitrag zur Geologie des Nordostsporns der Zentralalpen. Verh. Geol. B. A. Wien Jg., 1977, p. 23—33. PAHR, A . ( 1 9 8 0 ) : Die Fenster von Rechnitz, Bernstein und Möltern. (In: Der geologische Aufbau Österreichs. Springer Verlag Wien, New York, p. 320—326. SZEBÉNYI, L. (1948): Geology of the Hungarian Vashegy. Jel. Jöv. Mélykút. Münk. Budapest, p. 45—50. VARRÓK, K. (1954): Constitution géologique et les occurrences de talc et de minerai de fer des envi-rons de Felsőcsatár. MÁFI Évi Jel., 1953/11, p. 479—490. VENDEL, M. and KISHÁZI, P. (1967): Die Genese der Talklagerstätte von Felsőcsatár. Bány- Kut. Int. Közi., Sonderheft, p. 1—153. REFERENCES Manuscript received, 8 May, 1986 9 

Penninic ophiolites at the eastern margin of the Eisenberg-group (Felsőcsatár, W-Hungary)

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Penninic ophiolites at the eastern margin of the Eisenberg-group (Felsőcsatár, W-Hungary)

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