Geochemistry of subsurface Precambrian plutonic rocks from the Brunovistulian complex in the Bohemian massif, Czechoslovakia

Precambrian, Research, 62 ( 1993 ) 103-125 Elsevier Science Publishers B.V., Amsterdam

103

Geochemistry of subsurface Precambrian plutonic rocks from the Brunovistulian complex in the Bohemian massif, Czechoslovakia E. Jelinek and A. Dudek Faculty of Science, Charles University, Albertov 6, CS-128 43 Prague 2, Czechoslovakia (Received January 24, 1991 ; accepted after revision August 24, 1992 )

ABSTRACT Jelinek, E. and Dudek, A., 1993. Geochemistry of subsurface Precambrian plutonic rocks from the Brunovistulian complex in the Bohemian massif, Czechoslovakia. Precambrian Res., 62: 103-125. The Precambrian Brno pluton consists of ultramafic rocks, gabbronorites and gabbros, diorites, quartz diorites, leucotonalites, leucogranodiorites, granites and leucogranites that have the chemical characteristics of a volcanic arc assemblage. The granitoid components are subalkaline, meta-aluminous (l-type) with a calcium to sodium differentiation trend. The magmatic evolution of the Brno pluton started by generation of tholeiitic magma from the mantle, followed by possible contamination of ascending magma with immature crustal material and differentiation of tonalitic melt. The pluton is interpreted as representing the products of fractional crystallization of a melt oftonalitic composition. It is a late tectonic intrusion in the Brunovistulian complex which makes up the easternmost exposed part of the Bohemian massif and constitutes a juvenile segment of crust. Welding of the volcanic arc on to Fennosarmatia took place during the Cadomian orogeny, which is mainly Precambrian in age (630-550 Ma), although its latter stages span the Precambrian-Cambrian boundary (one age of arc magmatism is 584 + 5 Ma).

Introduction

The Precambrian Brunovistulian complex (BC; Brunovistulicum of Dudek, 1980) forms a unit situated between the eastern margin of the Hercynian and the Alpine fold belts in Moravia, Czechoslovakia. During Hercynian orogenesis its western part was reworked and incorporated into the structure of the Hercynian fold belt, so that the BC forms now the eastern margin of the Bohemian massif. Although the complex is covered mainly by nappes of the outer Western Carpathians and by the Carpathian foredeep, as well as by overthrusted tecCorrespondence to: Dr. E. Jelinek, Faculty of Science, Charles University, Albertov 6, CS-128 43 Prague 2, Czechoslovakia.

0301-9268/93/$06.00

tonic slices of the Hercynides, it is exposed in the Dyje and Brno massifs and in the tectonic windows below the Moravian and Silesian nappes. The BC is situated between the Odra lineament in the north and the Danube faults in the south. In Czechoslovakia, north of a line approximately from Brno to Gottwaldov, the BC consists of metamorphic rocks with several smaller gabbro and gabbronorite massifs. The southern part of the BC consists mainly of the Brno plutonic suite with minor occurrences of crystalline schists along its margin (Fig. 1 ). The crystalline schists in the north are primarily amphibolite facies monotonous metasediments, with minor amounts of a volcanosedimentary series containing metababasites showing lower metamorphic grade in the south.

© 1993 Elsevier Science Publishers B.V. All rights reserved.

104

E. JELINEKAND A. DUDEK

D

BORES iNTO CRYSTALLINE BASEMENT

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BORDEROF SURFACE OUTCROPS Of BOHEMIAN MASSIF

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UNDIFFERENTIATED CRYSTALLINE SCHISTS- - MOSTLY TWO-MICA OR BIOTITE PARAGNEISS OCCASIONALLY WiTH AMPHIBOLITE LAYERS

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Fig. 1. Geological map of the covered parts of the Brunovistulicum. Bores into the crystalline basement: D u = H o r n i Dunajovice; H• = Hole~ov; Hu = Hulin; Jb = Jablunkov; Je= Je2ov: Kr= Kory~any; Lu = Lubn~; Lut = Lutin; Mi = Mikulov; M o = M o r k o v i c e ; M u = M u ~ o v ; Nt=Nitkovice; N M = N o v 6 Ml~ny; Os=Osv6timany; P o = P o p i c e ; R u = R u s a v a : SI= Slavkov; Sr= Strachotin; 7"1=Tluma~ov; Uh = Uhfice; VI= Vlko~; 2~d= Zd~inice.

The plutonic rocks range from an ultramafic composition through gabbronorites, gabbros, diorites, quartz diorites, leucotonalites, leucogranodiorites and granites, to leucogranites. These plutonic rocks form an independent magmatic suite in the Bohemian massif. Formation and consolidation of the Brunovistulian complex prior to Hercynian or•genesis is documented by the transgression of Middle and Upper Devonian sediments. Furthermore, as sediments of probably Cambrian age occur below the Devonian elastics in Poland (Kotas, 1973; Roth, 1981 ), it is probable that the whole Brunovistulian complex is Precambrian in age, including the post-orogenic Brno pluton. Metamorphism of the elastic and volcanoclastic rocks, and intrusion of

the plutonic rocks prior to Hercynian or•genesis is also documented by geochronological data. K-Ar, Rb-Sr and U-Pb age determinations all yield values reflecting the Cadomian orogeny (630-550 Ma, Dudek and Melkov~L 1975; Dudek, 1980; zircon age of 584_+ 5 Ma, Van Breemen et al., 1982 ). The exposed parts of the BC has recently been described by ~telcl and Weiss (1986), Scharbert and Batik (1982), Ch~ib et al. (1984) and Finger et al. (1989). The covered parts were studied in Poland by Bukowy (1972) and in Austria by Wieseneder et al. (1976). Petrological and geochemical data from Frasl and Finger (1988) suggest a correlation between the BC and Cetic massif, in the basement of the Eastern Alps.

GEOCHEMISTRY OF SUBSURFACE PRECAMBRIAN PLUTONIC ROCKS, BOHEMIAN MASSIF

The petrology and geochemistry of the covered portion of the BC in Czechoslovakia recorded here has been studied from the cores of over 100 deep boreholes drilled mainly by the Moravian Oil Concern ( M N D ) . Field relations

The geological and relative age relationships of the different rock types are of primary importance for understanding the development of the Brno pluton. The relationships between some rock types, however, can only be determined from incompletely cored boreholes. These observations, complemented by those from exposed parts of the Brno and Dyje massifs, indicate that the ultramafic rocks occur only as inclusions in other rock types. According they are interpreted as being the oldest. Similarly, diorites and quartz diorites occur as xenoliths and as larger bodies of rock enclosed in leucotonalites and leucogranodiorites. The leucogranites are apparently the youngest member of this magmatic suite since they intrude into the other plutonic rocks. Biotite granites, leucogranodiorites and granodiorites grade into each other. Granites form schlieren or extensive bodies in the granodiorites, and are interpreted as younger differentiates. The age relationship of granodiorite and leucotonalite is not yet clear. Gabbronorites and gabbros form independent bodies which intrude the crystalline schists in the northern part of the BC, but are not in direct contact with other rock types of the Brno pluton. Hornblendebiotite tonalites are present only in the western part of the gabbronorite Rusava massif (borehole Ho 1--Holegov). Petrographic examination of cores from boreholes in the covered part of the Brno pluton have identified the following rock types (see Dudek, 1980, for detailed petrographic description ): ( 1 ) Leucogranites of the Lubn~i type are exposed on the northern margin of the Brno pluton, which probably extends further to the

105

south, based on gravity data (Dole~al, 1980). These rocks are homogeneous but occasionally contain basic inclusions and schlieren and are cut by aplite veins. Modal analyses of two studied samples (Table 1 ) reveal that they are richer in plagioclase and poorer in perthite than the average mode (49 determinations) of the Lubn~i type leucogranites. (2) Biotite granites form bodies in the southern part of the Brno pluton and probably small schlieren on the southeastern border of the Zd~inice massif (boreholes Os-2 and Je-3 ). Minor occurrences of biotite granites are also present at the northern margin of the pluton (borehole Mo-4). Biotite granites grade into granodiorites. In contrast to the leucogranites, granites are characterized by a somewhat higher content of biotite and usually contain traces of muscovite. Large poikilitic microcline is typical (Table l ). (3) Biotite leucogranodiorites (of the Stupava type ) are exposed mainly in the northern and northeastern parts of the pluton and, together with somewhat darker granodiorites, are the most common rock type of the Brno pluton. They are relatively homogeneous but occasionally contain small phenocrysts or large poikilitic crystals of microcline. Their weakly schlieren-like structure is dependent on modal variations of biotite. (4) Hornblende biotite leucotonalites (of the Slavkov type) form a large body east of Brno. They are relatively light coloured rocks that sometimes enclose small diorite bodies. Idiomorphic sphene is a frequent and characteristic accessory phase. A similar rock occurs at one site in the southern part of the pluton (borehole Mi-2 ). ( 5 ) Hornblende biotite quartz diorite of the Zd~nice type, southeast of Brno, forms a 20 km long E-W-oriented body, which exhibits pronounced gravity and magnetic anomalies (Dolegal, 1980). Quartz diorite is dark and foliated in places. These rocks occasionally have a coarse schlieren structure and enclose small bodies or xenoliths of diorite (borehole Je-3 ).

K-f (%)

150 151 163 164 165 166 174 175 176 183

Strachotin 2 Strachotin 2 Uhfice4 Ubi'ice 5 Uhi'iee 6 Zchinise 14 Je~ov 2 Je~ov 2 Uhi-ice 5 Hole~ov I

3088.5 3092.5 1898.5 1976.3 1379 843 2853.4 2955.5 2047.6 1046.5 50 43

35 33 42-53 47

43.7 25.6 56.3 13.1 58.5 13.9 55.9 11.3 59.3 15.5 58.4 15.4 64.8 5.5 60.5 7:5 63.6 21.5 47.4 25.0

3.6 1.9 0.5 1.8 3.2

Hbl (%)

7.0 9.3 1.9 10.8 18.9 0.5 13.3 6.0 6.9 0.4 16.9 0.1 17.7 0.1 4.5

2.6

3.2 10.0 8.1 10.t 6.5

73 108 110 180 of

69.6 16.3 65.8 13.3 62.1 24.8 52.9 26.8 61.8 18.7

7.0 17.1 13.7 5.5 13.5

104 Zxhtnice5 1020.1 12-26 61.1 27.1 106 Osv6timany 1 2717.0 62.4 14.9 168 Kory~any 1 1737 06-36 53.6 28.4 201 Kory~any 3 2051.4 10 64.5 26.4 O of 58 anatyses of the Stupava type 55.4 26.6

Slavkov 2 1340.0 30 Siavkov 2 1350.7 30 Nitkovice 2 1777 70 Mikulov 2 2345 18 analyses of the Slavkov type

28.7 19.9 26.4 49.7 14.8 21.4 15.4 26.4

25.6 23.7 29.7 20.9 31.3 29.8 18.9 28.2

08-28 12 04 06-12 12 12-33 02

39.1 53.5 41.6 26.8 48.7 44.6 60.6 40.5

%

Qz (%)

99 H. Dunajovice 1 1803.5 169 Osv~timany2 2325.8 170 Popicel 2364.5 177 Popice2 1803.5 181 Osv~timany2 2378.7 204 Je~ov3 2003.4 205 Morkovice4 1164 O of 20analysesofbiotite granites

Depth Plag (m) An% 38.5 28.9 29.3 45.3 26.8 25.1 23.6 34.2 38.9

Drilling

171 Lubmi28 1634.8 10 188 Lubn~18 1856 10 O of 49 analysesofthe Lubmi type

No.

20.6 20.4 13.0 11.7 10.5 12.2 11.5 11.9 9.5 24.4

5.1 7.5 3.1 7.8 7.2

3.5 0.6 3.3 2.8 3.3

1.3 3.1 3.4 3.7 3.9

+

0.3

4.7

0.3

0.9 0.5

0.5 0.8 0.9 1.6 0.7 0.9

0.9

+

0.9 0.3 0.6 0.3

0.6 0.2 0.9 0.6

0.1 0.3 0.7 1.2 1.1 0.4 0.9

6.4 2.0

Ore (%) 0.5 0.5 0.4

0.1 0.6

Mu (%)

2.5 2.0 2.9

Bi (%)

0.4

0.1 0.3

0. I 0.7 0.5

0.6 0.7 0.6 0.2

0.1 +

0.1

0.3

Ti (%)

+ 0.1 0.5 0.2 0.3 + + 0.6 0.1 0.1

0.4 0.2 0.2 0.1

0.1

0.1

0.1

+

+

Ap (%)

a. Quantitative mineral composition (modal) of granitoid and dioritoid rocks of the Brunovistulicum

TABLE 1

+

+

2.5

0.9

0.7

Zr (%)

1.8

+ 0.1 0.1

0.1

0.2

0.6

0.1 + + O.l

Ep (%)

biotite leucogranodiorite leucquartzmonzodiorite biotite leucogranodiorite biotite leucogranodiorite

tonalite quartzdiorite quartzdiorite 0.3 quartzdiorite quartzdiorite + quartzdiorite hbl. bi. diorite 0.2 quartzdiorite hbl. ti. tonalite + hbl. bi. tonalite, epidotized 0.1

0.3 leucoquartzdiorite quartzmonzodiorite leucogranodiorite granodiorite

0.1

biotite granite + biotite leucogranodiorite 4.5 leucogranite biotite leucogranite biotite leucogranodiorite biotite leucogranite O. I biotite leucogranodiorite

0.3 biotite leucogranite 0.3 biotite leucogranite

Carb Rock (%)

~2

~7

r zI-n

76.5 49.7 58.4 61.3

152 191 203 ,~ of 5.3 1.4

18.0 14.2 16.3

9.9 6.0 9.6

7.1 45.1 25.6 0.8 23.1

2.2

1.2 2.5 1.4 10.8 3.9 9.0 10.7

8.6 15.3 12.0 0.5 0.3 1.2

0.7 1.6

+ 0.1

0.7 0.3 0.2 0.2 0.4

0.2 +

Vlkog 1 Popice 1

75 167

784.5 2398.5

Vlko~ 1 736.2 Rusava 2 1093.0 Rusava 2 1078.0 Rusava 9 822.3 Rusava 9 823.4 Jablunkov 1 3159.1 Jablunkov 1 3197 analyses ofgabbroic

78 154 153 192 193 206 207 ~of9 rocks

Depth

Drilling

No.

80 54 50 70 60 63 67

An%

Plag

58.3 62.2 53.6 53.2 59.3 60.8 63.4 58.8

%

1.8 + 1.0 3.1 0.2 0.7

Qz (%)

21.0

+ 21.8

Opx (%)

Cpx (%)

+ 6.3 11.1 20.7 15.7 10.7 8.0 22.5 3.0 23.5 0.3 8.3 11.1

Ol (%)

56.8

26.4 7.4 20.6 10.1 3.8 16.2

41.7

Hbl (%)

2.1

1.0 1.0 1.0

2.3 1.0 1.6

Bi (%)

0.1

6.8 6.7 1.2 0.2 2.2 2.6

Ore (%)

Ti (%)

b. Quantitative mineral composition (modal) of gabbroid and ultramafic rocks of the Brunovistulicum

Mugov 1 1606.5 39 Nov6 Ml~,ny 1 3998 49 Je~ov 3 2087.7 45 10 analyses of diorites

60.7 57.7 59.1

190 Zd~inice 16 974.8 200 Zd~nice29 880.4 37 of 47 analyses of the Zdfinice type

3.4

0.3 0.3

0.6 0.3

Ap (%)

+ 2.8

+

1.6

Rock

0.7 hbl. bi. diorite 0.4 hbl. diorite + bi. hbl. diorite

altered enstatitite 20.0 altered olivine-phlogopite hornblendite

hornblende gabbro biotite gabbronorite amphibolized gabbronorite O. 1 gabbronorite amphibolized gabbronorite amphibolized gabbro gabbro olivine-bearing

Chl (%)

2.0 0.4

+ hbl. bi. quartzdiorite 2.4 hbl. bi. tonalite

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108

(6) Diorites occur in the Brno pluton as small bodies enclosed in more silicic granitoids and are often veined by these rocks (borehole NM-1 ). Diorites also occur as dykes or small stocks in metamorphic rocks in the northeastern part of the BC (borehole K r ~ m t 1, cf. Dudek, 1980). The content ofmafic phases in the diorites is variable but hornblende usually predominates over biotite. In some areas diorite grades into quartz diorite. (7) Gabbros and gabbronorites occur as independent bodies in the northern part of the BC, which includes the gabbro-peridotite Vlko~ massif, the gabbronorite Rusava massif, and the large Jablunkov massif in the north. The Vlko~ massif is a layered magmatic body which could indicate the crystal accumulation during the solidification. Most of the gabbronorites from the Rusava massif, with signs of cumulate texture (opx), are partially amphibolized, as are the rocks from the Jablunkov massif. (8) Ultramafic rocks, serpentinized dunites and enstatitites, occur occasionally in the Vlko~ gabbro-peridotite massif. A core from the Po1 borehole contains xenolithic olivine hornblendite enclosed in granite. Hornblendite consists of poikilitic crystals of hornblende, several centimetres long, enclosing small serpentinized olivines. The modal compositions of samples used in this study are given in Table 1, as well as average modes of individual groups of magmatic rocks identified in the BC. Geochemistry Major element analyses were made in the laboratory of the Institute of Geological Sciences of Charles University. Trace element contents were determined by X-ray fluorescence ( X R F ) at the laboratories of Geoindustria by V. Budil. Rare-earth element and some other trace element (Hf, Sc, Ta, Cs, Th and U ) contents were determined by instrumental neutron activation analysis (INAA) at the Institute of Mineral Raw Materials in Kutmi

E. JELINEKAND A. DUDEK

Hora by J. Lenk and Z. l~anda. All element concentrations determined by INAA are precise within _+5% (Tm and U within _+30%). Major and trace element abundances are reported in Table 2. The accuracy of the rubidium determinations was tested at four different laboratories by two methods: X R F - Geoindustria Prague, Department of Geology, University of Glasgow, and the Technische Hochschule, Miinchen; and INAA--IMRM Kutmi Hora. Rubidium abundances are estimated to be precise within + 10% as determined by replicate analyses.

Major elements Silica content of the magmatic suite in the Brunovistulian complex varies from 50 to 70 wt% and is negatively correlated with respect to variation of F e O t o t , C a O , MgO, A1203 and TiO2 (Fig. 2 ), if the ultramafic rocks (samples 75 and 167) and gabbros with cumulate textures (samples 154, 192 and 193) are excluded from the sample population. On the other hand the Na20 and K20 vs. SiO2 correlate positively (Fig. 3 ). These linear trends can be interpreted either indicating genesis as a comagmatic suite or as the result of mixing processes. The Brno plutonic rocks are subalkaline (Fig. 3), show a calcium to sodium differentiation trend (Fig. 4) and K 2 0 / N a 2 0 ratios less than one; these features are typical of lower crust I-type granitoids. Plank and Langmuir (1988) noticed low CaO/Na20 ratios for island arc rocks built upon thick crust. The BC could thus represent magma emplaced into thick immature island arc crust. More evidence concerning this primary environment assign the study of metamorphic country rocks (Dudek and Jelinek, in prep. ). The Brno plutonic rocks are meta-aluminous like lower crust I-type granitoids (cf. Taylor and MacLennan, 1988 ). The molecular A 1 2 0 3 / ( C a O + N a 2 0 + K 2 0 ) ratio is positively correlated with SiO2 content and only the

99.54

74 436 663 16 18 18 116 43 8.9 43 12 42 10 55 10 7.5 40.90 72.0 25.0 3.90 0.96 2.9 0.38 0.39 1.90 0.27 3.2 0.77 0.85 18.20 1.9

Rb Sr Ba Nb Ga Y Zr V Co Cr Ni Cu Pb Zn As Sc La Ce Nd Sm Eu Gd Tb Tm Yb Lu Hf Ta Cs Th U

63.08 0.89 15.91 2.90 2.79 0.20 2.51 3.47 3.07 2.72 0.12 0.56 1.22 0.22

SiO2 TiO2 A1203 Fe203 FeO MnO MgO CaO Na20 K20 P2Os COz H20 ÷ H20S Total

150

Tonalites

38 562 931 10 18 21 143 65 14.0 63 13 23 3 77 7 10.6 15.80 35.0 22.0 4.70 1.32 3.5 0.49 0.34 1.75 0.25 3.7 0.55 0.70 1.05 1.2

58.92 0.30 17.05 3.15 4.18 0.16 2.96 4.42 3.47 1.65 0.40 0.46 2.57 0.13 0.07 99.61

151

28 425 1412 9 18 24 150 91 22.0 301 21 43 25 75 7 17.6 19.10 43.0 24.0 5.70 1.25 4.2 0.58 0.48 2.60 0.40 4.3 0.55 0.70 2.46

99.52

58.21 1.37 16.08 5.16 2.62 0.25 4.17 5.24 3.66 1.50 0.30 0.35 0.25 0.26

163

34 717 513 8 18 21 106 155 23.5 165 17 154 1 86 10 22.3 13.70 34.0 17.0 5.60 1.42 4.4 0.83 0.30 2.10 0.31 3.0 0.44 1.10 3.10 1.5

99.79

54.69 1.76 16.95 6.80 2.30 0.21 3.94 6.23 3.71 1.54 0.24 0.47 0.67 0.22

164

22 594 814 9 18 19 131 122 24.0 115 17 87 8 81 8 17.6 17.30 41.0 26.0 5.20 1.28 5.1 0.61 0.60 1.90 0.34 3.7 0.48 0.60 1.12 0.9

99.51

54.70 1.47 16.98 4.00 3.77 0.33 3.73 6.07 3.76 1.47 0.24 0.75 1.84 0.40

165

Major and rare element data for plutonic rocks of the Brunovistulicum

TABLE 2

174 55.96 1.26 17.10 2.96 5.10 0.08 4.38 1.80 4.24 3.10 0.34 0.33 2.83 0.22 0.02 99.62 45 407 531 8 18 24 150 129 29.0 31 14 121 30 126 15 18.3 15.20 36.0 25.0 5.40 1.30 4.9 0.57 0.50 2.40 0.36 4.4 0.50 1.90 2.50 1.0

166 60.15 1.27 15.80 2.60 3.58 0.23 2.91 4.51 3.73 2.13 0.24 0.67 1.62 0.26 0.33 100.03 41 536 716 11 18 19 134 100 13.0 42 16 77 20 102 12 14.7 19.30 42.0 25.0 5.00 1.18 4.0 0.58 0.25 1.80 0.77 4.3 0.65 1.30 3.80 1.5

33 547 350 8 18 28 149 127 27.0 55 20 172 55 142 11 21.7 19.80 44.0 27.0 7.10 1.65 7.9 0.78 0.40 2.80 0.50 4.9 0.50 1.80 2.70 1.0

55.44 1.50 18.41 3.54 4.48 0.08 3.23 4.58 3.67 2.36 0.24 0.20 2.13 0.14 0.08 100.18

175

48 485 730 7 16 15 120 88 12.4 29 12 135 37 120 9 11.8 13.00 27.0 13.0 2.90 0.70 2.3 0.31 0.20 1.25 0.28 4.1 0.42 1.70 3.15 0.9

59.53 0.85 17.10 2.91 2.95 0.05 2.30 5.68 3.24 2.50 0.45 0.88 1.24 0.32 0.08 99.87

176

74 235 843 13 16 16 234 104 16.0 36 19 131 18 201 16 18.2 26.30 55.0 22.0 4.20 1.42 5.0 0.43 0.38 1.50 0.20 6.7 0.60 1.50 3.70 1.0

0.16 100.24

62.41 1.26 15.73 1.51 4.89 0.11 2.16 3.66 3.20 2.54 0.29 0.84 1.32

183

45 503 592 10 17 18 143 118 19.0 27 13 21 7 85 5 14.9 14.00 34.0 17.0 3.70 1.10 2.8 0.48 0.25 1.60 0.26 3.9 0.45 0.80 2.30 1.1

99.57

3.58 3.24 3.70 3.05 0.23 0.25 2.80 0.05

59.93 0.55 16.04 3.59 2.50

190

43 521 844 10 15 17 137 79 12.4 85 10 29 3 59 5 11.0 17.90 53.0 19.0 4.00 1.01 3.1 0.46 0.29 1.85 0.21 3.9 0.60 0.75 3.60 1.0

99.76

59.08 0.70 15.09 2.78 3.16 0.13 2.28 5.16 3.32 2.43 0.40 2.74 2.62 0.04

200

110 150 768 16 15 19 157 21 4.4 990 16 56 15 19 7 2.9 34.50 65.0 22.0 3.30 0.58 2.4 0.35 0.17 1.40 0.26 4.4 1.15 3.20 18.70 3.3

99.66

71.23 0.81 12.92 1.10 1.82 0.13 1.00 1.10 3.86 3.81 0.14 0.98 0.66 0.10

171

188

93 190 1095 16 17 21 153 22 3.6 29 17 192 43 366 30 3.6 29.00 57.0 20.0 3.40 0.68 2.6 0.40 0.30 1.60 0.18 5.2 1.22 2.80 18.00 3.6

0.12 100.46

72.01 0.40 13.67 1.32 1.13 0.04 0.50 0.99 4.36 4.05 0.43 0.75 0.69

Leueogranites

E

N

z

©

©

Z "0

rll ¢3

¢)

©

t-n

m

Rb Sr Ba bib Ga Y Zr V Co Cr Ni Cu Pb Zn As Sc La Ce Nd Sm Eu Gd Tb Tm Yb Lu Hf Ta Cs Th U

SiO2 TiO2 A!203 Fe203 FeO MnO MgO CaO Na20 K~O P205 CO2 H20 + H20S Total

99.89

17 28 2 2.4 12.30 32.0 13.0 2.50 0.49 2.4 0.32 0.13 0.75 0,13 3.3 0.77 1.10 5.20 0.5

49 377 1121 10 16 12 88 13 1.5 13 5 50 18 29 3 1.9 11.40 25.0 I0.0 1.70 0.44 I. 1 0.16 0,09 0.66 0.12 2.6 0.55 1.20 3.20 1.0

100.38

115 226 558 19 20 18 110 14 1.6 120 2

72.19 0.65 13,90 0.95 0.54 0.10 0.50 1.15 4.49 3.11 0.30 1.17 0.70 0.14

169

71.83 0.19 14.68 0.37 1.64 0,06 0.76 0.88 3.89 4,42 0.05 0.01 1,48 0.12

99

Biotite granites

TABLE 2 (Continued)

47 142 431 14 II 11 39 8 3.1 8 6 64 16 5 7 1.6 6.90 15.0 6.0 1.15 0.29 1.1 0.18 0.21 0.80 0.15 1.9 1.10 0.40 7.90 1.5

74.16 0.58 11.37 0.61 0.42 0.07 0.87 1.89 4,40 3.12 0.00 2.21 0.10 0.08 0.15 99.88

170

124 181 825 19 16 20 145 16 2.6 12 9 88 48 72 7 3.5 49,40 88.0 31.0 4.50 0.57 3.4 0.39 0.36 1.70 0.22 4.6 0.79 1.40 1Z00 2.7

71.42 0.51 14.80 1.21 1.26 0.02 0.48 0.63 3,40 4.30 0.14 0,70 0.60 0.06 0.03 99.68

177

54 395 1038 9 16 10 96 17 2.2 24 17 268 142 285 8 2.2 13.70 27.0 11.0 1.70 0.47 1.0 0.20 0.20 0.65 0.07 2.6 0.45 1.40 2.40 0.5

99.56

72.09 0.54 13.67 1.55 0.53 0.03 0,43 1.35 4.16 3.34 0,16 0.81 0.83 0,04

181

68 417 ! 524 12 17 11 98 13 1.6 98 1 4 18 28 6 2.5 26.20 58.0 17.0 2.70 0.58 1.9 0.23 0.14 0.87 0.13 3.1 0.53 0,85 6.80 2.0

99,77

71.50 0.38 13.94 0.73 1.60 0.06 0.80 1.23 4.04 3.46 0.00 0.46 1,50 0.07

204

34 323 948 14 16 12 143 21 2.8 77 1 6 10 51 5 2.8 19.20 46.0 16.0 2,85 0.87 2.2 0.28 0.20 0.83 0.15 3,6 0.54 0.93 2.60 3.7

67.53 0.36 15.00 1,35 1.96 0.06 1.14 1.20 5.38 2.68 0.00 0.91 1.94 0,24 0.00 99.75

205

48 734 972 11 18 11 141 25 2.0 128 2 5 15 38 4 3.3 18.50 38,0 17,5 2.60 0.69 2.5 0.27 0.10 0,80 0.14 3.6 0.45 0.80 2.70 1.5

99.32

68.36 0.26 15.90 0.92 1.62 0.07 0.78 2.44 5.04 2.41 0.12 0.09 1.21 0.10

104

44 388 646 12 16 I1 75 8 0.9 122 2 1 18 11 7 2.1 8.00 16.0 7.0 1.10 0.35 1.1 0.14 0.08 0.68 0.11 L0 0~55 0.80 0.96

99.67

0.89 0.04 0.23 0.98 5.02 2.71 0.05 0.16 0.87 0.10

74.08 0.05 14.49

106

Leucogranodiorites 168

61 562 863 10 17 13 122 23 3.6 41 8 50 13 56 12 2.4 10.20 24.0 12.0 2.20 0.55 1.4 0.19 0.12 1.00 0.13 2.7 0.44 1.50 2.00

99,94

70.48 0.81 14.35 1.83 1.13 0,16 0.79 1.29 4.51 3.03 0.14 0.46 0.78 0.18

45 756 1261 8 18 11 130 19 2.5 81 1 8 12 33 3 2.7 18.40 37.0 13.0 2.40 0.62 1.6 0.26 0.16 0.82 0.15 3.2 0.40 0.93 3.00 2.0

72.01 0.38 14,55 1.28 1,03 0.06 0.72 1.44 4.40 2.28 0.00 0.29 1.40 0.04 0.11 99.88

201

24 1054 1112 11 21 15 174 68 3.0 73 6 8 7 65 8 7.5 29.0 65.0 34.0 5.80 1,35 3.9 0.45 0.25 1.t0 0.!4 4.8 0.70 0.70 3.45

1.36 0.10 0.02 99.7 t

62.46 0.65 17.53 2.10 2.18 0.07 1.90 4.46 4.56 2,14 0.20

73

31 961 778 8 21 12 161 54 5.8 104 5 2 10 53 4 4.1 25.00 45.0 19.0 4.40 0.80 2.5 0.26 0.10 0.50 0.12 3.0 0.38 0.50 2.10 1,9

61.47 0.80 17.38 2.23 2.14 0.08 1.83 4.51 4.84 1.96 0.20 0.62 1.04 0.39 0.01 99.60

108

Leucotonalites

23 1073 1189 7 21 15 165 33 4.9 85 3 2 14 49 4 4.4 17.40 46.0 25.0 4.30 1.08 2.8 0.40 0.09 1.30 0.16 4.2 0.48 1.30 2.30 1.5

99.51

66.67 0.40 16.43 1.35 1.30 0.06 1.01 1.61 6.10 2.16 0.17 0.77 1.22 0.24

110

94 258 857 18 18 18 135 28 4.3 20 14 217 59 173 21 4.1 23.10 46.0 22.0 3.90 0.80 2.9 0.52 0.24 1.20 0.18 4.3 1.68 0.90 7,60 1.7

99.66

67.54 0.61 15.08 1.74 2.15 0.05 1.90 0.87 3.76 3.60 0.20 0.52 1.53 0.10

180

3:z Z7 .>

rn

t"

O

99.87

100.29

13 710 351 6 18 19 93 147 29.0 101 24 42 1 87 7 24.2 15.60 44.0 23.0 5.50 1.46 4.3 0.66 0.33 2.20 0.48 3.2 0.42 0.40 1.80 2.0

Rb Sr Ba Nb Ga Y Zr V Co Cr Ni Cu Pb Zn As Sc La Ce Nd Sm Eu Gd Tb Tm Yb Lu Hf Ta Cs Th U

5 549 345 3 16 16 62 208 44.0 176 22 9 0 70 4 34.0 12.00 28.0 20.0 4,30 1.30 1.6 0.48 0.18 1.90 0.19 1.9 0.15 0.60 0.70

6.51 7.85 3,02 1.50 0.48 0.48 2.32 0.15 0.21 99.01

50.60 0.83 16.30 8.75 0.01

0.75 0.35 0.9 0.11 0.17 0.60 0.42 0.5 0.30 0.55 0.53 1.0

45 132 235 3 10 9 4 79 21.0 140 65 12 6 29 3 32.5 1.36 2.0

0.46 3.32 0.40 0.01 99.13

49.82 0.17 16.27 0,54 3.83 0.15 10.23 10.43 1.78 1.72

20 361 291 14 17 26 59 214 49,0 100 26 77 3 108 10 31.8 19.80 42.0 28.0 7.00 2.15 7,2 0,98 0.60 2.70 0.38 1.7 1.05 0.95 0,90

49.52 1.57 18.05 3.14 8,47 0.25 4.42 7.28 3.52 1.17 0.30 0.05 1.59 0.09 0.10 99.52

153

5 212 227 3 14 27 138 118 41.0 494 75 62 2 95 10 41.5 8.60 19.0 15.0 4.90 1.38 5.2 0.82 0.48 3.40 0.50 4.2 0.23 1.00 0.63

99.95

50.51 0.36 16.30 3.77 7.55 0.21 6.55 9.72 2.26 0.98 0.10 0.20 1.38 0.06

154

10 160 51 2 14 10 15 114 40.0 422 128 73 0 45 5 29.2 2.30 5.5 3.0 0.98 0.45 0,7 0.28 0.33 0.96 0.19 0.7 0.10 1.10 0.40 0.2

9.41 8.75 1.95 0.55 0.32 0,69 1.80 0.23 0.16 99.61

51,78 0.37 16.92 2.02 4.66

192

16 152 101 5 13 10 29 132 44.0 485 135 54 5 51 7 28.0 2.70 9.5 6.0 1.20 0.61 2.0 0.21 0.21 1.10 0.30 1.6 0.16 0.80 0.48

7.93 7.54 3.45 1.05 0.22 1.61 3.82 0,30 0.15 99.67

51.75 0.34 15.91 1.98 3.62

193

23 269 320 9 16 28 137 294 60.0 164 40 71 0 76 3 59.7 15.40 45.0 25.0 5.90 1.94 7,0 1.34 0.49 3.60 0,60 5.2 0.90 1.60 3.60

99.98

48.68 2.45 14.45 3.48 8.16 0.15 5.48 8.62 2.80 1.00 0.33 0.85 2.81 0.72

206

16 308 365 11 18 28 141 237 56.0 153 41 39 0 72 5 36.5 15.50 38.0 28.0 6.00 1.87 6.7 1.06 0.55 3.10 0.40 4.9 0.80 1.30 2.70 2.9

100.11

49.47 1.86 14.81 3.44 7.35 0.13 6.74 5.80 3.22 1.05 0.32 0.41 3,95 1.56

207

0.55 0.21

0.076 0.06

27.6 0.14 1.0

56

100 98.0 3490 663 213

6 4

1

51.66 0.12 1.85 1.99 5.58 0.13 28.97 0.90 0.13 0.08 0.01 0.83 6.22 0.53 0.11 99.11

75

Ultramafics

12 203 2830 6 10 9 47 91 117.0 1850 216 22 166 100 12 15.0 8.90 22,0 9.0 2.10 0.72 2,0 0.35 0.19 0,60 0.12 1.4 0.21 1.10 1.30 0.6

99.53

43.32 1.00 7.18 5.09 5.96 0.22 21.70 5.01 0.97 0.62 0.14 0.72 6.12 1.08

167

Major elements analyses: Geological Institute of Faculty of Science, Charles University, Prague (analyst J. Adam). Trace elements: from Rb to Zn; XRF, Laboratory o! Geoindustria, Prague (analyst V. Budil ); from As to U, neutron activation analyses, Institute of Raw Materials, Kutn~i Hora (analysts J. Lenk and Z. l~anda).

30 765 757 14 21 21 334 79 18.0 38 21 43 3 84 8 15.2 36,10 70.0 30.0 6.70 2.00 5.7 0.72 0.25 2.00 0.40 8.2 0,60 0.40 1.62

52.85 0.65 18.49 4.70 4.35 0.14 3.46 5.44 4.65 1.88 0.06 0.27 2.83 0.10

53.49 1.07 16.71 3.56 4.85 0.13 5.02 7.04 3.34 1.I 4 0.40 0.35 2.91 0.28

SiO2 TiO2 A1203 Fe203 FeO MnO MgO CaO Na20 K20 P2Os CO2 H20 ÷ H 20S Total

78

191

203

152

Gabbros

Diorites

z

©

o

© z

¢¢

/:

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m

t~

E. JELINEK AND A. DUDEK

112 CaO (wt%

12

)

18

n 10

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m 14

m

8 i

n

.

c

n

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‘e

2

I 2-

0

v

*

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.

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.

a

I

FeOtot(wt

1

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0 0 A

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.

n3 F*

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MgO (wt %)

%I mm

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LEUCOGRANITE

o

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n

BIOTITE A LEUCOGRANODIORITE

n

v

q HORNBLENDE-BIOTITEQUARTZ DIORITE

mU l n

.

DIORITE

m GABBRO,GABBRONORlTE

.

l

n

HORNBLENDE-BIOTITE LEUCOTONALITE

0 0

a \nv

ULTRAMAFIC

ROCKS

D

SiO2 I

50

60

70

1

50

VOA

(wt%) I

1

60

I

A

%L

L

&O A I

70

Fig. 2. Variation diagrams of selected major elements plotted vs. SO2 for the BC granitoids.

most silicic rocks are slightly peraluminous. Even though the more evolved rocks have A1203/ (CaO + NazO + KzO ) > 1, for most of the granitoids it falls below 1.1 (Fig. 5 ), i.e., below the lower limit for most peraluminous S-type granitoids (Chappell and White, 1984).

Trace elements There is a general correlation between trace element and SiOz contents (e.g., Rb, Ba and Th positively and Sr, Ti and V negatively ) . The BC granitoids are characterized by a low rubidium content and exhibit wide range of K/ Rb ratios (290- 1600; cf. Fig. 7 ) . Most of these

values are greater than K/Rb values for mature continental crust ( 100-300). Potassium and rubidium contents increase and K/Rb ratios decreases from gabbros through diorites, tonalites to biotite granites. Only some samples of biotite granite and leucogranites of the Lubna type have K/Rb ratios in the range typical for continental crust. Leucotonalite and biotite granite have rather variable ranges of K/Rb ratios. The leucogranodiorites and leucogranites form tighter clusters. The coherent tonalite-granodiorite-biotite granite trends could result from fractionation of plagioclase, hornblende and biotite (cf. Hildreth and Moorbath, 1988 ) . More acidic differentiates (some samples of biotite granite and leuco-

GEOCHEMISTRY OF SUBSURFACE PRECAMBRIAN PLUTONIC ROCKS, BOHEMIAN MASSIF

4a 2 0 + K20 (wt %)

1 13

~

O V °

O

[] / [

[]

LKALINE

iie m ~ e

oe

•

[]

SUBALKALINE

• •

A

Do [] [] O0 °o LEUCOGRANITE

o

BIOTITE GRANITE

A

BIOTITE LEUCOGRANODIORITE

?

HORNBLENDE- BIOTITE LEUCOTONALI TE

[]

Si 0 2 (wt % )

,, 0

VV

O

•

oOo A O0

HORNBLENDE- BIOTITEQUARTZ DIORITE

•

DIORITE

•

GABBRO, GABBRONORITE ULTRAMAFIC ROCKS

"/r I

I

I

50

60

70

Fig. 3. SiC2 vs. total alkaliesplot of BC granitoids;fields after Irvine and Baragar ( 1971). granites) cluster off the main trends and this could reflect a higher contribution of mature crustal material. The primitive character of possible source of the BC granitoids is documented by the low Rb/Sr ratios ( < 0.1 ), as well as by the very low 87Sr/86Sr ratios (0.704-0.705; Th6ni and Finger, 1991 peTs. commun.). Their parent melt could be derived from mantle or lower crust. Higher 87Sr/S6Sr ratio (0.710) has been found in the leucogranites of the Lubmi type. The granitoids from the BC are, in general, characterized by having low Zr and Hf contents (Fig. 6), which do not correlate with SIC2. Instead, the contents of these elements are controlled by presence of zircon in the rocks with the quartz diorites, diorites and tonalites containing scattered zircon and being richest in Zr. Recent experimental studies (e.g. Watson and Harrison, 1983; Watson et al., 1989) indicate, that zircon has low solubility in a melt of broadly granitic composition and that is un-

likely to be present in basaltic magma. This control is probably intracrustal. The content of Zr in peraluminous granitic melts is limited to approximately 60-100 ppm ( D r u m m o n d et al., 1988 ). Zr contents in granitic melts can be greater, however, if the melt is more alkaline, or if the melt contains inherited zircon (cf. Sylvester, 1989). The Zr contents from the BC meta-aluminous granites and more mafic rocks are greater than 100 ppm implying that these rocks may contain inherited zircon. The overall rare-earth-element concentrations in the BC granitoids are relatively low and the L-'REE rarely exceeds 110 ppm. The highest REE concentrations ( 115-130 ppm) are in the leucogranites, followed by hornblende-biotite quartz diorites (62-116 ppm), leucotonalites (98-102 ppm), hornblende diorites (71-99 ppm), hornblende gabbros (60-112 ppm), biotite granites (32-108 ppm), leucogranodiorites (35-81 ppm). The lowest REE contents are in cumulate gabbros (7-24 ppm). The

114

E. JELINEKAND A. DUDEK

CaO HORNBLENDE-BIOTITEQUARTZ DIORITE

[]

<)

LEUCOGRANITE

O

BIOTITE

A.

BIOTITE LEUCOGRANODIORITE

GRANITE •

~

DIORITE

• GABBRO~ GABgRONORITE

V

HORNBLENDE-BIOTITE LEUCOTONALITE

iio

°l n °

oo I

1 I

o o

I

•

Ji oi / "

o

I

/ No20

I

~°oo

I

Oa

/

l

I ! GRANODIORITES

I

o °

I

I QUARTZMONZONITES

x K20

Fig. 4. N a 2 0 - C a O - K 2 0 ternary plot o f BC granitoids.

greatest variation in REE concentrations is in the biotite granites and the leucogranodiorites. REE patterns in average rock types of the BC granitoids are shown in Fig. 8. Like the LREE/ HREE ratio, the overall REE content is variable for the different rock types. The marie rocks have the lowest LREE/HREE ratio (CeN/Ybn = 1.2-4.0 in groups of cumulate and hornblende gabbros and 3.8-7.4 in diorites, quartz diorites and tonalites, respectively). These rocks are characterized by high HREE contents. Melting of the material of eclogitic or garnet-bearing granulitic composition could produce a tonalitic magma with HREE enrichment (Hildreth and Moorbath, 1988 ). The cumulate and hornblende gabbros exhibit flat REE patterns, which are similar to distribution of REE in tholeiitic MORB basalts, This gabbros could be first differentiates of basaltic magma. The degree of LREE enrichment increases for the series leucogranodiorite (CeN/ YbN=6.2-12.2), biotite granite (9.8-14.2),

leucogranite (12.3-16.5) and leucoquartzdiorite (9.2-23.2). Compared to the Hercynian plutonic rocks (Central Bohemian pluton, Bou~ka et al., 1984) are the REE contents of BC granitoids much lower (Fig. 9 ). The BC granitoids usually have either weak positive or negative Eu anomalies, but sometimes no anomaly at all. Relatively large positive Eu anomalies (Eu/Eu* 1.2-1.6) are present only in the cumulate gabbro samples, indicating accumulation ofpl~oclase. Most of the other rock types exhibit small negative Eu anomalies, except for the leucogranites which have larger negative Eu/Eu* (0.6-0.7). In general, the Eu/Eu* ratio decreases with increasing SiO2 content and LREE/HREE ratio. The REE patterns of the BC granitoids can be explained by fractionalcrystallization. Gromet and Silver ( 1983 ) found that sphene and allanite contain nearly 80% of the REE in a granodioritic melt. The common accessory in the tonalites and granodiorites of the BC is

GEOCHEMISTRY OF SUBSURFACE PRECAMBRIAN PLUTONIC ROCKS, BOHEMIAN MASSIF

AI203 (CaO+ Na20+ K20)

1.5

(mol. °'o)

1.4

1.3

1.2

1 15

PERALUMINOUS

v

O

LEUCOGRANITE

o

BIOTITE GRANITE

t,

BIOTITE LEUCOGRANODIORITE

v

HORNBLE NDE- BtOTITE LE UCOTONALITE

o

HORNBLENDE-BIOTITEQUARTZ DIORITE

n •

DIORITE

•

GAB BROp GA BBRONORITE

1.1

O

n

[]

~

o v

[] []

O 0 - o o

~

1-0 -

O0

V v •

0

0-9 -

[] []

•

[] []

METALUMINOUS

[]

•

0'8

0

0'7

SiO2 (wt %) I 50

I 55

I 60

I 65

i 70

Fig. 5. Plot of the molecular ratio of A1203/(CaO + Na20 + K20) vs. SiO2. The peraluminous-meta-aluminousfield is after Chappel and White

(1974).

sphene. The significant positive correlation of Ti concentrations and Yb + Lu in more mafic members of the BC, shows the important role of this mineral, whose precipitation can reduce REE concentration in residual melt. Therefore the higher total content of REE in tonalites and granodiorites rather than in the granites. This fact is also documented by depletion of HREE in more acidic rocks (sphene preferentially incorporates HREE). The correlations between Zr and REE is not as good as between Ti and HREE but there is a weak positive correlation between zirconium and L a + C e concentrations. The LREE enrichment in some rocks could be explained by zircon fractionation. However, this mineral is thought not to have played an important role. Other controlling factors on REE distribu-

tion appears to be the presence of hornblende, pyroxene and biotite, respectively, with half the HREE contents in tonalites and diorites probably be bound in hornblende and biotite. The enrichment of LREE in the leucogranites is probably due to biotite crystallization from a residual melt. The fractionation of the Ca-rich plagioclase in early solidified phases is the main controlling factor of Eu distribution in residual melts. Petrogenesis of the BC granitoids The existence of a wide spectrum of rock types (from gabbros to granites), the good correlation between some major and trace elements and relative age relationship suggest that this suite of rocks is comagmatic. The very

1 16

E. JELINEK AND A, DUDEK

j~

/"

/ "7f ' °,x,S7

/

L4// / 2

o

z, lppm.,

I 10

/

I 100

I

O

BIOTITE G R A N I T E

A

BIOTITE LEUCOGRANODIORITE

~7

H O R N B L E N D E -BIOTITE LEUCOTONALIT E

[]

H O R N B L E N D E - - B I O T I T E -QUARTZ DIORITE

i

DIORITE

•

GABBRO, GABBRONORITE

!

I

200

! 300

Fig. 6. Plot of Zr vs. Hf of BC granitoids. Lines are isopleths of the Zr/Hf ratio. primitive nature of the original magma which produced most of the BC granitoids is shown by the low content of REE and very low Rb, Zr, Y, Nb and Ta. If such low contents are a primary magmatic signature and not a result of metamorphism, then they must be a result of the magma being formed from a source which was depleted in these elements. Material with such features is found only in the lower crust or in the upper mantle. This is consistent with members of the BC plutonic suite being Itype granitoids. The increasing values of Rb, K, Ba, Th as well as progressively increasing CeN/YbN ratios in the most felsic differentiates (like leucogranites and some biotite granites) imply an increasing assimilation of a mature material and could indicate an elevated continental crust contribution (cf. Hildreth and Moorbath, 1988 ). The primary melt, from which the grani-

toids could have differentiated, may have formed by one of the following mechanisms: ( 1 ) partial fusion of lower crustal material of basaltic composition (e.g., eclogite, basic granulite, amphibolite), (2) partial fusion of crustal complexes (e.g., immature greywackes), or (3) by direct partial fusion of mantle material (cf. Martin, 1987 ). Metamorphic rocks of the BC, known from drilling in Czechoslovakia and Poland, are represented by paragneisses, in some places migmatized, with leucosomes of granodioritic composition. Metabasites (amphibolites) are present only in limited areas, with these rocks forming less than 5% of the metamorphic complex. The origin of magmas by partial fusion of such rock types is unlikely as their geochemical characteristics (higher 87Sr/a6Sr---0.714, very low content of Rb, Sr, ~REE, etc.; Dudek and Jelinek, in prep. ) are similar to the BC grano-

G E O C H E M I S T R Y O F S U B S U R F A C E P R E C A M B R 1 A N P L U T O N I C ROCKS, B O H E M I A N MASSIF

/ (P'P'm')

1 17

/

/

°o

>o/~

0

0

3000

/o

0

E]O0

°/°;

2000

[]

/

lOOO

I

/

[] •

/

] • • [ w•--

/

. [ll~ 1/7 / I/j ~.

I 10

/

o B~OrIT~NITE

/

•

/

/

/

/

A

~

Ko[p.p.m.) I 30

.O-,-NBLE.OE Or/(E

LEUCOTO.AL TE

[] • •

HORNBLENDE-BIOTITEQUARTZ DIORITE DIORITE GABBRO~GABBRONORITE

,jr I 50

BIOTITE LEUCOGRANODIORITE

v

/ ,-,i .

.,,',/

ULTRAMAFIC ROCKS

I 70

I 90

I 110

Fig. 7. Plot of K vs. Rb o f B C granitoids. Lines are isopleths of the K / R b ratio.

diorites. In addition, no material of a residual character after partial melting of crustal material (e.g., granulitic composition, cf. Vielzeuf and Holloway, 1989) has been found. However, this crustal material could have been assimilated by a parent melt (cf. inherited zircon), but only slight contamination was involved in the first steps of the magma evolution. The magmatic evolution of BC plutonic suite may have followed the assimilation-fractional crystallization (AFC) model proposed by De Paolo ( 1981 ), Barker et al. ( 1986 ) or Martin (1987). This model proposes that tholeiitic basalt magma, derived by partial fusion of the mantle or near the mantle-crust transition, ascended into the crust, following by crystallization of cumulate (Rusava, samples 153, 154, 192 and 193 ) and hornblende gabbros (cf. high K / R b ratio, flat REE patterns and positive eu-

ropium anomaly). The next process could be contamination with immature crustal material and then differentiation of the resultant melt of tonalitic composition. The late stage products (e.g., leucogranites) could also have incorporated mature continental crustal material. Based on the studies of Allegre et al. ( 1977 ) and MacCaskie (1984) dealing with use of trace elements in igneous processes, Knil (1990) wrote programs DMODEL, IDENT and FKRYST (these programs are available at the Department of Mineralogy, Charles University). The programs were used to test the hypothesis mentioned above. Mixing, contamination, partial or modal melting, and simple crystal fractionation were investigated as possible processes controlling magmatic evolution (using La, Ce---elements with low values of partition coefficient D, and Co---high D). Mixing models do not give satisfactory results

118

E. JELINEKANDA. DUDEK

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-----

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DIORITE

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GABBRO~GABBRONORITE

HORNBLENDE-BIOTITE LEUCOTONAI.

ITE

1

Lo Ce

Nd

Sm Eu G

Tb

Tm Yb

Lu

Fig. 8. REE plot ofBC granitoids normalized to the chondrite values of Boynton (1984).

(low coefficient of correlation ). It is the crystal fractionation model that best fits all the geochemical data. The fractional crystallization model used an average tonalite as the parental magma composition and the partition coefficient values (D) of Martin (1987). The concentrations of Ce, Nd, Sm, Eu, Yb, Rb and Sr were used to test if such a parental tonalite melt could fractionate or accumulate crystals to produce the spectrum of compositions present in the BC suite ofplutonic rocks. As it is not clear whether the first crystal cumulates were gabbros or diorites, both possibilities were tested. The

similarity function (Euclidean distances between model and actually observed data) was used to test the validity of the models. From this it can be seen that formation of diorite as the result of crystal accumulation from a tonalite magma produces a better fit than the other alternative (lower similarity values cf. Table 3 ) which is, in addition, complicated by absence of clear relationships of gabbros and granitoids. The various steps for the model are (Table 3): ( 1 ) crystal accumulation of a crystallizing tonalitic magma to produce diorite (represented by sample 191 );

GEOCHEMISTRY OF SUBSURFACE PRECAMBRIAN PLUTONIC ROCKS, BOHEMIAN MASSIF

\ 100

\

\

\

1| 9

"\

50

x' "...'

'.'. •.

'. ".'.'5." .-°~" ....- .:..~......... • . ~ - ~.'.. .

...

10 •

~•

"".i::.~ ~°

"

•.~.

I

Rock / /'/"

Chondrite

/ TONALITE Q U A R T Z DIORITE

B,OTITE ORANITE -2/ "/ ;/'/7/- ~

LEUCOORA.O~IORnE

~Q..

CENTRAL

, , Lo Ca

,

Nh

,

, , Gh Sm Eu

GABBRO~ GABBRONORITE

im

BOHEMIAN

, Tb

,

PLUTON

,

,

, T ,m Yb

, Lu

Fig. 9. REE plot comparing the BC granitoids and Variscan age granitoids from the Central Bohemian Pluton, data from Bou~ka et al. (1984).

(2) fractional crystallization of tonalite to produce leucotonalite melt (sample 180); (3) fractionational crystallization of leucotonalite melt to produce leucogranodiorite (sample 168); and (4) fractional crystallization of leucotonalite melt to produce biotite granite (sample 99). However, the origin of neither the gabbro nor the leucogranite is well constrained. The leucogranites could be younger (cf. higher Sr isotope ratio) or they represent the solidified part of the most differentiated magma possibly contaminated by upper crustal material•

The fractionation phases can be identified by chemical element variations. Trace elements and their ratios, like Sr and Eu/Eu*, positively correlate with the plagioclase-controlledmajor element (CaO), Ti, V and Cr with pyroxene and hornblende (FeO, MgO and CaO), Rb, Sr and Ba with biotite (KzO, MgO, FeO), all of which substitute in the mineral lattices, indicating fractionation of these minerals. Decreasing values of the K/Rb ratio with increasing SiO2 can be produced by plagioclase, hornblende and biotite fractionation. The positively correlating content of REE with single-

41.9 21.8 4.84 1.2 2 41 521.2

0.8342 2.0236 3.5771 3.4012 3.8313 0.1583 2.2243

47 10.7 0.81 0.23 0.28 73.48 223

L

0.5

39.2 21.7 2.9 0.77 1.08 11.63 496

S

0.5

0.2079 0.2027 0.2575 1.3817 0.24877 0.32348 3.30124

D

0.53 pig 0.1 K f 0.08 bi 0.02 hbl 104.99

62.3 14.25 1.06 0.2 0.37 93.53 98.17

L

0.7

No, 180 granodiorite

2

12.96 2.89 0.27 0.27 0.09 30.26 324.09

S

0.7

0.1628 0.1188 0.0847 1.3291 0.04824 0.1738 3.7028

D

130.68

0.54 pig 0.14 K f 0.03 bi

65.08 14.91 1.11 0.19 0+39 97.58 85.46

L

0.95

10.6 1.77 0.09 0.26 0.02 16.96 316.45

S

0.95

No. 168 leucogranodiorite

3

0.1397 0.093 0.0799 1.186 0.06279 0.3238 4.4636

D

68.23

0.39 pig 0.29 K f 0+06 bi

78.86 18.25 1.36 0.t9 0.48 113.47 39.46

L

0.8

No. 99 biot. granite

4

11.02 1.7 0.11 0.22 0.03 36.74 176.12

S

0.8

D = Distribution coefficient, literary data (Martin, 1987 ) and mineralogical composition of BC rocks were used for calculation. D = Z'(w~Di), where w~is mass of mineral, i and D~ is distribution coefficient of mineral i. F = coefficient of fractionation for different steps ( F = M/Mo ) where M is the mass of melt produced by differentiation process and M0 is the mass of rock undergoing melting. S = concentration of elements (in ppm ) in solid products of crystallization. L = concentration of elements (in ppm ) in residual melts of hypothetical model. *The agreement between model data for individual steps of the differential sequence with those actually observed was assessed using the so-called similarity function (Euclidean distance between both data sets). Low similarity values indicate close agreement. The bulk similarity is 199.88; similarity between the residual model melt and real values ofteucogranite (sample 188 ) is 217.22.

Ce Nd Sm Eu Yb Rb Sr

D

84.83

Similarity*: F

No. 191 hbl. diorite

1

0.5 pig 0.45 hbl 0.04 bi

Initial composition Average tonalite

Mineral proportion:

Sample:

Step:

Fractional crystallization model of the Brunovistulicum's granitoids using average tonalite as initial m a g m a composition. Individual steps are represented by selected samples (see Table 1 )

TABLE 3

zr

r~

B9 O

12 1

GEOCHEMISTRY OF SUBSURFACE PRECAMBRIAN PLUTONIC ROCKS, BOHEMIAN MASSIF

phase elements such as Zr (LREE) and Ti (HREE) reflect REE depletion of the melt by early precipitation of sphene or zircon, respectively.

granitoids produced by continental collision with peraluminous granites; the Caledonian type in post-closure situations with magnetitebearing granites allied with appinites. The tectonic setting ofBC granitoids was established according to geochemical criteria using various major and trace elements discrimination plots (Bachelor and Bowden, 1985; Pearce et al., 1984). The presence of syncollision or post-collision granites can be excluded due to the absence of high-K types, cordieritebearing granites and hyperaluminous leucogranites (Lameyre, 1988). The major elements geochemistry of BC granitoids and whole rock association is consistent with these rocks being calc-alkaline and having formed in a subduction zone setting (Fig. 10). Spider diagrams of trace elements distribution in BC granitoids normalized to average ocean ridge granite (ORG) indicate a pattern similar to that for VAG (Fig. 12, cf. Pearce et al., 1984). In discrimination diagrams using trace elements (Fig. 11 ) the BC granitoids are all in the field for volcanic arc granitoids (VAG). The close correspondence of the major elements chemistry of the BC granitoids to that of mag-

Tectonic setting of the BC granitoids The Brunovistulian complex forms only a small part of the Cadomian mountain chain, which is separated from its original continuation and relations, and mostly covered by younger sediments and overthrusted nappe suites of the Hercynian and Alpidic orogens. The observable geological and structural data on the environment of the BC granitoids with their 1-type characteristics are lacking. Therefore, their tectonic setting can be postulated only from their petrological and geochemical features and has a speculative character. Four types of granitoids of different orogenic areas were recognized by Pitcher ( 1979, 1983): the Pacific types corresponding to island arcs with small plutons including gabbros and plagiogranites; the Andinotype in active continental margins with granodiorites, tonalites and associated gabbros; the Hercynotype

SOURCE TREND THROUGH THE OROGENIC CYCLE/

R2

(HATCHEDARROW)/ \A,,

2000

0

fl.',Z' Post-

Pre- plate \ • ~ision~x

collision

" Mantle fractionates

uplift 1000

\ late orogenic

Q

v

Anorogenic IQ I

I

1000

Syn -

o

collision

,,. __o_-o-~..,,_:.o" \ r"- "~ Post-orogenic ~ ' ~ .,/ R1 I I I 2000 3000

Fig. 10. Tectonic discrimination plot after Bachelor and Bowden ( 1985 ) of BC granitoids.

122

E. JELINEK AN[) A. DI.IDEK

IP' bm

Rb(p.p.m.) synCOLG

\

100

....

~

I

,oo

noaa

I//" 50

0

!

~

~

G

10

/

//

ORG

VAG

Y+Nb (p.pm,) I0 100

100

I

1000

Ta (p.p.m.)

I

lO

1ooo

lOO

Rb (p.p.m.) syn COLG

WPG

/ J

WPG

lO

///

k syn CI

/fl

/

O

1// ~00

oDZJ

/

~ 10

ORG VAG o-1

• Ill !

•

•

I I

VAG

Yb (p.p.m.) i 10

i 100

I

I 1

Yb+Ta ( p.p.rn.) I 10

I !0(

Fig. 11. Trace element tectonic discrimination plot of BC granitoids. Fields after Pearce et al. (1984). t'~G = island arc granitoids; ORG = ocean ridge granites; WPG = within plate granitoids; syn COLG = collision zone granitoids. matic arcs at convergent plate boundaries also supports this conclusion. This assumption is substantiated by the presence o f a highly probable ophiolite complex in the basic zone o f the exposed Brno massif (Hrouda, 1985; ~telcl and Weiss, 1986). The geochemistry o f the BC granitoids is thus similar to that o f rocks from island arcs or active continental margins. In such tectonic settings, m a g m a can interact with mantle and oceanic or continental crust. This interaction can produce homogeneous melt, which subse-

quently can fractionate to produce the spectrum o f rocks which form the Brno plutonic suite. The BC with its plutons probably represents a Cadomian-consolidated margin of the Fennosarmatian platform. It exhibits a similar tectonic position as the Neo-Proterozoic calcalkaline intrusions of St. Brieux-Coutance on the margin o f the Icartian block in the Armorican massif (Lameyre, 1988). The types more influenced by continental crust, as the peraluminous Mancellian granites of Jouin ( 1981 ) are not developed in the BC, or they are cov-

123

G E O C H E M I S T R Y O F S U B S U R F A C E PRECAMBR1AN P L U T O N I C ROCKS, BOHEMIAN MASSIF

lot #OoI-./ /k.,~.... :.. /,a\ .,i/.,

"/.:

,-~

/./

05

x

'\\

¢ ROCK ORG

"$ l[ \

• ..

\

,/

\

"'X

~,

:-

"\ \

0.1

0.05

O

LEUCOGRANITE

o

BIOTITE GRANITE

Lx

BIOTITE LEUCOGRANODIORITE

v

..........

N

N

"\ \

/" "\

HORNBLENDE-BIOTITE LEUCOTONAL ITE

l \.

/ "v'

HORNBLENDE- BIOTITEQUARTZ DIORITE

•

.....

•

DIORITE

......

•

GABBRO~ GABBRONORITE

0-01

K20

Rb

Ba

Th

To

Nb

Ce

Hf

Zr

Sm

Y

Yb

Fig. 12. Spider diagram of BC granitoids normalized to the average ocean ridge granite (ORG) values of Pearce et al. (1984)•

ered by the overthrusted Hercynian units. In similar tectonic position on the margin of the Fennosarmatia are also complexes now exposed to the southeast in Dobrogea (Kr~iutner et al., 1988 ) and to the north in the marginal Timan-Pechora zone (Krasilschikov et al., 1986; V. Zoubek, pers. commun., 1990). Acknowledgements The authors would like express their thanks to Brian Beard and Donald R. Bowes for thorough language improvement and valuable suggestions. The constructive review of anonymous reviewers are gratefully acknowledged.

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124 ments in the rocks of the Central Bohemian pluton. Geol. Zb. Geol. Carpatica, 35: 355-376. Boynton, W.V., 1984. Cosmochemistry of the rare earth elements: Meteorite studies. In: P. Henderson (Editor), Rare Earth Element Geochemistry. Elsevier, Amsterdam, 510 pp. Bukowy, S., 1972. Budowa podloza karbony Gornoslaskiego Zaglebia Weglowego. Pr. Inst. Geol., 61 : 23-59. Chfib, J., Figera, M., Fediukov& E., Novotn~, M., Opletal, M. and Sk~icelovfi, D., 1984. Probl6my tektonick6ho a metamorfniho v~voje v~chodni ~fisti Hrub6ho Jeseniku. Sb. Geol. V~d, Geol., 39: 27-72. Chappell, B.W. and White, A.J.R., 1974. Two contrasting granite types. Pac. Geol., 8:173-174. De La Roche, H., Leterrier, J., Grandclaude, P. and Marchal, M., 1980. A classification of volcanic and plutonic rocks using R1 R2-diagram and major element analyses---its relationships with current nomenclature. Chem. Geol., 29: 183-210. DePaolo, D.J., 198 I. Trace element and isotopic effects of combined wallrock assimilation and fractional crystallization. Earth Planet. Sci. Lett., 53: 189-202. Dole2al, J., 1980. Hlubinn~i stavba autochtonniho pod1o2i Karpat na jihov,)chodni Morav6 podle gravimetrick~ch a geomagnetick~ch dat. Zfipadn6 Karpaty, S6r. Geol., 6:133-140. Drummond, M.S., Wesolowski, D. and Allison, D.T., 1988. Generation, diversification and emplacement of the Rockoford granite, Alabama Appalachians: Mineralogic, petrologic, isotopic (C and O ) and p - T c o n straints. J. Petrol., 29: 869-897. Dudek, A., 1980. The crystalline basement block of the Outer Carpathians in Moravia: Bruno-Vistulicum. Rozpr. (~s. Akad, V~d, l~. Mat. P/'ir. V~d, 90(8): 185. Dudek, A. and Melkov~i, J., 1975. Radiometric age determination in the crystalline basement of the Carpathian foredeep and of the Moravian flysch. V6st. Ost~'ed. Ustavu Geol., 50: 257-264. Finger, F , Frasl, G., H6ck, V. and Steyrer, H.P., 1989. The granitoids of the Moravian zone of northeast Austria: Products of a Cadomian active continental margin? Precambrian Res., 45: 235-245. Frasl, G. and Finger, F., 1988. The "Cetic Massif" below the Eastern Alps characterized by its granitoids. Schweiz. Mineral. Petrogr. Mitt., 68: 433-439. Gromet, L.P. and Silver, LT., 1983. Rare earth element distributions among minerals in a granodiorite and their petrogenetic implications. Geochim. Cosmochim. Acta, 47: 925-939. Hildreth, W. and Moorbath, S., 1988. Crustal contributions to arc magmatism in the Andes of Central Chile. Contrib. Mineral. Petrol., 98: 455-489. Hrouda, F., 1985. The magnetic fabric of the Brno massif. Sb. Geol. V~d, UG Ser., 19:89-112. lrvine, T.N. and Baragar, W.R.A., 1971. A guide to chem-

E. JELINEK AND A. DI JDEK

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GEOCHEMISTRY OF SUBSURFACE PRECAMBR1AN PLUTONIC ROCKS, BOHEMIAN MASSIF

Crust: its Composition and Evolution. Blackwell, Oxford. Van Breemen, O., Aftalion, M., Bowes, D.R., Dudek, A., Misa~, Z., Povondra, P. and Vr~na, S., 1982. Geochronological studies of the Bohemian Massif, Czechoslovakia, and their significance in the evolution of Central Europe. Trans. R. Soc. Edinburgh, Earth Sci., 73: 89-108. Vielzeuf, D. and Holloway, J.R., 1988. Experimental determination of the fluid absent melting relations in the pelitic system. Contrib. Mineral. Petrol., 98: 257-276.

125

Watson, E.B. and Harrison, T.M., 1983. Zircon saturation revisited: Temperature and composition effects in a variety of crustal magma types. Earth Planet. Sci. Lett., 64: 295-304. Watson, E.B., Vicenzi, E.P. and Rapp, R.P., 1989. Inclusion/host relations involving accessory minerals in high-grade metamorphic and anatectic rocks. Contrib. Mineral. Petrol., 101: 220-231. Wieseneder, J., Freilinger, G., Kittler, G. and Tsambourakis, G., 1976. Der Kristalline Untergrund tier Nordalpen in Osterreich. Geol. Rundsch., 65: 512-525.