GeolCarp_Vol49_No5_369

GEOLOGICA CARPATHICA, 49, 5, BRATISLAVA, OCTOBER 1998

369376

PHASE RELATIONS IN OLIVINE-ORTHOPYROXENE-CHLORITE-

SPINEL-HORNBLENDE METAULTRAMAFICS

FROM THE MALÁ FATRA MTS., WESTERN CARPATHIANS

SERGEY P. KORIKOVSKY

, MARIAN JANÁK

and BRANISLAV LUPTÁK

Institute of Geology, Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences,

Staromonetny per. 35, 109 017 Moscow, Russia

Geological Institute, Slovak Academy of Sciences, Dúbravská 9, 842 26 Bratislava, Slovak Republic; geolmjan@savba.savba.sk

Department of Mineralogy and Petrology, Comenius University Bratislava, Mlynská dolina, 842 15 Bratislava, Slovak Republic

(Manuscript received June 19, 1997; accepted in revised form September 1, 1998)

Abstract: Metaultramafic rocks from the Malá Fatra Mts. (Western Carpathians) preserve mineral assemblages char-

acterized by coexistence of hercynitic spinel, Ca-amphibole (Mg-hornblende), Mg-rich chlorite, olivine (forsterite)

and orthopyroxene (enstatite). A large amount of hercynite and Ca-amphibole (up to 3040 %) is characteristic.

Prograde metamorphism reached P-T conditions close to the equilibrium chlorite = forsterite + enstatite + spinel +

O and the upper stability of Ca-amphibole which corresponds to the temperature of about 700800

C in the model

system CMASH. Retrograde reactions lead to the replacement of spinel by secondary chlorite, orthopyroxene by talc

and olivine by serpentine. Metaultramafic rocks in the Malá Fatra Mts. reached the conditions of the upper amphibo-

lite facies. They most probably represent the fragments of metaperidotites, attached to the lower continental crust

during Variscan tectonometamorphic events.

Key words: Western Carpathians, Malá Fatra Mts., Variscan orogeny, high-grade metamorphism, phase equilibria,

metaultramafic rocks.

Introduction

Metaultramafic rocks occur only sporadically in the pre-Me-

sozoic basement complexes of the Western Carpathians

(Hovorka et al. 1985; Hovorka 1994).

Among occurrences in the Tatric Unitone of the major

tectonic units of the Western Carpathians, the metaultramafic

rocks in the Malá Fatra Mts. have been investigated by

Ivanov & Kamenický (1957), Hovorka (1965, 1977), Hovorka

& Spiiak (1985) and Hovorka et al. (1985).

According to Hovorka & Spiiak (1985) and Hovorka et

al. (1985), the hornblende peridotites from the Malá Fatra

Mts. are composed of olivine, clinopyroxene, orthopyroxene,

tremolite and spinel whose microprobe analyses were pre-

sented. According to the above mentioned authors, these

rocks represent so called deuteroperidotites whose miner-

al assemblage has been generated at 640680

C by contact-

metamorphic recrystallization of serpentinite (tremolite + an-

tigorite + talc + Mg-chlorite + magnetite), due to the thermal

effect of granite intrusion. Retrogression at lower tempera-

ture led to the formation of lizardite (serpentine), chlorite and

talc (Hovorka et al. 1985).

The aim of this paper is to present additional data on

mineral compositions together with paragenetic analysis of

co-existing minerals. Metamorphic conditions have been

estimated using mineral activity-composition relationships

together with internally consistent thermodynamic data of

Berman (1988). Phase equilibria were calculated using the

computer program GEO-CALC.

We suggest that the metamorphic evolution of the me-

taultramafics in the Malá Fatra Mts. is consistent with high

grade, upper-amphibolite facies regional metamorphism and

not contact metamorphism. The investigated metaultramafics

are isofacial with the surrounding metamorphic crustal rocks,

i.e. high-grade metapelites and metabasites, as demonstrated

by previous studies (Perchuk et al. 1984; Korikovsky et al.

1987; Krist et al. 1992; Hovorka & Méres 1991; Lupták

1996; Janák & Lupták 1997).

Geological setting

The Malá Fatra Mts. (Fig. 1) belong to the Tatric Unit of

the Western Carpathians and represent a typical core com-

plex located in the northwestern part of Slovakia. In general,

the pre-Mesozoic basement of the Malá Fatra Mts. is com-

posed of high-grade metamorphic rocks and granitoids, over-

lain by Mesozoic and Cenozoic sedimentary cover sequences

and nappes.

The granitoids consist of the so called hybrid and

Magura types according to Ivanov & Kamenický (1957)

and Kamenický et al. (1987), which correspond to the I- and

S- types, respectively (Broska et al. 1997). They are

crosscut by lamprophyric dykes (Ivanov & Kamenický

1957). The U-Pb zircon age of a tonalite is 353 Ma,

according to Scherbak et al. (1990).

Metamorphic rocks are exposed in the southern part of the

Malá Fatra Mts., i.e. Ve¾ká Lúka Massif (Fig. 1) and con-

PHASE RELATIONS IN OLIVINE-ORTHOPYROXENE-CHLORITE-SPINEL-HORNBLENDE METAULTRAMAFICS 371

act size and shape of metaultramafic body is not known, but

it may range up to several tens of metres. Smaller blocks and

lenses of several m to dm occur sporadically also on the

south-eastern slopes of Ve¾ká Lúka (Fig. 1), intimately asso-

ciated with migmatized paragneisses and amphibolites.

Metamorphic P-T conditions in the Malá Fatra Mts. have

been estimated by thermobarometry in the metapelites and

metabasites (Perchuk et al. 1984; Korikovsky et al. 1987;

Krist et al. 1992; Hovorka & Méres 1991; Lupták 1996; Ja-

nák & Lupták 1997). According to these studies, peak meta-

morphic conditions reached medium-pressure, upper am-

phibolite to granulite facies. However, symplectitic and

kelyphitic textures in some garnet-clinopyroxene metabasites

indicate also a higher-pressure, eclogite facies metamor-

phism, strongly overprinted by lower-pressure and high tem-

perature recrystallization (Hovorka et al. 1992; Lupták 1996;

Janák & Lupták 1997). Most of metamorphic rocks exhibit

widespread migmatization due to partial melting, dehydra-

tion-melting during decompression has been

suggested by Janák & Lupták (1997). Although

the timing of metamorphism in the Malá Fatra

Mts. is not well constrained by geochronologi-

cal data, regional metamorphism and granitoid

magmatism are generally thought to be

Variscan, with only very weak Alpine overprint

(e.g. Krist et al. 1992).

Petrography and mineral compositions

Metaultramafics from the Malá Fatra Mts.

are dark-grey, medium-grained rocks, massive

or only weakly foliated. Their texture is nem-

atogranoblastic.

Mineral compositions were analyzed by

CAMSCANLink EDS microprobe with a point

beam at operating conditions of 10nA and 15

kV using synthetic and natural standards. The

data were reduced by the ZAF method.

Amphibole is pale-green and occurs as small

inclusions in olivines and orthopyroxenes, as

well as large prismatic grains in the matrix. The

compositions of amphibole inclusions and larg-

er matrix grains are similar (Table 1). Both cor-

respond to Mg-hornblende according to Leake

(1978; 1997) with low Na (Na

O = 0.240.88

wt. %), Ti and relatively high Al (Al

8.7910.61 wt. %) contents. The hornblendes

are sometimes replaced by tremolite at the rims,

which is attributed to retrogression.

Orthopyroxene is present in the form of rath-

er subhedral, pale-green to brownish porphyro-

blasts, sometimes enclosing amphiboles. Some

orthopyroxenes are replaced by talc at the rims.

The compositions of orthopyroxenes (Table 2)

correspond to enstatite, containing 1.832.49

wt. % Al

and 0.190.28 % CaO; the ratio of

Fe/Fe+Mg is 0.160.18.

Olivine forms mostly euhedral, colourless

Hornblende inclusions in opx (1, 2, 3) and olivine (4, 5)

large hornblendes in matrix (6, 7, 8, 9)

Sample

MF12

MF16

MF4 MF12a

MF16

MF12 MF12a

MF16

MF4

Anal. no.

SiO

50.58

50.00

49.23

49.47

50.16

50.33

48.99

49.86

50.51

8.86

10.12

9.62

10.44

9.52

9.1

10.61

9.73

9.44

TiO

0.65

0.76

0.80

0.67

0.76

0.59

0.92

0.61

0.68

0.05

0.18

0.28

0.07

0.09

0.17

0.12

0.15

MgO

19.23

18.37

19.06

18.16

18.98

18.82

17.86

18.86

18.72

FeO

6.07

5.94

6.20

6.51

5.75

6.51

6.71

5.77

5.97

MnO

0.00

0.07

0.16

0.03

0.19

0.12

0.11

0.08

0.17

CaO

11.89

12.13

11.92

12.01

12.06

12.03

11.88

11.98

0.67

0.40

0.77

0.70

0.39

0.64

0.63

0.61

0.13

0.26

0.22

0.28

0.22

0.12

0.25

0.17

0.14

Total

98.13

98.23

98.26

98.25

98.38

98.13

98.29

97.71

98.37

Formulas based on 23 oxygens and 15 cations excluding Na, K

7.023

6.941

6.844

6.893

6.957

6.984

6.833

6.950

7.006

0.977

1.059

1.156

1.107

1.043

1.016

1.167

1.050

0.994

Al total

1.450

1.656

1.577

1.715

1.556

1.489

1.745

1.599

1.544

0.473

0.597

0.421

0.608

0.514

0.473

0.578

0.549

0.550

0.068

0.079

0.084

0.070

0.079

0.062

0.097

0.064

0.071

0.160

0.131

0.288

0.111

0.134

0.283

0.159

0.160

0.097

0.005

0.020

0.031

0.008

0.009

0.010

0.019

0.013

0.016

3.980

3.801

3.949

3.771

3.924

3.892

3.713

3.918

3.870

0.545

0.560

0.433

0.648

0.533

0.473

0.624

0.513

0.596

0.000

0.008

0.019

0.004

0.022

0.014

0.013

0.009

0.020

1.769

1.805

1.775

1.780

1.785

1.793

1.798

1.774

1.781

Na(M

)

0.000

Na(A)

0.180

0.107

0.208

0.190

0.189

0.105

0.173

0.170

0.164

0.023

0.046

0.039

0.050

0.039

0.021

0.044

0.030

0.025

Fe/Fe+Mg

0.120

0.128

0.099

0.147

0.120

0.108

0.144

0.116

0.133

Table 1: Representative microprobe analyses of amphiboles.

grains, only slightly serpentinized. In some places, the oliv-

ine porphyroblasts enclose small hornblendes. The composi-

tion of olivine (Table 3) corresponds largely to forsterite and

the individual grains are very homogeneous. The Fe/Fe+Mg

ratio (0.180.21) is higher than that in the coexisting ortho-

pyroxenes.

Spinel occurs as small subhedral grains of green colour,

intergrown with amphiboles, orthopyroxenes and olivines.

According to their compositions, the spinels are hercynites

(Table 4) with 1.35 to 4.1 wt. % Cr

, the ratio of Fe/

Fe + Mg is 0.380.40. Individual grains are homogeneous, no

relics of chromite were identified. Consequently, the absence

of chromite as well as Cr-magnetite indicates that hercynitic

spinel has not originated from chromite but most probably

from chlorite, i.e. during prograde metamorphism as dis-

cussed below.

Chlorite forms pale-green, mostly scattered flakes, which

tend to concentrate in the interstices between olivine, ortho-

372 KORIKOVSKY, JANÁK and LUPTÁK

pyroxene and spinel. Such chlorite is clinochlore with Fe/

Fe + Mg = 0.10.12 (Table 5) and it is considered to be a

relict phase, being partially consumed by olivine, spinel and

orthopyroxene during prograde metamorphism. On the other

hand, chlorites whose Fe/Fe + Mg and Al contents are lower

than those of primary ones (Table 5) form reaction rims

around spinels and are considered to be retrograde phases, as

discussed below.

Serpentine commonly replaces olivines in the rims. It also

occurs in the veinlets crosscutting the matrix, in some cases

it contains minor inclusions of magnetite. The composition

of serpentine (Table 6) corresponds to antigorite.

Talc mostly replaces orthopyroxenes, or together with oth-

er retrograde phasesserpentine and magnesiteit fills the

crosscutting veinlets.

Textural relationships in the Malá Fatra Mts. metaultra-

mafics as described above suggest that olivine, orthopyrox-

ene, spinel and Ca-amphibole form a stable assemblage, gen-

erated close to the peak of prograde metamorphism. The

preservation of a small amount of primary chlorite coexisting

with olivine, orthopyroxene and spinel indicates that the re-

action chlorite

= olivine + orthopyroxene + spinel + H

took place during temperature increase. This is similar to ob-

servations in the amphibolite facies metaultramafics, where

Mg-rich chlorite coexists with forsterite, enstatite and spinel

(Bucher-Nurminen 1988; Bucher & Frey 1994). The retro-

grade overprint of peak metamorphic assemblages was only

weak, and is manifested by replacement of spinel by second-

ary chlorite, orthopyroxene by talc and olivine by serpentine.

Phase equilibria

On the basis of mineral compositions, the phase relation-

ships in the Malá Fatra Mts. ultramafics can be described in

the system CM(F)ASH (C = CaO, M = MgO, F = FeO, A =

, S = SiO

, H = H

O). Phase equilibria of selected re-

actions were calculated using the thermodynamic data of

Berman (1988, updated in June 1993) and the computer pro-

gram GEO-CALC (Berman et al. 1987). The activity-compo-

sition relationships of analysed mineral phases assuming ide-

al two-site mixing (olivine, orthopyroxene), ideal on-sites

mixing (chlorite, talc) and unity activity of antigorite have

been calculated by the program AX of T.J.B. Holland, in-

Sample

MF12

MF12a

MF16

MF4

Sample

MF12

MF12a

MF16

MF4

Anal. no.

SiO

54.30

54.22

54.65

54.11

SiO

38.29

38.34

38.77

38.56

TiO

0.09

0.15

0.08

0.15

TiO

0.01

0.00

0.03

0.08

2.36

2.12

2.30

2.13

0.00

0.03

0.00

0.14

0.00

0.09

0.03

0.00

1.58

2.06

1.42

2.25

1.66

1.32

0.73

1.30

FeO

11.70

11.33

10.76

10.55

FeO

18.84

19.25

18.40

16.80

MnO

0.27

0.32

0.35

0.29

MnO

0.34

0.35

0.23

0.39

MgO

29.54

29.72

30.27

30.14

MgO

40.92

40.74

41.78

42.48

CaO

0.26

0.20

0.28

0.22

CaO

0.00

0.02

0.04

0.00

0.02

0.00

0.02

0.03

0.00

0.06

0.00

Total

100.12

100.19

100.11

99.98

Total

100.13

100.11

99.99

99.65

Formulas based on 4 cations for 6 oxygens

Formulas based on 3 cations for 4 oxygens

1.928

1.924

1.931

1.920

0.985

0.987

0.992

0.986

0.002

0.004

0.002

0.004

0.000

0.001

0.002

0.099

0.089

0.096

0.089

0.000

0.001

0.000

0.004

0.000

0.002

0.001

0.000

0.042

0.055

0.038

0.060

0.032

0.026

0.014

0.025

0.347

0.336

0.318

0.313

0.405

0.414

0.394

0.359

0.008

0.010

0.009

0.007

0.008

0.005

0.008

1.563

1.572

1.594

1.593

1.568

1.563

1.593

1.619

0.010

0.008

0.011

0.008

0.000

0.001

0.000

0.001

0.000

0.001

0.000

0.002

0.000

Fe/Fe+Mg

0.182

0.176

0.166

0.164

Fe/Fe+Mg

0.205

0.209

0.198

0.181

Table 2: Representative microprobe analyses of orthopyroxenes.

Table 3: Representative microprobe analyses of olivines.

PHASE RELATIONS IN OLIVINE-ORTHOPYROXENE-CHLORITE-SPINEL-HORNBLENDE METAULTRAMAFICS 373

Sample

MF12

MF12 MF12a

MF16

MF4

Anal.no.

1-core

2-rim

SiO

0.00

0.07

0.00

0.05

TiO

0.03

0.00

0.10

0.00

0.06

0.00

60.38

60.63

60.45

61.92

60.69

60.77

57.97

1.61

1.44

2.47

1.70

2.71

2.00

4.10

4.91

4.81

4.04

3.24

3.16

4.41

4.88

FeO

17.93

17.89

17.25

17.36

17.85

18.33

17.66

MnO

0.13

0.29

0.05

0.11

0.16

0.27

0.07

MgO

15.44

15.37

15.96

15.94

15.57

15.22

15.34

CaO

0.00

0.02

0.00

0.03

0.04

0.00

Total

100.45

100.34

100.29

100.28

101.02

100.11

Formulas based on 3 cations for 4 oxygens

0.000

0.002

0.000

0.001

0.000

0.002

0.000

0.001

0.000

1.868

1.875

1.865

1.901

1.875

1.872

1.814

0.033

0.030

0.051

0.035

0.056

0.041

0.086

0.097

0.095

0.080

0.064

0.062

0.087

0.098

0.394

0.393

0.378

0.391

0.400

0.392

0.003

0.006

0.001

0.002

0.004

0.006

0.002

0.605

0.601

0.623

0.619

0.609

0.593

0.607

0.000

0.001

0.000

0.001

0.000

Fe/Fe+Mg

0.394

0.395

0.378

0.379

0.391

0.403

0.392

Fig. 2. Chemography of the prograde reaction chlorite

= olivine

+ orthopyroxene + spinel in the system (Mg, Fe)SiAl. Chemog-

raphy of retrograde replacement of olivine, orthopyroxene and

spinel by secondary assemblage serpentine + chlorite

+ talc is

shown by dashed lines. Note the shift of the retrograde assemblage

towards the Si corner.

Fig. 3. Chemography between coexisting Ca-amphibole, olivine,

orthopyroxene and chlorite in the system (Mg, Fe)SiCa; pro-

jection from spinel.

Table 4: Representative microprobe analyses of spinels.

cluded in THERMOCALC and described in Holland &

Powell (1990) and Will et al. (1990). The phase equilibria

have been calculated assuming water-saturated conditions,

i.e. pure water (X

H2O = 1

) in the fluid and H

O pressure = total

pressure. Consequently, the calculated dehydration equilibri-

um curves may be regarded as the maximum stability limits,

which would be shifted towards a lower temperature in the

presence of additional fluid components, mainly CO

, as in-

dicated by the presence of a small amount of magnesite.

The prograde phase equilibria between coexisting chlorite,

orthopyroxene, olivine, amphibole and spinel are demon-

strated by several diagrams. Fig. 2 shows the chemography

of the reaction:

chlorite

= olivine + orthopyroxene + spinel (R1)

in the system (Mg, Fe)SiAl, reflecting the replacement of

Mg-rich chlorite by hercynitic spinel, forsterite and enstatite.

An equilibrium curve of this reaction (R1) plots bettween

700800

C and 210 kbars (Fig. 4).

Chemography between coexisting Ca-amphibole (Mg-

hornblende), olivine (forsterite), orthopyroxene (enstatite)

and Mg-rich chlorite is expressed by the projection from

spinel in the system (Mg, Fe)SiCa on Fig. 3. This

chemography also shows that clinopyroxene is not stable in

the assemblage with Ca-amphibole, olivine, orthopyroxene

and chlorite. The microprobe analyses of clinopyroxene in

Hovorka & Spiiak (1985, Table 1) as well as Hovorka et al.

(1985, Table 1) correspond to amphibole and not clinopyrox-

ene. They are similar to our analyses of hornblende in this

paper (Table 1). Consequently, the absence of Ca-clinopy-

roxene (diopside) suggests that a) peak conditions were

above low-temperature stability of diopside, i.e. 8 diopside +

antigorite = 18 forsterite + 4 tremolite + 27 H

O (e.g. Spear

1993; Bucher & Frey 1994), b) the peak conditions were be-

low equilibrium reaction Ca-amphibole + olivine = Ca-cli-

nopyroxene + orthopyroxene + H

O (Fig. 4). As pointed out

above, the amphibole is Mg-hornblende, indicating its high-

374 KORIKOVSKY, JANÁK and LUPTÁK

Fig. 4. Phase equilibria of the Malá Fatra Mts. metaultramafics in

the system CMASH (P

H2O

= P

total

). Reactions R1, R2 and R3 were

calculated from the thermodynamic data of Berman (1988, updat-

ed in June 1993) and activity-composition relationships of analy-

sed mineral phases (Tables 16) using the computer program

GEO-CALC. The equilibria involving diopside, tremolite and

anthophyllite as well as the upper stability of Ca-amphibole are

adopted from Bucher & Frey (1994). The tentative P-T path is

shown by arrows.

Prograde (1, 2, 3) and retrograde (4) chlorites

Sample

MF12

MF12a

MF16

MF12

Sample

MF12a

MF16

MF12

Anal. no.

SiO

29.73

29.91

30.32

31.81

SiO

56.82

57.23

42.26

TiO

0.06

0.04

0.16

0.00

TiO

0.06

0.00

0.03

22.04

21.63

20.47

18.15

4.67

3.20

0.76

0.13

0.12

0.19

0.00

0.08

0.05

0.000

0.54

0.82

0.00

FeO

7.18

6.99

5.71

3.55

FeO

4.34

6.66

2.69

MnO

0.15

0.01

0.11

0.14

MnO

0.11

0.03

0.00

MgO

28.75

29.71

30.34

32.53

MgO

28.30

26.71

40.42

CaO

0.07

0.04

0.11

0.00

CaO

0.04

0.07

0.00

0.07

0.36

0.31

0.00

0.01

0.04

0.01

0.27

0.00

Total

88.11

88.45

87.42

86.29

Total

95.32

95.35

86.21

Formulas based on 10 cations for 14 oxygens

7 cations for 11 oxygens

2.817

2.821

2.878

3.022

3.699

3.768

1.993

0.004

0.003

0.011

0.000

0.003

0.000

0.001

2.462

2.405

2.290

2.033

0.358

0.248

0.042

0.010

0.009

0.014

0.000

0.004

0.003

0.002

0.000

0.026

0.041

0.000

0.569

0.551

0.453

0.282

0.236

0.367

0.106

0.012

0.001

0.009

0.011

0.006

0.002

0.000

4.060

4.176

4.291

4.605

2.745

2.621

2.841

0.007

0.004

0.011

0.000

0.003

0.005

0.000

0.013

0.045

0.040

0.000

0.001

0.005

0.001

0.023

0.000

Fe/Fe+Mg

0.123

0.117

0.095

0.058

Fe/Fe+Mg

0.079

0.123

0.036

er-temperature stability than that of pure tremolite end-member

(Fig. 4), i.e. close to the amphibolite to granulite facies transi-

tion in ultramafic rocks (Spear 1993; Bucher & Frey 1994).

The pressure conditions cannot be constrained precisely

because of steep dP/dT slopes of equilibrium reactions in the

system CMASH (Fig. 4). However, the absence of antho-

phyllite may indicate that the pressure was above the stabili-

ty field of anthophyllite + olivine in the Fig. 4.

Retrograde reactions in the Malá Fatra Mts. metaultra-

mafics are indicated by replacement of spinel by secondary

chlorite, orthopyroxene by talc and olivine by serpentine.

This is demonstrated by chemographic phase relations in the

system (Mg, Fe)AlSi on the Fig. 2. This projection, how-

ever, shows that the secondary assemblage Srp + Chl

+ Tlc

is slightly shifted towards the Si corner, probably indicating

some metasomatic input of silica during retrogression. This

assumption may be supported by the slightly silica-enriched

bulk composition of the Malá Fatra Mts. metaultramafics

(Table 7) with respect to the majority of the mantle rocks, as

illustrated in the Fig. 5. Despite possible metasomatic influ-

ence, the bulk composition of the Malá Fatra Mts. metaultra-

mafics approach that of the garnet or spinel peridotite and

websterite.

Talc could have originated according to the reaction:

orthopyroxene + H

O = talc + olivine (R 2)

Table 5: Representative microprobe analyses of chlorites.

Table 6: Representative microprobe analyses of talc (1, 2) and
antigorite (3).

PHASE RELATIONS IN OLIVINE-ORTHOPYROXENE-CHLORITE-SPINEL-HORNBLENDE METAULTRAMAFICS 375

at higher temperature than antigorite during retrogression,

the latter being formed by the reaction:

talc + olivine + H

O = antigorite (R 3)

at temperatures below ca. 450

C (Fig. 4).

The estimated peak temperature in the Malá Fatra Mts.

metaultramafics is similar to that in the surrounding silli-

manite + K-feldspar bearing metapelites as well as garnet-

clinopyroxene metabasites, which have equilibrated at 700

750

C and 610 kbar according to the geothermometric

calculations of Korikovsky et al. (1987); Hovorka & Méres

(1991); Lupták (1996); Janák & Lupták (1997). Such P-T

conditions are higher than those of contact-metamorphism by

granitoid magma, i.e. 640680

C, proposed by Hovorka et

al. (1985). On the other hand, possible metamorphic evolu-

tion from serpentinite to metaperidotite as well as the weak

retrograde overprint of the Malá Fatra Mts. metaultramafics

are consistent with previous observations of Hovorka et al.

(1985).

Conclusions

The metaultramafic rocks from the Malá Fatra Mts. are

characterized by coexistence of prograde assemblages contain-

ing hercynitic spinel, Ca-amphibole (Mg-hornblende), Mg-

rich chlorite, olivine (forsterite) and orthopyroxene (enstatite).

A large amount of hercynite and Ca-amphibole (up to 3040

%) is characteristic.

Prograde metamorphism of the Malá Fatra Mts. metaultra-

mafics reached the P-T conditions close to the equilibrium

chlorite = olivine + orthopyroxene + spinel + H

O, which cor-

responds to temperature of 700800

C in the upper amphibo-

lite facies condition. This is also corroborated by the stability

of Ca-amphibole with olivine and the absence of clinopyrox-

ene. The retrogression was only weak, leading to the origin of

talc, serpentine (antigorite) and secondary chlorite.

The metaultramafic rocks in the Malá Fatra Mts. may be

regarded as isofacial and completely equilibrated with the

surrounding high-grade crustal rocks. They most probably

represent fragments of metaperidotites or garnet and spinel

websterite (e.g. Medaris & Carswell 1990), attached to the

lower continental crust during the Variscan tectonometamor-

phic events (mantle upwelling after delamination or slab de-

tachment of the subducted lithosphere).

Acknowledgements: We thank Olga Unanova and Ján Spi-

iak for providing wet chemical analyses of the metaultrama-

fic rocks.

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MF-4

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MF-16

SiO

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44.13

TiO

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2.82

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FeO

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MgO

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CaO

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99.84

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