GeolCarp_Vol58_No6_511

GEOLOGICA CARPATHICA, DECEMBER 2007, 58, 6, 511—530

www.geologicacarpathica.sk

Petrology, geochemistry and tectonic significance of Mesozoic

ultramafic rocks from the Zagorje-Mid-Transdanubian Zone

in Croatia

BOŠKO LUGOVIĆ

, DAMIR SLOVENEC

, JOSIP HALAMIĆ

and RAINER ALTHERR

Institute of Mineralogy, Petrology and Mineral Deposit, Faculty of Mining, Geology and Petroleum Engineering,

University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia; blugovic@rgn.hr

Croatian Geological Survey, Sachsova 2, HR-10000 Zagreb, Croatia

Mineralogisches Institut, Universität Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany

(Manuscript received June 13, 2006; accepted in revised form March 15, 2007)

Abstract: Ultramafic cumulates of Medvednica Mts form mega-blocks in the ophiolite mélange from the Zagorje-
Mid-Transdanubian segment of the Sava Zone. The blocks consist of chromite-olivine cumulates and pyroxenites.
The rocks crystallized in an open system under low pressure. Early crystallization of Al-Ti-chromite and Ti-edenite/
pargasite indicate high oxygen fugacity hydrous parental magma. The Medvednica Mts ultramafic cumulates are
analogous to plutonic rocks from recent immature island arcs. Subsolidus reactions indicate rapid exhumation with the
final equilibration resembling prehnite-pumpellyite facies. The Medvednica Mts ultramafic cumulate sequence shows
common features with the analogous sequence of the Bükk Mts ophiolites from NE Hungary and differ from
analogues from the Vardar/Dinaric ophiolite belts. Mantle peridotites lacking overlying crustal members crop out in
the Medvednica Mts and Kalnik Mts, and were cored in drill-holes. The peridotites range in composition from
lherzolite via transitional harzburgite to depleted harzburgite. Lherzolite resembles abyssal peridotite and together
with transitional harzburgites are akin to the peridotites from the South Sandwichs and Mariana arc—back-arc system.
Depleted harzburgites are typical of fore-arc peridotites and are similar to the harzburgites of the Inner Dinaride
Ophiolite Belt. Assuming that ultramafic rocks from the Zagorje-Mid-Transdanubian Zone were generated in a single
oceanic domain, the South Sandwich arc-basin system appears as the most similar analogue. If it holds true, then these
ultramafic rocks must have been derived from the Meliata-Maliac ocean domain and not from the Dinaric/Vardar
strands as was previously thought.

Key words: Croatia, Zagorje-Mid-Transdanubian Zone, Medvednica Mts, geochemistry, petrology, ultramafic rocks,
ophiolite mélange.

Introduction

Ultramafic cumulate rocks form the deepest sequence of
the oceanic type crust and form the transitional zone to
the mantle peridotites (e.g. Moores & Jackson 1974).
Both units are integral parts of an ophiolite complex
(e.g. Coleman 1977) and are often found in ophiolite mé-
langes worldwide. Such ultramafic rocks may make a cru-
cial contributions to the interpretation of petrogenesis
and geodynamic evolution of an ophiolite complex (e.g.
Parlak et al. 1996, 2002; Huot & Maury 2002).

In the Sava Zone (SZ) segment of the Zagorje-Mid-

Transdanubian Zone (ZMTDZ) fragments of ophiolite
derived rocks are embedded along with blocks of various
rocks of different geotectonic setting in chaotic sedimen-
tary collages (ophiolite mélange) exposed at the SW tips
of the ZMTDZ in the NW Croatia (Slovenec 2003, and
references therein) and at the Bükk Mts in NE Hungary
(e.g. Harangi et al. 1996; Aigner-Torres & Koller 1999;
Faryad 2005). In general, both ophiolite mélanges con-
tain scarce ultramafic cumulates and virtually lack man-
tle peridotites. Tectonic slices of mantle peridotites were
found in the Medvednica Mts and Kalnik Mts and were

drilled in a few oil-wells in the Sava Depression. Unlike
in the ideal ophiolite pile (Anonymus 1972) and in many
ophiolite complexes in the Dinarides (Robertson & Kara-
mata 1994; Pamić et al. 2002, and references therein),
these peridotite slices lack overlying ophiolite crustal
members. This is the reason why the origin and relation-
ship of these peridotites to the ultramafic cumulates, as
well as to the other ophiolite members of the ophiolite
mélange, are still obscure. Lugović & Slovenec (2004)
have already attempted to research this problem.

The aim of this paper is to give overall characteristics

of tectonite and cumulate ultramafic rocks from the SZ
segment of the ZMTDZ with the intention of interpreting
their genesis and working out the geotectonic setting of
the formation, and finally, to correlate them with analo-
gous rocks of ophiolite belts in the adjacent Dinarides.

Geological outlines

In the Dinarides ophiolites occur in two belts (Fig. 1A)

with different characteristics (Nicolas & Jackson 1972;
Pamić 1983; Smith & Spray 1984). The western belt,

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LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

called the Central Dinaride Ophiolite Belt (CDOB), is
dominated by mantle lherzolite (Lugović et al. 1991;
Trubelja et al. 1995). The eastern belt, known as the Var-
dar Ophiolite Zone and corresponding to the Inner Dinar-
ide Ophiolite Belt (IDOB, Smith & Spray 1984), is char-
acterized by depleted mantle peridotites and has well
developed igneous suites (Karamata et al. 1980). Its west-
ern segment stretches to the WNW and meets the CDOB
in the SZ, whereas the eastern zone goes to the NE and
continues to the Apuseni/Mures ophiolites in Romania
(Karamata et al. 2000). Both ophiolite belts lay NW of
the Scutari-Peć transform fault and are separated by the
continental fragment called the Drina-Ivanjica element
(Dimitrijević 1983; Robertson & Karamata 1994).

The ZMTDZ is located on the triple junction of the

South Alpine Unit, Tisia block and the Internal Dinaridic
Unit (Fig. 1A,B) and may correspond to the Gemer-Bükk
subunit, located in the southern part of the Alcapa (Al-
pine-Carpathian-Pannonian) block of the Intra-Car-
pathian Area (ICA) (Harangi et al. 1996). The investigated
realm is located at the SW termination of the ZMTDZ
(Fig. 1A,B) and is composed of heterogeneous tectonos-
tratigraphic units with ambiguously superimposed Dinar-
idic and Alpine structural elements (Herak 1999; Haas et
al. 2000; Haas & Kovács 2001; Tomljenović 2002; Pam-
ić 2003). The area is bounded by the north Croatian
mountains, which include Medvednica, Kalnik, Ivanšči-
ca and Strahinjščica.

Fig. 1. A – Geotectonic sketch map of the Alps, Dinarides and Hellenides showing position of the Zagorje-Mid-Transdanubian Zone
(ZMTDZ) (modified after Pamić 2002). Legend: 1 – External units, 2 – Central Dinaric Ophiolite Belt (CDOB) and Mirdita Zone,
3 – Periadriatic-Sava-Vardar Zone, including the Inner Dinaric Ophiolite Belt (IDOB), 4 – Serbo-Macedonian Massif, 5 – Pelagonides,
6 – Drina-Ivanjica element, 7 – Zagorje-Mid-Transdanubian Zone, 8 – Pannonian Basin. Faults: BL – Balaton Line, PL – Periadriatic
Lineament, SF – Sava Fault, SN – Sava Nappe, SP – Skadar-Peć Fault, VF – Vardar Fault, ZZL – Zagreb-Zemplín Line. Moun-
tains: B – Bükk Mts, I – Ivanščica, K – Kalnik, Ko – Kopaonik, Md – Medvednica, SG – Samoborska Gora. B – Geological sketch
map of the ZMTDZ in Croatia (modified after Pamić & Tomljenović 1998). Legend: 1 – Neogene and Quaternary of the Pannonian
Basin, 2 – Late Cretaceous-Paleocene flysch, 3 – Ophiolite mélange, 4 – Late Triassic platform carbonates, 5 – Late Paleozoic and Tri-
assic clastics and carbonates interlayered with volcanics and tuffs, 6 – Lower Cretaceous metamorphic complex, 7 – deep oil-well penetrated
ultramafic rocks (LA – Laktec, BS – Banje Selo, LNJ – Lonjica, LP – Lepavina, JA – Jagnjedovac), 8 – Site locations: 1 – Medvedni-
ca Mts, 2 – Gornje Orešje, 3 – Kalnik Mts, 4 – Sava Depression, oil wells. Faults: BL – Balaton Line, DF – Donački Fault, NMF – North-
ern Medvednica Fault, PL – Periadriatic Lineament, SF – Sava Fault, ZZL – Zagreb-Zemplín Line. Insets – Geological sketch maps of the
sites 1 and 2 (modified after Pamić & Tomljenović 1998). Legend: 1 – Neogene and Quaternary sedimentary rocks, 2 – Late Cretaceous-
Paleocene flysch, 3 – Ophiolite mélange with the mapable blocks of: 4 – ultramafics, 5 – mafics, 6 – limestones, 7 – Mesozoic, mostly
Triassic clastics and carbonates, 8 – Lower Cretaceous metamorphic complex, 9 – normal faults, 10 – reverse or thrust faults. Geological
sketch maps of the site 3 (modified after Šimunić et al. 1982). Legend: 1 – Neogene sedimentary rocks, 2 – Paleogene sedimentary
rocks, 3 – Ophiolite mélange with ultramafic blocks (4), 5 – normal faults, 6 – reverse or thrust faults.

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MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

The Medvednica Mts are composed of a Lower Creta-

ceous basement consisting of very low- to low-grade
metamorphic complex (Belak et al. 1995) in reversed-re-
folded thrust contact with the Middle Jurassic-Lower
Cretaceous ophiolite mélange (Tomljenović 2002).
These two units are the Medvednica Unit (MU) and
Kalnik Unit (KU), respectively (Hass et al. 2000). The
MU consists of metasedimentary successions of Silurian
to early Carnian ages (Belak et al. 1995, and references
therein), which are tectonically overlain by the Mesozoic
metabasites (greenschists) of intraoceanic island arc
provenance (Lugović et al. 2006). The KU contains frag-
ments of different ophiolitic and sedimentary rocks rang-
ing in age from Middle Triassic to Middle Jurassic
(Halamić & Goričan 1995; Halamić 1998; Slovenec
1998; Halamić et al. 1998). The age of KU was palyno-
logically dated as Middle Jurassic—Hauterivian (Babić et
al. 2002). The ages of crystallization of ophiolitic extru-
sives from the KU are obscure since the whole-rock K-Ar
measurements yielded Early to Middle Jurassic and Early
to Late Cretaceous apparent ages (Pamić 1997) which are
not consistent with the radiolarian ages of coherent
chert-pillow basalt slices of late Ladinian—Carnian
(Halamić & Goričan 1995; Goričan et al. 2005) and Ju-
rassic ages (Halamić 1998; Halamić et al. 1999).

Cumulate ultramafites along with tectonite peridotites

crop out only in the Medvednica Mts (Fig. 1B, sites 1
and 2). Ultramafic cumulate rocks form cm-dm to hm-km
sized blocks (Kišpatić 1918; Crnković 1963; Šimunić et
al. 1982) representing integral members of the KU
(Fig. 1, inset 1). Some large blocks show the transition
from ultramafic cumulate rocks to mafic cumulate and to
isotropic gabbros (Crnković 1960; Slovenec 1998; Slo-
venec & Lugović 2000). The Medvednica Mts mantle
peridotites were found near the village of Gornje Orešje
in the form of two tectonic slices inserted within the
Campanian-Maastrichtian rudist limestones (Šimunić &
Pamić 1989) (Fig. 1, inset 2). The peridotites are trans-
gressively overlain by sedimentary successions compris-
ing Upper Cretaceous polymictic conglomerates and
covered by Upper Badenian-Sarmatian conglomerates,
limestones and marls. Peridotite exhumation must have
happened before the Late Cretaceous as is inferred from
the serpentinite infilling in rudist shells.

Tectonite peridotites were reported from the three lo-

calities in the Kalnik Mts (Fig. 1B, site 3) (Poljak 1942;
Šimunić et al. 1981). Here, only one location was con-
firmed as a few meters large composite slice of serpenti-
nized lherzolites underlain by amphibolites inserted in
the upper Lower to Upper Cretaceous sedimentary suc-
cession (Fig. 1, inset 3). The amphibolites were interpret-
ed as metamorphic sole (Šegvić et al. 2005).

Severely serpentinized mantle peridotites were cored in

oil-wells in the ZMTDZ at Lonjica (LNJ), Laktec (LA) and
Banje Selo (BS) (Fig. 1B, site 4) and SE from the Kalnik
Mts at Lepavina (LP) and Jagnjedovac (JA) (Vragović &
Marci 1973; Pandžić 1982). These peridotites are uncon-
formably overlain by a Badenian sedimentary succession
composed of conglomerates, sandstones and marls.

Analytical techniques

Mineral analyses from 10 representative samples were

performed at the Mineralogisches Institut, Universität
Heidelberg, using a CAMECA SX51 electron microprobe
equipped with five wavelength-dispersive spectrometers.
The operating parameters were 15 kV accelerating volt-
age, 20 nA beam current,

~1 µm beam size (10 µm for pla-

gioclase) and 10 s counting time for all elements. Natural
minerals, oxides (corundum, spinels, hematite and rutile)
and silicates (albite, orthoclase, anorthite and wollasto-
nite) were used for calibration. The raw data for all analy-
ses were corrected for matrix effects with the PAP algo-
rithm (Pouchou & Pichoir 1984, 1985) implemented by
CAMECA. Formula calculations were done using a soft-
ware package designed by Hans-Peter Meyer (Mineralo-
gisches Institut, Universität Heidelberg).

Bulk-rock powders for chemical analyses of 10 samples

were obtained from rock chips free of visible veins. Major
elements and trace elements Rb, Ba, Sr, Zr, Cr and Ni were
measured by wavelength dispersive XRF using conven-
tional techniques. The trace elements: Cs, Th, U, Nb, Ta,
Hf, Y and REE were analysed by ICP-MS at Actlab Labo-
ratories in Toronto, Canada. Trace elements were deter-
mined from diluted solution after leaching 500 mg sample
in 3 ml HCl—HNO

—H

O at 95

ºC for one hour and REE

were analysed after LiBO

/Li

fusion of 200 mg sam-

ple. Fe

was determined by manganometric titration in

Zagreb. The H

O was analysed by Karl-Fischer titration.

The CO

contents were measured by infrared spectrome-

try after heating and combustion of the sample. H

O and

were analysed in Karlsruhe.

Petrography

Ultramafic cumulates

Peridotite cumulates are poikilitic orthocumulates with

chromite and olivine as ubiquitous cumulii crystals
(Fig. 2A and 2B). Orthopyroxene, clinopyroxene and rare
brown amphibole may also occur as cumulii. Early crystal-
lized olivine and orthopyroxene cumulii are rounded and
enclose opaque chromite. Intercumulus space is filled with
up to 6 mm large postcumulus brown amphibole, clear cli-
nopyroxene or orthopyroxene oikocrystals. All three inter-
cumulus phases may be assembled in a single sample. In
several samples calcic plagioclase (An

82—84

) forms intersti-

tial mesostasis. Igneous layering was not observed and
neither mineral shows solid state deformation. Different
modal proportion of cumulus and postcumulus phases al-
low us to distinquish the following peridotite cumulate
types (Streckeisen 1974): amphibole lherzolite (P-6, Ta-
bles 1—6), plagioclase lherzolite (PB-1),

amphibole

harzburgite (MP-8, P-1) and plagioclase wehrlite (P-4).

Pyroxenite samples are either chromite-orthopyroxene-

clinopyroxene adcumulates to mesocumulates (Fig. 2C) or
chromite-olivine-orthopyroxene orthocumulate (Fig. 2D).
Following the modal mineral classification and nomencla-

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LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

ture scheme of Streckeisen (1974), the analysed pyroxeni-
tes are represented by amphibole websterite (MP-2) and
amphibole-olivine websterite (MP-2B). In the amphibole
websterite, orthopyroxene and clinopyroxene are coa-
lesced in adcumulate domains and the rest of the sample
shows mesocumulate domains with interstitial brown am-
phibole. Amphibole-olivine websterite contains chromite,
olivine and orthopyroxene as cumulus assemblage en-
closed in large poikilitic brown amphibole and/or cli-
nopyroxene.

Ultramafic cumulates show different alteration paragen-

esis. Relics of olivine are preserved only in peridotite cu-
mulates. Olivine may be altered to or pseudomorphosed
by the aggregate of chrysotile and magnetite, and occa-
sionally of talk. Orthopyroxene is altered to lizardite

along the cracks and chloritized at the grain periphery.
Unlike in the cumulus peridotite, wherein clinopyroxene
is slightly altered to actinolite and chlorite, in pyroxenites
it occurs as relic in an aggregate consisting of various sub-
solidus Ca-amphiboles and cummingtonite. Plagioclase
mesostasis in peridotite cumulate is soussiritized or re-
placed by the aggregate of prehnite and pumpellyite.

Tectonite peridotites

Tectonite peridotites are highly altered and their clas-

sification as lherzolite, transitional harzburgite and de-
pleted harzburgite was inferred from the bulk-rock chem-
ical composition and mineral chemistry of primary
phases (see below).

Fig. 2. A—D – Microphotographs of thin sections of ultramafic cumulates from the ZMTDZ taken with transmitted light and crossed
polarizers. Abbreviations of mineral names are: Spin = spinel, Oliv = olivine, Opx = orthopyroxene, Cpx = clinopyroxene, Amph =
amphibole. A – Sample PB-1, chromite-olivine-orthopyroxene-clinopyroxene orthocumulate (plagioclase lherzolite). The photo shows
the domain where poikilitic amphibole fills intercumulus space. Other domains (not shown) contain clinopyroxene in intercumulus space.
Chromite is enclosed in olivine relics floating in meshwork serpentine. B – Sample P-6, chromite-olivine orthocumulate with plagioclase
mesostasis (plagioclase lherzolite). The photo shows a domain where poikilitic clinopyroxene fills intercumulus space. Other domains (not
shown) contain amphibole or orthopyroxene as intercumulus infillings. Chromite occurs enclosed in olivine and as individual cumulii
within the intercumulus. C – Sample MP-2, chromite-orthopyroxene-clinopyroxene adcumulate to mesocumulate (amphibole websterite).
The photo shows adcumulate and mesocumulate domains of the sample. D – Sample MP-2B, chromite-olivine-orthopyroxeneorthocumu-
late (amphibole-olivine websterite). Large poikilitic amphibole and clinopyroxene fill the intercumulus space. Olivine is totally altered to
serpentine-type mineral.

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MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

Lherzolite. In the lherzolite sample (KC) brown-red

spinel surrounded by ferrite-chromite is the only remain-
ing primary mineral (Fig. 3A). Olivine is totally altered to
serpentine. Orthopyroxene is replaced by bastite in the
form of characteristic pseudomorphs indicating porphyro-
clastic texture. There are no virtual clinopyroxene pseudo-
morphs in the sample.

Transitional harzburgites. Transitional harzburgites

(GO-1, GO-5 and GO-B) show porphyroclastic texture with
the huge, ductile deformed orthopyroxene porphyroclasts
set in the modest schistous matrix (Fig. 3B and 3C). The
orthopyroxene porphyroclasts have thin lamellae ( < 3 µm)
or granulae of exsolved clinopyroxene (Fig. 3C). Clinopy-
roxene occurs as small porphyroclast or individual grains
in the matrix exsolving < 4 µm wide lamellae (orthopyrox-
ene?) totally altered to chlorite. In the samples GO-1 and
GO-5, the matrix is composed of chrysotile/lizardite, mag-
netite and quartz with minor chlorite, talk, prehnite, and

zeolite (Fig. 3B) whereas in the sample GO-B matrix also
consists of relatively fresh, meshwork textured olivine, cli-
nopyroxene (Fig. 3C) and minor calcic plagioclase
(An

~95

). Ameboid opaque spinel is confined to the matrix

as grains of variable size. Dolomite impregnations are
abundant in the samples GO-5 and GO-B.

Depleted harzburgite. Although it shows comparative-

ly the highest intensity of recrystallization, the depleted
harzburgite (LNJ-1) is the least serpentinized sample
(Fig. 3D). The sample has granuloblastic texture (Harte
1976) characterized by the clusters enriched in orthopy-
roxene and spinel with minor fresh olivine and accessory
clinopyroxene surrounded by nearly pure, strongly ser-
pentinized mosaic olivine. Primary amphibole fills the
interstitial space of these clusters and may show a series
of Ca-amphibole alterations. Spinel is idiomorphic
rounded, dark brown to opaque, typical of hydrous peri-
dotites.

Fig. 3. A—D – Microphotographs of thin sections of tectonite peridotites from the ZMTDZ taken with transmitted light and crossed
polarizers. Lam = lamellae, Gran = granulae; other abbreviations are as in Fig. 2. A – Sample KC, serpentinized lherzolite. Relic of
ameboid to holly-leaf spinel in ferrit-chromite. Olivine is totally serpentinized and orthopyroxene bastitized. B – Sample GO-1,
transitional harzburgite. Partly serpentinized and bastitized orthopyroxene porphyroclasts in the matrix of serpentinized olivine and
minor relic clinopyroxene. C – Sample GO-B, plagioclase-bearing transitional harzburgite. Ductile deformed orthopyroxene
porphyroclast in fresh matrix composed of olivine, clinopyroxene and spinel. Note clinopyroxene exsolution lamellae and granulae in
orthopyroxene. D – Sample LNJ-1, amphibole-bearing depleted harzburgite. Amphibole is interstitial to orthopyroxene and olivine.

516

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

Mineral chemistry

Ultramafic cumulates

Selected chemical compositions of primary and some

secondary phases from the analysed ultramafic cumulates
are given in the Tables 1—5.

Spinel. Cumulii spinel is chromite. Chromite shows a

narrow range of Cr# (0.506—0.644) and wide variation of
Mg# (0.067—0.381) (Table 1; Fig. 4A). The spinels are sig-
nificantly oxydized with Fe

# ranging from 0.170 to

0.480. TiO

content is generally high ( > 1.17 wt. %).

Chromite cumulii embayed in amphibole oikocrystal in
amphibole harzburgite (MP-8) has the highest TiO

(6.5—

7.0 wt. %), shows the lowest Mg# values (0.674—0.139)
and the highest Fe

# (0.461—0.480). The NiO content of

chromite ranges from 0.16 to 0.33 wt. %.

Olivine. Olivine shows a narrow compositional range

with Mg# = 78.7—82.6 (Table 2). NiO content is typical of
cumulus olivine (0.23—0.33 wt. %) and is positively corre-
lated to Mg# (Fig. 4B). CaO is atypically low (0.02—
0.15 wt. %).

Table 1: Selected microprobe analyses and formulae of spinel from the Mesozoic ultramafic rocks of ZMDTZ.

Orthopyroxene. Orthopyroxene is enstatite (Wo

2.5—3.7

78.4—81.5

15.5—18.4

) showing Mg# between 81.3 and 84.1

(Table 3; nomenclature after Morimoto 1988). The con-
tent of Al

is low (1.39—1.95 wt. %). Rare orthopyrox-

ene cumulii with low CaO (Wo

< 1.1

) contain significantly

lower Al

and Cr

than coexisting intercumulus or-

thopyroxene (Fig. 4C).

Clinopyroxene. Clinopyroxene oikocrystals show com-

positional variation Wo

40.1—46.1

46.3—49.9

7.3—10.0

(Ta-

ble 4) typical of magnesian augite to magnesian diopside
(Morimoto 1988). Their Mg# (83.2—86.6) is higher than in
coexisting orthopyroxene. Al

is relatively low (2.07—

2.95 wt. %; Fig. 4D) and Al

/Al

ratio is also low

( < 0.46). The content of Na

O ranges from 0.21 to

0.43 wt. % and of Cr

from 0.25 to 0.89 wt. %. TiO

ranges from 0.30 to 0.76 wt. %.

Amphibole. Amphibole oikocrystals have Mg# from

75.7 to 80.8 (Table 5) and correspond to pargasite and
edenite (Fig. 5). In most samples amphibole oikocrystals
contain appreciable Na

O and Al

(2.01—2.44 wt. % and

9.80—12.01 wt. %, respectively), variable TiO

, and low

and K

O (0.43—1.55 wt. %, 0.12—0.78 wt. % and

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MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

0.05—0.24 wt. %, respectively). In the amphibole
harzburgite (MP-8), intercumulus amphibole shows a dis-
tinct composition being comparatively the richest in Na

and TiO

(2.59—2.87 wt. % and 2.67—3.64 wt. %, respec-

tively). Amphibole inclusions in intercumulus clinopy-
roxene in amfibole websterite (MP-2B) show composition
intermediate between these two groups but are apparently
rich in Cr

(1.19—1.57 wt. %). Retrograde Ca-amphib-

oles after primary amphiboles show a range of composi-
tions from magnesiohornblende to actinolite and tremolite
(Fig. 5) and cummingtonite (Table 5).

Tectonite peridotites

Selected chemical composition of primary and some

secondary phases from the analysed tectonite peridotites
are given in the Tables 1—5.

Spinel. In terms of Mg# and Cr# spinel shows a discon-

tinuous range of composition (Table 1; Fig. 4A) which is
typical of all three groups of Alpine-type peridotites (Dick
& Bullen 1984) and resembles the trend of increasing de-
pletion going from the spinel peridotites of passive mar-
gins through mature oceans to subduction-related active
margins (Bonatti & Michael 1989). Spinel from lherzolite
(KC) has the most fertile compositions, whilst the spinel
from depleted harzburgite (LNJ-1) displays the most de-
pleted compositions. Spinel from the transitional
harzburgites (GO-1, GO-5 and GO-B) shows intermediate

compositions (Mg# = 0.561—0.666; Cr# = 0.309—0.471).
The Fe

abundance of spinel is low (Fe

# < 0.048) and

systematic variation of Fe

with respect to the degree of

depletion was not observed. The TiO

content is low

( < 0.25 wt. %) and tends to increase as spinel Mg# de-
creases. The NiO content is < 0.19 wt. %.

Olivine. In transitional harzburgite (GO-B) olivine Mg#

ranges from 89.9 to 92.1, NiO content varies from 0.34 to
0.45 wt. % and are typical of mantle peridotites (Table 2;
Fig. 4B). There is positive correlation of NiO content with
Mg# in these olivines at concentration range > 0.40 wt. %
NiO. Olivine from depleted harzburgite (LNJ-1) shows re-
fractory composition with Mg# ranges from 92.7 to 93.5
and NiO content similar to the olivine from the transition-
al harzburgite (GO-B). The NiO content does not correlate
with Mg# in the latter case. The CaO concentration is typ-
ically low ( < 0.07 wt. %).

Orthopyroxene. Orthopyroxene porphyroclasts and thin

lamellae exsolved in clinopyroxene are enstatite with
Mg# as high as of coexisting olivine (Table 3). The most
depleted compositions are identical to the orthopyroxene
compositions of IDOB harzburgites (Fig. 4C). Individual
enstatite porphyroblasts from the transitional harzburgite
(GO-1) show the highest compositional variation by up to
2 wt. % Al

with maximum Al

content measured in a

lamella.

Clinopyroxene. Clinopyroxene is mostly chromian di-

opside, magnesian augite is rare (Table 4). Mg# ranges

Table 2: Selected micro-
probe analyses and formulae
of olivine from the Mesozoic
ultramafic rocks of ZMTDZ.

518

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

: S

s a

f o

rth

fro

ltra

fic

s o

f Z

520

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

Fig. 4. A—D – Plot of composition of spinel, olivine, orthopyrox-
ene and clinopyroxene from the studied ultramafic rocks from the
ZMTDZ. The compositional fields for CDOB and IDOB tectonite
peridotites contoured after the data of Maksimović & Majer
(1981), Lugović (1986), Maksimović & Kolomejceva-Jovanović
(1987) are shown for the comparison. A – Plot of Cr/(Cr+Al) vs.
Mg/(Mg+Fe

) in the spinel from the studied ultramafic rocks.

For the rock type see Table 1. B – Plot of NiO vs. Mg/(Mg+Fe

)

in the olivines from the studied ultramafic rocks. The boundary
lines of tectonite and cumulate fields are from Leblanc et al.
(1984). Symbols as in Fig. 4A. C – Plot of Al

vs. Cr

in the

orthopyroxene from the studied ultramafic rocks. Symbols are as
in Fig. 4A. Note that the points with the highest Al

(

~6 wt. %)

correspond to the lamellae exsolved in clinopyroxene. D – Plot
of Al

vs. Cr

in the clinopyroxene from the studied ultrama-

fic rocks. Symbols are as in Fig. 4A.

Fig. 5. Al

versus (Na + K)

classification diagram for amphiboles

(Leake et al. 1997) from studied cumulus rocks (full circles) and
depleted harzburgite, sample LNJ-1 (open circles). Primary
amphiboles from the ZMTDZ ultramafic cumulates cluster in the
fields of pargasite and edenite. The interstitial amphibole in
depleted harzburgite LNJ-1 is magnesiohornblende.

from 90.0 in transitional harzburgites (GO-1, GO-5 and
GO-B) to 96.2 in depleted harzburgite (LNJ-1) and is high-
er than in coexisting olivine and enstatite. Positive corre-
lation between Al

and Cr

exists only in the cli-

nopyroxenes from transitional harzburgites (Fig. 4D).
Clinopyroxene is slightly more aluminian and significant-
ly more chromian than coexisting enstatite. The Na con-
tent is low with < 0.18 wt. % in the transitional harzburg-
ites and < 0.50 wt. % Na

O in the depleted harzburgite.

The TiO

content does not exceed 0.21 wt. %. Exsolved

clinopyroxene, either lamellae or granulae, shows com-
positions similar to matrix clinopyroxene (samples GO-1
and GO-5).

Amphibole. Intestitial amphibole in depleted harzburg-

ite (LNJ-1) corresponds to magnesiohornblende (Fig. 5)
and shows a significant compositional variation accross
the grains (Table 5). Late stage low-temperature alter-
ations after clinopyroxene have an actinolitic to tremolitic
composition.

521

MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

Table 5: Selected microprobe analyses and formulae of amphibole from the Mesozoic ultramafic rocks of ZMTDZ.

Bulk-rock chemical composition

Ultramafic cumulates

The chemical composition of ultramafic cumulates is

shown in Table 6. High volatile values (8—11 wt. %) point
to severe alteration of ultramafic cumulate rocks. Mg# is
high and varies from 75.1 to 81.4. The abundances of in-
compatible elements Rb, Ta, U, and Nb in a few samples
are under the detection limits. The content of LILE (K, Na,
Ba, Cs) varies inconsistently. Immobile HFSE (Ti, Zr, Hf,
Y, P) and REE retain igneous ratios (Zr/Hf = 33.3—40.0,
Sm/Nd = 5.7—20.7). Contents of Cr and V are high and
there is no significant difference between their concentra-
tions in peridotites and websterite as it holds true for Ni
and Co. The contents of CaO (1.26—11.50 wt. %) and

(2.43—5.23 wt. %) reflect variable abundance of

modal augite and amphibole, as well as by intensity of
alteration. TiO

content is lower than 0.24 wt. %.

In the spider diagram with element concentrations nor-

malized to primitive mantle (Fig. 6), excluding Cs and
occasionally Ba which are extremely concentrated by al-
teration processes, the contents of other elements corre-
spond to primitive mantle values or are maximally twice
as high. The normalized patterns show slight negative P
and Ti anomalies. Amphibole harzburgite (MP-8), ex-
ceeding the Nb detection limit, shows negative Nb
anomaly [(Nb/La)

= 0.75].

Amphibole harzburgite (MP-8) has a flat REE pattern

consistent with Na-enrichment in the intercumulus am-
phibole (Fig. 7). Amphibole websterite (MP-2) shows typi-
cal MORB-type REE patern. All other samples follow sim-

523

MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

tion. On account of normative clinopyroxene contents, the
Al

and CaO of bulk rocks (expressed on H

O- and do-

lomite-free basis) peridotites from Gornje Orešje (Fig. 1B;
site 2) are akin to transitional harzburgites (moderately de-
pleted peridotites). For these harzburgites Mg# of 87.0 to
89.5 is apparently low suggesting significant loss of MgO
during serpentinization. Serpentinized peridotite from the

Fig. 7. Chondrite-normalized REE patterns of ultramafic rocks
from the ZMTDZ. Normalizing values are from Evensen et al.
(1978). For the rock type see Table 6; unlabelled full circle pattern
represents plagioclase wehrlite, sample P-4. Wehrlites from the
Bükk Mts (Downes et al. 1990; Aigner-Torres & Koller 1990) are
shown as D and ATK, respectively. Note high negative Eu
anomalies indicating a high fractionation level of Bükkian wehrlites.

Kalnik Mts (Fig. 1B; site 3) reveals lherzolitic composi-
tion and peridotite from the drill-hole (Fig. 1B, site 4) re-
sembles depleted harzburgite composition.

The primitive mantle normalized element abundance

patterns reveal significant enrichment in LILE (Cs, Rb, Ba
and Sr) in all samples, strong Pb spike in lherzolite (KC)
and depleted harzburgite (LNJ-1), and the peaks of U, Hf
and Zr in the lherzolite (not shown). These variations are
inconsistent and most likely reflect polyphase alterations
and, at least for Pb, also analytical uncertainly. We will
not use these data for petrological and geochemical con-
straints.

The chondrite normalized REE patterns of tectonite

peridotites are shown in Fig. 7. Lherzolite (KC) shows
smooth LREE-depleted profile down to Ce and flat HREE
profile. We assume that the shift of La concentration rela-
tive to Ce is an analytical error. Transitional harzburgites
GO-1 and GO-5 show strongly depleted LREE profiles
(La, Ce and Pr under detection limit) and MREE—HREE
profiles have steep slopes (Sm

/Lu

0.38) within the

range of 0.1 to 1 times chondrite content, typical of fertile
to moderately depleted peridotites, respectively (Parkin-
son et al. 1992). These transitional harzburgites and the
lherzolite show strong negative Eu anomaly (Eu/
Eu* = 0.57). Transitional harzburgite GO-B has a U-shap-
ed REE pattern, whilst depleted harzburgite (LNJ-1)
shows concave-up profile and neither show significant
Eu anomalies.

Geothermometry

A summary of geothermometric estimations is given in

Fig. 8.

In the ultramafic cumulates, high wollastonite in augite

and low in the coexisting enstatite measured at a single
contact, depict a low rate of subsolidus equilibrium. In the
graphic geothermometer of Lindsley (1983) analysed py-
roxenes yielded temperatures between 1100

ºC and

900

ºC. The equilibrium temperatures calculated for coex-

isting orthopyroxene and clinopyroxene for the geother-
mometers calibrated by Wells (1977) and Brey & Köhler
(1990) are similar and range from 983

ºC and 1029 ºC de-

picting igneous temperatures. The temperatures calculated
on the geothermometer Ca in enstatite (Brey & Köhler
1990) are significantly higher (1095

ºC to 1191 ºC) and,

for the volatile saturated system appear too high. Coexist-
ing pair of spinel inclusions in olivine yielded rim-to-rim
temperatures between 860

ºC and 790 ºC (Fabriés 1979).

In tectonite peridotites two pyroxene geothermometer

(Wells 1977) and olivine-spinel geothermometer (Fabriés
1979) gave the most consistent temperatures. The temper-
atures for coexisting orthopyroxene and clinopyroxene
from transitional harzburgites GO-1 and GO-5 are
1021 ± 26

ºC and 1004±19 ºC, respectively. The two py-

roxene temperatures are significantly lower in plagioclase-
bearing transitional harzburgite (GO-B) and depleted
harzburgite (LNJ-1) (972 ± 17

ºC and 883±23 ºC, respec-

tively). In these peridotites temperatures for olivine-spinel

Fig. 6. Primitive mantle-normalized trace element concentration di-
agram for ultramafic cumulates from the ZMTDZ. Normalization
values are from Hofmann (1988). For the rock type see Table 6.
Cumulus peridotites (wehrlites) from the Bükk Mts (Downes et al.
1990; Aigner-Torres & Koller 1990) are shown for comparison.
Note high positive Ta—Nb and Ti anomalies due to fractionation of
Fe-Ti oxides in the latter.

524

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

rim-to-rim pairs range from 810

ºC to 600 ºC and from

713

ºC to 676 ºC, respectively.

Discussion

Ultramafic cumulates

The textural patterns and mineral compositions of the

Medvednica Mts ultramafic cumulates indicate that early
chromite and olivine crystallized as cotectic minerals fol-
lowed by enstatite, augite ± pargasite cumulii, postcumulus
enstatite, augite, edenite/pargasite and finally by anorth-
ite. Excluding spinel, the apparent homogeneous chemis-
try and narrow compositional range of primary minerals
indicates an open crystallization system. Crystallization
of Ti-pargasite in early phase of magmatic evolution sug-
gests enhanced water content ( > 4 wt. %) in the parental
magma (Koepke & Seidel 2004; Kocak et al. 2005). In the
case of the Medvednica Mts ophiolitic rocks this is cor-
roborated by igneous amphibole in mafic cumulates
(Crnković 1960; Slovenec 1998). The cumulus and isotro-
pic mafic-ultramafic rocks crystallized from volatile-rich
magmas are almost exclusively found in subduction zones
either in island arcs or continental margins (Conrad & Kay
1984; DeBari & Coleman 1989; Kocak et al. 2005). In the
MORB setting, formation of Ti-pargasite is occasionally
confirmed to the late-magmatic evolution of an intrusive
sequence (Tribuzio et al. 2000).

The crystallization sequence of the Medvednica Mts cu-

mulate rocks is typical of crystallization at low pressure.
Relatively high Cr and low Al abundances and Al

/Al

ratio in augite (Table 4), as well as high Ti content in
edenite/pargasite (Table 5) are evidence for low to moder-
ate pressure fractionation of ultramafic cumulates related
to arc region (compare to Hébert & Laurent 1990). Very
low Ca in cumulus olivine (Table 2) points to subsolidus
re-equilibration with enclosing amphibole and clinopy-
roxene. This also holds true for chromite cumulii embayed
in amphibole oikocrystal in the amphibole harzburgite
(MP-8) since they have the highest TiO

and Fe

# and

show the lowest Mg# (Table 1). Cumulii spinel inclusions
in olivine show a narrow range of Cr# and wide variation
of Mg# (Table 1; Fig. 2A) which is typical of fast subsoli-
dus Mg-Fe re-equilibration (Ozawa 1983) causing signifi-
cantly lower blocking temperature compared to coexisting
orthopyroxene-clinopyroxene pairs (Fig. 8).

The overall chemical composition of pyroxenes from

the Medvednica Mts ultramafic cumulates and particular-
ly low Al in orthopyroxene and low Ti in clinopyroxene
are typical of pyroxenes assembled in the deepest intru-
sive sequences of magmatic arcs (Harris 1995) and fore-
arcs (Ballantyne 1992). Chromite is found as one of the
best petrologic and geotectonic indicators of the rocks
(Kamenetsky et al. 2001) especially when it is, like in SZ
ultramafic rocks, unique residual

primary mineral.

Medvednica Mts chromites are highly oxidized, show
moderately high Cr# and relatively low Mg# (Table 1). In
this respect they are similar to the plutonic spinels report-
ed from magmatic arcs on continental margins (Kepezhin-
skas et al. 1993). The plutonic spinels from the Medvedni-
ca Mts have relatively high Ti abundance although the Ti
contents of the bulk rock is low. This characteristic makes
them essentially different from the fore-arc and back-arc
intrusive spinels. Olivine from the Medvednica Mts ultra-
mafic cumulates (Table 2) crystallized from the melt hav-
ing Mg# 53—58 using olivine-melt K

( = olivine/bulk

rock FeO

total

/MgO) of 0.30 (Roeder & Emslie 1970).

Mafic island arc tholeiitic (IAT) extrusives from the
Medvednica Mts ophiolite mélange have Mg# of 51—60
(Slovenec 1998) and their magma appears as a plausible
source of olivine cumulii.

The geochemical affinity of the Medvednica Mts ultra-

mafic cumulates was not well constrained due to the con-
tent of some diagnostic trace elements being under the de-
tection limit. However, multi-element concentration
normalized patterns of some analysed ultramafic cumu-
lates show slight negative anomalies of HFS elements Ti,
P and Nb (Fig. 6) typical for suprasubduction magmas, and
the IAT magma affinity of these rocks is confirmed by
their REE patterns (Fig. 7). In general, ultramafic cumu-
lates from the ZMDT show similar normalized concentra-
tion patterns to cumulus wehrlites reported from the Bükk
Mts. The essential difference is significantly higher level
of fractionation in the latter case (Figs. 6 and 7), which
caused extensive fractionation of Fe-Ti oxides – a typical
characteristic of the North Hungarian ultramafic cumulates
(Balla et al. 1983; Balla 1984; Kubovics 1984; Kubovics

Fig. 8. Summary of geothermometric estimations for ultramafic
rocks from the ZMTDZ. W and F refer to the temperatures
calculated for coexisting orthopyroxene and clinopyroxene pairs,
and for olivine and spinel pairs according to the thermometers
calibrated by Wells (1977) and Fabriés (1979), respectively.
W/B&K refers to the consistent orthopyroxene-clinopyroxene
temperatures calculated after Wells (1977) and Brey & Köhler
(1990). Rock symbols as in Fig. 7.

525

MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

& Bilik 1984; Downes et al. 1990; Harangi et al. 1996;
Józsa 1999; Aigner-Torres & Koller 1999).

Tectonite peridotites

Although the mantle peridotites are severely serpenti-

nized, the overall geochemical signatures allow them to
be divided into three groups: (1) lherzolite from the
Kalnik Mts (Fig. 1B, site 3), (2) transitional harzburgites
from near Gornje Orešje in the Medvednica Mts (Fig. 1B,
site 2), and (3) harzburgite from the Sava Depression
(Fig. 1B, site 4). The spinel compositions clearly confirm
the mantle origin of these peridotites and samples preserved
coexisting olivine and spinel plot in the field of the oliv-
ine-spinel mantle array (OSMA) of Arai (1994) (Fig. 7).

The lherzolite from the Kalnik Mts (Table 6, sample

KC) resembles the composition of fertile peridotite. Strong
depletion in LREE relative to HREE (Fig. 7) suggests that
residual lherzolite was formed after removal of very small
increments of partial melts as was also concluded for
CDOB (Central Dinaride Ophiolite Belt) lherzolites
(Lugović et al. 1991). The low degree of partial melting of
the lherzolite is corroborated by relatively fertile composi-
tion of relic spinel (Table 1). Assuming that entirely ser-
pentinized olivine was coexisting with the relic spinel in
the Kalnik Mts lherzolite the lercolite would represent the
mantle residium after about 7 % partial melting (Fig. 7).
The spinel composition (Table 1) is similar to the CDOB
lherzolite spinel composition (Fig. 4A) and both spinels
are consistent with the composition of spinels from pre-
oceanic subcontinental and abyssal oceanic mantle peri-
dotites as defined by Bonatti & Michael (1989).

The Medvednica Mts transitional harzburgites (Table 6,

GO-1 and GO-5) are highly LREE depleted and show
MREE-HREE profiles representative of depleted supra-
subduction zone peridotites (Fig. 7). They are apparently
akin to the depleted lherzolites and harzburgites from the
recent (fore-arc) arc-basin systems such as the Mariana
Trough (Parkinson & Pearce 1998), South Sandwich and,
here, especially to the peridotites from the trench-fracture
zone intersection (Pearce et al. 2000), and from ancient in-
tra-oceanic arc settings such as that recorded by the South
Ladakh ophiolites of the Indian Himalayas (Mahéo et al.
2004). The olivine-spinel composition suggests that the
Medvednica transitional harzburgites represent mantle re-
sidium after approximately 20 % partial melting (Fig. 9).
The Medvednica Mts plagioclase-bearing transitional
harzburgite, sample GO-B (Table 6), shows LREE-MREE
profile of the REE pattern which reflects the metasoma-
tism of a peridotite similar to the transitional harzburgites
represented by the samples GO-1 and GO-5 (Fig. 7). This
transitional harzburgite recrystallized in the plagioclase-
peridotite field as shown by their lower equilibration tem-
peratures compared with unmetasomatized transitional
harzburgites (Fig. 8). The spinel compositions from the
Medvednica Mts transitional harzburgites indicate Type I
peridotite host rocks (Dick & Bullen 1984), which are
transitional between CDOB lherzolites and IDOB (Inner
Dinaride Ophiolite Belt) harzburgites (Fig. 4A).

Fig. 9. Plot of Cr/(Cr + Al) in spinel against 100*Mg/(Mg + Fe

)

in olivine for ultramafic rocks from the ZMTDZ. The fields of
spinels from the CDOB and IDOB peridotites contoured after data
sources listed in Fig. 4. Olivine-spinel mantle array (OSMA) and
partial melting trend annotated by % are from Arai (1994). FMM
is fertile MORB mantle. Average spinels from tectonite peridotite
samples KC, GO-1 and GO-5 were also plotted assuming their
equilibration with olivine. Lherzolite from Kalnik Mts is akin to
ocean ridge peridotites, whilst other analysed ZMTDZ peridotites,
resemble oceanic supra-subduction zone (SSZ) peridotites.
Ultramafic cumulates from the ZMTDZ form the poorly
developed trend of fractional crystallization. CDOB peridotites
plot in the fields of peridotites from passive margins and ocean
ridges whilst IDOB peridotites occupy the field of oceanic SSZ
peridotites.

The depleted harzburgite from the drill-hole in the Sava

Depression (Table 6, sample LNJ-1) shows high Ca- and
LREE-MREE-metasomatized signatures and in that re-
spect may be misunderstood for least differentiated cumu-
lus amphibole harzburgite (P-1) (Fig. 7). However, the
spinel (Table 1) and olivine compositions (Table 2) of the
sample indicate a mantle origin and suggest metasoma-
tism after 30—33 % partial melting (Fig. 9). By composi-
tion these spinels are very similar to the spinels from the
IDOB harzburgites (Fig. 4A). This sample showing the
lowest equilibration temperatures (Fig. 8) suggests final
equilibration in the plagioclase-peridotite facies. The
Medvednica Mts ultramafic cumulates are most likely ge-
netically related to the mantle peridotites represented by
the LNJ-1 type lithology (Fig. 4).

The chemical compositions of coexisting spinel and or-

thopyroxene in terms of the Al

in orthopyroxene and

Cr/(Cr + Al) ratio in spinel were used to compare the peri-
dotites of the Sava Zone with the peridotites from the
CDOB and the IDOB. The analyses reported for spinel and
orthopyroxene from active arc-basin systems, which ap-
pear to be the most liable recent analogues, were used as

526

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

referent compositions. The relationship shown in Fig. 10
suggests that the mineral pairs were generated in the man-
tle similar to depleted abyssal peridotites (Bonatti &
Michael 1989) and to analogues of recent arc-basin sys-
tems represented by the South Sandwichs (Pearce et al.
2000) or Mariana Trough (Ohara et al. 1996, 2002). Since
the overall chemical compositions of Medvednica Mts
transitional harzburgites are highly correlated with the re-
cent back-arc peridotites from the South Sandwichs, we
envisage a back-arc setting as the most plausible environ-
ment for these transitional harzburgites. The depleted
harzburgite from the Sava Depression correlates to Mari-
ana fore-arc peridotites (Ohara & Ishii 1998).

The CDOB peridotites (fertile lherzolites) are plotted

beyond the field of abyssal peridotites and the IDOB peri-
dotites (depleted harzburgites and dunites), repeatedly be-
lieved to have been formed in a back-arc setting (Robert-
son & Karamata 1994, and references therein) are stretched
in the field of the fore-arc peridotites defined by the Mari-
ana fore-arc peridotites.

The relationship of ultramafic cumulates to tectonite
peridotites and the geotectonic implications

The block of ultramafic cumulate rocks from the

Medvednica Mts ophiolite mélange is an integral part of
the Kalnik Unit (Slovenec 1998; Haas et al. 2000) deposit-
ed from the Middle Jurassic to Hauterivian (Babić et al.
2002). The unit stretches further to the North, to the Ivan-
ščica Mts, where an island-arc source was suggested for
extrusive rocks from the Lower Cretaceous clastic deposits
(Babić et al. 1979). The magmatic rocks found in the
Kalnik Unit were constrained to the northwesternmost out-
crops of the IDOB (Pamić 1997). The Kalnik Unit is pre-

sumed to stretch further to the NE in Hungary (Pamić &
Tomljenović 1998) where an ophiolitic mélange crops out
in the Mt Bükk (e.g. Balla et al. 1983). The origin in an
arc to back-arc system was recognized for igneous rocks of
this mélange (Balla 1984; Downes et al. 1990; Harangi et
al. 1996; Aigner-Torres & Koller 1999).

The ultramafic cumulates from the Dinaric ophiolites

crystallized from dry magmas and do not contain amphib-
ole oikocrystals at all (Pamić 1974; Karamata 1979;
Lugović 1986; Pamić & Desmons 1989; Majer 1993).
These rocks seem not to be affected by Alpine regional
low-grade metamorphism. Medvednica Mts ultramafic cu-
mulates are thus more correlative to the ultramafic se-
quences of the Bükk Mts ophiolites which also contain
abundant amphibole intercumulus and Ti-rich oxides
(Balla et al. 1983; Balla 1984; Kubovics 1984; Kubovics
& Bilik 1984; Downes et al. 1990; Harangi et al. 1996;
Aigner-Torres & Koller 1999; Józsa 1999) and underwent
similar prehnite-pumpellyite facies alterations during the
Alpine orogeny (Árkai 1983).

The spinel compositions in the Berrriasian to Lower Al-

bian clastic succession in the Gerecse Mts from the north-
ern Transdanubian Mid-Mountains (Árgyelán 1996) sug-
gest an origin from sources similar to the Medvednica Mts
transitional harzburgite and ultramafic cumulates (Slo-
venec & Lugović 2000; Lugović & Slovenec 2004) and to
depleted harzburgite from the Sava Depression. We ex-
plain this feature by the exposition of these types of peri-
dotites to the weathering and accumulation of spinels in
the sediments from this clastic succession. The spinel
compositions of the Kalnik Mts lherzolite were not found
in the Gerecse Mts clastic succession.

The variety of mantle peridotite composition revealed

in only five samples from the Transdanubian segment of
the Sava Zone suggest a diversity of tectonic settings of
their formation. This is consistent with observations from
elsewhere showing different tectonic settings for the ophi-
olite complexes within the same orogenic belt. Assuming
that the mantle peridotites from the Transdanubian seg-
ment of the Sava Zone were generated in a single oceanic
domain then they should resemble a fore-arc—arc—back-arc
oceanic system. Similar relations may be inferred from the
geochemical and petrological characteristics reported for
ultramafic cumulates associated within the ophiolites from
NW Hungary (Balla et al. 1983; Balla 1984; Kubovics
1984; Kubovics & Bilik 1984; Réti 1987; Downes et al.
1990; Harangi et al. 1996; Józsa 1999; Aigner-Torres &
Koller 1999) and the diversity of mantle peridotites from
the adjacent SW Slovakia (Hovorka et al. 1985).

The formation of MORB-type ocenic crust in the Trans-

danubian segment of the Sava Zone commenced in the
late Ladinian (Halamić et al. 1998; Goričan et al. 2005).
Ocean spreading may be traced till the Middle Jurassic
(Halamić & Goričan 1995) when an accretionary wedge in
front of the intra-oceanic arc was formed (Babić et al.
2002). The closure of this oceanic domain started around
120 Ma ago (Barremian—Aptian) by formation of a meta-
morphic sole (Šegvić et al. 2005) followed by obduction
and greenschist facies metamorphism of the island arc

Fig. 10. Plot of Al

content in orthopyroxene against Cr/(Cr + Al)

in spinel for the tectonite peridotites and mafic cumulates from the
ZMTDZ. Data source for CDOB and IDOB as in Fig. 4. The field of
abyssal peridotites is given by Bonatti & Michael (1989) and the
field for southern Mariana fore-arc peridotites comes from Ohara et
al. (1996) and Ohara & Ishii (1998). Transitional harzburgites from
the ZMTDZ plot in the field of abyssal peridotite of back-arc prov-
enance whilst depleted harzburgite (LNJ-1) and IDOB peridotites
plot in the field defined by fore-arc peridotites.

527

MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

onto the continental platform (Belak 1995; Lugović et
al. 2006).

The CDOB metamorphic sole was dated by five five-

points Sm-Nd isochrons to around 171 Ma (Olker et al.
2001) and between 172 and 159 Ma by K-Ar measure-
ments on hornblende and white mica separates (Okrusch et
al 1978). The emplacement of the Vardar ophiolites,
namely the IDOB ophiolites, on the Pelagonian Continent
was recorded by the ophiolitic detritus in the Middle to
Upper Bathonian sediments, while ocean floor was still
forming (Baumgartner et al. 1993).

Following all statements we consider the original oce-

anic domain where these ultramafic rocks were formed
more akin to the Meliata-Maliac segment of the Tethys as
defined by Stampfli & Borer (2002) (their Fig. 8) then to
either Dinaric oceanic strand.

Conclusions

(1) The Medvednica Mts ultramafic cumulates consist

of genetically related chromite-olivine ± opx ± cpx cumu-
lates with abundant intercumulus edenite-pargasite. The
rocks crystallized in a shallow open magma chamber from
volatile-rich magmas favouring precipitation of Ti-rich
spinel and amphibole.

(2) The ultramafic cumulates show a tholeiitic affinity

typical of plutonic rocks from suprasubduction setting,
most akin to fore-arc setting. They are genetically linked
to depleted harzburgites from the Sava Depression.

(3) Subsolidus paragenesis shows a large temperature in-

terval of alterations indicating fast exhumation of the ul-
tramafic sequence. The most widespread alterations are of
low-grade prehnite-pumpellyite facies.

(4) The Medvednica Mts ultramafic cumulate sequence

shows different features than equivalent sequences in the
CDOB and IDOB ophiolite complexes and correlates with
the analogue from the Bükk Mts.

(5) The mantle peridotites resemble a diversity of tec-

tonic settings typical of recent fore-arc—arc—back-arc oce-
anic systems. There is a correlative relationship to the tec-
tonic setting of the Bükk Mts ophiolites in NW Hungary
and to ophiolites in SW Slovakia.

(6) On the basis of the geochemical and petrogenetic

signatures of analysed ultramafic rocks we locate the do-
main from which these rocks are derived in the Meliata-
Maliac segment of the Tethys.

Acknowledgment: Financial support by the Croatian Min-
istry of Sciences, Technology and Sports to the ceased
Projects Nos. 01959025, 0181001 and 0181006 is grate-
fully acknowledged. D.S. likes to acknowledge a current
grant from the Ministry (Project 181-1951126-1141).
Thanks are due to the charged people from INA-Naftaplin
for easy access to relevant drill-cores. We thank I. Fin and
H-P. Meyer from Mineralogisches Institut in Heidelberg
for preparing polished thin sections and for providing ex-
cellent microprobe facilities, respectively. Constructive

reviews by Friedrich Koller and Csaba Szabó helped to
achieve the final version of this paper.

References

Aigner-Torres M. & Koller F. 1999: Nature of the magma source

of the Szarvaskö complex (NE Hungary): petrological and
geochemical constraints. Ofioliti 24, 1—12.

Anonymus 1972: Penrose field conference on ophiolites. Geotimes

17, 24—25.

Arai S. 1994: Characterization of spinel peridotites by olivine-

spinel compositional relationships: Review and interpretation.
Chem. Geol. 113, 191—204.

Árgyelán G.B. 1996: Geochemical investigations of detrital spinels

as a tool to detect an ophiolitic source area (Gerecse Moun-
tains, Hungary). Acta Geol. Hung. 39, 341—368.

Árkai P. 1983: Very low- and low- and low-grade regional meta-

morphism of the Paleozoic and Mesozopic formations of the
Bükkium, NE-Hungary. Acta Geol. Hung. 26, 83—101.

Babić Lj., Zupanić J. & Crnjaković M. 1979: The recognition of

the two units in the ”clastic formation with ophiolites” of Mt.
Ivanščica and the role of a magmatic belt and an active conti-
nental margin. Zbornik radova, Znan. savj. naftu JAZU, Sekc.
primj. geol., geofiz., geokem., 4. god. znanstv. skup, 115—123.

Babić Lj., Hochuli A.P. & Zupanič J. 2002: The Jurassic ophiolitic

mélange in the NE Dinarides: Dating, internal structure and
geotectonic implications. Eclogae Geol. Helv. 95, 263—275.

Balla Z. 1984: The North Hungarian Mesozoic mafics and ultra-

mafics. Acta Geol. Hung. 27, 341—357.

Balla Z., Hovorka D., Kuzmin M. & Vinogradov V. 1983: Mesozo-

ic ophiolites of the Bükk Mountains (North Hungary). Ofioliti
8, 5—45.

Ballantyne P. 1992: Petrology and geochemistry of the plutonic

rocks of the Halmahera ophiolite, eastern Indonesia, an ana-
logue of modern oceanic forearcs. In: Parson L.M., Murton
B.J. & Browning P. (Eds.): Ophiolites and their modern ocean-
ic analogues. Geol. Soc. Spec. Publ. 60, 179—202.

Baumgartner P.O., Danelian T., Dumitrica P., Goričan S., Jud R.,

Dogherty L.O., Carter B., Conti M., De Wever P., Kito N.,
Marcucci M., Matsuoka A., Murchey B. & Urquart E. 1993:
Middle Jurassic-Early Cretaceous radiolarian biochronology
of Tethys: implications for the age of radiolarites in the Hel-
lenides. Bull. Geol. Soc. Greece XXVIII/3, 13—23.

Belak M., Pamić J., Kolar-Jurkovšek T., Pécskay Z. & Karan D.

1995: Alpine regional metamorphic complex of Mt.
Medvednica (northwestern Croatia). In: Vlahović I., Velić I.
& Šparica M. (Eds.): Proceedings of the 1

Croatian Geologi-

cal Congress, Opatija, 18—21.10.1995. Inst. Geol., Zagreb, 1,
67—70 (in Croatian).

Bonatti E. & Michael P.J. 1989: Mantle peridotites from continental

rifts to ocean basins to subduction zones. Earth. Planet. Sci.
Lett. 91, 297—311.

Brey G.P. & Köhler T. 1990: Geothermobarometry in four-phase

lherzolites II. New thermobarometers, and practical
assessment of existing thermobarometers. J. Petrology 31,
1353—1378.

Coleman R.G. 1977: Ophiolites. Springer Verlag, New York, 1—229.
Conrad W.K. & Kay R.W. 1984: Ultramafic and mafic inclusions

from Adak Islands: Crystallization history, and implications
for the nature of primary magmas and crustal evolution in the
Aleutian arc. J. Petrology 25, 88—125.

Crnković B. 1960: The hornblende-peridotite on the north side of

Medvednica-Zagrebačka gora Mountain. Geol. Vjesnik 13,
57—64 (in Croatian, English summary).

528

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

Crnković B. 1963: Petrography and petrogenesis of the magma-

tites of the northern part of Medvednica Mountain. Geol.
Vjesnik 16, 63—160 (in Croatian, English summary).

DeBari S.M. & Coleman R.G. 1989: Examination of the deep lev-

els of an island arc: Evidence from the Tonsina ultramafic-
mafic assemblage, Tonsina, Alaska. J. Geophys. Res. 94,
4373—4391.

Dick H.J.B. & Bullen T. 1984: Chromian spinel as a petrogenetic

indicator in abisal and alpine-type peridotites and spatially as-
sociated lavas. Contr. Mineral. Petrology 86, 54—76.

Dimitrijević M.D. 1983: Geology of Eastern Yugoslavia: a short re-

view. Guide-book, Field Meeting International Working
Group IGCP Project 5, Correlation of Pre-variscan and
Variscan events in the Alpine-Mediterranean Mountain Belt in
Yugoslavia, Yugoslavian Comm. IGCP, 1—65.

Downes H., Pantó Gy., Árkai P. & Thirlwall M.F. 1990: Petrology

and geochemistry of Mesozoic igneous rock, Bükk Mountains.
Lithos 24, 201—215.

Evensen N.M., Hamilton P.J. & O’Nions R.K. 1978: Rare earth

abundances in chondritic meteorites. Geochim. Cosmochim.
Acta 42, 1199—1212.

Fabriés J. 1979: Spinel-olivine geothermometry in peridotites from

ultramafic complexes. Contr. Mineral. Petrology 69, 329—336.

Faryad S.W., Spišiak J., Horvát P., Hovorka D., Dianiška I. & Józsa

S. 2005: Petrological and geochemical features of the Meliata
mafic rocks from the sutured Triassic oceanic basin, Western
Carpathians. Ofioliti 30, 27—35.

Goričan S., Halamić J., Grgasović T. & Kolar-Jurkovšek T. 2005:

Stratigraphic evolution of Triassic arc-back-arc system in
northwestern Croatia. Bull. Soc. Géol. France 176, 3—22.

Haas J. & Kovács S. 2001: The Dinaridic-Alpine connection – as

seen from Hungary. Acta Geol. Hung. 44, 345—362.

Haas J., Mioč P., Pamić J., Tomljenović B., Árkai P., Berczi-Makk

A., Koroknai B., Kovács S. & Felgenhauer E. 2000: Complex
structural pattern of the Alpine-Dinaridic-Pannonian triple
junction. Int. J. Earth Sci. 89, 377—389.

Halamić J. 1998: Lithostratigraphic characterisation of Jurassic

and Cretaceous sediments with ophiolites at Mts Medvednica,
Kalnik and Ivanščica. Ph.D., Univ. Zagreb, 1—188 (in Croat-
ian, English summary).

Halamić J. & Goričan Š. 1995: Triasic and Jurassic radiolarites

from the Mts. Medvednica and Kalnik. Geol. Croatica 48,
129—146.

Halamić J., Slovenec D. & Kolar-Jurkovšek T. 1998: Triassic pe-

lagic limestones in pillow lavas in the Orešje quarry near
Gornja Bistra, Medvednica Mt. (Northwest Croatia). Geol.
Croatica 51, 33—45.

Halamić J., Goričan Š., Slovenec Da. & Kolar-Jurkovšek T. 1999:

A Middle Jurassic radiolarite-clastic succession from the
Medvednica Mt. (NW Croatia). Geol. Croatica 52, 29—57.

Harris R.A. 1995: Geochemistry and tectonomagmatic affinity of

the Misgeguk massif, Brooks range ophiolite, Alaska. Lithos
35, 1—25.

Harangi Sz., Szabó Cs., Józsa S., Szoldán Zs., Árva-Sós E., Balla M.

& Kubovics I. 1996: Mesozoic igneous suites in Hungary: Im-
plications for genesis and tectonic setting in the northwestern
part of Tethys. Int. Geol. Rev. 38, 336—360.

Harte B. 1976: Rock nomenclature with particular relation to defor-

mation and recrystallization textures in olivine-bearing xeno-
liths. J. Geol. 85, 279—288.

Herak M. 1999: Tectonic interrelation of the Dinarides and the

Southern Alps. Geol. Croatica 52, 83—98.

Hébert R. & Laurent R. 1990: Mineral chemistry of the plutonic

section of the Troodos ophiolite: new constraints for genesis of
arc-related ophiolites. In: Malpas J., Moores E., Panayiotou A.
& Xenophontos C. (Eds.): Ophiolites—Oceanic Crustal ana-

logues. Proceedings of Troodos Ophiolite Symposium. Geol.
Surv. Department, Cyprus, 149—163.

Hofmann A.W. 1988: Chemical differentation of the Earth: the re-

lationship between mantle, continental crust, and oceanic crust.
Earth Planet. Sci. Lett. 90, 297—314.

Hovorka D., Jaroš J., Kratochvíl M., Reichwalder P., Rojkovič I.,

Spišiak J. & Turanová L. 1985: Ultramafic rocks of the West-
ern Carpathians, Czechoslovakia. Geol. Inst. Dionýz Štúr, Bra-
tislava, 1—258.

Huot F. & Maury R.C. 2002: The Round Mountain serpentinite

mélange, northern Coast Ranges of California: An association
of backarc and arc-related tectonic units. GSA Bull. 114,
109—123.

Józsa S. 1999: Petrological and geochemical investigations of the

oceanic crust-related magmatic rocks of Darno Hill. Ph.D.
Thesis, Univ. Budapest, 1—173 (in Hungarian, English sum-
mary).

Kamenetsky V.S., Crawford A.J. & Meffre S. 2001: Factors con-

trolling chemistry of magmatic spinel: an empirical study of
associated olivine, Cr-spinel and melt inclusions from primi-
tive rocks. J. Petrology 42, 655—671.

Karamata S. 1979: The transitional zone between tectonite ultrama-

fic rocks and igneous cumulate rocks in the ophiolite com-
plexes of Yugoslavia. Bull. SANU 66, 57—62.

Karamata S., Majer V. & Pamić J. 1980: Ophiolites of Yugoslavia.

In: Rocci G. (Ed.): Tethyan Ophiolites. Ofioliti, Spec. Issue 1,
105—125.

Karamata S., Olujić J., Protić L., Milovanović D., Vujnović L.,

Popević A., Memović E., Radovanović Z. & Resimić-Šarić K.
2000: The western belt of the Vardar Zone – the remnant of a
marginal sea. In: Karamata S. & Janković S. (Eds.): Interna-
tional Symposium Geology and Metallogeny of the Dinarides
and the Vardar zone. The Academy of Sciences and Arts of
the Republic of Srpska, Banja Luka, Sarajevo, 131—135.

Kepezhinskas P.K., Taylor R.N. & Tanaka H. 1993: Geochemistry

of plutonic spinels from the North Kamchatka Arc: compari-
son with spinels from other tectonic settings. Mineral. Mag.
57, 575—589.

Kišpatić M. 1918: Die Eruptivgesteine und kristallinische Schiefer

des Agramer Gebirges. Glasn. Hrv. Prir. Druš. 30, 1—23.

Kocak K., Isôk F., Arslan M. & Zedef V. 2005: Petrological and

source region characteristics of ophiolitic hornblende gabbros
from the Aksaray and Kayseri regions, central Anatolian crys-
talline complex, Turkey. J. Asian Earth Sci. 25, 883—891.

Koepke J. & Seidel E. 2004: Hornblendites within ophiolites of

Crete, Greece: evidence for amphibole-rich cumulates derived
from an iron-rich tholeiitic melt. Ofioliti 29, 159—175.

Kubovics I. 1984: On the petrogenesis of the north Hungarian ba-

sic-ultrabasic magmatic rocks. Acta Geol. Hung. 27, 163—189.

Kubovics I. & Bilik I. 1984: Comparative investigation of the Hun-

garian Mesozoic basic-ultrabasic and some ophiolitic magmat-
ic rocks in the Alp-Carpathian chain. Acta Geol. Hung. 27,
321—339.

Leake B.E. & group of authors 1997: Nomenclature of amphiboles.

Eur. J. Mineral. 9, 623—651.

Leblanc M., Dupuy C. & Merlet C. 1984: Nickel content of olivine

as a discriminatory factor between tectonite and cumulate peri-
dotite in ophiolites. Sci. Géol. Bull. 37, 131—135.

Lindsley D.H. 1983: Pyroxene thermometry. Amer. Mineralogist

68, 477—493.

Lugović B. 1986: Gabbro-peridotite rock association from the

northwestern flanks of Mt. Maljen ophiolite massif. Ph.D.
Thesis, Univ. Zagreb, 1—207 (in Croatian).

Lugović B. & Slovenec Da. 2004: Mantle harzburgites (serpen-

tinites) from Gornje Orešje (Medvednica Mts., Croatia). In:
Halamić J. (Ed.): Excursion Guide, Joint Meeting of Croatian

529

MESOZOIC ULTRAMAFIC ROCKS FROM THE ZAGORJE-MID-TRANSDANUBIAN ZONE (CROATIA)

ide ophiolite zone. Ofioliti 14, 13—32.

Pamić J. & Tomljenović B. 1998: Basic geologic data from the

Croatian part of the Zagorje-Mid-Transdanubian Zone. Acta
Geol. Hung. 41, 389—400.

Pamić J., Tomljenović B. & Balen D. 2002: Geodynamic and petro-

genetic evolution of Alpine ophiolites from the central and
NW Dinarides: an overview. Lithos 65, 113—142.

Pandžić J. 1982: Tertiary base of the Northern Croatia and the neigh-

bouring areas. 10. Jub. Kongr. Geol. Jugoslavije 1, 73—85.

Parkinson I.J. & Pearce J.A. 1998: Peridotites from the Izu-Bonin-

Mariana Forearc (ODP Leg 125): evidence for mantle melting
and melt-mantle interaction in a supra-subduction zone setting.
J. Petrology 39, 1577—1618.

Parkinson I.J., Pearce J.A., Thirlwall M.F., Johnson K.T.M. & In-

gram G. 1992: Trace element geochemistry of peridotites from
the Izu—Bonin—Mariana forearc, Leg 125. Proc. Ocean Drill.
Program Sci. Results 125, 487—506.

Parlak O., Delaloye M. & Bíngöl E. 1996: Mineral chemistry of ul-

tramafic and mafic cumulates as an indicator of the arc-related
origin of the Mersín ophiolite (southern Turkey). Geol. Rdsch.
85, 647—661.

Parlak O., Höck V. & Delaloye M. 2002: The suprasubduction

zone Poznati-Kersanti ophiolite, southern Turkey: evidence
for high-pressure crystal fractionation of ultramafic cumulates.
Lithos 65, 205—224.

Pearce J.A., Barker P.F., Edwards S.J., Parkinson I.J. & Leat P.T.

2000: Geochemistry and tectonic significance of peridotites
from the South Sandwich arc-basin system, South Atlantic.
Contr. Mineral. Petrology 139, 36—53.

Poljak J. 1942: Ein Beitrag zur Geologie des Kalnik-Gebirges. Vjes.

Hrv. Drž. Geol. Zav. Hrv. Drž. Geol. Muz. 1, 53—92.

Pouchou J.L. & Pichoir F. 1984: A new model for quantitative

analyses. I. Application to the analysis of homogeneous sam-
ples. La Recherche Aérospatiale 3, 13—38.

Pouchou J.L. & Pichoir F. 1985: “PAP” ( - -Z) correction proce-

dure for improved quantitative microanalysis. In: Armstrong
J.T. (Ed.): Microbeam analysis. San Francisco Press, 104—106.

Réti Z. 1987: Comparison of the Mesozoic mafic and ultramafic

complexes in northern Hungary. Ofioliti 12, 43—52.

Robertson A.H.F. & Karamata S. 1994: The role of subduction—ac-

cretion processes in the tectonic evolution of the Mesozoic
Tethys in Serbia. Tectonophysics 234, 73—94.

Roeder P.L. & Emslie R.F. 1970: Olivine-liquid equilibrium. Contr.

Mineral. Petrology 29, 275—289.

Slovenec Da. 1998: Ophiolitic rocks in the area of the Bistra creek

on the northern slopes of Medvednica Mt. B.Sc. Thesis, Univ.
Zagreb, 1—104 (in Croatian, English summary).

Slovenec Da. 2003: Petrology and geochemistry of the ophiolitic

rocks from Medvednica Mt. Ph.D. Thesis, Univ. Zagreb, 1—180
(in Croatian, English summary).

Slovenec Da. & Lugović B. 2000: Ultramafic cumulate rocks

from the Medvednica Mts. ophiolite complex (Northwestern
Croatia). In: Vlahović I. & Biondić R. (Eds.): Proceedings
of the 2

Croatian Geological Congress, Cavtat-Dubrovnik,

17—20.5.2000. Inst. Geol., Zagreb, 379—385 (in Croatian,
English summary).

Smith A.G. & Spray J.G. 1984: A half-ridge transform model for

the Hellenic-Dinaric ophiolites. In: Dixon J.E. & Robertson
A.H.F. (Eds.): The geological evolution of the Eastern Medi-
terranean. Geol. Soc. London, Spec. Publ. 17, 629—644.

Stampfli G.M. & Borel G.D. 2002: A plate tectonic model for the

Paleozoic and Mesozoic constrained by dynamic plate bound-
aries and restored synthetic oceanic isochrons. Earth Planet.
Sci. Lett. 196, 17—33.

Streckeisen A.L. 1974: Classification and nomenclature of plutonic

rocks. Recommendations of the IUGS subcommission on the

and Hungarian Geological Societies on Geology of the Zagor-
je-Mid-Transdanubian Zone. Inst. Geol., Zagreb, 40—45.

Lugović B., Altherr R., Raczek I., Hofmann A.W. & Majer V.

1991: Geochemistry of peridotites and mafic igneous rocks
from the Central Dinaric Ophiolite Belt, Yugoslavia. Contr.
Mineral. Petrology 106, 201—216.

Lugović B., Šegvić B. & Altherr R. 2006: Petrology and tectonic

significance of greenschists from the Medvednica Mts. (Sava
unit, NW Croatia). Ofioliti 31, 39—50.

Mahéo G., Bertrand H., Guillot S., Villa I.M., Francine Keller F. &

Capiez P. 2004: The South Ladakh ophiolites (NW Himalaya,
India): an intra-oceanic tholeiitic arc origin with implication
for the closure of the Neo-Tethys. Chem. Geol. 203, 273—303.

Majer V. 1993: Ophiolite complex of the Banija and Pokuplje re-

gion in Croatia and Mt. Pastirevo in northwestern Bosnia.
Acta Geol. HAZU 23, 39—84 (in Croatian, English summary).

Maksimović Z. & Kolomejceva-Jovanović L. 1987: Composition

of coexisting minerals of Yugoslav peridotites and the prob-
lems of geothermometry and geobarometry of two ultramafic
zones. Glas SANU, Odel. Prirod.-Matemat. Nauka 51, 21—52.

Maksimović Z. & Majer V. 1981: Accesory spinels of two main

zones of Alpine ultramafic rocks in Yugoslavia. Bull. Acad.
Sci. Serbe, Sci. Naturell. 21, 47—58.

Moores E.M. & Jackson E.D. 1974: Ophiolites and oceanic crust.

Nature 250, 136—139.

Morimoto N. 1988: Nomenclature of pyroxenes. Schweiz. Mineral.

Petrogr. Mitt. 68, 95—111.

Nicolas A. & Jackson E.D. 1972: Répartition en deux provinces des

péridotites des chaînes alpines longeant la méditerranée: im-
plications géotectoniques. Bull. Swiss. Miner. Petrology 53,
385—401.

Ohara Y. & Ishii T. 1998: Peridotites from southern Mariana

forearc: Heterogeneous fluid supply in mantle wedge. Island
Arc 7, 541—558.

Ohara Y., Kasuga S. & Ishii T. 1996: Peridotites from the Parece

Vela Rift in the Pilippine Sea. Upper mantle material exposed
in a extinct back-arc basin. Proc. Japan. Acad. 72B, 118—123.

Ohara Y., Stern R.J., Ishii T., Yurimoto H. & Yamazaki T. 2002:

Peridotites from the Mariana Trough: first look at the mantle
beneath an active back-arc. Contr. Mineral. Petrology 143, 1—18.

Okrusch M., Sidel E., Kreuzer H. & Harre W. 1978: Jurassic age of

metamorphism at the base of the Brezovica peridotite (Yugo-
slavia). Earth. Planet. Sci. Lett. 39, 291—297.

Olker B., Altherr R. & Lugović B. 2001: Metamorphic evolution of

mafic granulites from the metamorphic sole of Central Dinaric
Ophiolites (Bosnia-Herzegovina). Abstracts EUG XI Meeting,
8—12 April 2001, Strasbourg, France, 320—321.

Ozawa K. 1983: Evaluation of olivine-spinel geothermometry as an

indicator of thermal history of peridotites. Contr. Mineral. Pe-
trology 82, 52—65.

Pamić J.J. 1974: Alpine-type gabbros within the Krivaja-Konjuh ul-

tramafic massif in the Ophiolite Zone of the Dinarides, Yugo-
slavia. Tschermaks Min. Petr. Mitt. 21, 261—279.

Pamić J. 1983: Considerations on the boundary between lherzolite

and harzburgite subprovinces in the Dinarides and northern
Hellenides. Ofioliti 8, 153—164.

Pamić J. 1997: The northwesternmost outcrops of the Dinaridic

ophiolites: a case study of Mt. Kalnik (North Croatia). Acta
Geol. Hung. 40, 37—56.

Pamić J. 2002: The Vardar Zone of the Dinarides and Hellenides

versus the Vardar Ocean. Eclogae Geol. Helv. 95, 99—113.

Pamić J. 2003: The allochthonous fragments of the Internal Dinar-

idic units in the western part of the South Pannonian Basin.
Acta Geol. Hung. 46, 41—62.

Pamić J. & Desmons J. 1989: A complete ophiolite sequence in

Rzav, area of Zlatibor and Varda ultramafic massifs, the Dinar-

530

LUGOVIĆ, SLOVENEC, HALAMIĆ and ALTHERR

systematics of igneous rocks. Geol. Rdsch. 63, 773—786.

Šegvić B., Lugović B. & Ignjatić S. 2005: Petrochemical and geo-

tectonic characteristics of amphibolites from the Zagorje-Mid-
Transdanubian shear zone (Mt. Kalnik, Croatia). In: Vlahović
I. & Biondić R. (Eds.): 3

Croatian Geological Congress,

Opatija, 29.09.—01.10.2005. Abstract Book, Croat. Geol. Sur-
vey, Zagreb, 143—144.

Šimunić A. & Pamić J. 1989: Ultramafic rocks from the neighbour-

hood of Gornje Orešje on the nortwestern flanks of Mt.
Medvednica (northern Croatia). Geol. Vjesnik 42, 93—101.

Šimunić An., Pikija M., Hećimović I. & Šimunić Al. 1981: Basic

geological map 1 : 100,000. Sheet Varaždin, explanatory
notes. Inst. Geol. Istraž., Zagreb—Sav. Geol. zavod Beograd,
1—74 (in Croatian).

Šimunić An., Pikija M., Hećimović I. & Šimunić Al. 1982: Basic

geological map, 1 : 100,000. Sheet Varaždin. Inst. Geol. Is-

traž., Zagreb—Sav. Geol. zavod Beograd.

Tomljenović B. 2002: Structural characteristics of Medvednica and

Samoborska Gora Mts. Ph.D. Thesis, Univ. Zagreb, 1—206 (in
Croatian, English summary).

Tribuzio R., Tiepolo M. & Thirlwall M.F. 2000: Origin of titanian

pargasite in gabbroic rocks from the Northern Apennine ophi-
olites (Italy): insights into the late-magmatic evolution of a
MOR-type intrusive sequence. Earth Planet. Sci. Lett. 176,
281—293.

Trubelja F., Marchig V., Burgath K.P. & Vujović Ž. 1995: Origin

of the Jurassic Tethyan ophiolites in Bosnia: a geochemical ap-
proach to tectonic setting. Geol. Croatica 48, 49—66.

Vragović M. & Marci V. 1973: Carbonate serpentinite from drill-

ing-holes near Lepavina. Geol. Vjesnik 26,159—167.

Wells P.R.A. 1977: Pyroxene thermometry in simple and complex

systems. Contr. Mineral. Petrology 62, 129—139.