GeolCarp_Vol58_No2_169

GEOLOGICA CARPATHICA, APRIL 2007, 58, 2, 169—179

www.geologicacarpathica.sk

Igneous rock clasts from the Maastrichtian Bovec flysch

(Slovenia): petrology and geodynamic aspects

ANGELO DE MIN

, ALBERTO ROSSET

, GIORGIO TUNIS

, CRISTINA KOCMANN

ALESSANDRO TOSONE

and DAVIDE LENAZ

Dipartimento di Scienze della Terra, via Weiss 8, 34127 Trieste, Italy; demin@univ.trieste.it

Dipartimento di Scienze Geologiche, Ambientali e Marine, via Weiss 2, 34127 Trieste, Italy

Hydrotech S.r.l. – AREA Science Park, Padriciano 99, 34012 Trieste, Italy

(Manuscript received January 13, 2006; accepted in revised form October 5, 2006)

Abstract: About sixty well sorted (average diameter 0.8 cm) volcanic clasts with tholeiitic affinities were found in the
midst of an lower Maastrichtian conglomerate outcropping close to Bovec (Slovenian Basin, NW Slovenia) and inter-
preted as evidence of a deltaic system. The clasts appear to be variably spilitized (i.e. albitization of plagioclase and
anomalous Na content), however, they do not show any evidence of sub-solidus recrystallization. The analysis, carried
out on nineteen selected samples, point out similar petrographic textures and a strong arc-type chemical signature (i.e.
deep Nb negative anomaly, quite low La/Sm and Th/Zr ratio and normative corundum). Chemical data allow us to
distinguish, for comparable grade of evolution, variable LREE contents which cannot be related only to crystal fraction-
ation or to a variable grade of crustal contamination, but require compositional differences in the protolithic sources. To
have an indication of the provenance of these clasts, and about their related hydrographic system, their chemical features
were compared to those of similarly evolved pre-Maastrichtian magmatic rocks of different ages, locations and geologi-
cal settings, mainly belonging to the Dinaridic-Carpathian region. Such a comparison seems to indicate a particular
affinity with the arc-type magmas which outcropped in the Vardar Ocean in Jurassic times. In particular Bovec clasts
show strong chemical similarities with metabasites from the ophiolitic complexes of the Evros (Rhodopes) and Vardar
Zone, while they appear quite different from both the more depleted samples from Bükk Mountains (Hungary), and all
the calc-alkaline compositions considered. The grain size of the clasts and the complete absence of recrystallization
suggest a provenance from a quite delimited and close protolithic area (1—3 hundred kilometers) that did not suffer from
sub-solidus recrystallization during Late Cretaceous times.

Key words: Maastrichtian, Bovec (NW Slovenia), Vardar Zone, sedimentary petrology, conglomerates, arc-type
tholeiitic clasts.

Introduction

Traditional provenance studies investigate the large-scale
geodynamic framework of ancient geological setting and
infer the types of eroded rocks which supplied clastic sys-
tems in order to improve our knowledge of paleogeogra-
phy. Thus they could successfully identify the rock types
which sourced a certain clastic body, and finally their pa-
leogeographical location, by combining petrologic data
with basin analysis studies. A comparison of the geochem-
ical data from pebbles of the flysch and potential source
rocks will help to elucidate the flysch provenance.

In this way, the conglomerates of the Bovec Basin (part

of Slovenian Basin), which probably represents a branch
in the evolution of the Pindos Sea at this latitude during
early Maastrichtian times, appears related to a not extend-
ed hydrographic basin and associated with the develop-
ment of an orogenic wedge. Moreover, the deposits of the
inner margin of the Slovenian Basin are rarely observed:
the lower Maastrichtian conglomerates outcropping near
Bovec, represent a significant exception.

Thus, the chemical features of the clasts and the present

day Peri-Tethys plate reconstruction models could pro-
vide an important clue both to define the protolithic areas

and to insert the Bovec sector of the Slovenian Basin
within the geodynamic evolution of the Alpidic-Dinaric
and Carpathian domains.

Geology and stratigraphy

The studied area (Fig. 1) is located inside the Bovec

sedimentary basin, situated between Mt Rombon and Mt
Polovnik structural highs (NW Slovenia; Fig. 2) close to
Bovec village. The oldest terrains (Fig. 2) of the strati-
graphic succession belong to the Julian Carbonate Plat-
form (Buser 1986a,b), and are represented by Norian and
Rethyan limestones to dolostones (Dachstein and Main
Dolomite formations), which are interpreted as peritidal
carbonates. Early-Middle Jurassic is represented by oolith-
ic limestones and minor carbonate breccias (Buser 1986a)
testifying to the presence of a shallow sea (carbonate
ramp) and short-lasting periods of emersion of the carbon-
ate platform, respectively (Selli 1947). From the Dogger,
the Julian Carbonate Platform was eroded (Buser 1986a,b)
due to compressive NE-SW trending faults which led to
the folding of the area (Selli 1947), and to the raising of a
deep marine plateau, now represented by Mt Rombon and

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DE MIN, ROSSET, TUNIS, KOCMANN, TOSONE and LENAZ

Fig. 1. Geological sketch map of the studied area showing the flysch
outcrops (modified after Kušcer et al. 1974 and Buser 1986a,b). In-
set: Geographical location of Bovec Basin.

Fig. 2. Stratigraphic column and stratigraphic section of Bovec Basin (modified from Selli 1947). Inset: tectonic settings of the Julian
Alps during Late Cretaceous times (modified from Selli 1947).

The Cretaceous deposits of the Bovec area include red-

dish marly limestone and marl with chert (Scaglia Rossa
Formation) and grey marly limestone with chert (Volče
limestone) which are interpreted as thin-bedded calcitur-
bidites (Ogorelec et al. 1976). These turbidites, deposited
during the Campanian (Pavšič 1994), are linked to the be-
ginning of a new tectonic phase which is traditionally re-
lated to the Ressen compressive phase (Kuščer et al. 1974).
Calci-turbiditic clasts mostly derived from resedimented
shallow marine carbonates (i.e. Friuli Carbonate Platform)
situated at the outer side of the Slovenian Basin. Succes-
sively, during the Maastrichtian, a gradually increasing in-
put of terrigenous material, started in the Bovec area
(Kuščer et al. 1974) so that a gradual variation from a calci-
clastic deep-water system to a siliciclastic one occurred.

Conglomerate beds 5—10 meter thick on the whole can be

observed about 400 m above the base of the flysch succes-
sion. The most common lithologies observed among the
clasts of the conglomerates include Mesozoic limestone
and dolostone derived both from an inner carbonate plat-
form and plateau areas (see the above mentioned forma-
tions), chert, lydites, quartzites, plagioclase-rich and chro-
mite-bearing sandstones (Lenaz et al. 2000), metapelites
and scarce unmetamorphosed occasionally spilitized volca-
nic clasts (Rosset et al. 2003).

According to Selli (1947) and Kuščer et al. (1974), the

conglomerates indicate the existence, at that time, of a

Mt Polovnik highs (Fig. 2). Due to this tectonic event, the
Mt Polovnik high acted as a partition between two small
distinct deep-water sub-basins, known in literature as
Bovec and Kobarid sub-basins (Kušcer et al. 1974).

171

IGNEOUS ROCK CLASTS FROM THE MAASTRICHTIAN BOVEC FLYSCH (SLOVENIA)

deltaic system. More probably, these deposits represent a
“mixed system” as proposed by Mutti et al. (2003) charac-
terized by an association of immature, turbidite like bod-
ies and deltaic deposits situated at the internal margin of
the Slovenian Basin, which was strongly influenced by
the proximity of a growing orogen.

Petrography and classification of the clasts

Igneous clasts are quite rare in the Bovec conglomerates

and only 69 items have been sampled so far. They have a
mean size diameter variable from 0.4 to 2.0 cm (average
0.8 cm) and their shape appear to be compatible with flu-
vial transport as suggested by Kuščer et al. (1974). In fact,
their grain size and the quite high density (about 2.7—
2.9 g/cm

), together with associations with facies typical

of immature turbidite, suggest transport by small to medi-
um-sized rivers, presumably characterized by relatively
short and high-gradient transfer zones.

Optically, all the volcanic clasts show intersertal and/or

micro-porphyritic textures. Rare pheno- and micropheno-
crystals of plagioclase, augite, pigeonite and opaques
have been observed. Olivine, completely altered into id-
dingsitic products appears to be occasional. Microlites are
quite abundant and mainly represented by albitized pla-
gioclase and clinopyroxene. Secondary mineral phases are

Fig. 3. A – Distribution of the Bovec volcanic clasts in R1-R2
classification diagram of De La Roche et al. (1980) as modified
by Bellieni et al. (1981). B – SiO

vs. FeO

/MgO diagram for ba-

sic sub-alkaline rocks (Miyashiro 1974).

represented by carbonates such as plagues inside plagio-
clase and/or inside glass, and by scarce zeolites filling mi-
cro-fractures and very rare vacuoles. Glass is very
abundant and partially recrystallized into clay minerals. In
general, due to their mineralogical assemblage the clasts

Table 1: Microprobe compositions of pyroxenes of the Bovec volcanic clasts. E and L – early and late crystallized pyroxene. Aug –
augite; Pig – pigeonite. Fe

calculated according to Papike et al. (1974); Fe* = Fe

+ Mn+Fe

172

DE MIN, ROSSET, TUNIS, KOCMANN, TOSONE and LENAZ

appear to be tholeiitic basalts, andesitic basalts and transi-
tional-basalts with tholeiitic affinity (i.e. coexistence of
quite altered olivine and pigeonite). Moreover, the petro-
graphic features indicate an effusive or sub-effusive origin
characterized by a rapid quench. The coexistence of albi-
tized and Ca-rich plagioclase suggests spilitization pro-
cesses. On a petrographical basis, nineteen quite fresh
samples were selected, analysed for major elements and
plotted (Fig. 3A) in the R1-R2 classification diagram of De
La Roche et al. (1980) as modified by Bellieni et al. (1981),
here preferred to the most common TAS (Total Alkali Sili-
ca; Le Bas et al. 1986) because it gives clear petrographic
evidence of Na mobilization. The samples, in agreement
with the optical features, plot in the transitional and sub-al-
kaline fields, from transitional- and andesi-basalt to latites
and lati-andesites. The tholeiitic affinity is supported by the
SiO

vs. FeO

/MgO diagram of Miyashiro (1974; Fig. 3B),

in which most of the samples fall in the tholeiitic field; only
a few samples fall between the tholeiitic and the calc-alka-
line fields and only one sample falls in the calc-alkaline
one. Finally, most samples are both Q and C normative.

Mineral chemistry

Microprobe analyses were carried out on the largest

samples ( >1 cm; BV17, BV28, BV32 and BV33) using a
Cameca—Camebax operating at 15 kV and 15 nA, at the
Dipartimento di Mineralogia e Petrologia, University of
Padova (Italy). The PAP Cameca program has been used to
convert X-ray counts into weight percent of the corre-
sponding oxides. Results are considered accurate within
2—3 % for major elements and 9 % for minor elements.

The analysed pyroxenes (Table 1) are mainly represented

by micro-phenocrysts of augite (Wo

39—42

41—48

11—20

)

quite homogeneous in composition, which plot over the
Skaergaard trend (Brown & Vincent 1963). The rare un-al-
tered associate pigeonites (Wo

48—49

37—38

) confirm the

tholeiitic affinity of these rocks. Kretz’s (1982) crystalliza-
tion temperature of late-crystallized augite, obtained for sam-
ple BV32, yielded values of 1060—1067 ºC.

Feldspar

microprobe compositions (Table 2) show two

main feldspar groups in agreement with the optical fea-
tures. They are represented by albite-oligoclase (An

0—13

;

Table 2: Microprobe plagioclase compositions of the Bovec volcanic clasts. E and L – early and late crystallized plagioclase. Or, Ab
and An – orthoclase, albite and anorthite, respectively. Crystallization temperatures (T

ºC) were obtained using the geothermometer of

Kudo & Weill (1970).

173

IGNEOUS ROCK CLASTS FROM THE MAASTRICHTIAN BOVEC FLYSCH (SLOVENIA)

average An

) and plagioclase with anorthitic contents

ranging from An

(average An

). The first group

is represented by spilitized plagioclases, while the other
appears to be quite compatible with the evolution degree
of the rocks (Mg#=0.4—0.6; Mg#=[Mg]/[Mg+Fe

] for

/FeO=0.15). Temperatures of 1024 and 1048 ºC,

comparable with those of pyroxenes, were obtained on
two anorthitic plagioclase belonging to sample BV33 by
using the geothermometer of Kudo & Weill (1970) and as-
suming a P

H2O

= 500 MPa. In the same clast a Ca-rich pla-

gioclase (An

) gave a higher temperature of 1211 ºC.

The microprobe analyses indicate that opaques and oli-

vine

are completely transformed respectively into colloi-

dal hydroxides and iddingsite.

Geochemistry

Major and trace elements were determined at the Diparti-

mento di Scienze della Terra, University of Trieste, by using
a PW-1404 XRF spectrometer and the procedures of Phil-
ips

for the correction of matrix effects. Major element

abundances were recalculated to 100 % on a volatile-free
basis. The analytical uncertainties are estimated at less than
2 and 5 % for major and trace elements, respectively. REE
(as well as all the trace elements) determinations in the sam-
ples BV17 and BV33 were carried out by ICP-MS at the
Centre de Recherches Petrographiques et Geochimiques,

CNRS, Vandoeuvre (France), and the analytical uncertain-
ties are estimated between 5 and 10 % (Govindaraju &
Mevelle 1987).

Major elements

Despite the clastic nature of the volcanics, the most

abundant major elements (Table 3, Fig. 4) show broad cor-
relation with SiO

, here used as a possible evolution in-

dex, and indicate a provenance from variably evolved
magmatic rocks. Moreover, the decrease of MgO, CaO and
FeOt, together with a poor Al

increase, shows that a

general gabbroic fractionation (olivine, pyroxene and pla-
gioclase) from similar parental melts may have played a
role in the genesis of the single protolithes. The evident
positive correlation shown by Na

O, unlike the one shown

by K

O, is here interpreted as a consequence of the albiti-

zation processes that occurred during spilitization.

Trace elements

In the Log-Log diagrams (Fig. 4), LREE (for example

La) for comparable SiO

contents, point out two groups,

defined LL (low in LREE) and HL (high in LREE). Such
characteristics are not shown by High Field Strength Ele-
ments (HFSE) such as Zr, whose concentration in the pri-
mary parental melts of the LL and HL groups are
comparable. The different behaviour of LREE and some

Table 3: Major (wt. %) and trace (ppm) element contents of the Bovec volcanic clasts. Major elements recalculated to 100 % on a vola-
tile-free basis. PM – Primitive Mantle (La = 0.648 ppm and Nb = 0.658 ppm; McDonough & Sun 1995); La/Y

(PM)

– La/Y ratio of

samples normalized to the Primitive Mantle; HL and LL – samples with La/Y

(PM)

> and < 3, respectively; (a) – values recalculated on

/FeO ratio of 0.15; Q and C – normative Quartz and Corundum.

175

IGNEOUS ROCK CLASTS FROM THE MAASTRICHTIAN BOVEC FLYSCH (SLOVENIA)

present to indicate that a variable plagioclase fractionation
occurred.

The LL samples are characterized by a flat La to Y pat-

tern with a La/Y

(Primitive Mantle normalized; McDon-

ough & Sun 1995) ratio (La/Y

=1.5 to 2.8; Fig. 5A)

comparable with the E-MORB one (La/Y

=1.9; Sun &

McDonough 1989), to suggest a depleted component in the
mantle source. Moreover, a strong similarity with arc-type
basalts (i.e. Tonga – Gill 1976; Kamchatka – Kersting &
Arculus 1994) is strongly supported by the LILE pattern,
the comparable Nb anomaly (mean Nb/Nb*=0.10 vs. 0.11
and 0.06, respectively) and by the similar La/Y

ratio

Fig. 5. Incompatible element patterns of Bovec volcanic clasts normalized to Primitive
Mantle (PM; McDonough & Sun 1995). A – LL samples. E-MORB = Enriched Middle
Oceanic Ridge basalt (Sun & McDonough 1989); Kamchatka (Kersting & Arculus 1994);
Tonga (Gill 1976). Inset: grey field = LL samples; Bükk (Downes et al. 1990); Evros
(Magganas 2002). B – HL samples. Upper Crust (Rudnick & Gao 2004). Inset: Dolo-
mites (original data); Banat (Dupont et al. 2002); Vardar Zone (Pamić et al. 2001). Other
abbreviations as in Fig. 4.

(1.9 vs. 1.7 and 2.6). Conversely, the
HL group shows a higher La/Y

ratio

(La/Y

=3.14 to 8.37; Fig. 5B), and its

La-Y pattern approaches the Upper
Crust one (La/Y

=9.8; Rudnick &

Gao 2004).

To define possible provenance con-

straints, the studied igneous clasts
have also been compared with several
metabasites from the Vardar Zone
(Pamić et al. 2001), Rhodope (Evros;
Magganas 2002) and Bükk (Downes et
al. 1990) areas (see insets of Fig. 5A,B).
Furthermore, to evaluate whether a few
samples could belong to a calc-alkaline
suite, Triassic and Cretaceous calc-alka-
line samples from the Dolomites (un-
published data) and Pannonian Basin
(Banat; Dupont et al. 2002) have also
been considered for comparison.

It must be pointed out that only the

samples which best approach the
chemical features of the studied clasts
have been selected from each locality.

Among all the possible protoliths,

the LL tholeiites (inset of Fig. 5A)
show similarities with the less deplet-
ed samples from Evros and Bükk (La/
Y

= 1.1—2.0 and 1.2—1.3, respective-

ly), Ti contents excepted. On the con-
trary, the HL tholeiites well approach
the pattern of the Vardar Zone select-
ed magma (La/Y

= 6.21; inset of

Fig. 5B), and more generally, they
show a better affinity with all the pro-
posed samples with a calc-alkaline
signature. It should be noted that from
all the considered patterns, only the
Vardar Zone magma and Bovec volca-
nic clasts do not show a TiO

negative

anomaly (Ti/Ti* values higher than
one).

Rare Earth elements

Due to the scarcity of material, only

one sample per group (BV33 for LL

and BV17 for HL) has been analysed for REE contents
(Table 4); these are characterized by quite different La/
Yb

(chondrite normalized; Boynton 1984) ratios (1.8

and 3.1, respectively). The Eu/Eu* ratio approaches 1 for
both the samples showing a quite low evolution. In
Fig. 6A inset, the selected samples, particularly LL, show
both E-MORB-like (La/Yb

=1.8) and arc-type lavas

(Tonga; La/Yb

=2.0) signatures, while they strongly dif-

fer from the Upper Crust (La/Yb

=10.5). Notably

(Fig. 6A), the calc-alkaline magmas from Banat and Dolo-
mites, with an incompatible element pattern recalling
those of the HL samples, highlight an Upper Crust-like

176

DE MIN, ROSSET, TUNIS, KOCMANN, TOSONE and LENAZ

pattern (La/Sm

=3.9) given by high La/Sm

ratio (3.8

and 2.4), strongly different from the studied HL clasts
(1.1—1.5).

The volcanics from Evros (La/Yb

=1.6) and Vardar

Zone (La/Yb

=2.3; Fig. 6B), again show an affinity with

the LL and HL samples. Bükk lavas differ by showing a
flatter REE pattern, to indicate the presence of a very im-
portant N-MORB like component in their genesis
(Downes et al. 1990).

Fig. 7. La vs. La/Y diagram of Bovec volcanic clasts. The black
line represents a mixing curve. Abbreviations and source data as in
Figs. 4 and 5.

Fig. 8. Zr/Al

vs. TiO

/Al

tectonomagmatic diagram (Müller

et al. 1992). Abbreviations and source data as in Figs. 4 and 5.

Table 4: Rare Earth Element (REE) and Th contents (ppm) of the
Bovec volcanic clasts. CN – chondrite normalized (Boynton 1984).

Petrogenetic aspects

Multi-elemental and REE patterns emphasize that the

studied volcanics have an ocean-arc type affinity and
show the strongest similarities with less recrystallized me-
tabasites from the Vardar Zone and Rhodope areas. This
implies that the La/Y ratio of the clasts covers all the com-
positive range shown by the Jurassic arc-type magmatites.
This affinity could better appear in Fig. 7 (La/Y vs. La)
where all the studied clasts span from the more depleted
arc-tholeiites type (Evros and Bükk, which plot close to E-
MORB and the selected arc-type end-members) towards
the enriched ones (Vardar Zone selected sample), which
approximate an upper crustal composition for the La/Y ra-
tio. In the TiO

/Al

vs. Zr/Al

tectonomagmatic dia-

gram (Müller et al. 1992), all the clasts fall inside the
post-collisional and continental arc basalts, as well as
Tonga, Evros, Vardar and Bükk selected samples (Fig. 8).

Fig. 6. Rare Earth element patterns of Bovec volcanic clasts 33
and 17 (HL and LL group, respectively) normalized to chondrite
(CN; Boynton 1984). VZ = Vardar Zone. Other abbreviations and
source data as in Figs. 4 and 5.

177

IGNEOUS ROCK CLASTS FROM THE MAASTRICHTIAN BOVEC FLYSCH (SLOVENIA)

Fig. 9. 100*Th/Zr vs. 100*Nb/Zr tectonomagmatic diagram (mod-
ified after Beccaluva et al. 1991). UC = Upper Crust composition.
Other abbreviations and source data as in Figs. 4 and 5.

The Kamchatka sample, which plots at the border with the
oceanic arc basalts, is an exception. This suggests a fairly
high TiO

(and Zr) content in the source able to contrast

the oxide fractionation due to the high oxygen fugacity
which generally characterizes arc magmatism. Moreover,
in the most significative tectonomagmatic diagram of
Fig. 9 (modified after Beccaluva et al. 1991), the selected
clasts plot over the Tonga-Kermadec field, to suggest a
petrogenetic affinity with the recent arc-type tholeiites.
The higher Th/Zr ratios, shown by the depleted arc-type
magmas from Evros, Bükk and Vardar, are probably due to
Th mobilization during secondary metamorphic and/or
hydrothermal events.

Notably, the high La/Yb

and low Th/Zr ratios of HL

type clasts, not linked with the important La/Sm

in-

crease, which characterizes the considered calc-alkaline
magmas (Dolomites and Banat), suggest that the chemical
differences between LL and HL clasts could not be related
to contamination involving a mixing or an AFC process
between LL and an upper crustal component. In fact the
mixing line of Fig. 7, suggests that to increase the La/Y ra-
tio from LL to HL groups, the involvement of about
60 wt. % of an upper crustal component would be neces-
sary; a percentage not compatible with major elements
composition. Thus, La/Y and La/Yb, as well as Th/Zr ra-
tios seem to indicate different mantle sources character-
ized by different LREE and Th content for LL and HL
groups. Considering the recent Vardar Jurassic arc recon-
struction (Csontos & Vörös 2004) it is possible that the LL
volcanic clasts could be related to the inner parts of an arc,
while the HL ones could represent marginal products, situ-
ated closer to a continental plate.

Discussion

The Vardar Ocean was characterized from Early Jurassic

to Early Cretaceous by an arc system which evolved
through a movement toward the Bihor Getic—Austroalpine
junction (Fig. 9 inset; modified after Csontos & Vörös
2004). The relative movements between the Bihor-Getic
plate and Dinaric High Karst margin, led to Vardar Ocean
closure. Thus, most of the arc-magmatic products obduct-
ed and developed into the ophiolitic complexes, mostly
outcropping in the Internal Dinarides (mainly represented
by Vardar Zone), Rhodope and Bükk Mountains. From the
Aptian up to the end of the Maastrichtian, according to
Csontos & Vörös (2004), only a portion of such magma-
tism seems not affected by the compressive movements,
being trapped inside the core of a fold (current Vardar-
Mures nappe) developed inside the Bihor-Getic platform
(Fig. 10), which was probably deformed by the arc struc-
ture. Probably, during the Maastrichtian, such a structure
was located fairly near the Bovec area, which represented
a marginal portion of the Slovenian Basin inside the outer
margin of the Pindos Sea (Fig. 10).

The studied volcanic clasts are tholeiites with a strong

arc-type signature. Moreover, the studied clasts show a
chemical affinity with the tholeiites from the Internal Di-

Fig. 10. Mesozoic plate reconstruction of the Carpathian region
(modified after Csontos & Vörös A. 2004). BGB = Bihor-Getic
block; DHK = Dinaric High Karst margin; Rho = Rhodope Moun-
tains; Mo = Moesia; ALM = Aniso-Ladinian calc-alkaline magmatism.

178

DE MIN, ROSSET, TUNIS, KOCMANN, TOSONE and LENAZ

narides, as well as with all the Jurassic arc magmatism of
the Dinaridic-Carpathian region; however these tholeiites
cannot be considered as protoliths, having probably meta-
morphosed during obduction and being located someway
from the Bovec area, as is suggested by the homogeneous
grain size and shape shown by both the clast groups and
by their comparable grade of alteration which, indeed, in-
dicate a very close provenance. The protolithic rocks
probably belonged to the Vardar arc system, but the LL
and HL groups show chemical features not related to sim-
ple fractional crystallization, and imply significative dif-
ferences in the source composition of the protolithic
rocks. Notably, different magmatic sources have also been
proposed by Lenaz et al. (2000), through the chemistry of
the Julian Basin flysch detrital Cr-spinels. Moreover,
Lenaz et al. (2000, 2003) suggested that this spinel detri-
tus is related to the Vardar Ocean closure.

In the authors’ opinion an important role has been

played by the fold (probably arc-driven) located within
the Bihor-Getic plate, where different portions of unmeta-
morphosed magmatic arc-type lavas were approaching.

Acknowledgments:

The authors would like to thank Miss

Christine Smith for the revision of English text and Mr
Lorenzo Furlan for thin sections.

References

Aubouin J. 1963: Essai sur la paléogeographie post-triasique et

l’évolution secondaire et tertieire du versant sud des Alpes ori-
entales (Alpes méridionales; Lombardie et Vénétie, Italie;
Slovénie occidentale, Yougoslavie). Bull. Soc. Geol. France
71, 730—766.

Beccaluva L., Digirolamo P. & Serri G. 1991: Petrogenesis and tec-

tonic setting of the Roman Volcanic Province, Italy. Lithos 26,
191—221.

Bellieni G., Piccirillo E.M. & Zanettin B. 1981: Classification and no-

menclature of basalts. I.U.G.S. subcommissions on the systemat-
ics of igneous rocks. Circular 34, Contribution n. 86, 1—19.

Boynton W.V. 1984: Cosmochemistry of the rare Earth elements:

meteorite studies. In: Henderson P. (Ed.): Rare Earth element
geochemistry. Elsevier, Amsterdam, 63—114.

Brown G.M. & Vincent E.A. 1963: Pyroxenes from the late stages

of fractionation of the Skaergaard Intrusion, East Greenland.
J. Petrology 4, 175—197.

Buser S. 1986a: Geological map of SFRJ 1:100,000. Sheets Tolmin

and Videm (Udine). Geol. Zavod, Beograd, 1—103.

Buser S. 1986b: Geological map of SFRJ 1:100,000 Sheets Tolmin

and Videm (Udine). Explanatory text. Zvezni Geol. Zavod,
Beograd, 1—103.

Cousin M. 1970: Esquisse géologique des confins italo-yougo-

slaves: leur place dans les Dinarides et les Alpes méridionales.
Boll. Soc. Geol. France 7, XII, 6, 1034—1047.

Csontos L. & Vörös A. 2004: Mesozoic plate tectonic reconstruc-

tion of the Carpathian region. Palaeogeogr. Palaeoclimatol.
Palaeoecol. 210, 1—56.

De La Roche H., Leterrier P., Grandclaude P. & Marchal M. 1980:

A classification of volcanic and plutonic rocks using R1-R2 di-
agram and major-element analysis. Its relationships with cur-
rent nomenclature. Chem. Geol. 29, 183—210.

De Min A., Piccirillo E.M., Marzoli A., Bellini G., Renne P.R.,

Ernesto M. & Marques L.S. 2003: The Central Atlantic Mag-
matic Province (CAMP) in Brazil: Petrology, geochemistry,

Ar/

Ar ages, paleomagnetism and geodynamic implications.

In: Hames W.E., McHone J.G., Renne P.R. & Ruppel C.
(Eds.): The Central Atlantic Magmatic Province: Insights from
fragments of Pangea. AGU, Geophys. Monograph, 136.

Downes H., Pantó GY., Arcai P. & Thirlwall M.F. 1990: Petrology

and geochemistry of Mesozoic igneous rocks, Bükk moun-
tains, Hungary. Lithos 24, 201—215.

Dupont A., Vander Auwera J., Pin C., Marincea . & Berza T.

2002: Trace element and isotope (Sr, Nd) geochemistry of
porphyry- and skarn-mineralising Late Cretaceous intrusions
from Banat, western South Carpathians, Romania. Mineral.
Deposita 37, 568—586.

Gill J.B. 1976: Composition and age of Lau Basin and ridge volca-

nic rocks: implications for evolution of interarc basin and rem-
nant arc. Bull. Geol. Soc. Amer. 87, 1384—1395.

Govindaraju K. & Mevelle G. 1987: Fully automated dissolution

and separation methods for inductively coupled plasma atomic
emission spectrometry rock analysis: application to the deter-
mination of rare earth elements. J. Analytical Atomic Spec-
trometry 2, 615—621.

Kersting A.B. & Arculus R.J. 1994: Klyuchevskoy volcano, Kam-

chatka, Russia: the role of high-flux recharged, tapped and
fractionated magma chamber(s) in the genesis of high-Al

from high-MgO basalt. J. Petrology 35, 1—41.

Kretz R. 1982: Transfer and exchange equilibria in a portion of py-

roxene quadrilater as deduced from natural and experimental
data. Geochim. Cosmochim. Acta 46, 411—421.

Kudo A.M. & Weill D.F. 1970: An igneous plagioclase thermome-

ter. Contr. Mineral. Petrology 25, 52—65.

Kušcer D., Grad K., Nosan A. & Ogorelec B. 1974: Geology of

the Soca Valley between Bovec and Kobarid. Geologija 17,
425—476.

Le Bas M.J., Le Maitre R.W., Streckeisen A. & Zanettin B. 1986: A

chemical classification of volcanic rock based on the total al-
kali-silica diagram. J. Petrology 27, 745—750.

Lenaz D., Kamenetsky V.S., Crawford A.J. & Princivalle F. 2000:

Melt inclusions in detrital spinel from the SE Alps (Italy-Slov-
enia): a new approach to provenance studies of sedimentary
basin. Contr. Mineral. Petrology 139, 748—758.

Lenaz D., Kamenetsky V.S. & Princivalle F. 2003: Cr-spinel supply

in the Brkini, Istrian and Krk Island flysch basins (Slovenia, It-
aly and Croatia). Geol. Mag. 140, 335—342.

Magganas A.C. 2002: Constraints on the petrogenesis of Evros

ophiolite extrusives, NE Greece. Lithos 65, 165—182.

McDonough W.F. & Sun S. 1995: The composition of the Earth.

Chem. Geol. 120, 223—253.

Miyashiro A. 1974: Volcanic rock series in island arcs and active

continental margins. Amer. J. Sci. 274, 321—355.

Müller D., Rock N.M.S. & Groves D.I. 1992: Geochemical discrim-

ination between shoshonitic and potassic volcanic rocks in dif-
ferent tectonic settings: a pilot study. Miner. Petrology 46,
259—289.

Mutti E., Tinterri R., Benevelli G., di Biase D. & Cavanna G. 2003:

Deltaic, mixed and turbidite sedimentation of ancient foreland
basins. Mar. Petrol. Geol. 20, 733—755.

Ogorelec B., Šribar L. & Buser S. 1976: On lithology and bios-

tratigraphy of Volče limestone. Geologija 19, 126—151.

Pamić J., Tomljenović B. & Balen D. 2002: Geodynamics and

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

Papike J.J., Cameron K.L. & Baldwin K. 1974: Amphiboles and

pyroxenes. Characterisation of other than quadrilateral compo-
nents and estimates of ferric iron from microprobe data. Geol.
Soc. Amer. — Abstract with Program 6, 1053—1054.