composition and evolution of lithosphere beneath the
TRANSCRIPT
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Tectonophysics 393 (
Composition and evolution of lithosphere beneath the
Carpathian–Pannonian Region: a review
C. Szabo*, Gy. Falus, Z. Zajacz, I. Kovacs, E. Bali
Lithosphere Fluid Research Lab, Department of Petrology and Geochemistry, Eotvos University,
Pazmany Peter setany 1/C, Budapest H-1117, Hungary
Accepted 21 April 2004
Available online 28 September 2004
Abstract
Our knowledge of the lithosphere beneath the Carpathian–Pannonian Region (CPR) has been greatly improved through
petrologic, geochemical and isotopic studies of upper mantle xenoliths hosted by Neogene–Quaternary alkali basalts. These
basalts occur at the edge of the Intra-Carpathian Basin System (Styrian Basin, Nograd-Gfmfr and Eastern Transylvanian Basin)and its central portion (Little Hungarian Plain, Bakony-Balaton Highland).
The xenoliths are mostly spinel lherzolites, accompanied by subordinate pyroxenites, websterites, wehrlites, harzburgites
and dunites. The peridotites represent residual mantle material showing textural and geochemical evidence for a complex
history of melting and recrystallization, irrespective of location within the region. The lithospheric mantle is more deformed in
the center of the studied area than towards the edges. The deformation may be attributed to a combination of extension and
asthenospheric upwelling in the late Tertiary, which strongly affected the central part of CPR subcontinental lithosphere.
The peridotite xenoliths studied show bulk compositions in the following range: 35–48 wt.% MgO, 0.5–4.0 wt.% CaO and
0.2–4.5 wt.% Al2O3 with no significant differences in regard to their geographical location. On the other hand, mineral
compositions, particularly of clinopyroxene, vary according to xenolith texture. Clinopyroxenes from less deformed xenoliths
show higher contents of dbasalticT major elements compared to the more deformed xenoliths. However, clinopyroxenes in more
deformed xenoliths are relatively enriched in strongly incompatible trace elements such as light rare earth elements (LREE).
Modal metasomatic products occur as both hydrous phases, including pargasitic and kearsutitic amphiboles and minor
phlogopitic micas, and anhydrous phases — mostly clinopyroxene and orthopyroxene. Vein material is dominated by the two
latter phases but may also include amphibole. Amphibole mostly occurs as interstitial phases, however, and is more common
than phlogopite. Most metasomatized peridotites show chemical and (sometimes) textural evidence for re-equilibration between
metasomatic and non-metasomatic phases. However, amphiboles in pyroxenites are sometimes enriched in K, Fe and LREE.
The presence of partially crystallized melt pockets (related to amphiboles and clinopyroxenes) in both peridotites and
pyroxenites is an indication of decompression melting and, rarely, incipient partial melting triggered by migrating hydrous melts
or fluids. Metasomatic contaminants may be ascribed to contemporaneous subduction beneath the Carpathian–Pannonian
Region between the Eocene and Miocene.
0040-1951/$ - s
doi:10.1016/j.tec
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2004) 119–137
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ding author. Fax: +36 1 381 2108.
ess: [email protected] (C. Szabo).
C. Szabo et al. / Tectonophysics 393 (2004) 119–137120
Sulfide inclusions are more abundant in protogranular and porphyroclastic xenoliths relative to equigranular types. In mantle
lithologies, sulfide bleb compositions vary between pentlandite and pyrrhotite correlating with the chemistry and texture of the
host xenoliths. While sulfides in peridotites are relatively rich in Ni, those in clinopyroxene-rich xenoliths are notably Fe-rich.
D 2004 Elsevier B.V. All rights reserved.
Keywords: Carpathian–Pannonian Region; Upper mantle xenoliths; Lithosphere; Deformation; Sulfide inclusions; Melt pockets; Metasomatism
1. Introduction and geodynamic setting
The history of shallow subcontinental lithospheric
mantle, its geochemical mass balances and physical
state, can be constrained by studies of upper mantle
xenoliths commonly hosted in alkali basalts. The
spatial–temporal pattern of volcanic activity in the
Carpathian–Pannonian Region (CPR) (Fig. 1a) is
closely related to geodynamic evolution, particularly
the subduction of the European Plate beneath the
ALCAPA and Tisza–Dacia blocks, and the subsequent
extension and inversion events (Fodor et al., 1999;
Csontos et al., 2002). These effects were instrumental
in producing Early Miocene acidic calc-alkaline
ignimbrites and tuff deposits, Middle Miocene to
Recent calc-alkaline volcanic formations, and Late
Miocene to Recent alkali basalts (Szabo et al., 1992).
Knowledge of the lithosphere beneath the region has
been further improved by petrographic, geochemical
and isotope geochemical studies of upper mantle
xenoliths entrained in Neogene–Quaternary alkali
basalts (Embey-Isztin et al., 1989; Kurat et al.,
1991; Downes et al., 1992; Szabo and Taylor, 1994;
Szabo et al., 1995a; Vaselli et al., 1995, 1996;
Rosenbaum et al., 1997; Chalot-Prat and Boullier,
1997; Chalot-Prat and Arnold, 1999; Dobosi et al.,
1999; Falus et al., 2000; Embey-Isztin et al., 2001;
Bali et al., 2002) and bear fundamentally on geo-
dynamic evolution of the Intra-Carpathian Basin
System (Szabo et al., 1992; Embey-Isztin et al., 1993).
The Pannonian Basin (Fig. 1a) is a Mediterranean-
type back-arc system that opened in response to
lithospheric stretching behind the Carpathian arc
during two extensional episodes: (1) Early to Middle:
a Miocene passive rifting phase driven by subduction
rollback (Royden et al., 1983), and (2) a Late Miocene
syn- to post-rift phase accompanied by asthenospheric
upwelling and active thinning of the mantle litho-
sphere. The second of these dominated the evolution
of central parts of the basin (d=4–8), while both
western and eastern margins of the basin were subject
to compressional regimes (Fig. 1a,b) (Huismans et al.,
2001, additional references therein). The Neogene–
Quaternary alkali basalts, sampling the upper mantle
and lower crust, erupted in the central (Little
Hungarian Plain, Bakony-Balaton Highland), western
and northern marginal regions (Styrian Basin and
Nograd-Gfmfr, respectively) of the Pannonian Basin.
Similar alkali basalt also occurs at the Eastern
Transylvanian Basin within the CPR (Fig. 1a) and
yield a unique opportunity to give an insight into the
nature and evolution of the lithosphere by study of the
xenoliths and to constrain such mantle processes as
partial melting, deformation and mantle metasoma-
tism in the different portions of the region which
processes must have been related to the formation of
the Intra-Carpathian Basin System (we use the term
Intra-Carpathian Basin System in sense of Csontos
1995).
The purpose of this contribution is twofold: (1) to
summarize the most significant lithologic, textural and
geochemical knowledge of the subcontinental litho-
spheric mantle beneath the region, and (2) to show the
possible relation between the formation and evolution
of the Intra-Carpathian Basin System and the system-
atic geochemical and textural variability observed in
the xenoliths using previous studies, but also incor-
porating results of our current researches, i.e.,
deformation analysis and detailed study of melt
pockets and sulfide blebs of the upper mantle
xenoliths.
2. Mantle petrology and deformation
Based on studies of upper mantle xenoliths hosted
in the Neogene–Quaternary alkali basalts from the
CPR (e.g., Embey-Isztin et al., 1989; Kurat et al.,
1991; Downes et al., 1992; Szabo and Taylor, 1994;
Szabo et al., 1995a; Vaselli et al., 1995, 1996; Chalot-
Fig. 1. (a) Lithospheric thickness of the Carpathian–Pannonian Region after Lenkey (1999). Calk-alkaline volcanic fields and major upper
mantle xenolith localities in the Plio-Pleistocene alkali basaltic occurrences are also indicated: SBVF—Styrian Basin Volcanic Field; LHPV—
Little Hungarian Plain Volcanic Field; BBHVF—Bakony-Balaton Highland Volcanic Field; NGVF—Nograd-Gfmfr Volcanic Field; ETBVF—Eastern Transylvanian Basin Volcanic Field. (b) Schematic W–E cross section of the area studied through alkali basaltic occurrences of SBVF,
BBHVF and ETBVF (Szabo et al, 1995b).
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 121
C. Szabo et al. / Tectonophysics 393 (2004) 119–137122
Prat and Boulier, 1997; Bali et al., 2002), the
lithospheric mantle lithologically is relatively hetero-
geneous because spinel lherzolites, harzburgites and
dunite are all present and there is a peculiar abundance
of wehrlites, websterites, clinopyroxenites (Fig. 2).
Breakdown products of garnet-bearing mantle frag-
ments have been found in pyroxenite xenoliths
(Torok, 1995) and some peridotite xenoliths, too
(Falus et al., 2000). The orthopyroxene/clinopyroxene
ratio of the CPR mantle xenoliths shows a great
variability (between 0 and 32) compared to the
subcontinental lithospheric mantle rocks around the
world, which generally exhibit values around 2 or
slightly higher (Downes et al., 1992) (Fig. 2). The
very high ratios can be observed not only in pyroxene-
rich rock types (i.e., websterites) but also in clinopyr-
oxene-rich lherzolites and clinopyroxene-bearing dun-
ites particularly in the Styrian Basin (e.g., Bali et al.,
submitted for publication).
The peridotite (basically spinel lherzolite) xeno-
liths, representing residual material of the mantle with
complex history, show variable textural features
strongly related to the locations within the CPR. The
xenoliths from the eastern and western portions of the
CPR are characterized by the dominance of proto-
Fig. 2. Xenoliths from all major alkali basaltic localities (LHPVF, BBHV
(Streckeisen, 1976). Data source for SBVF: Kurat et al. (1991) and Vase
Embey-Isztin et al. (1989), Downes et al. (1992) and Szabo et al. (1995a); f
NGVF: Szabo and Taylor (1994) and Kovacs et al. (this volume); for E
European subcontinental lithospheric mantle (SCLM) (Downes, 1997) is
granular and protogranular to porphyroclastic textures
(after Mercier and Nicolas, 1975), whereas in the
central part of the region more deformed and
recrystallized xenoliths (equigranular and secondary
recrystallized or poikilitic as Embey-Isztin et al., 1989
called the latter one) are also present in considerable
abundance (e.g., Kurat et al., 1991; Embey-Isztin et
al., 1989; Szabo et al., 1995b). The Nograd-GfmfrVolcanic Field (NGVF) located at the northern edge of
the Pannonian Basin, however, represents a wide
variety of upper mantle xenolith textures ranging from
the less protogranular and protogranular to porphyro-
clastic textural types at the northern part of the
volcanic field to porphyroclastic, equigranular and
secondary recrystallized textures towards the southern
part of the xenolith occurrences (Szabo and Taylor,
1994).
Significant correlation was found between textural
types and equilibrium temperatures, estimated from
the major element content, of the CPR xenoliths
(Szabo et al., 1995b). Mantle xenoliths with proto-
granular textures always show the highest equilibrium
temperatures (1150–1050 8C), except for the ETBVF
suite which displays slightly lower temperatures
(1050–1000 8C). Whereas porphyroclastic, equigra-
F, SBVF, NGVF, ETBVF) of the CPR in the Streckeisen diagram
lli et al. (1995); Bali et al. (submitted for publication); for LHPVF:
or BBHVF: Embey-Isztin et al. (1989) and Downes et al. (1992); for
TBVF: Vaselli et al. (1995). For comparison, composition field of
also shown.
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 123
nular and secondary recrystallized samples (if present)
show lower equilibrium temperatures (ranging from
1080 in porphyroclastic to 850 8C in some poikilitic
samples; Szabo et al., 1995b; Embey-Isztin et al.,
2001).
Xenoliths from all the five Neogene–Quaternary
major volcanic fields (i.e., xenolith localities) were
selected for careful textural and deformation analysis
in order to describe the behavior of the lithospheric
mantle beneath the region during the formation of
the whole Intra-Carpathian Basin System (Falus et
al, 2000; Falus and Szabo, 2002). Textural patterns
recognized in the xenoliths from SBVF display
minor to moderate deformation and recrystallization
Fig. 3. Photomicrographs of upper mantle xenoliths from the CPR sho
displaying mylonitic deformation. Shearing parallel to horizontal axis o
Pyroxene-spinel clusters as breakdown products of garnet olivine reaction.
Peridotite from BBHVF. Moderate elongation subparallel to horizontal axis
to strong preferred orientation—[100](010) slip. Horizontal lines on ste
elongation of grains from bottom left to top right of the image. Cross-
[100](010) slip. Horizontal line on stereograms indicates lineation. Abbrevi
spinel; mp—melt pocket; mx—matrix.
producing dominantly protogranular, porphyroclastic
textures also recognized earlier (Kurat et al., 1991;
Vaselli et al., 1995). The often-observed tilt walls in
olivine and orthopyroxene porphyroclasts clearly
indicate that the deformation occurred in the
dislocation creep regime (Falus, 2004). Some inten-
sively deformed xenoliths are clearly observed from
the ETBVF (Vaselli et al., 1996). Moreover, some of
the xenoliths display strong mylonitic deformation
(Fig. 3a), which is a unique feature in the CPR
(Falus, 2004). Similar textural feature has been quite
rarely observed in xenoliths derived from the mantle
worldwide (e.g., Pike and Schwartzmann, 1977).
Nevertheless, the extent of deformation in the eastern
wing characteristic textural features. (a) Peridotite from ETBVF
f the image. Cross-polarized light. (b) Peridotite from the SBVF.
Plain-polarized light. Dashed line showing outline of the cluster. (c)
of the image. Cross-polarized light. LPO pattern showing moderate
reograms indicate lineation. (d) Peridotite from BBHVF. Uniform
polarized light. LPO pattern shows strong preferred orientation—
ations: ol—olivine; opx—orthopyroxene; cpx—clinopyroxene; sp—
C. Szabo et al. / Tectonophysics 393 (2004) 119–137124
and western margins of the basin system was low
enough to preserve the products of garnet breakdown
due to decompression (Fig. 3b) in both regions
(Falus et al., 2000). These textures were formed in
the dislocation creep regime indicated by the
moderate to strong lattice preferred orientation
(LPO) (Falus and Szabo, 2002). We suggest that
the same type of deformation took place in the upper
mantle beneath the central part of the Pannonian
Basin as indicated by porphyroclastic to equigranular
xenoliths from the LHPVF and BBHVF (Embey-
Isztin et al, 1989; Downes et al., 1992; Szabo et al.,
1995a) displaying moderate (Fig. 3c) to strong LPO
(Fig. 3d). This deformation, however, was partly
overprinted due to annealing and static recrystalliza-
tion (Falus, 2004). The marginal lithospheric sections
could have avoided recrystallization due to their
marginal position, thicker lithosphere (Fig. 1a,b) and
the cooling effect of the suspected subducted slab in
the North and East (Bielik et al., 1991; Tomek and
Hall, 1993).
The high abundance of statically recrystallized
equigranular and secondary recrystallized xenoliths
in the BBHVF, and some of the LHPVF and South
NGVF, recognized also earlier (Embey-Isztin et al.,
1989; 2001; Downes et al., 1992; Szabo and Taylor,
1994; Szabo et al., 1995a), clearly indicates a
strong deformation and subsequent annealing proc-
ess in the upper mantle beneath the central part of
the CPR. This latter thermally activated process
(Lloyd et al., 1997) clearly suggests the anoma-
lously high position of the asthenosphere (Fig. 1a,b)
shown also by geophysical studies (e.g., Horvath,
1993) and geophysical modeling (Royden et al.,
1983, Lankreijer et al., 1995; Huismans et al.,
2001).
Rare orthopyroxene porphyroclasts in equigranular
xenoliths display lobated grain boundaries. These
porphyroclasts display remarkable zonation in Al- and
Na-contents decreasing towards the rims, whereas Ca
displays considerable increase towards the rims.
Similar orthopyroxene porphyroclasts were described
from the Oman ophiolite (Dijkstra et al., 2002). This
feature is suggested to represent reaction of these
orthopyroxenes with migrating fluids, suggesting that
annealing and recrystallization were not in every case
an isochemical process, but also involved migrating
fluids/melts.
3. Major, trace element and radiogenic isotope
geochemistry of peridotite assemblages
The peridotite xenoliths from the alkali basalts of
the CPR have a bulk compositions ranging from 35 to
48 wt.% MgO, 0.5 to 4.0 wt.% CaO, 0.2 to 4.5 wt.%
Al2O3, and 0.01 to 0.24 wt.% TiO2. There are no
significant chemical differences of xenoliths among
the major localities although, the compositional range
of the NGVF covers the highest MgO-bearing
xenoliths, whereas ranges of the SBVF and ETBVF
xenoliths involve samples containing the lowest MgO
content. Xenoliths from the BBHVF and LHPVF
show a transitional character (Fig. 4). Concentration
of basaltic elements, representing Al2O3 and TiO2,
and of CaO displays a negative correlation with MgO
(Fig. 4) as Downes and Vaselli (1995) have already
noted. These chemical features of the CPR xenoliths
are in agreement with xenoliths from other localities
(e.g., Rhenish Massive, Massif Central) and with
alpine massive peridotites (e.g., Lherz) (Bodinier et
al., 1988; Downes et al., 1991; Wilson and Downes,
1991). It is suggested that gradual depletion in basaltic
elements is connected at first consideration to partial
melting event(s).
Nevertheless, mineral composition in the CPR
xenoliths, particularly clinopyroxene, varies accord-
ing to the xenolith textures as pointed out by
Downes (1990) and Szabo et al. (1995b). Less
deformed xenoliths have clinopyroxene with high
amount of basaltic major elements (Al, Ti, Na and
Fe) compared to more deformed samples. However,
clinopyroxenes in the more deformed and more
intensively recrystallized xenoliths show higher
content of strongly incompatible trace elements such
as light rare earth elements than the undeformed
ones. This feature can rather be explained by the
influence of an incompatible element-rich fluid phase
impregnated the preexisting deformed peridotitic
assemblage, which provided a more permeable
pathway for the migrating fluids than the unde-
formed peridotite (Downes, 1990) and resulted only
in cryptic metasomatism and contemporaneous
annealing. However, depletion in basaltic major
elements may also be related to fluid/melt migration
and reaction with the peridotitic wall-rock as Kele-
men et al. (1992) pointed out. This would also
explain the observed decoupling between major and
Fig. 4. Harker diagrams of bulk compositions of CPR xenoliths for TiO2, Al2O3, CaO vs. MgO. Data source for SBVF: Kurat et al. (1991),
Vaselli et al. (1995) and Bali et al. (submitted for publication); for LHPVF: Embey-Isztin et al. (1989), Downes et al. (1992) and Szabo et al.
(1995a); for BBHVF: Embey-Isztin et al. (1989) and Downes et al. (1992); for NGVF: Szabo and Taylor (1994); for ETBVF: Vaselli et al.
(1995). For comparison, the field of the European subcontinental lithosphere mantle (Downes, 2001) is also shown.
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 125
trace elements world wide (Frey and Green, 1974;
Wilshire and Shervais, 1975).
The Sr and Nd isotopic compositions of separated
clinopyroxenes of the CPR peridotite xenoliths are
shown in Fig. 5. The 87Sr/86Sr and 143Nd/144Nd
values range from 0.7016 to 0.7048 and 0.5126 to
0.5136, respectively, and show negative correlations.
The highest 143Nd/144Nd and lowest 87Sr/86Sr values
can usually be observed in the SBVF and ETBVF
xenoliths (Vaselli et al., 1995; 1996; Bali et al.,
submitted for publication). Whereas, the clinopyrox-
enes from xenoliths of the central part of the
Pannonian Basin (BBHVF and LHPVF) and Nog-
rad-Gfmfr (northern Pannonian Basin) have low143Nd/144Nd and high 87Sr/86Sr values (Downes et
al., 1992; Szabo and Vaselli, unpublished). It is also
clear that the radiogenic isotopic behavior of the
BBHVF xenoliths show strong correlation with
textural types; the less deformed xenoliths display
the most depleted isotopic character, whereas the
deformed samples have the strongest enrichment in
radiogenic Sr. The enrichment of radiogenic isotopes
in the central segment of the CPR could be related to
reaction of peridotites with percolating melts/fluids
(Downes et al., 1992; Downes and Vaselli, 1995)
causing cryptic metasomatism, mentioned above.
The origin of these melts/fluids can be related by
either asthenospheric melts similar to the host basalt
or to subduction related calc-alkaline melts in case of
those samples displaying strongly radiogenic
Fig. 5. The Sr and Nd isotopic compositions of separated clinopyroxenes of the CPR xenoliths. Data source for SBVF: Vaselli et al. (1995) and
Bali et al. (submitted for publication); for LHPVF: Downes et al. (1992); BBHVF: Downes et al. (1992); for NGVF: Szabo and Vaselli
(unpublished); for ETBVF: Vaselli et al. (1995). For comparison, the isotopic compositions of the host basalts (Embey-Isztin et al., 1993),
MORB and bulk earth (Zindler and Hart, 1986) are also shown.
C. Szabo et al. / Tectonophysics 393 (2004) 119–137126
87Sr/86Sr ratios (Downes et al., 1992; Rosenbaum et
al, 1997).
4. The modification of dry peridotitic material by
modal metasomatism
Besides the dry olivine-rich peridotitic assemblage,
xenoliths showing enrichment in both anhydrous
phases (as clino- and orthopyroxenes) and/or hydrous
minerals (such as amphiboles and phlogopites) are
also present. Such clinopyroxenite and composite
(clinopyroxenite/peridotite) xenoliths occur in all
localities. Although most of the pyroxenite xenoliths
from the CPR have igneous textures and do not reflect
deformation (Embey-Isztin et al., 1990; Kovacs et al.,
this volume), some of the rocks derived from the
ETBVF do display textural evidence for stress-
induced recrystallization. Undulatory extinction and
subgrain development are frequently identified fea-
tures (Szasz, unpublished).
Chemical composition of clinopyroxene-rich xen-
oliths generally shows enrichment in basaltic and light
rare earth elements. These rock fragments are the
products of asthenosphere-derived mafic melts crys-
tallized as pyroxenite cumulates either in the litho-
spheric mantle or lower crust (e.g., Dobosi et al.,
2003; Kovacs et al., this volume) similar to those
studied in the East Eifel (Sachs and Hansteen, 2000)
and Penghu Islands xenoliths (Ho et al., 2000). In
several peridotite xenoliths from the BBHVF not only
clinopyroxenite but websterite veins can also be
observed, which are interpreted as reaction products
of mafic melts and wall-rock peridotites. This mafic
melt could be similar to those that produced the
clinopyroxene salvages (Bali et al., submitted for
publication).
In contrast with the clinopyroxene-rich bands, the
orthopyroxene-enriched rocks (i.e., orthopyroxene-
rich websterites and orthopyroxenites), occurring
rarely in the BBHVF (Bali, 2004; submitted for
publication) and LHPVF (Szabo et al., 1995a,b), were
produced by the infiltration of Si-rich silicate melt or
fluid. This melt/fluid transported high amount of
incompatible trace elements and reacted with the
strongly depleted peridotitic assemblage suggested by
the U-shaped chondrite normalized REE-patterns of
the clinopyroxenes (Bali, 2004; Bali et al., submitted
for publication). Based on the Sr–Pb-isotopic compo-
sition of the separated clinopyroxenes of these
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 127
orthopyroxene-rich rocks, the reagent Si-rich melt/
fluid might have been released from subducted slab.
Hydrous phases as pargasitic and kearsutitic
amphiboles and phlogopitic micas also occur as
modal metasomatic minerals in both peridotite and
pyroxenite xenoliths from the CPR. Amphiboles,
occurring as interstitial phases, veins and selvages,
are more common than phlogopites. In spite of the
significant textural variation of amphiboles, they
display moderate variation in major element compo-
sition. The majority of amphiboles from the NGVF,
LHPVF, SBVF and ETBVF peridotites are pargasites,
whereas BBHVF amphiboles show wide composi-
tional range (Fig. 6). Amphiboles in clinopyroxene-
rich xenoliths and amphibole megacrysts were also
plotted and it is clearly revealed that amphibole
megacrysts display both higher Fe3+/[Fe3++Al(VI)]
ratio and Ti-content than amphiboles in pyroxene-rich
xenoliths and veins (Fig. 6). The occurrence of
Fig. 6. Fe3+/[Fe3++Al(VI)] vs. Ti for amphiboles in upper mantle xenolith
source for SBVF: Vaselli et al. (1996) and Bali et al. (submitted for public
(1976), Bali et al. (2002), Dobosi et al. (2003) and Bali (2004); for NG
ETBVF: Zanetti et al. (1995) and Vaselli et al. (1995). The fields of pargasit
of Fe3+ were calculated using equation of Droop (1987). Amphiboles defin
clinopyroxene-rich xenoliths and megacrysts).
amphiboles in the SBVF and ETBVF shows weak
preference to textural types, presumably because of
the low variability of textures in these regions.
Nevertheless, amphiboles in the xenoliths from the
central part of the basin show strong preference to the
most deformed and recrystallized rocks. They are
absent from protogranular xenoliths. Presence or
absence of amphiboles is independent from both
texture and chemistry of clinopyroxenite xenoliths in
the NGVF (Kovacs et al., this volume) and in the
BBHVF (Bali, 2004).
Considering the trace elements in amphiboles,
large differences can be observed in all localities. At
the SBVF mostly interstitial amphiboles have been
found in peridotite xenoliths, which show the widest
compositions, ranging from LREE-depleted to LREE-
enriched primitive mantle normalized patterns. In the
case of the ETBVF, interstitial amphiboles from
peridotite xenoliths also display a wide compositional
s and also for amphibole veins and megacrysts from the CPR. Data
ation); for LHPVF: Szabo et al. (1995a); for BBHVF: Embey-Isztin
VF: Szabo and Taylor (1994) and Kovacs et al. (this volume); for
e, Mg-hastingsite and kaersutite are taken after Leake (1978). Values
e well-expelled fields according to their occurrence (i.e., peridotite,
Fig. 7. Primitive mantle normalized (Sun and McDonough, 1989) rare earth element patterns of amphiboles in xenoliths from the CPR.
Amphiboles in peridotite xenoliths display wider compositional range and relatively lower abundance of either light or heavy rare earth elements
compared to amphiboles in veins and clinopyroxene-rich xenoliths (data from Kurat et al., 1991; Szabo and Taylor 1994; Szabo et al., 1995a,b;
Zanetti et al., 1995; Vaselli et al. 1995, 1996; Dobosi et al., 2003; Kovacs et al., this volume; Bali, 2004).
C. Szabo et al. / Tectonophysics 393 (2004) 119–137128
range with the lowest REE-contents, whereas amphi-
boles from amphibole-rich veins have the most
enriched compositions in LREEs and amphiboles
from relatively common clinopyroxenite xenoliths
show a moderately enriched REE pattern. Interstitial
amphiboles are frequent phases in the NGVF peri-
dotite xenoliths. They show a relatively wide compo-
sitional range with a slight depletion in LREEs,
whereas amphiboles, occurring often in clinopyro-
xenite xenoliths, show the same REE pattern as those
Fig. 8. Amphibole/clinopyroxene partition coefficients using composition o
and Bali et al. (submitted for publication); for LHPVF: Szabo et al. (1995
ones which are the most REE-enriched in the NGVF
peridotite xenoliths. Amphiboles from the central part
of the Pannonian Basin (BBHVF, LHPVF), occurring
as very rare interstitial phases in peridotites xenoliths,
have a flat REE-pattern. Amphiboles in the clinopy-
roxene-rich veins also show flat or n-shape REE
distribution (Fig. 7). Based on major- and trace-
element characteristics of these amphiboles, occurring
either as interstitial phase in peridotites or as
constituent in veins or clinopyroxenite xenoliths, the
f the coexisting minerals. Data source for SBVF: Vaselli et al. (1996)
a); for ETBVF: Vaselli et al. (1995).
Fig. 9. Photomicrographs of silicate melt pockets in upper mantle
xenoliths from the CPR. The photos were taken under plane
polarized light. (a) Melt pocket, occurring interstitial to olivine (ol
and orthopyroxene (opx), containing resorbed pargasitic amphibole
(amp), glass (gl) and newly formed clinopyroxene and spinel in
protogranular BBHVF peridotite. (b) Melt pocket (mp) occurring
interstitial to olivine (ol) and orthopyroxene (opx) close to the hos
basalt in secondary recrystallized NGVF dunite. Melt pocke
consists of newly formed fine-grained clinopyroxene, spinel and
plagioclase.
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 129
metasomatic agents that produced them could have
been volatile-bearing silicate melt which originated
from either subducted slab or asthenospheric mantle
(Szabo and Taylor, 1994; Kovacs et al., this volume).
However, in several cases, textural equilibrium
cannot be assumed as the amphiboles consume the
surrounding mantle phases; the majority of the
hydrous phases are chemically in equilibrium with
the anhydrous mantle minerals in the peridotites as
suggested by the calculated partition coefficients (e.g.,
Embey-Isztin, 1976; Szabo and Taylor, 1994; Szabo et
al., 1995a; Vaselli et al., 1995; 1996; Bali et al., 2002;
Bali et al., submitted for publication, Kovacs et al.,
this volume). Only three xenoliths in the suites
studied, occurring as clinopyroxene-rich veins from
ETBVF and SBVF (Vaselli et al., 1995; 1996; Bali et
al., submitted for publication), show disequilibrium
(Fig. 8). This means that either they could not reach
the chemical equilibrium with the depleted clinopyr-
oxene from the peridotitic wall-rock or they formed
further from the vein conduit, which transferred
metasomatic agents as Tiepolo et al. (2001) and Ionov
et al. (2002) concluded studying peridotite xenoliths
and clinopyroxene veins in them from Spitsbergen.
Melt pockets in peridotite xenoliths are often
related to melting and breakdown of metasomatic
amphiboles. These amphiboles often went through
mantle processes as they became dsource materialsTfor the subsequent silicate melt pocket formation,
which were reported in several xenolith locations in
the central part of the CPR (Szabo et al., 1995a, 1996;
Embey-Isztin and Scharbert, 2000; Demeny et al.,
2000; Bali et al., 2002), although Schiano and
Bourdon (1999) summarized that the interstitial
silicate melt pockets can be considered as open
systems and their phases preserve only the last
equilibrium state. Consequently, study of the melt
pockets provides direct insight into the melting and
crystallization processes, as well as mechanism of
mixing and migration of melts in the mantle. This
way, we can obtain more information on the spatial
particularities in thermal evolution of the subcon-
tinental lithospheric mantle of the Pannonian Basin
system.
In the LHPVF, BBHVF and NGVF melt pockets
can be considered to be common although minor
constituents of mantle xenoliths containing assemb-
lages of glass, Fclinopyroxene, Folivine, Fspinel,
Fplagioclase phenocrysts, and Fcarbonate, Fsulfide,
Fapatite. Their size corresponds to those of the
mantle minerals (Fig. 9a,b). They occur solely in
deformed and recrystallized xenoliths. Detailed
microprobe and trace element studies revealed that
the melting of mantle amphibole (and coexisting
clinopyroxene) played a significant role in the
formation of the melt pockets even in those cases
when the amphibole was completely missing in the
assemblage of the studied xenoliths (Fig. 10).
-
)
t
t
Fig. 10. Al2O3, CaO, FeOt, MgO, Na2O vs. MgO variation diagrams of bulk compositions of melt pockets from the BBHVF and NGVF
xenoliths. Data source for BBHVF: Bali et al. (2002); for NGVF: Szabo et al. (1996). For comparison, composition of average BBHVF
pargasitic amphibole (Bali et al., 2002), NGVF mantle clinopyroxene (Szabo and Taylor, 1994), BBHVF alkali basalt (Embey-Isztin et al.,
1993), NGVF alkali basalt (Szabo, unpublished) and NGVF andesite (Szabo, unpublished) is also shown.
C. Szabo et al. / Tectonophysics 393 (2004) 119–137130
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 131
Furthermore, in case of few xenoliths from both the
BBHVF and NGVF, external melts/fluids should be
also assumed as the bulk composition of the melt
pockets strongly differ from the mantle minerals
(Szabo et al., 1996, Bali et al., 2002). The trace
element composition of the BBHVF melt pockets
further shows strong enrichment in highly incompat-
ible elements displaying similar primitive mantle
normalized patterns to the calc-alkaline andesites of
the CPR. This suggests that the external melt/fluid
phase incorporated into the composition of those melt
pockets was released from subducted oceanic slab
(Bali et al., 2003).
5. Significance of sulfide inclusions and chalcophile
elements in mantle processes
Recent studies showed that knowledge of distribu-
tion of chalcophile [Cu and platinum group elements
(PGEs)] provides important contribution to the under-
standing of mantle process such as partial melting
(Frey et al., 1985; Peach et al., 1990; Fleet et al.,
1996; Gueddari et al., 1996; Gaetani and Grove, 1997;
Handler and Bennet, 1999; Rehkamper et al., 1999;
Ripley et al., 2002). Distribution of these elements is
basically controlled by sulfide inclusions in the
lithospheric mantle during partial melting (Fleet et
al., 1996; Handler and Bennet, 1999; Alard et al.,
2000; Burton et al., 2000; Lorand and Alard, 2001).
Consequently, a synthesis of petrographical and
geochemical results of sulfide blebs in the CPR
xenoliths reported by Szabo and Bodnar (1995); Falus
(2000); Zajacz and Szabo (2003) and Torok et al.
(2003) provides a profound insight into the evolution of
the mantle beneath the area studied. Four different
types of sulfide inclusions can be distinguished in the
CPR peridotite xenoliths: (1) Single, isolated, spherical
primary inclusions, which are enclosed in orthopyrox-
ene, clinopyroxene and rarely olivine (Fig. 11b,c,d).
Their grain size ranges between 10 and 120 Am. The
majority of the studied sulfide inclusions in the CPR
peridotites belong to this group. (2) Interstitial polyg-
onal sulfide grains to the mantle silicates with curvi-
linear or linear boundaries, which indicate textural
equilibrium with their environments (Fig. 11a). The
size of these sulfide grains ranges from 50 to 220 Am.
Interstitial sulfide grains can be found dominantly in
protogranular and protogranular to porphyroclastic
xenoliths in the CPR. (3) Large (up to 300 Am)
isometric primary sulfide blebs or elongated sulfide
pods intergrown with hydrous minerals such as
amphibole or rarely phlogopite that were found in
modally metasomatized SBVF and NGVF xenoliths.
(4) Tiny (b15 Am) spherical or negative crystal-shaped
sulfide blebs, occurring along healed fractures in
primary mantle minerals as secondary inclusions.
Deformation and recrystallization of the mantle
rocks play important role in the sulfide abundance in
mantle peridotites. A clear relation between the degree
of deformation and sulfide abundance has been found
in the NGVF xenoliths (Szabo and Bodnar, 1995),
where protogranular to porphyroclastic peridotites
contain the highest modes of sulfides (~0.5 vol.%)
and the recrystallized equigranular samples have the
lowest sulfide contents (~0.02 vol.%). This relation is
less evident in the xenoliths from BBHVF because
only strongly deformed peridotites (characteristic for
this region as described above) were studied (b0.05
vol.%). Furthermore, xenoliths, derived from the
Styrian and Eastern Transylvanian Basins all have
protogranular and protogranular to porphyroclastic
textures and are characterized by very low sulfide
content (b0.01 vol.%) (Falus, 2000).
The enclosed and interstitial sulfide grains (Fig.
11a–d) interpreted as primary inclusions consist of Ni-
poor monosulfide solid solution (mss), and pentlan-
dite or Ni-rich mss, and a Cu-bearing phase:
chalcopyrite or intermediate solid solution (iss). Bulk
composition of primary sulfide inclusions (Fig. 12)
shows a wide range of Ni+Co content between 12 and
32 wt.%, and Cu content between 0.1 and 7.9 wt.%;
however, some sulfide blebs from ETBVF have
extremely high Cu-content up to 14.7 wt.%.
The bulk Cu content of sulfide blebs shows
negative correlation with the degree of depletion of
the host xenolith represented by the mg# of clinopyr-
oxenes (Fig. 13). We believe that behavior of copper
during melting in the mantle is controlled by sulfide
inclusions. This behavior could be a straight conse-
quence of its high partition coefficient for sulfide/
silicate melt (ranging from order of 102 to 103)
depending on the sulfur fugacity (Frey et al., 1985;
Peach et al., 1990; Gueddari et al., 1996; Ripley et al.,
2002) and the high incompatibility of Cu in rock
forming silicate and oxide phases. The texture of
Fig. 11. Photomicrographs of different textural types of sulfide inclusions. The photos were taken under reflected light: (a) two-phase sulfide
inclusion composed of pentlandite (pn) and chalcopyrite in olivine of protogranular to porphyroclastic spinel lherzolite from the NGVF; (b)
sulfide inclusion composed of chalcopyrite, monosulfide solid solution (mss), and pentlandite enclosed in olivine of protogranular to
porphyrocalstic spinel lherzolite from the NGVF; (c) enclosed sulfide inclusion composed of chalcopyrite and pentlandite in clinopyroxene of
porphyroclastic spinel lherzolite xenolith from the SBVF; (d) enclosed multiphase sulfide inclusion in spinel of porphyroclastic spinel lherzolite
from the ETBVF. Pentlandite occurs as exsolved lamellae in the monosulfide solid solution. Chalcopyrite occurs at the outer edges of the
inclusion.
C. Szabo et al. / Tectonophysics 393 (2004) 119–137132
xenoliths studied also correlate with the Cu content of
the sulfide inclusions showing a profound Cu
depletion in the more deformed samples (Fig. 13).
The negative correlation between the bulk Cu content
of sulfide inclusions and mg# of coexisting clinopyr-
oxenes is a clear evidence for the incompatible
behavior of copper in the subcontinetal lithospheric
mantle. Based on experimental works (Fleet and Pan,
1994; Li et al., 1996), partial melting of sulfide
produces liquid phase enriched in Cu and solid mss
phase depleted in copper. This leads us to suggest that
partial melting of sulfide inclusions and mobilization
of the low viscosity sulfide melt fraction (Gaetani and
Grove, 1999) could occur during deformation and
partial melting processes. This supposition is also
confirmed by the systematic difference in sulfide
abundance of different textural types of xenoliths
showing lower sulfide content in the more deformed
samples. This also suggests that higher degree of
deformation in the lithospheric mantle corresponds to
stronger depletion (or higher degree of partial melting)
in the studied mantle segment as we discussed above
relying on previous studies (Downes, 1990; Downes
and Vaselli, 1995; Szabo et al., 1995b).
Ni is also a sensitive element during partial melting
of sulfides and may be enriched in the sulfide melt,
but it was taken out of consideration because of the Ni
equilibrium distribution between olivine and sulfide
Fig. 12. Bulk chemical composition of sulfide blebs from different locations of the CPR upper mantle xenoliths plotted in the Cu–Fe–(Ni–Co)–S
system (Kullerud et al., 1969). Data source for SBVF, BBHVF and ETBVF: Falus (2000); for LHPVF: Szabo (unpublished); for NGVF: Szabo
and Bodnar (1995). For comparison, clinopyroxene-rich NGVF xenoliths are also shown (Zajacz and Szabo, 2003).
Fig. 13. Mg# of clinopyroxenes vs. bulk Cu content of sulfide
inclusions enclosed in silicate phases of different textural types of
upper mantle xenoliths of the CPR. Data source for SBVF: Vaselli et
al. (1996), Bali et al. (submitted for publication); for LHPVF: Szabo
et al. (1995a), Falus (2000) and Szabo (unpublished); for BBHVF:
Falus (2000) and Bali et al. (2002); for NGVF: Szabo and Taylor
(1994), and Szabo and Bodnar (1995); for ETBVF: Vaselli et al.
(1995) and Falus (2000).
C. Szabo et al. / Tectonophysics 393 (2004) 119–137 133
which is able to modify the Ni content of sulfide
inclusions (Fleet and MacRae, 1988; Fleet and Stone,
1990).
6. Concluding remarks
Previous studies of the CPR have established that
the Intra-Carpathian Basin System evolved in two
stages during the Miocene, involving: passive rifting
as a response to subduction rollback, and subsequent
active rifting and lithosphere thinning in the central
part of the basin. On the basis of the evidence from
basalt-hosted xenoliths, we can offer several addi-
tional conclusions regarding the evolution of subcon-
tinental lithosphere in the Intra-Carpathian Basin
System:
(1) A significant correlation exists between dominant
xenolith textural types and their geographic
locations. Basically undeformed (protogranular)
or only slightly deformed (protogranular to
porphyroclastic) xenoliths occur at the margins
of the basin system and lack any lattice-preferred
orientation. Statically recrystallized, annealed
C. Szabo et al. / Tectonophysics 393 (2004) 119–137134
(equigranular, secondary recrystallized) xenoliths
occur more frequently towards the center of the
basin, show moderate to strong lattice-preferred
orientation, and systematic correlation between
geochemical character and texture. Compared to
undeformed samples, annealed samples are rela-
tively depleted in dbasalticT major elements,
whereas trace elements and radiogenic isotopes
are relatively enriched in equigranular and
recrystallized samples. Bulk Cu contents and the
abundance of sulfide blebs in upper mantle
xenoliths also correlate with inferred partial melt
degree and deformation state of the mantle.
Sulfides in the equigranular and recrystallized
samples (depleted in basaltic major elements)
show relatively low bulk Cu contents.
(2) The widespread occurrence of modal amphibole
in CPR xenoliths indicates that subcontinental
lithospheric mantle in the region was perva-
sively metasomatized. Xenolithic amphiboles
from the central portion of the Pannonian Basin
show a marked tendency to deformed textural
types, suggesting relationship of metasomatic
processes to basin formation. While it has been
assumed that metasomatic agents affecting the
region mainly comprise percolating basaltic
melts, the geochemical data suggest that at
least some derive from subducting slabs asso-
ciated with the Carpathian arc-trench rollback
system.
(3) Silicate melt pockets were observed in xenoliths
from the central and northern part of the CPR.
These features and their geographic confinement
are attributed to two possible factors:
(a) The interaction of migrating slab-derived
melts or fluids with pre-existing amphib-
oles and clinopyroxenes to produce new,
metasomatically induced melt fractions;
(b) Decompression melting of amphibole-
dominated assemblages, prevalent in cen-
tral parts of the basin where melt pockets are
more abundant and ratios of amphibole to
melt pocket abundance in xenoliths are
lower. This type of process is consistent
with the notion of mantle upwelling beneath
the central part of the Pannonian Basin cau-
sing decompression and reheating during
the second, syn-rift stage of basin evolution.
Acknowledgements
The authors express their thanks to K. Tfrfk, L.Csontos, Sz. Harangi, K. Hidas (Eftvfs University),
H. Downes (Birkbeck College), O. Vaselli (University
of Firenze), and N. Seghedi and S. Szakacs (Institute
of Geodynamics, Romanian Academy) for the helpful
discussions. We also thank all the members of
Lithosphere Fluid Research Lab for their cooperation
and F. Martin for his encouragement. Z. Zajacz and I.
Kovacs are grateful to Pro Renovanda Cultura
Hungariae foundation for financial support. Com-
ments by F. Chalot-Prat and an anonymous reviewer
are gratefully acknowledged.
This work was also supported by the Hungarian
National Science Foundation (OTKA; credit T030846)
to C. Szabo.
This is the No. 13 publication of the Lithosphere
Fluid Research Lab of the Department of Petrology
and Geochemistry at Eftvfs University, Budapest.
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