composition and evolution of lithosphere beneath the

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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

* Correspon

E-mail addr

2004) 119–137

ee front matter D 2004 Elsevier B.V. All rights reserved.

to.2004.07.031

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


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.


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—


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.


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.


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


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).


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.


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.



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.


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).


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


(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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