GEOLOGICA CARPATHICA, AUGUST 2005, 56, 4, 359368
Mantle peridotite xenoliths in alkali basalts from the East
Thrace region (NW Turkey)
FAHRù ESENLù and ª. CAN GENÇ*
Istanbul Technical University, Department of Geological Engineering, 34469 Maslak, Istanbul, Turkey
*Corresponding author: firstname.lastname@example.org
(Manuscript received May 21, 2004; accepted in revised form March 17, 2005)
Abstract: This paper represents the first report on the peridotitic mantle xenoliths including spinel harzburgites and
spinel lherzolites found in the Late Miocene-Pliocene basaltic rocks (Thracean alkaline basalts TAB) of the Thrace
region, northwestern Turkey. The lavas formed and extruded during the north-south extension of western Anatolia, are
olivine basalts and basanites displaying within-plate affinity. The estimated modal mineralogy of the peridotite xenoliths
is olivine (5884 %) + orthopyroxene (1235 %) + clinopyroxene (012 %) + spinel (15 %). They are characterized
mainly by protogranular and also transitional protogranular to porphyroclastic and fine-grained equigranular textures.
Melt pockets are recognized in only one sample. Deformation features in olivine and pyroxenes are zoning, twinning,
including inclusions, kink banding, triple junction and undulatory extinction. Bulk-rock analyses indicate that the xeno-
liths are depleted in basaltic components (e.g. CaO 0.391.50 wt. %, Al
0.801.78 wt. %). Light rare-earth
element (LREE) enrichment is significant (e.g. La
26), which suggests a cryptic metasomatic history.
Key words: Northwestern Turkey, geochemistry, petrology, mantle xenolith, alkali basalt, peridotite.
Peridotite xenoliths in alkali basalts can be used as indicators
of the composition of the upper mantle. The structures, tex-
tures, mineralogy, and chemical compositions of peridotite xe-
noliths provide information on the character of the lithospher-
ic and/or astenospheric mantle (Frey & Green 1974;
Nielson-Pike & Schwarzman 1977; Embey-Isztin et al. 1989).
In this study, the peridotite xenoliths in two basalt eruptions
from the Tekirda region (eastern Thrace, northwestern Tur-
key) were studied at Hacôköy (H) and Karatepe (K) (Fig. 1a
c). Eight xenoliths from Hacôköy and six xenoliths from the
Karatepe eruptions were investigated petrographically. More-
over, three xenolith samples from Hacôköy and three from Ka-
ratepe were studied chemically. Xenoliths in alkali basalts
from the Thrace were first reported by Esenli (1999), in which
only the petrography and major element chemistry of the
Hacôköy xenoliths were presented. In this study we present the
major and trace elements, as well as REE data for the Hacôköy
and Karatepe xenoliths and their petrologic and geochemical
properties. In addition, the geochemical characteristics of the
host basalts are treated and discussed briefly.
The mantle-derived xenolith-bearing basaltic lavas of
Hacôköy and Karatepe are located in the Tertiary Thrace Sedi-
mentary Basin, northwestern Turkey (Fig. 1ac). The Thrace
Basin is founded on the Intra-Pontide suture zone which was
developed by the northward subduction of the northern branch
of Neotethys Ocean during the Late Cretaceousearly Tertiary
period (ªengör & Yôlmaz 1981; Yôlmaz et al. 1997) and conti-
nental collision of the Strandja and Sakarya Zones (Okay &
Tüysüz 1999). The Thrace Basin started to open at the end of
the Middle Eocene, and turned into a mature basin during the
Oligocene time. In the center of the basin the thickness of the
sedimentary rocks reaches up to 8 km (Turgut et al. 1991).
There are different views on the origin and the development
mechanism of the Thrace Basin, as follows: a it formed un-
der the effects of a NS directed extensional tectonic regime
during the Middle Eocene to the latest Oligocene period after
the closing of the Intra-Pontide Ocean (i.e. Turgut et al. 1991);
b it is a fore-arc basin formed during the Middle Eocene
Oligocene (i.e. Görür & Okay 1996); c it is a ramp basin,
which developed during the end of the EoceneOligocene pe-
riod (i.e. Yôlmaz et al. 1997; Yôlmaz & Polat 1998) and d it
is a transtensional basin which is controlled by the Thrace-
Eskiþehir wrench fault (i.e. Yaltôrak & Alpar 2002).
The young volcanic activity of the Thrace Basin occurred
mainly in two major phases. The first phase formed during the
Late EoceneEarly Miocene period which is assumed to be a
product of Tibetan-type volcanism developed under the N-S
compressional regime of northwestern Anatolia (i.e. Genç
1998; Yôlmaz & Polat 1998). Calc-alkaline intermediate vol-
canic products alternating with the siliciclastics of the Thrace
Basin extruded during this period. The second volcanic phase
started during the Late Miocene (84 Ma), and produced dis-
tinctly different volcanic association. During this phase, the
mantle-derived xenolith-bearing alkaline basaltic lavas ex-
truded sporadically in different parts of the Thrace region
The Thracean alkaline basalts (TAB) interfinger with the
sediments of the Ergene Formation of the Late Miocene
360 ESENLù and GENÇ
Pliocene consisting of the conglomerates, sandstones, silt-
stones and claystones. It unconformably overlies the older
rock units of the region (Lebküchner 1974; Umut et al.
1983, 1984; Umut 1988a,b). The Quaternary alluvial deposits
Fig. 1. Location map (a), simplified geological map of the Thrace region (b) (after Yôlmaz et al. 1997), and the detailed geology map of
the area studied (c) (compiled from Lebküchner 1974; Umut 1988a,b). Abbreviations for location map (a): IPS Intra-Pontide Suture
zone, RPF Rhodope-Pontide Fragment, SC Sakarya Continent, IAS Izmir-Ankara Suture zone, KB Kôrþehir Block, TAP
Tauride-Anatolide Platform, ITS Inner Tauride Suture zone, BZS Bitlis-Zagros Suture zone, AP Arabian Platform.
unconformably overlies the Thracean alkaline basalts repre-
sented by olivine basalt, basanite, trachybasalt lavas, and re-
lated pyroclastic rocks (Parejas 1939; Ternek 1949; Kopp et
al. 1969; Lebküchner 1974; Ercan 1979; Umut et al.
MANTLE PERIDOTITE XENOLITHS IN ALKALI BASALTS FROM THE EAST THRACE REGION 361
1983, 1984; Sümengen et al. 1987; Ercan 1992; Yôlmaz & Po-
lat 1998; Esenli 1999). The K-Ar radiometric dating obtained
from the TABs indicate the Late MiocenePliocene interval
(6.7±0.74.88±2.19 Ma) (Sümengen et al. 1987; Yôlmaz &
Polat 1998 and the references therein).
It was proved that the Thracean alkaline basalts were
formed under a N-S extensional tectonic regime, and thought
to be extruded from the strike-slip fault zones cutting the en-
tire Thrace lithosphere and the extensional cracks between the
major fault zones (cf. Yaltôrak 1996; Yôlmaz & Polat 1998).
The host basalt lavas and the xenoliths were studied petro-
graphically by polarizing microscope. The secondary minerals
of the basalt lavas and some minerals of the xenoliths, particu-
larly olivines were studied by X-ray powder diffraction analy-
sis (XRD) method. For this purpose, the samples were ground
and sieved to a grain size of 44 µm. A Philips diffractometer
with CuKα radiation was used for X-ray analysis and holder
samples were scanned at 1°2θ per minute. Xenolith and basalt
samples were ground by agate mill for chemical analysis. Be-
fore these analyses, the rock specimens were crushed and xe-
noliths were separated from basalt. The thin outer rims of xe-
noliths were trimmed carefully from main bodies to make sure
that the rest of the samples were pure xenolith. The chemical
compositions of six xenolith and two basalt samples were
analysed by using Spectro Ciros Vision ICP-ES for major ox-
ides, Ba and Sc (0.200 g pulp sample by LiBO
Cu, Zn and Ni (0.50 g sample leached with 3 ml 222 HCl
O at 95 °C for one hour, diluted to 10 ml) and by
Perkin Elmer Elan 6100 ICP-MS for the other elements in
ACME Analytical Laboratories, Vancouver, Canada. A 0.2 g
sample aliquot is weighed into a graphite crucible and mixed
with 1.5 g of LiBO
flux. The flux/sample charge is heated in
a muffle furnace for 15 minutes at 1050 °C. The molten mix-
ture is removed and immediately poured into 100 ml of 5%
(ACS grade nitric acid in de-mineralized water). The
solution is shaken for 2 hours then an aliquot is poured into a
polypropylene test tube. Calibration standards, verification
standards and reagent blanks are added to the sample se-
The xenoliths are commonly rounded, subrounded, ellipti-
cal and rarely angular in shape. Their diameters vary from
0.5×0.5 to 5×7 cm, but most of them are 2×2 and 2×3 cm in
size. They are yellowish-green and pale green in colour. The
boundaries between xenoliths and host rock are clear and
sharp, and there is not a transition zone between them on the
The xenoliths are commonly spinel harzburgite and rarely
spinel lherzolite. Only two samples (HX4 and KX4) are classi-
fied as spinel lherzolite according to the IUGS systematics (Le
Bas & Streckeisen 1991). Olivine-forsterite (5884 %) + ortho-
pyroxene-enstatite (1235 %) + clinopyroxene-diopsite (0
12 %) + Cr-Spinel (15 %) assemblage is determined by using
petrographic and XRD methods.
Texture features, rock type and estimated modal composi-
tions (from the thin sections) of the Hacôköy and Karatepe xe-
noliths are given in Table 1. The texture of the xenoliths is
commonly protogranular following the nomenclature of Mer-
cier & Nicolas (1975). Considering the less common middle-
grained crystals, it may be described as middle to coarse-
grained texture (Fig. 2a,b). Elongated crystals together with
the foliation and lineation are not recognized in the xenoliths.
In some xenoliths, microcrystalline olivine and pyroxene ag-
gregates are also recognized (Fig. 2c). Although these zones
are similar to local transitions into the porphyroclastic texture,
the typical porphyroclastic and equigranular textures are rare.
In sample KX6, however, these aggregates are recognized as a
crystallized melt pocket (Fig. 2e,h). In this melted area a
smaller amount of plagioclase and serpentine occur among the
olivine and pyroxene grains, but silica glass is not found.
Spinel crystals are also present in this melted area (Fig. 2e),
probably due to the interaction of the xenolith with the basal-
tic liquid (i.e. Bali et al. 2002). It is further supported that
Protogranular to porphyroclastic
Protogranular to fine-grained equigranular
Protogranular to fine-grained equigranular
Protogranular to porphyroclastic
Protogranular to fine-grained equigranular, with melt pockets
Table 1: Petrographic features of the Thracean mantle xenoliths. Ol olivine, Opx orthopyroxene, Cpx clinopyroxene, Sp spinel.
362 ESENLù and GENÇ
brown transparent spinels are surrounded by an opaque rim in
the samples of KX4 and KX6 (Fig. 2f). Some of the spinels
are interstitial having holly leaf shape indicating the pro-
togranular textures (Fig. 2g).
In all studied xenoliths, olivines are generally 0.53.0 mm
in size and colourless or rarely pale green under the micro-
scope. Large olivine grains have typically curvilinear bound-
aries in the Hacôköy xenoliths, whereas they have curvilinear
and straight boundaries in the Karatepe xenoliths (Fig. 2d).
The olivine was identified as forsterite by using XRD analy-
sis. The d value of 222 spacing which is the distinguishable
line among the four types of olivines was found to be
0.1749 nm. This spacing value confirms the forsterite
(d: 0.1750 nm). Orthopyroxenes (enstatite) are optically co-
lourless or pale green in colour and 0.51.0 mm in size
Fig. 2. Photomicrographs of the Thracean xenoliths. a Spinel lherzolite xenolith with protogranular texture from the Hacôköy area (Ol
olivine, Opx orthopyroxene, Cpx clinopyroxene). b Protogranular spinel lherzolite from the Karatepe area. On the upper right side
of the photo, there is a melted and recrystallized area including the large spinel (Sp) crystal. c Protogranular to porphyroclastic spinel
harzburgite from the Karatepe area. The orthopyroxene displaying the deformation lamellae (DL) and a crushed zone (CZ) are also seen
from the photo. d The spinel harzburgite xenolith from the Karatepe area. The large olivines (Ol) display the rounded fracture patterns
(RF) and deformation lamellae (DL).
(Fig. 2c). Clinopyroxenes (diopsite) were found in five sam-
ples (Table 1). Cr-spinels are anhedral in shape and their di-
ameters are less than 0.5 mm (Fig. 2e,f,g).
Common characterictics of the Thracean xenoliths are zon-
ing, inclusions and twinning, deformation lamellae, undulato-
ry extinction, kink banding and triple junction (granoblastic-
polygonal texture) in olivines and pyroxenes (Fig. 2c,d,g).
Spongy and crushed zones around the pyroxenes and sym-
plectic spinel-pyroxene coexistence is rarely recognized.
The geochemical data for the Hacôköy and Karatepe xeno-
liths are presented in Table 2. The Hacôköy and Karatepe xe-
noliths are uniform with respect to their Al
MANTLE PERIDOTITE XENOLITHS IN ALKALI BASALTS FROM THE EAST THRACE REGION 363
Fig. 2. Continued. e Protogranular spinel harzburgite xenolith from the Karatepe area. The fine-grained melted-recrystallized area (M
A) and the large spinel (Sp) crystals embedded into this area. f Spinel crystals with opaque rim and transparent core crystallized in the
melted areas in the spinel harzburgite xenoliths from the Karatepe area. g Protogranular and granoblastic-polygonal textures (GPT) in
the spinel lherzolite xenolith from the Karatepe area. Spinel crystals are interstitial with holly leaf shape indicative for the protogranular tex-
ture. h The melt pocket bearing spinel lherzolite xenolith from the Karatepe area. A plagioclase crystal (Plj) crystallized in the melted/re-
crystallized area (MA) is also seen.
1.78 wt. %) and MgO contents (43.8947.26 wt. %). This sit-
uation appears to be in contrast with the peridotite xenoliths
from other areas of the world (for example: the Pannonian Ba-
sin Downes et al. 1992; west Hungary Embey-Isztin et
al. 1989; eastern China Song & Frey 1989). All xenolith
samples of the Hacôköy and Karatepe areas are highly deplet-
ed in basaltic components. Therefore, the Al
the two locations vary from 0.800.84 wt. % to 1.68
1.78 wt. %, respectively (see Table 2). On the other hand, the
CaO contents of the Hacôköy and Karatepe xenoliths range
from 0.390.97 wt. % to 1.391.50 wt. % respectively. These
CaO values imply that the Hacôköy xenoliths are extremely
depleted (<1 wt. %), and the Karatepe xenoliths are strongly
depleted (13 wt. %) xenoliths (cf. Wiechert et al. 1997). The
Mg# of the two groups of xenoliths falls in a narrow range.
The Mg# of the Hacôköy xenoliths is 0.91 and that of the Ka-
ratepe xenoliths is 0.90. The geochemical difference between
the Hacôköy and Karatepe xenoliths may clearly be seen in
their major element (i.e. TiO
O), trace ele-
ment (e.g. Rb, Sr, Y), and the REE (La-Lu serie) contents
Use of MgO as a depletion/enrichment index for the mantle
xenoliths is common. For this purpose, major and trace ele-
ments and REE of the xenoliths are plotted on the Harker-type
diagrams versus MgO (Fig. 3). Ni, Cr, Co and Ga show a posi-
tive correlation, whereas SiO
, CaO, Fe
O, Sc, Y, V, and Lu display a negative correlation with
MgO (Fig. 3).
The Hacôköy and Karatepe xenoliths are REE-depleted and
when compared with the C1 chondrite (Sun & McDonough
364 ESENLù and GENÇ
Fig. 3. The MgO versus major, trace and REE diagrams for the Thracean peridotite xenoliths.
MANTLE PERIDOTITE XENOLITHS IN ALKALI BASALTS FROM THE EAST THRACE REGION 365
1989), their (<10) × chondritic nature (Fig. 4) can clearly be
seen. There is a considerable difference in REEs between the
Hacôköy and Karatepe xenoliths. As seen on Figs. 4 and 5, the
Karatepe xenoliths are more enriched in LREE, MREE and
HREE compared to the Hacôköy xenoliths. The chondrite nor-
malized patterns of xenoliths indicate that the Hacôköy sam-
ples are 0.2 to 2 × chondritic, while the Karatepe xenoliths are
0.5 to 8 × chondritic in nature (Fig. 4). The xenoliths display
slightly concave-upward patterns (Fig. 4) in chondrite (C1)
normalized diagram. LREE enrichment is also evident from
the ratios of (La/Yb)
: (2.47.2) and (Sm/Nd): (0.510.76).
The Hacôköy and Karatepe basalts (TAB) are dark grey and
black, massive, homogenous and locally fractured and slightly
altered. Their textures are commonly microlitic. Although
there are some differences between the Hacôköy and Karatepe
lavas, the general mineralogical compositions and estimated
mineral proportions are plagioclase (4560 %) + olivine (10
14 %) + clinopyroxene (1828 %) + orthopyroxene (38 %) +
opaque (58 %) + amphibole (13 %) + secondary minerals in
all studied basalt samples. They contain 1530 % modal phe-
nocrysts, among which pyroxene usually dominates. Ground-
mass consists mostly of microlites (plagioclase, pyroxene, and
olivine) and a low percent of volcanic glass. Most of the oliv-
ines are represented by large phenocrysts. They are euhedral
or subhedral in shape and rarely altered to iddingsite, carbon-
ate and serpentine. Some of the olivines and orthopyroxenes
in the Hacôköy and Karatepe basalts are probably xenocrysts
derived from the xenoliths. Deformation features, such as
strain lamellae, irregular extinction and kink banding are rec-
ognized in such olivine crystals. Clinopyroxene content rang-
es generally from 20 % to 25 % and most of them occur as mi-
crophenocrysts and microlites. Corona texture has formed
around some pyroxene and olivine grains. In such grains the
green outer zone and the pink inner zone can easily be identi-
fied. Plagioclases in the Karatepe basalts are larger (up to
0.5 mm) than the plagioclases in the Hacôköy basalts
(<0.1 mm). Opaque minerals are found as disseminated grains
in the Hacôköy samples or zoned agglomerated crystals in the
Karatepe samples and their content range up to 10 % in the
Host Basalt Host Basalt
Table 2: Geochemical data for the Hacôköy and Karatepe basalt lavas and related peridotite xenoliths (Mg# = Mg/(Mg+Fe); Fe
total iron; n.d. = not determined).
366 ESENLù and GENÇ
As the geochemical features of TABs were presented in de-
tail in the previous works (i.e. Yôlmaz & Polat 1998), their
main characteristics are only presented briefly in the following
paragraphs to avoid repetition. The two representative
geochemical data for the Hacôköy and Karatepe basalts (sam-
ples HB1 and KB1) are given and pointed together with xeno-
lith samples (see Table 2 and Figs. 4 and 5). The lavas display
typical within plate alkaline (WPA) affinity. The evidence for
this is as follows: 1 curved convex patterns on spider dia-
grams, 2 positive Nb anomaly, 3 smoothly enriched
REE patterns, 4 relatively high contents of incompatible el-
ements (for example Nb=6466 ppm, La=3447 ppm) and,
5 high values of the ratios of Nb/La (1.31.9), Zr/Y (10.7
11.5) and Zr/Nb (33.5). These data are closely similar to
WPA basalts reported from various regions of the world
(Wood 1980; Sun & Mc Donough 1989).
In the Thrace region, the alkaline basaltic volcanism formed
under the extensional tectonic regime and extruded along deep
fracture zones, is characterized by a HIMU type OIB signa-
ture, and originated from the asthenospheric mantle source ac-
cording to the Yôlmaz & Polat (1998).
According to the work of Mercier & Nicolas (1975), the xe-
noliths with protogranular texture are common in the Europe-
an Tertiary and Quaternary volcanics, but the equigranular
textured xenoliths are only present in the Quaternary volca-
Fig. 5. Primordial mantle-normalized multi element variation dia-
gram for the Thracean peridotite xenoliths and host basaltic lavas
(normalization values are taken from Sun & McDonough 1989).
nics. This conclusion is in good agreement with the case of the
Thracean xenoliths. In the Thracean xenoliths, the sizes of oli-
vine and pyroxene crystals are typically coarse. The other tex-
tural features of the Thracean xenoliths are as follows: in some
xenoliths there are triple-junctions (granoblastic-polygonal
texture) between the olivine and pyroxene crystals. Spongy
and crushed zones around the pyroxenes and symplectic
spinel-pyroxene coexistence are rarely recognized. The triple-
junctions and rounded fracture patterns in the olivines suggest
mantle deformation. Additionally, the curvilinear grain
boundaries of olivine crystals and pyroxenes with spongy rims
together with the crushed zones between the pyroxene and oli-
vine crystals clearly indicate that the xenoliths are subjected to
the partial melting at depths, and then recrystallized (Mercier
& Nicolas 1974; Nielson Pike & Schwarzman 1977 and the
references therein). It is evident from the melted area (recog-
nized only in one sample) that the interactions between the ba-
saltic liquids and xenoliths occurred (Embey-Isztin et al.
1989; Wiechert et al. 1997; Bali et al. 2002). Although the
typical metamorphic textures such as foliation and lineation
are not observed in the Thracean xenoliths, some undulatory
extinction, deformation lamellae and the banding similar to
twinning are the evidence for mantle deformations (Nielson
Pike & Schwarzman 1977).
The Thracean xenoliths are the foreign fragments and do not
represent the initial crystallization phases of basaltic liquids.
The evidence for this may be given as follows: the composi-
tions of the olivines, the deformation structures in the olivines
and the pyroxenes, the triple-junctions and the granoblastic-
Fig. 4. Chondrite (C1)normalized REE pattern for the Thracean
peridotite xenoliths and host basalt lavas (normalization values are
taken from Sun & McDonough 1989).
MANTLE PERIDOTITE XENOLITHS IN ALKALI BASALTS FROM THE EAST THRACE REGION 367
polygonal textures, and some textural features indicating the
partial melting such as the spongy borders of pyroxenes and
symplectic spinel-pyroxene growths, as mentioned above.
The decrease in SiO
, CaO and Na
O with the
increase of MgO (Fig. 3) in the Thracean xenoliths indicates
partial melting of original mantle material, and it is similar to
the xenoliths reported in different areas of the world (i.e. Maa-
loe & Aoki 1977; Frey et al. 1985; Bodinier 1988; Embey-Isz-
tin et al. 1989; Song & Frey 1989; Downes et al. 1992; Qi et
al. 1995). All of the Thracean xenoliths cluster far from the
primitive mantle composition (Fig. 3). The strong negative
correlations of SiO
and CaO with MgO suggest con-
siderable melt extraction from the original source, and its mi-
gration from the source region (c.f. Carter 1970; Kuno & Aoki
1970; Nickel & Green 1984; Downes 1987; Embey-Istzin et
al. 1989). According to Frey et al. (1985), the negative varia-
tions of the moderately incompatible elements such as Sc, V
and Y with MgO indicate that the amount of partial melting of
the original source is less than 30 %. The positive correlation
of Ni, and strong negative variations of Sc, V and Y with the
MgO are in a good agreement with the spinel peridotitic man-
tle xenoliths examined by Jagoutz et al. (1979) and Jochum et
The La/Nb ratio for the Thracean xenoliths ranges from 0.45
to 0.71 which is 0.96 for the C1 chondrite (Sun & McDon-
ough 1989). Generally, the upward-concave affinity of the
REE patterns and the considerable LREE enrichment of the
Thracean xenoliths (see Figs. 4 and 5) are in a good agreement
with the metasomatically enriched mantle peridotites reported
from the different regions of the world (e.g. OReilly & Grif-
fin 1988; Zangana et al. 1998). This is supported by the ratio
>1. It is known that the values of (La/Yb)
mantle-derived xenoliths higher than one indicate the metaso-
matic enrichment (cf. Wiechert et al. 1997). On the other
hand, occurrence of significant LREE enrichments and lack of
O-bearing phases such as amphibole and/or phlogopite in
Thracean xenoliths indicates the xenoliths were affected by
the cryptic metasomatism. The LREE depletion have already
been reported from the typical mantle-derived peridotite xeno-
liths in numerous studies (e.g. Vaselli et al. 1995, and the ref-
The LREE enrichment in the mantle xenoliths is commonly
attributed to metasomatic fluids chromatographically percolat-
ed through upper mantle peridotite previously depleted in in-
compatible elements (e.g. Song & Frey 1989; Franz et al.
1997; Fodor et al. 2002). The LREE enrichment in the Thra-
cean xenoliths may either be the result of subduction-related
magmatism which occurred during the Late Cretaceous to ear-
ly Tertiary period (ªengör & Yôlmaz 1981; Yôlmaz et al. 1997)
or formed during the Upper MiocenePliocene extensional al-
kali basaltic volcanism. In the first case, the volatile and silica-
rich melts could have been released from the subducted slab
and could have caused the LREE enrichments above the sub-
ducting slab recorded in the Thracean mantle xenoliths similar
to that of the Western Hungarian case (Bali et al. 2002).
The original depth of the Thracean xenoliths may be esti-
mated from their mineralogical composition. According to the
results of experimental petrology, the phase boundary be-
tween the spinel-peridotite and garnet-bearing peridotite is at
~1250 °C T and ~22.2 GPa P, corresponding to approxi-
mately 65 km of depth (e.g. ONeill 1981; Qi et al. 1995; Shi
et al. 1998; Klemme & ONeill 2000; Fodor et al. 2002).
Therefore, the lack of the garnet-peridotites in Thracean xeno-
liths constrains the maximum depth as 65 km.
The mantle-derived peridotite xenoliths occur in the Late
MioceneQuaternary Thracean alkaline basaltic suite. They
display within plate alkaline affinity and are derived from the
asthenospheric mantle reservoir. The xenoliths are sampled
from two different localities, called Hacôköy and Karatepe,
which are close to each other. The xenoliths are dominantly
spinel-harzburgites, and less commonly spinel-lherzolites.
These are thought to be the samples of the upper mantle be-
neath the Thrace region. The xenoliths are extremely and
strongly depleted in basaltic components. The Thracean xeno-
liths are depleted in REE initially, and then enriched in LREE.
The LREE enrichment either is probably a result of mantle
metasomatism during the northward subduction of Neotethys
ocean floor beneath the Pontides in the Late Cretaceous-early
Tertiary period or due to the N-S directed extensional tectonic
regime during which the alkaline basaltic volcanism were de-
veloped in the Late MiocenePliocene period.
Acknowledgments: The authors thank A. Okay, E. Demirba
and O. Tüysüz who read and improved the text. Comments by C.
Szabó and an anonymous reviewer are gratefully acknowledged.
Bali E., Szabó C., Vaselli O. & Török K. 2002: Significance of silicate
melt pockets in upper mantle xenoliths from the Bakony-Balaton
Highland volcanic field, Western Hungary. Lithos 61, 79102.
Bodinier J.L. 1988: Geochemistry and petrogenesis of the Lanzo peri-
dotite body, western Alps. Tectonophysics 149, 6788.
Carter J.L. 1970: Mineralogy and chemistry of the Earths upper man-
tle based on the partial fusion-partial crystallization model. Geol.
Soc. Amer. Bull. 81, 202134.
Downes H. 1987: Relationship between geochemistry and textural
type in spinel lherzolites, Massif Central and Languedoc, France.
In: Nixon P.H. (Ed.): Mantle xenoliths. John Wiley, New York,
Downes H., Embey-Isztin A. & Thirlwall M. 1992: Petrology and
geochemistry of spinel peridotite xenoliths from the western Pan-
nonian Basin (Hungary): evidence for an association between en-
richment and texture in the upper mantle. Contr. Mineral.
Petrology 109, 340354.
Embey-Isztin A., Scharbert H.G., Dietrich H. & Poultidis H. 1989: Pe-
trology and geochemistry of peridotite xenoliths in alkali basalts
from the Transdanubian volcanic region, western Hungary. J. Pe-
trology 30, 79105.
Ercan T. 1979: Cenozoic volcanism in western Anatolia, Thrace and
Eagean Island. Jeoloji Mühendislii Dergisi 9, 2346 (in Turkish
with English abstract).
Ercan T. 1992: Cenozoic volcanism in Thrace and its regional distri-
bution. Jeoloji Mühendislii Dergisi 41, 3750 (in Turkish with
Esenli F. 1999: Peridotitic xenoliths in alkali basalts of Tekirdag re-
368 ESENLù and GENÇ
gion (Thrace). Maden Tetkik Arama Enstitüsü Dergisi 121, 125
139 (in Turkish with English abstract).
Fodor R.V., Sial A.N. & Gandhok G. 2002: Petrology of spinel peridot-
ite xenoliths from northeastern Brazil: lithosphere with a high geo-
thermal gradient imparted by Fernando de Noronha plume. J.
South Amer. Earth Sci. 15, 199214.
Franz L., Seifert W. & Kramer W. 1997: Thermal evolution of the man-
tle underneath the mid-German crystalline rise: evidence from
mantle xenoliths from the Rhön area (Central Germany). Contr.
Mineral. Petrology 61, 125.
Frey F.A. & Green D.H. 1974: The mineralogy, geochemistry and ori-
gin of lerzolite inclusions in Victorian basanites. Geochim. Cos-
mochim. Acta 38, 10231050.
Frey F.A., Suen C.J. & Stockman H.W. 1985: The Ronda high temper-
ature peridotite: geochemistry and petrogenesis. Geochim. Cos-
mochim. Acta 49, 24692491.
Genç ª.C. 1998: Evolution of the Bayramiç magmatic complex, north-
western Anatolia. J. Volcanol. Geotherm. Res. 85, 233249.
Görür N. & Okay A.I. 1996: A fore-arc origin for the Thrace Basin,
NW Turkey. Geol. Rdsch. 85, 662668.
Jagoutz E., Palme H., Baddenhausen H., Blum K., Cendales M., Drei-
bus G., Spettel B., Lorenz V. & Wanke H. 1979: The abundances
of major, minor and trace elements in the Earths mantle as de-
rived from primitive ultramafic nodules. In: R.B. Merrill (Ed.):
Proceedings of the 10
Lunar and Planetary Science Conference.
Pergamon, New York, 20312050.
Jochum K.P., McDonough W.F., Palme H. & Spettel B. 1989: Composi-
tional constraints on the continental lithospheric mantle from trace
elements in spinel peridotite xenoliths. Nature 340, 548550.
Klemme S. & ONeill H.S. 2000: The near-solidus transition from gar-
net lherzolite to spinel lherzolite. Contr. Mineral. Petrology 138,
Kopp K.O., Pavoni N. & Schindler C. 1969: Geologie Thrakiens IV:
Das Ergene Becken. Beihefte Geol. Jb. Heft. 76, 136.
Kuno H. & Aoki K. 1970: Chemistry of ultramafic nodules and their
bearing on the origin of basaltic magmas. Phys. Earth Planet. In-
ter. 3, 273301.
Le Bas M.J. & Streckeisen A.L. 1991: The IUGS systematics of igne-
ous rocks. J. Geol. Soc. 148, 825833.
Lebküchner R.F. 1974: Betrag zur kenntnis der geologie des Oligosans
von mittel Thrakien (Türkei). Bull. Miner. Res. Explor. Inst. Tur-
key 83, 130.
Maaloe S. & Aoki K. 1977: The major element composition of the
mantle estimated from the composition of lherzolites. Contr. Min-
eral. Petrology 63, 161173.
Mercier J-C.C. & Nicolas A. 1975: Textures and fabrics of upper man-
tle peridotites as illustrated by xenoliths from basalts. J. Petrolo-
gy 16, 454487.
Nickel K.G. & Green D.H. 1984: The nature of the upper-most mantle
beneath Victoria, Australia, as deduced from ultramafic xeno-
liths. In: Kornprobet J. (Ed.): Kimberlites. II. The mantle and
crust-mantle relationships. Elsevier, Amsterdam, 161178.
Nielson Pike J.E. & Schwarzman E.C. 1977: Classification of textures
in ultramafic xenoliths. J. Geol. 85, 4961.
Okay A.I. & Tüysüz O. 1999: Tethyan sutures of northern Turkey. In:
Durand B., Jolivet L., Horvath F. & Seranne M. (Eds.): The Med-
iterranean Basins: Tertiary extension within the Alpine orogen.
Geol. Soc. London, Spec. Publ. 156, 475515.
ONeill H.S. 1981: The transition between spinel lherzolite and garnet
lherzolite, and its use as a geobarometer. Contr. Mineral. Petrolo-
gy 77, 185194.
OReilly S.Y. & Griffin W.L. 1988: Mantle metasomatism beneath
western Victoria, Australia. I. Metasomatic processes in Cr-diop-
side lherzolites. Geochim. Cosmochim. Acta 52, 433447.
Parejas E. 1939: Trakya linyitleri jeolojik etüdü, Uzunköprü, Keºan,
Malkara, Hayrabolu môntôkasô. MTA Rapor No. 981, Ankara (un-
published report, in Turkish).
Qi Q., Taylor L.A. & Zhou X. 1995: Petrology and geochemistry of
mantle peridotite xenoliths from SE China. J. Petrology 36, 5575.
Shi L., Francis D., Ludden J., Frederiksen A. & Bostock M. 1998: Xe-
nolith evidence for lithospheric melting above anomalously hot
mantle under the northern Canadian Cordillera. Contr. Mineral.
Petrology 131, 3953.
Song Y. & Frey F.A. 1989: Geochemistry of peridotite xenoliths in ba-
salt from Hannuoba, Eastern China: Implications for subcontinen-
tal mantle heterogeneity. Geochim. Cosmochim. Acta 53, 97113.
Sun S.S. & McDonough W.F. 1989: Chemical and isotopic systemat-
ics of oceanic basalts: implications for mantle composition and
processes. In: Saunders A.D. & Norry M.J. (Eds.): Magmatism in
ocean basins. Geol. Soc. Spec. Publ. 42, 313345.
Sümengen M., Terlemez ù., Sentürk K., Karaköse C., Erkan E.N.,
Ünay E., Gürbüz M. & Atalay Z. 1987: Stratigraphy, sedimentol-
ogy and tectonics of the Gelibolu peninsula and SW Thracean
Tertiary basin. MTA Rapor No. 8128, Ankara (unpublished re-
port, in Turkish).
ªengör A.M.C. & Yôlmaz Y. 1981: Tethyan evolution of Turkey: a
plate tectonic approach. Tectonophysics 75, 181241.
Ternek Z. 1949: Geological study of the region Kesan-Korudag. Ph.D
Thesis, Istanbul Univ., Istanbul, 178.
Turgut S., Türkaslan M. & Perinçek D. 1991: Evolution of the Thrace
sedimentary basin and its hydrocarbon prospectivity. European
Assoc. Petroleum Geoscientists Spec. Publ. 1, 415437.
Umut M. 1988a: Explanatory text for Kôrklareli-C4 sheet. MTA Genel
Müdürlüûü 100,000 ölçekli açônsama nitelikli Türkiye Jeoloji
Haritalarô Serisi, Ankara (in Turkish).
Umut M. 1988b: Explanatory text for Kôrklareli-C5 sheet. MTA Genel
Müdürlüûü 1:100,000 ölçekli açônsama nitelikli Türkiye Jeoloji
Haritalarô Serisi, Ankara (in Turkish).
Umut M., ùmik M., Kurt Z., Özcan ù., Ateº M., Karabôyôkolu M. &
Saraç G. 1984: Geology of the Edirne-Kôrklareli-Lüleburgaz
(Kôrklareli)-Uzunköprü (Edirne) area and surroundings. MTA
Rapor No. 7604, Ankara (unpublished report, in Turkish).
Umut M., Kurt Z. & ùmik M. 1983: Geology of the TekirdaSilivri
(Istanbul)Pônarhisar (Kôrklareli) area and surroundings. MTA
Rapor No. 7349, Ankara (unpublished report, in Turkish).
Vaselli O., Downes H., Thirlwall M., Dobosi G., Coradossi N., Seghe-
di I., Szakács A. & Vannucci R. 1995: Ultramafic xenoliths in
Plio-Pleistocene alkali basalts from Eastern Transylvanian basin:
depleted mantle enriched by vein metasomatism. J. Petrology 36,
Wiechert U., Ionov D.A. & Wedepohl K.H. 1997: Spinel peridotite xe-
noliths from the Atsagin-Dush volcano, Dariganga lava plateau,
Mongolia: a record of partial melting and cryptic metasomatism
in the upper mantle. Contr. Mineral. Petrology 126, 345364.
Wood D.A. 1980: The application of Th-Hf-Ta diagram to problems of
tectonomagmatic classification and to establishing the nature of
crustal contamination of basaltic lavas of the British Tertiary vol-
canic province. Earth Planet. Sci. Lett. 50, 1130.
Yaltôrak C. 1996: Ganos fay sisteminin tektonik tarihi. Türkiye Petrol.
Jeol. Der. Bült. 81, 137150 (in Turkish with English abstract).
Yaltôrak C. & Alpar B. 2002: Kinematics and evolution of the northern
branch of the North Anatolian Fault (Ganos fault) between the
Sea of Marmara and the Gulf of Saros. Mar. Geol. 190, 351366.
Yôlmaz Y., Tüysüz O., Yiitbaþ E., Genç ª.C. & ªengör A.M.C. 1997:
Geology and tectonic evolution of the Pontides. In: Robinson
A.G. (Ed.): Regional and petroleum geology of the Black Sea and
surrounding region. AAPG Memoir 68, 183226.
Yôlmaz Y. & Polat A. 1998: Geology and evolution of the Thrace vol-
canism, Turkey. Acta Volcanol. 10, 2, 293303.
Zangana N.A., Downes H., Thirlwall M.F., Marriner G.F. & Bea F.
1998: Geochemical variation in peridotite xenoliths and their
constituent clinopyroxenes from Ray Pic (French Massif Cen-
tral): implications for the composition of the shallow lithospheric
mantle. Chem. Geol. 153, 1135.