Introduction
Intracontinental basaltic volcanism provides samples which
can be used to investigate mantle compositions and crustal
assimilations, and numerous studies have documented evi-
dence for crustal assimilations and compositional heteroge-
neities on a range of scales (Hart 1984; McDunough et al.
1985; Zindler & Hart 1986; McDunough 1990; Saunders et
al. 1992; White & McKenzie 1995; Turner & Hawkesworth
1995; Saunders et al. 1998; Reiners 2002). Studies of these
basalts suggest that the compositions of the intracontinental
basalts are similar to ocean-island basalts (OIB), which are
suggested to be generated in the convecting mantle (Wilson
1989, 1993; White & McKenzie 1995). These melts are of-
ten compositionally modified during ascent from asthenos-
pheric mantle including partial melting, fractionation, con-
tamination of crustal rocks and magma mixing (Hawkesworth
et al. 1984; Wooden et al. 1993; Turner & Hawkesworth
1995). Crustal contamination of mantle-derived magmas has
also been invoked to account for trace element signatures
(Arndt & Christensen 1992; Arndt et al. 1993; Wooden et al.
1993; Baker et al. 1997; Fram & Lesher 1997). Identification
of mantle source and evolution processes of primary magmas
of the intracontinental basalts have been a major goal of the
studies concerned with many continental basaltic provinces
(Hawkesworth et al. 1979; Heming 1980; McDunough et al.
1985; Weaver 1991; Coffin & Eldholm 1992; Saunders et al.
1992, 1998).
Geodynamic models suggest that the Anatolian plate was
deformed as a result of the collision of the Eurasian and Arabi-
an plates along the Bitlis Suture Zone (McKenzie 1972;
ªengör 1980). This collision, which initiated the Neotectonic
period, resulted in the shortening of Eastern Anatolia (McKen-
zie 1972; ªengör & Kidd 1979; ªengör et al. 1985). Conver-
gence between the Eurasian and Arabian plates along the Bit-
lis Suture Zone caused a compressionalcontractional tectonic
regime at the end of late Miocene and late early Pliocene
(Koçyiûit et al. 2001). In late early Pliocene, three major neo-
tectonic structures, the North Anatolian and East Anatolian
Transform Faults and the Anatolian plate, formed and the
Anatolian plate commenced to escape in a WSW direction
onto the oceanic lithosphere of the African plate (Hempton
1987). Thus, an earlier compressionalcontractional tectonic
regime was replaced by a compressionalextensional tectonic
regime at the late early Pliocene, with extrusion tectonics
dominated by strike-slip faulting (Koçyiûit et al. 2001).
Extensive volcanic activity took place in Eastern Anatolia
during the neotectonic period, as a result of which volcanic
rocks covered large areas of Eastern Anatolia. A number of re-
searchers discussed the origin, age and tectonic settings of the
post-collisional volcanic rocks in the Eastern Anatolia (Lam-
bert et al. 1974; Innocenti et al. 1976; ªaroûlu & Yôlmaz 1984;
GEOLOGICA CARPATHICA, 55, 6, BRATISLAVA, DECEMBER 2004
487500
Ý
Ý
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Ý
GEOCHEMISTRY OF POST-COLLISION PLIOCENE-QUATERNARY
KARASAR BASALT (DVR -S VAS, EASTERN TURKEY):
EVIDENCE FOR PARTIAL MELTING PROCESSES
MUSA ALPASLAN
1
, HÜSEYùN YILMAZ
2
and ABùDùN TEMEL
3
1
Mersin Üniversity, Department of Geology, 33343 Mersin, Turkey; malpaslan@mersin.edu.tr; musaalp@yahoo.com
2
Cumhuriyet University, Department of Geophysics, 58140 Sivas, Turkey
3
Hacettepe University, Department of Geology, 06532 Beytepe-Ankara, Turkey
(Manuscript received February 5, 2003; accepted in revised form December 16, 2003)
Abstract: The Pliocene-Quaternary Karasar basalt is located in the western part of the post-collisional volcanic field in
Eastern Anatolia and occurs as lava flows on the continental sediments. According to normative mineralogy and geochem-
istry, Karasar basalt samples have hyperstene-normative tholeiites, nepheline-normative basalts, trachybasalts, and ba-
saltic andesites with quartz-xenocrysts which occur at the base of the lava flows. Trace and rare element variations
indicate that the trachybasalts are enriched in highly incompatible trace and light-rare earth elements relative to hyperstene-
and nepheline-normative basalts. Hy-normative tholeiites have higher concentrations of medium-heavy rare earth ele-
ments relative to ne-normative basalts and trachybasalts. The trace element characteristics of the Karasar basalt imply
that the quartz-bearing rocks indicate some crustal contributions, but the basaltic samples have a minimal or no crustal
assimilation. Th/Yb-Nb/Yb and Hf/Sm
N
-Ta/La
N
diagrams coupled with HFSE depletions display a subduction signature
in the source region of these volcanics. REE modeling exhibits that the magmas forming the Karasar basalt originated
from a spinel-peridotite source, although trachybasalts require mixing between melts from spinel- and garnet-peridotite
source. Discrimination plots based on trace element data exhibit a within-plate character of the Karasar basalts. Correla-
tions between trace element ratios (Ba/Nb-La/Nb and Ba/La-Ce/Pb) imply that the source of Karasar basalt is lithos-
pheric rather than the asthenospheric mantle. These data reveal that the Karasar basalt is linked to a post-collisional
extensional tectonic regime following the collision between the Eurasian and Arabian plates. Volcanism in this part of
Anatolia is consistent with a model in which melting of lithospheric mantle occurred in response to lithospheric extension.
Key words: Eastern Anatolia, within-plate, extensional, post-collision, alkaline, tholeiitic, petrology.
488 ALPASLAN, YILMAZ and TEMEL
Gülen 1984; Tokel 1984; Alpaslan & Terzioûlu 1996; Keskin
et al. 1998; Yôlmaz et al. 1998; Buket & Temel 1998; Fig. 1)
and suggested that the alkaline volcanics closely related to the
extentional regime during Neogene period (Pearce et al. 1990;
Yôlmaz et al. 1998).
The objective of this study is to explain the origin and pro-
cesses that determined the geochemical characteristics of the
Karasar basalt in the western part of Eastern Anatolia.
Geological setting
The study area is located in the CentralEastern Anatolia
(east of Sivas,
Fig. 1
) and is a part of the region, which is un-
der approximately north-south and NNESSW shortening re-
lated to the collisional processes between the Anatolian and
Arabian plates along the Bitlis Suture Zone (Bozkurt 2001).
As a result of the collision between the Arabian and Anatolian
plates, the eastern part of Anatolia has experienced an intra-
continental convergence (McKenzie 1969) that resulted in
Fig. 1. Location map of the study area and distribution of the Neo-
gene volcanics in Eastern Turkey (simplified from Pearce et al.
1990).
crustal thickening and uplift (ªengör & Kidd 1979) and colli-
sion related volcanics indicated by 1215 Ma calc-alkaline
Yamadaûô volcanics in the study area (Fig. 2; Yôlmaz et al.
1998; Ekici 2003). Following the continental collision, the
earlier compressional tectonic regime was replaced by a new
compressionalextensional tectonic regime by the early
Pliocene (Koçyiûit et al. 2001). This has resulted in the gener-
ation of intra-continental strike-slip faults namely the North
Anatolian and East Anatolian Fault Zones (Fig. 1). The forma-
tion of these fault zones and subsequent westward escape of
the Anatolian plate along its boundary structures has resulted
in the generation of the Central Anatolian Ova Province in the
eastern parts of the Anatolian plate (ªengör & Yôlmaz 1981).
The structural elements of the study area affecting Neogene
units have been dominated by second order NWSE left and
NESW right lateral strike-slip faults (Fig. 2) which may be
accompanied by North Anatolian and East Anatolian faults.
Basaltic volcanics outcropping as thick lava flows, namely the
Karasar basalt, postdates 1215 Ma collision-related Ya-
madaûô volcanics (Ekici 2003) and overlie the basic pyroclas-
tics and continental sediments named the ùnallô Formation
(Gültekin 1993; Figs. 2, 3).
Petrography
The Karasar basalt is mainly dominated by hyperstene-nor-
mative and nepheline-normative basalts and trachybasalts (ha-
waiite) (Fig. 4 and Table 1) but quartz-xenocrysts-bearing
rocks found at the base of the volcanic sequence have been
obtained from drilling core samples.
Xenocryst-bearing rocks have strongly prophyrytic texture
and include olivine and plagioclase phenocrysts. Quartz xe-
nocrysts are surrounded by a reaction rim with clinopyroxene
microlithes. Olivines are iddingsitizated. Plagioclases occur as
sieve-textured phenocrysts and microlithes. The groundmass
of these samples consists of volcanic glass, clinopyroxene and
plagioclase microlithes, and scarce opaque minerals. These
rocks fall into the basaltic andesite field in the total alkali-sili-
ca nomenclature diagram (Fig. 4) of the Le Maitre (1989).
Samples which fall on the basalt field of the nomenclature
diagram (Fig. 4) have a holocrystalline-intersertal texture.
Their normative mineralogies indicate that these samples are
hyperstene-normative and nepheline-normative basalts. The
mineral assemblages of these rocks are olivine, clinopyroxene,
plagioclase and minor opaque minerals. The euhedral and sub-
hedral olivines occur as phenocrysts and microphenocrysts.
They are generally serpentinitizated and also iddingsitizated in
some rock samples. The plagioclases have commonly been
seen as microlithes which are perpendicular to each other. The
clinopyroxenes are generally subhedral and fill the areas be-
tween the plagioclases laths.
Trachybasalts (hawaiite) occur as last flows in the study
area. They are characterized by fine-grained and aphanitic tex-
ture. These rocks have a holocrystalline-intersertal texture un-
der the microscopy and include olivine, clinopyroxene, pla-
gioclase, and minor opaque minerals. Olivines occur as
euhedral and subhedral shaped phenocrysts and microphenoc-
rysts, and are iddingsitizated. They also occur in glomerophy-
GEOCHEMISTRY OF PLIOCENE-QUATERNARY KARASAR BASALT (TURKEY) 489
Fig. 2. Simplified geological map of the study area.
ric aggregates. Plagioclases have been seen as microlithes
which are perpendicular to each other. Clinopyroxenes are
generally subhedral.
Carbonates and zeolites can be seen as secondary minerals
in the rock samples of all the lava flows.
Analytical techniques
Twenty-seven samples of the Karasar basalt were analysed
for major and twenty-six samples for trace element concentra-
tions (Table 1). For major-element analyses, fused disks were
prepared by using six parts of prepared flux (lithium tetrabo-
rate) and one part of rock powder. The mixtures were fused in
crucibles of 95 % Pt and 5 % Au at 1050 °C for 60 minutes to
form a homogeneous melt. The melt was then poured into a
preheated mold to chill to a thick glass disk. Whole rock anal-
yses were performed at Hacettepe University using PHILIPS
PW 1480 X-ray spectrometer. Trace element and rare element
concentrations of 17 samples were analysed at ACME labora-
tories (Canada) by ICP-MS using fusion method.
Geochemistry
Representative geochemical data and normative mineralogy
are listed in Table 1. Figure 5 exhibits that the xenocryst bear-
ing rocks plot in subalkaline field. These rocks will not be
shown in geochemical interpretative diagrams because of their
quartz-xenocryst contents. Samples seen in basalt field in
Fig. 4 fall into both the alkaline and subalkaline fields. On the
basis of normative mineralogy, these rocks can be named as
hyperstene-normative tholeiites and nepheline-normative ba-
salts (Table 1). Trachybasalts have an alkaline character in
Fig. 5. Selected elements are illustrated in Fig. 6. Trachyba-
salts are characterized by high TiO
2
, P
2
O
5
, K
2
O and Na
2
O and
incompatible elements such as Rb, Nb and Zr. Nepheline-nor-
Fig. 3. Generalized tectonostratigraphical columnar section of the
study area.
490 ALPASLAN, YILMAZ and TEMEL
m1
m2
m3
m3a
m6
m7
m8
m9
m10
m11
m12
SiO
2
46.52
46.32
47.64
45.47
47.41
47.80
46.00
48.84
49.10
48.09
45.22
TiO
2
1.28
1.32
1.42
1.30
1.36
1.34
1.34
1.55
1.53
1.34
1.24
Al
2
O
3
16.06
15.93
16.39
16.25
16.76
17.07
16.65
16.94
17.18
17.23
16.02
Fe
2
O
3
10.70
10.80
11.11
10.05
10.38
10.46
10.26
11.02
10.90
11.14
10.37
MnO
0.16
0.16
0.17
0.15
0.16
0.16
0.16
0.16
0.16
0.17
0.15
MgO
7.59
7.60
7.66
4.15
4.85
4.41
5.19
4.89
4.82
4.49
4.87
CaO
8.99
8.86
8.73
12.86
11.16
10.87
11.55
9.55
9.56
9.93
12.97
Na
2
O
2.79
2.84
3.17
3.22
3.41
3.45
3.40
3.53
3.55
3.38
3.10
K
2
O
0.74
0.69
0.51
0.54
0.55
0.56
0.55
0.76
0.76
0.57
0.51
P
2
O
5
0.19
0.18
0.20
0.19
0.19
0.19
0.18
0.28
0.28
0.20
0.18
LOI
4.05
4.43
2.76
4.88
3.30
3.42
3.87
2.45
2.36
2.93
4.53
Total
99.07
99.13
99.76
99.06
99.53
99.72
99.15
99.47
100.2
99.47
99.16
Normative Mineralogy
Q
Or
4.61
4.31
3.11
3.39
3.38
3.43
3.41
4.63
4.60
3.49
3.19
Ab
24.84
25.37
27.65
18.84
26.62
30.29
21.74
30.63
30.70
29.62
16.98
An
30.67
30.31
29.91
30.06
29.95
30.57
29.98
28.87
29.36
31.27
29.92
Ne
5.47
1.82
4.58
5.82
Di
12.39
12.31
11.13
30.33
21.88
19.80
24.02
14.93
14.45
15.46
30.63
Hy
6.90
6.58
7.20
0.57
4.41
4.98
4.66
Ol
14.38
14.79
14.49
5.79
10.13
7.25
10.11
9.65
9.12
9.09
7.43
Mag
3.26
3.31
3.32
3.09
3.13
4.19
3.12
3.28
3.23
3.35
3.18
Il
2.56
2.65
2.78
2.62
2.68
2.64
2.67
3.02
2.97
2.64
2.49
Ap
0.47
0.45
0.49
0.48
0.47
0.46
0.45
0.68
0.68
0.49
0.45
Pb
2.50
3.30
2.60
2.10
2.80
2.90
2.20
3.20
3.00
2.80
2.40
V
187
183
205
181
179
181
184
200
195
219
174
Rb
12.7
13.5
12.2
10.2
10.5
11.1
11.8
15.6
14.7
11.6
8.9
Cs
0.30
0.40
0.50
0.10
0.10
0.10
0.60
0.30
0.30
0.10
0.10
Ba
126.5
113.9
132.6
178.5
145.2
165
303.1
227.3
235.5
262.6
329.2
Sr
508
516.4
552
353.8
351.4
355.6
344.3
391.1
387.9
346.9
333.5
Ga
16
17
17
17
16
17
18
16
17
18
17
Ta
0.50
0.40
0.52
0.40
0.40
0.40
0.40
0.70
0.70
0.50
0.40
Nb
5.2
5.3
5.2
6.1
6.0
6.0
6.1
8.8
8.4
6.1
5.4
Hf
2.70
2.90
3.40
2.90
2.80
2.70
3.20
3.90
3.70
2.80
2.90
Zr
109
111
119
110
113
111
113
136
136
117
111
Y
26.6
26.9
30.8
25.1
27.9
26.2
27
27.8
26.7
28.5
26.7
Th
1.80
3.00
2.50
2.1
2.2
2.3
2.8
3.5
3.3
2.4
3.4
U
0.4
0.8
0.8
0.2
0.3
0.4
0.3
0.6
0.3
0.7
0.3
La
10.9
11.0
11.7
10.7
11.0
10.4
11.0
15.7
15.9
12.1
10.9
Ce
21.6
23.0
25.0
24
24.1
22.8
24.3
30.9
31.8
25.8
23.6
Pr
2.90
2.94
3.14
3.06
2.97
2.97
3.11
3.97
3.89
3.22
2.97
Nd
12.3
12.8
13.3
14.0
14.7
13.7
14.3
16.3
17.8
13.5
13.6
Sm
3.8
3.4
3.6
3.3
3.6
3.6
3.2
4.5
4.5
3.7
3.0
Eu
1.17
1.15
1.26
1.34
1.23
1.26
1.26
1.38
1.36
1.19
1.19
Gd
3.86
3.95
4.34
4.06
4.15
4.01
3.97
4.61
4.17
4.21
3.84
Tb
0.68
0.72
0.72
0.72
0.78
0.75
0.76
0.79
0.69
0.72
0.72
Dy
4.43
4.63
5.05
4.36
4.73
4.00
4.43
4.72
4.33
4.65
3.97
Ho
0.94
0.93
1.03
0.89
0.96
0.94
0.88
0.97
0.98
0.95
0.95
Er
2.74
2.93
3.04
2.47
2.64
2.55
2.69
2.71
2.75
2.87
2.53
Tm
0.39
0.45
0.46
0.38
0.43
0.41
0.43
0.41
0.40
0.43
0.36
Yb
2.40
2.75
3.00
2.79
2.34
2.66
2.53
2.90
2.57
2.71
2.55
Lu
0.42
0.43
0.47
0.37
0.39
0.41
0.41
0.45
0.39
0.42
0.39
Zr/Nb
20.86
20.84
22.92
17.96
18.76
18.51
18.57
15.47
16.19
19.22
20.53
Zr/Y
4.07
4.10
3.87
4.36
4.02
4.24
4.19
4.89
5.09
4.11
4.15
Ba/Nb
24.32
21.49
25.50
29.26
24.20
27.5
49.68
25.82
28.03
43.04
60.96
Ba/La
11.02
9.80
10.99
16.68
13.20
15.86
27.55
14.11
14.49
20.95
30.20
(La/Sm)
N
1.85
2.09
2.10
2.09
1.97
1.86
2.22
2.25
2.28
2.11
2.27
Table 1: Geochemical analyses results of the Karasar basalt. (Total iron as Fe
2
O
3
, LOI as loss on ignition, major oxides and trace and
rare earth elements as per cent and ppm, respectively.)
mative and hyperstene-normative basalts generally overlap
with each other, although hyperstene-normative tholeiites
have relatively high contents of Fe
2
O
3
, MgO and V (Fig. 6).
Primitive mantle-normalized La/Sm ratios [(La/Sm)
N
] of the
Karasar basalt range between 1.85 and 3.33 (Table 1). Tra-
chybasalts have high (La/Sm)
N
ranging between 2.99 and
3.33, whereas tholeiites 1.852.57 and nepheline-normative
basalts 1.862.67. Trachybasalts (hawaiite) have higher TiO
2
,
K
2
O, Na
2
O, P
2
O
5
and Zr contents with correspondingly high-
er LREE (La=27.0822.91 ppm) contents relative to hyper-
stene-normative tholeiites (19.9611.47) and nepheline-nor-
mative basalts (10.7015.30) and more fractionated REE pat-
terns. La/Yb
N
ratios vary between 6.19 and 8.48 for trachyba-
salts (hawaiite), 4.90 and 2.80 for hy-normative basalts and
4.282.75 for ne-normative basalts, whereas Gd/Yb
N
ratios
vary between 1.46 and 1.87 for trachybasalts (hawaiite), 1.62
and 1.19 for hy-normative basalts, and 1.47 and 1.20 for ne-
normative basalts. The LILE (large-ion lithophile elements,
e.g. K, Rb, Ba, Sr) and HFSE (high-field strength elements;
Nb, Th, U, Ta) are also relatively co-enriched along with
LREE in the trachybasalts compared to nepheline-normative
basalt and hyperstene-normative tholeiites (Table 1).
GEOCHEMISTRY OF PLIOCENE-QUATERNARY KARASAR BASALT (TURKEY) 491
Table 1: Continuing.
On a primitive mantle normalized trace element diagram in-
dicate that all types of the Karasar basalt have parallel patterns
to each other (Fig. 7a). Trachybasalts have higher concentra-
tions of more incompatible elements than those of nepheline-
normative basalt and hyperstene-normative tholeiites, al-
though hyperstene-normative tholeiites have higher
concentrations of less incompatible elements such as Y and
Yb, than those of other basalts (Fig. 7a). Decreases of greater
magnitude from trachybasalt to nepheline-normative and hy-
perstene-normative basalts are generally associated with more
incompatible elements (e.g. La, Rb, K), so that ratios of high-
ly to moderately incompatible elements show similar decreas-
es in the same manner. All other incompatible elements (e.g.
K
2
O, Na
2
O and P
2
O
5
) show a decrease from trachybasals to
others. All samples display marked, but variable, depletions in
Nb and Ta. A Nb-Ta trough is a common feature in continen-
tal flood basalts. This signature also resembles that of volca-
nic arc basalts. Furthermore, negative Nb and Ta anomalies
could also result from crustal contamination of magmas (Win-
ter 2001).
Primitive mantle normalized rare earth element (REE) pro-
files of the Karasar basalt are shown in Fig. 7b. Figure 7b
m13
m14
m15
m16
m17
m18
m19
m20
m21
m22
m23
SiO
2
47.09
48.59
48.91
48.52
54.42
54.99
50.30
50.71
54.34
55.07
49.44
TiO
2
1.41
1.54
1.29
1.34
1.16
1.13
1.73
1.67
1.15
1.14
1.75
Al
2
O
3
16.60
16.75
17.62
17.00
16.17
16.24
15.96
15.93
16.31
16.30
16.31
Fe
2
O
3
10.41
11.04
10.59
10.57
8.48
8.27
10.03
9.86
8.38
8.34
10.45
MnO
0.15
0.16
0.21
0.19
0.14
0.12
0.14
0.14
0.14
0.13
0.15
MgO
4.71
5.62
5.33
5.91
4.94
4.50
6.36
5.23
4.82
4.85
4.64
CaO
11.18
9.50
9.70
9.97
7.71
7.53
6.96
7.18
7.80
7.47
8.16
Na
2
O
3.34
3.46
3.50
3.51
3.60
3.75
3.97
4.05
3.74
3.70
4.05
K
2
O
0.69
0.74
0.52
0.54
1.11
1.18
1.31
1.38
1.13
1.20
1.19
P
2
O
5
0.26
0.29
0.19
0.18
0.17
0.19
0.37
0.38
0.17
0.18
0.34
LOI
3.42
2.48
2.55
2.03
2.21
1.88
2.04
2.40
2.16
2.27
2.61
Total
99.29
100.17
100.41
99.76
100.1
99.78
100.17
99.93
100.14
100.38
99.10
Normative mineralogy
Q
5.96
6.53
5.18
6.24
Or
4.26
4.49
3.14
3.27
6.68
7.15
7.98
8.45
6.80
7.21
7.27
Ab
25.71
29.97
30.26
30.39
31.14
32.41
34.61
35.54
32.32
31.82
35.54
An
29.51
28.69
31.53
29.73
13.25
24.50
22.48
21.95
24.89
24.73
23.63
Ne
2.05
Di
22.17
14.77
13.67
16.33
10.32
10.05
8.53
10.03
10.91
9.49
13.06
Hy
3.48
4.84
0.29
13.56
12.33
12.05
13.22
12.81
13.46
5.56
Ol
9.80
11.75
10.52
13.87
4.64
1.24
5.15
Mag
3.15
3.28
3.13
3.15
3.89
3.84
4.76
4.68
3.87
3.86
4.80
Il
2.79
2.99
2.50
2.60
2.24
2.18
3.38
3.29
2.22
2.20
3.44
Ap
0.64
0.71
0.46
0.44
0.39
0.44
0.88
0.90
0.39
0.42
0.81
Pb
2.80
2.60
1.90
3.80
1.80
2.70
1.40
1.40
1.80
7.90
4.90
V
192
222
209
210
152
148
151
159
157
148
143
Rb
13.7
18
10.5
11.9
37.1
36.9
33.2
35.6
32.7
32.5
22.6
Cs
0.10
0.50
0.10
0.10
2.40
2.20
1.20
0.70
1.80
1.60
0.30
Ba
222.9
566.1
237.2
225.2
222.5
240.3
273.8
289
215
233.4
217.4
Sr
416.3
403.9
371.6
360.8
353.7
362.4
536.2
568.9
360.6
355.2
529.3
Ga
17
17
17
18
18
17
17
18
17
18
18
Ta
0.60
0.60
0.40
0.50
0.60
0.50
1.0
1.0
0.40
0.30
0.60
Nb
8.4
9.2
6.4
5.8
7.1
7.0
15.4
15.6
7.5
7.1
13.2
Hf*
2.60
3.40
2.90
2.50
3.90
3.50
4.80
4.90
3.30
3.10
4.60
Zr
131
144
117
117
128
129
197
206
127
132
171
Y
28.6
30.2
27.5
27
24.3
24.2
25.9
24.9
23.1
25.7
28.7
Th
3.6
3.3
1.9
2.5
6.2
6.8
7.2
7.1
7.4
6.6
4.7
U
0.5
0.8
0.5
0.7
2.3
2.1
1.4
2.2
2.1
2.2
0.3
La
15.3
19.5
11.6
11.3
16.7
17.8
26.3
26.5
26.1
19.3
22.1
Ce
33.0
34.9
22.9
23.1
31.7
31.5
51.3
53.1
32.0
34.3
41.8
Pr
3.98
4.54
3.12
3.02
3.56
3.68
5.79
5.85
3.56
4.10
4.78
Nd
18.6
18.8
12.7
14.1
14.8
15.0
24.1
22.1
14.4
16.4
20.5
Sm
3.7
4.9
3.4
3.5
3.5
3.7
5.1
5.6
3.2
4.7
4.5
Eu
1.36
1.43
1.24
1.19
1.17
1.18
1.65
1.60
1.11
1.25
1.55
Gd
4.49
5.12
3.63
4.08
4.06
4.04
4.81
5.06
3.61
4.19
4.51
Tb
0.73
0.80
0.69
0.69
0.63
0.57
0.77
0.82
0.60
0.76
0.75
Dy
4.52
5.12
4.54
4.76
4.11
3.79
5.05
4.49
4.03
4.36
4.56
Ho
0.91
1.05
0.97
0.93
0.78
0.77
0.88
0.90
0.82
0.85
0.88
Er
2.50
3.01
3.00
2.80
2.36
2.41
2.68
2.41
2.44
2.56
2.72
Tm
0.42
0.43
0.44
0.42
0.35
0.32
0.35
0.33
0.37
0.35
0.35
Yb
2.56
2.85
2.68
2.60
2.07
2.30
2.41
2.24
2.51
2.60
2.56
Lu
0.37
0.41
0.38
0.41
0.34
0.36
0.39
0.36
0.33
0.37
0.35
Zr/Nb
15.57
15.60
18.20
20.10
18.08
18.40
12.77
12.89
17.13
18.54
12.97
Zr/Y
4.55
4.75
4.23
4.31
5.28
5.32
7.59
7.28
5.56
5.12
5.96
Ba/Nb
26.53
61.51
37.06
38.82
31.33
34.32
17.77
18.06
28.66
32.87
16.46
Ba/La
14.56
28.35
20.01
19.47
13.04
13.21
10.11
10.52
13.08
11.89
9.49
(La/Sm)
N
2.67
2.57
2.20
2.08
3.08
3.10
3.33
3.05
3.25
2.65
3.17
492 ALPASLAN, YILMAZ and TEMEL
Table 1: Continuing.
shows that the trachybasalt has a steeper slope in light rare el-
ement (LREE) contents than the hy-normative tholeiites and
nepheline-normative basalts, whereas the hy-normative
tholeiites have higher concentrations of HREE (Fig. 7b).
LREE patterns exhibit a characteristic feature that there is a
decrease from trachybasalt to nepheline-normative and hyper-
stene-normative basalts, although hyperstene-normative
tholeiitic basalts have higher heavy rare earth element
(HREE) contents relative to others.
Discrimination plots (Fig. 8) based on trace element data
show that the Karasar basalt was derived from the melts gen-
erated in a within-plate environment.
Fig. 4. Total alkali-silica nomenclature diagram (LeMaitre 1989)
for the Karasar basalt. Black circles hy-normative tholeiites,
grey-circles ne-normative basalts, open circles trachyba-
salts, open squares: samples with quartz xenocrysts.
Fig. 5. Total alkali-silica diagram of Irvine & Baragar (1971)
showing that the Karasar basalt falls into the alkaline field, but
samples containing quartz xenocrysts fall in the subalkaline field.
(Symbols as in Fig. 4.)
Discussion
In this study, the petrogenetic features of both types of the
Karasar basalt have been determined using trace and rare earth
element geochemistry. Differences in the incompatible trace
and rare element contents of the Karasar basalt can be ex-
plained by fractionation, crustal contamination, source char-
acteristics and varying degrees of partial melting in a source
material. These will be discussed below.
Fractional crystallization
Although Karasar basalt samples do not satisfy the compo-
sitional criteria for identifying primary upper mantle partial
melts because of their Mg-numbers <63 %, the effects of frac-
tional crystallization in the evolution of the Karasar basalt la-
vas are suggested by the geochemical data (Fig. 6). MgO con-
tents ranging from 7.66 to 3.10 may suggest crystal
m24
m27
m28
m29
m30
SiO
2
49.89
45.21
45.08
48.89
46.39
TiO
2
1.80
1.35
1.43
1.43
1.45
Al
2
O
3
16.55
16.45
15.79
16.65
16.53
Fe
2
O
3
10.64
9.96
9.95
10.39
10.32
MnO
0.15
0.14
0.15
0.15
0.14
MgO
4.43
3.10
4.89
5.37
3.98
CaO
7.73
13.13
12.37
9.16
11.35
Na
2
O
4.17
3.30
3.23
3.12
3.50
K
2
O
1.22
0.64
0.65
0.65
0.70
P
2
O
5
0.35
0.23
0.23
0.23
0.24
LOI
2.29
5.49
4.79
2.99
3.99
Total
99.22
99.10
98.56
99.03
98.59
Normative mineralogy
Q
Or
7.65
4.05
4.10
4.01
4.38
Ab
36.39
18.23
18.45
27.49
24.52
An
23.55
30.16
28.45
30.74
28.90
Ne
6.30
5.79
3.68
Di
11.11
31.91
29.18
12.50
24.24
Hy
7.50
16.26
Ol
4.00
3.03
7.49
2.52
7.68
Mag
4.87
3.09
3.07
3.15
3.16
Il
3.53
2.74
2.90
2.83
2.91
Ap
0.83
0.58
0.58
0.57
0.60
Pb
5.80
3.20
2.20
3.40
V
150
194
198
206
Rb
25.2
15.6
18.4
17.9
Cs
0.30
0.40
1.20
0.50
Ba
221.6
206.1
135.6
166
Sr
530.6
387
371.1
402.7
Ga
17
17
17
18
Ta
1.50
0.5
5.90
0.50
Nb
14.7
7.4
7.5
7.6
Hf
4.20
2.90
2.90
3.20
Zr
182
127
119
135
Y
29.4
27.6
24.9
28.4
Th
5.9
3.1
3.3
3.4
U
0.6
0.3
0.5
0.5
La
23.2
13.3
13.2
10.4
Ce
43.9
28.8
28.6
29.7
Pr
5.13
3.58
3.29
3.66
Nd
20.6
17.7
14.3
18.9
Sm
5.0
3.6
4.1
3.8
Eu
1.58
1.37
1.25
1.43
Gd
4.90
4.29
4.02
4.46
Tb
0.80
0.72
0.67
0.85
Dy
4.90
4.96
4.52
4.35
Ho
0.91
0.97
0.83
1.01
Er
2.53
2.63
2.54
2.73
Tm
0.39
0.41
0.36
0.41
Yb
2.58
2.52
2.73
2.77
Lu
0.40
0.42
0.34
0.41
Zr/Nb
12.36
17.21
15.82
17.78
Zr/Y
6.18
4.61
4.76
4.76
Ba/Nb
15.07
27.85
18.08
21.84
Ba/La
9.25
15.49
9.86
11.77
(La/Sm)
N
2.99
2.38
2.08
2.33
GEOCHEMISTRY OF PLIOCENE-QUATERNARY KARASAR BASALT (TURKEY) 493
Fig. 6. Variation diagrams for selected elements. (Symbols as in Fig. 4.)
elements in the crust (Taylor & McLennan 1985).
Highly incompatible trace element abundances
and light-REE enrichments, which are seen in nor-
malized diagrams (Fig. 7), may either be a conse-
quence of crustal contamination or varying de-
grees of partial melting in the mantle source. In
general, the addition of crustal material to basaltic
magmas or their source region is expected to re-
sult in increasing of SiO
2
, Rb/Sr and K
2
O/P
2
O
5
(Carlson & Hart 1988), although this relationship
may be complicated by assimilationfractional
crystallization and partial melting effects (DePao-
lo 1981). In addition, crustal involvement results
in increasing Rb/Sr and K
2
O/P
2
O
5
relative to Ti/Zr
(Hoang & Flower 1998; Hoang & Uto 2003).
Plots of Ti/Zr against Rb/Sr and K
2
O/P
2
O
5
for
Karasar basalt samples (Fig. 9a,b) shown in rela-
tion to MORB, OIB, PM and continental crust
show that the samples cluster around a narrow
range of Rb/Sr (0.020.06) and K
2
O/P
2
O
5
(2.71
3.63), although quartz xenocryst-bearing rocks
have higher values of Rb/Sr (0.90.10) and K
2
O/
P
2
O
5
(6.216.67). On the other hand, continental
crust generally characterized by Zr/Nb>10 ratios
and high Ce/Y ratios (e.g. Taylor & McLennan
1985). The Karasar basalt samples form a trend
changing between OIB and MORB ratios, al-
though quartz-bearing rocks slightly differ from
the others (Fig. 9c). The quartz xenocryst-bearing
rocks of the Karasar basalt are actually displaced
away from the main array of data (Fig. 9c). Fur-
thermore, contamination of the melts with conti-
nental crust should result in negative correlations
between Nb/La and La/Sm
N
which are not ob-
served excluding quartz-bearing rocks (Fig. 9d).
In summary, it can be postulated that the Karasar
basalt samples show a minimal or no effect of the
crustal material, although the quartz-bearing rocks
show some evidence of the crustal material.
fractionation process during the ascent of magmas. Olivine
and clinopyroxene are the dominant fractionating phases.
Plagoclase+Fe-Ti oxides may also have been important frac-
tionated phases.
Crustal contamination
Because the Karasar basalt was extruded through the conti-
nental crust, it is essential to evaluate the possible effects of
crustal contamination before consideration the nature of man-
tle sources and melting processes. The extent of wall rock
contamination in continental basalts is controversial and diffi-
cult to identify unless chemical compositions of both contami-
nant and magmatic source are independently known (Carlson
& Hart 1988). Contamination by crustal rocks could mainly
increase the abundances of highly incompatible elements in
basaltic melts, but it has little effect on the contents of heavy
rare earth elements (HREE) and high-field strength elements
(HFSE, e.g. Nb, Ti and Ta) due to low concentrations of these
The source of the magmas: lithospheric or asthenospheric
mantle?
During the extension of the lithosphere, deeper parts of the
mantle ascend and melt adiabatically (McKenzie & Bickle
1988), thus both deep lithospheric mantle and the asthenos-
phere are possible magma sources. Karasar basalt exhibits
trace element ratios, which strongly differ from those of oce-
anic basalts (OIB and MORB, Fig. 10), as is the case of many
continental flood basalts (CFBs) and volcanic arc basalts.
Most of these CFBs have been interpreted as subcontinental
lithospheric mantle derived melts (Lightfoot et al. 1993; Frey
et al. 1996). The subcontinental lithospheric mantle is often
modified by fluids related to dehydration in subduction zones
(Noll et al. 1996; Brenan et al. 1996) and may have incorpo-
rated subducted sediments (Ben Othman et al. 1989; Sun &
McDunough 1989). These processes induce relative deple-
tions in Ti, Nb, and Ta and relative enrichments in Ba result-
ing in negative Nb-Ta anomalies on the normalized trace ele-
494 ALPASLAN, YILMAZ and TEMEL
Fig. 7. Primitive mantle normalized diagrams for Karasar basalt.
a Trace elements (normalized values from Sun & McDunough
1989); b Rare earth elements. (Normalized values from Sun
1982; symbols as in Fig. 4.)
Fig. 8. Geotectonic discrimination plots for the Karasar basalts. a
Zr/Y-Zr diagram of Pearce & Cann 1973; b Nb-Zr-Y diagram of
Meschede 1986. (Symbols as in Fig. 4.)
Fig. 9. a Ti/Zr-Rb/Sr, b K
2
O/P
2
O
5
-Ti/Zr, c Zr/Nb-Ce/Y,
d La/Sm
N
-Nb/La diagrams for the Karasar basalt. (MORB, OIB
and PM after Sun & McDunough 1989; LC lower crust, UC
upper crust and AC average crust after Taylor & McLennan
1985. Symbols as in Fig. 4.)
GEOCHEMISTRY OF PLIOCENE-QUATERNARY KARASAR BASALT (TURKEY) 495
ment patterns. It has been proposed that negative Nb-Ta
anomalies in the intra-continental basalts reflect a subconti-
nental lithospheric mantle source (e.g. Arndt et al. 1993;
Turner & Hawkesworth 1995). La/Nb ratio can be used to dis-
criminate between asthenospheric and lithospheric mantle
sources. Subcontinental lithospheric mantle sources typically
have La/Nb>1 whereas asthenospheric melts have La/Nb<1
(Fitton et al. 1991). All samples of the Karasar basalt have
La/Nb>1 implying their lithospheric signature. However,
some authors (Kelemen et al. 1990; Arndt & Christensen 1992)
have proposed that the relative depletion of HFSE, especially
Nb and Ta, in continental lavas, could result from interactions
between the subcontinental lithospheric mantle and asthenos-
pheric melt. The correlations observed between trace element
ratios (Fig. 10) indicate that the lithospheric signature of the
Karasar basalt cannot simply result from relative element de-
pletions due to crystallization of HFSE-bearing-oxides during
the transit and percolation of asthenospheric magmas through
the lithospheric mantle. Considering these characteristics, it
can be concluded that the source of the Karasar basalt is likely
to be as lithospheric rather than asthenospheric mantle.
Mantle source characteristics
All types of the Karasar basalt are characterized by a deple-
tion of Nb-Ta on the primitive mantle normalized diagram
Fig. 10. Selected trace element ratios diagrams for the Karasar ba-
salt. The fields of OIB, MORB, sediments, and subduction zone
magmas are from Weaver (1991), Sun & McDunough (1989), and
Ben Othman et al. (1989). (Symbols as in Fig. 4.)
(Fig. 7a). The large trough at Nb-Ta could reflect the exist-
ence of a residual Nb-Ta bearing phase in the source during
the partial melting, which has been explained in terms of re-
tention of this element in the source during partial melting
(Pearce 1996), by the effects of crustal contamination (Cox &
Hawkesworth 1985), or by the presence of subduction modi-
fied mantle (Peate et al. 1997). Rock samples have been plot-
ted on the Th/Yb-Nb/Yb diagram (Fig. 11a) modified from
Pearce (1983). These ratios are independent of fractional crys-
tallization and/or partial melting, and thus indicate source
variations. Basaltic magmas from mantle asthenosphere or
plume asthenosphere, all lie within or close to a diagonal
mantle array defined by Th/Nb ratios. However, source region
metasomatism by subduction processes results in enrichment
of Th with respect to Nb and hence Th/Yb ratios higher than
Nb/Yb, as subduction components generally carry Th but not
Nb or Yb. Figure 11a shows that all samples are displaced to
high Th/Yb ratios relative to mantle array. It should be noted
that the Karasar basalt samples are shifted from the mantle ar-
ray forming a sub-parallel trend to that array. This can reflect
a variety of processes from fractional crystallization and par-
tial melting acting on a magma derived from a mantle contain-
ing a subduction component. Furthermore, subduction-related
processes as a cause of metasomatism can readily be distin-
guished by HFSE and REE contents. If subduction-related
metasomatism was involved, one would expect a systematic
depletion of HFSE (e.g. Ta and Hf) relative to REE (e.g. La
and Sm), because REE are much more soluble than HFSE in
fluids (Jones et al. 1995). Considering the low HFSE/REE ra-
tios of the Karasar basalt, subduction-related metasomatism
appears as a more suitable enrichment process (Fig. 11b). In
addition, K/Nb ratios of the basaltic samples range between
7111243 compared to a value of 250 for average depleted
MORB (Hoffmann 1988) implying a relative enrichment in K.
An addition of these elements by partial melting processes ap-
pears unlikely because melting processes of spinel or garnet
peridotite do not fractionate these elements from another or
other highly incompatible elements (Haase et al. 2000). Fluid
metasomatism of continental lithospheric mantle (Hawkes-
worth et al. 1986) is a possible mechanism to produce the en-
richment of the alkaline and alkaline earth elements. This
mechanism also explains the observed patterns of the Karasar
basalt in the trace element patterns in Fig. 7a.
Partial melting in mantle
Varying concentrations of trace and rare earth elements in
the basaltic provinces can be explained by varying degrees of
partial melting of a single mantle source, derivation from dif-
ferent mantle sources and various degrees of fractionation
(Clague & Frey 1982; Hofmann et al. 1984; Wilson 1989;
Thomas et al. 1999). Low degrees of partial melting could
produce the enriched basaltic melts from a mantle source,
while high degrees of partial melting could generate the basal-
tic melts with lower concentrations of incompatible trace ele-
ments. All types of the Karasar basalt show patterns character-
ized by variable enrichments degrees relative to primitive
mantle concentrations in normalized trace and rare element
patterns (Fig. 7). The REE patterns indicate some differences
496 ALPASLAN, YILMAZ and TEMEL
between these basalts. Trachybasalt has steeper slope than the
other basalts in LREE. In general, primitive mantle normal-
ized REE patterns for the ne-normative basalt and trachybasalt
show a slight depletion in HREE relative to primitive mantle
values. These convex-downward patterns are characterized by
enrichments in LREE. Hy-normative tholeiites also contain
higher concentrations of medium-heavy rare earth elements
(Fig. 7b and Table 1).
Hy-normative tholeiites have generally higher concentra-
tions of total iron than the ne-normative basalts and trachyba-
salts, and trachybasalts have higher Na
2
O contents than the
others indicative of increasing melting pressure (i.e. depth)
coupled with decreasing degree of melting (SiO
2
). Na
2
O,
TiO
2
and K
2
O are moderately incompatible in mantle peridot-
ite and are concentrated in small melt fractions; as such their
concentrations in a melt decrease as the degree of melting
(SiO
2
) increases (Klein & Langmuir 1987). The trachybasalts
Fig. 11. a Th/Yb-Nb/Yb diagram (after Pearce 1983) for the
Karasar basalt. All samples exhibit a consistent displacement from
the mantle array indicating subduction-related metasomatism and/or
crustal contamination. b Hf/Sm
N
and Ta/La
N
diagram. All sam-
ples show the characteristic depletion of Ta relative to La observed
in basalts produced by mantle source metasomatized by subduction
related processes. Fields A and B: volcanic arc basalts taken from
Yogodzinski et al. (1995) and Francalanci et al. (1993), respective-
ly. (Depleted mantle (DM), normal-type MORB (N-MORB), en-
riched MORB (E-MORB) and ocean island basalts (OIB) after Sun
& McDunough 1989.)
of the Karasar basalt have higher concentrations of these ele-
ments suggesting different melting supporting evidence that
volcanism in this region is the result of partial melting rather
than changing composition of the mantle source.
Rare earth element ratios are useful for constraining the ex-
tent of partial melting along with the mineralogy and chemis-
try of the source. This is because the solid/melt partitioning is
different for spinel and garnet peridotite sources. Partial melt-
ing of either a garnet or spinel peridotite will prefentially en-
rich the LREE in the melt and produce La/Yb variations with
variable degrees of partial melting, although the La/Yb varia-
tions will be much larger for melting of garnet peridotite
source than of spinel peridotite source (Shaw et al. 2003). In
addition, the degree of enrichment of MREE relative to HREE
depends on whether garnet exists as a residual phase during
melting, as HREE are prefentially retained by garnet during
partial melting relative to MREE (e.g using distribution coef-
ficients from McKenzie & ONions 1991).
In the light of the above, a more useful approach to melt
modeling is the use of plots of LREE/HREE vs. MREE/HREE
ratios, e.g. La/Yb and Dy/Yb. These plots are particularly use-
ful as they distinguish between melting in the spinel and gar-
net peridotite sources (Thirwall et al. 1994; Baker et al. 1997).
Spinel-peridotite melting produces little change in Dy/Yb ra-
tios in melts compared with their mantle source and there is
also little change in Dy/Yb ratio of the Karasar basalt
(Fig. 12). In contrast, garnet-peridotite melting produces large
changes in Dy/Yb ratios. A second feature of such plots is that
mixing between different melt fractions will generate linear
mixing arrays.
Modelling of La/Yb and Dy/Yb ratios, coupled with Yb
abundances, is presented in Fig. 12. These plots show the
Dy/Yb
N
vs. La/Yb
N
data for the Karasar basalt data set along
with trajectories for non-modal fractional melts of garnet and
spinel-peridotite sources. The source concentrations use prim-
itive mantle values from Taylor & McLennan (1985), which is
a crude starting approximation of the likely source concentra-
tions. The following points can be gleaned from those models:
1. A depleted MORB mantle source does not have La/Yb
ratios high enough to reproduce the La/Yb ratios of most sam-
ples of the Karasar basalt (Fig. 12a). Primitive mantle normal-
ized diagram also implies a source more enriched than MORB
mantle.
2. Variable degrees of partial melting of a garnet-peridotite
source cannot generate the observed co-variation in Dy/Yb
N
ra-
tio with changing La/Yb
N
ratio (Fig. 12b,c). Melting of a garnet
peridotite should produce melts with much higher La/Yb
N
ra-
tios than the Karasar basalt samples at reasonable degrees of
partial melting, so that the lowest Dy/Yb
N
ratios of dataset re-
quire unrealistically large degrees of melting of garnet peri-
dotite source (>25 %). In addition, melting a garnet peridotite
source should produce melts exhibiting no co-variation be-
tween La/Yb
N
and Yb
N
(Fig. 12c) as Yb retained by garnet in
the source.
3. The Karasar basalt samples show small but significant
co-variation between La/Yb-and Yb, which suggests melting
involved a spinel peridotite source, although trachybasalt
samples of the Karasar basalt form a linear array toward the
garnet peridotite melting trajectory (Fig. 12c).
GEOCHEMISTRY OF PLIOCENE-QUATERNARY KARASAR BASALT (TURKEY) 497
In summary, melting extended in depth ranging from spinel
peridotite to garnet peridotite. For example, most samples in-
cluding hyperstene-normative and nepheline-normative ba-
salts appear to be derived from spinel-peridotite source where-
as trachybasalts require a mixing between a melt with a larger
degree of partial melting in a spinel-peridotite source and a
melt with a small degree of partial melting in a garnet-peridot-
ite source. This approximation also explains enrichments in
LREE and depletions in HREE for alkaline samples relative to
tholeiitic samples of the Karasar basalt.
Conclusions
1. The Karasar basalt mainly comprises the hyperstene-nor-
mative, nepheline-normative basalts, trachybasalts (hawaiites)
and quartz-bearing basaltic andesites. Quartz-bearing rocks,
which form the lowermost part of the Karasar basalt, obtained
from drilling core samples characterized by high silica con-
tents, varying from 54.3455.07 % SiO
2
, high Rb, Th, U, Cs
and light rare earth element concentrations (Table 1) relative
to basaltic samples.
2. All samples of the Karasar basalt have variable enrich-
ments in LILE and LREE in primitive mantle normalized
trace element patterns and characterized by negative anoma-
lies at Nb-Ta. The hy-normative tholeiites have higher con-
centrations of HREE relative to the ne-normative basalts and
trachybasalts, whereas the trachybasalts have higher concen-
trations of LREE resulting steeper slope in normalized REE
pattern relative to other basalts.
3. The Karasar basalt also shares several common composi-
tional trends. The most robust of these is an overall increase in
incompatible trace element concentrations from the hy- and
ne-normative basalts to the trachybasalts (Fig. 7). Increases of
greater magnitude are generally associated with highly incom-
patible elements (for Th, La, Rb, K, Zr, Nb etc.) and ratios of
highly to moderately incompatible elements (e.g. Ce/Y and
Zr/Y). There are also common compositional trends in some
of the major elements. Similarly, other highly incompatible
elements, both K
2
O and P
2
O
5
show a clear, large magnitude
increase from the hy- and ne-normative basalts to the trachy-
basalts. TiO
2
and SiO
2
(except quartz-bearing samples) also
increase in same manner.
4. The trace element characteristics of the Karasar basalt
imply that the crustal effects on the magmas have minimal or
no effect, but quartz-bearing samples have some influences of
crustal material.
5. Varying concentrations of the incompatible trace and rare
earth elements contents seen in primitive mantle normalized
diagrams suggest that the Karasar basalt can be explained by
varying degrees of partial melting in a single mantle source.
REE modeling indicates that the magmas forming the Karasar
basalt derived from a spinel-peridotite source, although tra-
chybasalts require an interaction between melts with larger
degree of partial melting in spinel-peridotite and melts with
lower degree of partial melting in garnet peridotite source.
6. The Karasar basalt was most likely derived from a meta-
somatized mantle source due to decompressional partial melt-
ing as the overlying continental crust was ruptured and
Fig. 12. La/Yb vs. Dy/Yb and Yb. Melt curves are point-average,
non-modal fractional melts of garnet and spinel lherzolites (garnet
lherzolite: 0.598 ol, 0.211 opx, 0.076 cpx, 0.115 gt which melts in
the proportions 0.05 ol, 0.20 opx, 0.30 cpx, 0.45 gt; spinel lherzo-
lite: 0.578 ol, 0.270 opx, 0.119 cpx, 0.033 sp which melts in the pro-
portions 0.10 ol, 0.27 opx, 0.50 cpx, 0.13 sp; Thirlwall et al. 1994).
Source compositions of depleted MORB, primitive mantle and dis-
tribution coeficients were taken from Taylor & McLennan 1985 and
McKenzie & ONions (1991), respectively.
The simplest model to account for the REE systematics of
the Karasar basalt samples involves mixing of small melt frac-
tions from garnet peridotite source with relatively larger melt
fractions from spinel peridotite source (Fig. 12b).
498 ALPASLAN, YILMAZ and TEMEL
thinned as a result of the lateral escape of the Anatolian plates
along both the east Anatolian and north Anatolian faults and
related secondary strike-slip fault systems during the post-col-
lisional extensional tectonic regime following the collision
between the Eurasian and Arabian plates. Volcanism in this
part of Anatolia is consistent with a model in which melting of
lithospheric mantle occurred in response to lithospheric exten-
sion.
Acknowledgments: This study was supported with a project
numbered as M-182 by the Cumhuriyet University Research
Foundation (CURF, Sivas-Turkey). We thank the CURF for
its supporting. We also thank the MTA for its logistical sup-
porting during the field study.
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