GeolCarp_Vol62_No6_547

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, DECEMBER 2011, 62, 6, 547—562 doi: 10.2478/v10096-011-0039-2

Introduction

The  Quaternary  alkaline  volcanism  of  NW  Iran  has  been
closely linked to the collision between the Afro-Arabian and
Eurasian plates. The northward motion of the Afro-Arabian
plate in the Late Mesozoic and Early Cenozoic was associat-
ed  with  subduction  under  the  southern  margin  of  Eurasia
(e.g.  engör  &  Yilmaz  1981;  Ricou  1994;  Mohajjel  et  al.
2003;  Agard  et  al.  2005;  Azizi  &  Moinevaziri  2009;  Saki
2010). Four structural zones developed in Iran as a result of
Neo-Tethys subduction beneath the Central Iran Microplate
(CIM)  and  the  following  collision  of  the  Iranian  and  Afro-
Arabian  plates  (Fig. 1a).  These  structural  zones  include  the
Urumieh-Dokhtar  magmatic  arc  (UDMA),  Sanandaj—Sirjan
Metamorphic  Zone  (SSMZ)  and  folded  Zagros  Zone  (High
Zagros  and  Zagros  Simply  Folded  Belt)  (Alavi  2004).  The
UDMA represents a continental arc that formed as a result of
the  subduction  of  the  Neotethyan  oceanic  crust  under  the
SSMZ in the Late Mesozoic (Alavi 1994).

This magmatic belt contains volcanic and plutonic rocks

of Eocene—Quaternary age that extend from NW to SE in
Iran. Magmatic activity in the UDMA started in the Late

Cretaceous and continued during the Eocene until Quaternary
period  (Ahmadzadeh  et  al.  2010).  However,  the  peak  of
magmatic activity is thought to be of Eocene age (e.g. Stock-
lin  1974;  Farhoudi  1978;  Emami  1981;  Jahangiri  2007).
Geochemical  studies  indicate  that  the  Urumieh-Dokhtar
magmatic  arc  is  generally  composed  of  subduction-related
calc-alkaline  rocks  (e.g.  Jung  et  al.  1976;  Dupuy  &  Dostal
1978; Berberian et al. 1982; Azizi & Jahangiri 2008). Alka-
line  rocks  are  also  reported  locally  by  Amidi  et  al.  (1984),
Hassanzadeh (1993), Moradian et al. (1997), Hajalilou  et al.
(2009), Khairkhah et al. (2009), Saadat et al. (2010), Saadat
&  Stern  (2011).  These  researchers  have  discussed  the
geochemistry, origin, magmatic processes (such as fractional
crystallization,  crustal  contamination  and  magma  mixing),
age  and  tectonic  settings  of  Quaternary  volcanic  rocks  in
Iran. The younger volcanic activity in the Urumieh-Dokhtar
magmatic  arc  is  mainly  alkaline  in  nature  and  is  associated
with tectono-magmatic processes related to post-collisional,
intra-continental  rifting  events  (Richards  2003).  In  this  pa-
per, we present new geochemical characteristics and Sr, Nd
data  on  lavas  from  the  Quaternary  alkaline  volcanism  in
northwest  Iran,  filling  a  gap  in  the  knowledge  of  the  post-

Quaternary post-collision alkaline volcanism NW of Ahar

(NW Iran): geochemical constraints of fractional

crystallization process

RAHIM DABIRI

, MOHAMAD HASHEM EMAMI

, HABIB MOLLAEI

, BIN CHEN

MANSOR VOSOGI ABEDINI

, NEMATALLAH RASHIDNEJAD OMRAN

and MITRA GHAFFARI

Department of Geology, Science and Research Branch, Islamic Azad University, Tehran, Iran; * r.dabiri@srbiau.ac.ir

Department of Geology, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Department of Geology, Mashhad Branch, Islamic Azad University, Mashhad, Iran

School of Earth and Space Sciences, Peking University, Beijing 100871, P. R. China

Department of Geology, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran

(Manuscript received January 5, 2011; accepted in revised form June 9, 2011)

Abstract: Major and trace elements and Sr—Nd isotopic data are presented for the Quaternary alkaline volcanism NW
of Ahar (NW Iran). The exposed rocks mainly consist of alkali basalts, trachybasalts, basaltic trachyandesites and
trachyandesites. Alkali basalts and trachybasalts display microlithic porphyritic texture with phenocrysts of olivine,
clinopyroxene, and plagioclase in microlithic groundmass. In the more evolved rocks (basaltic trachyandesites and
trachyandesites), amphibole and biotite have appeared. Major and trace element abundances vary along continuous
trends of decreasing MgO, TiO

, Fe

, CaO, Co, Cr, V and Zn, and increasing K

O, Al

, Ba and Th with increasing

SiO

. The Sr and Nd isotopic ratios vary from 0.704463 to 0.704921 and from 0.512649 to 0.512774, respectively.

Alkali basalts with high

143

Nd/

144

Nd ratio, low

Sr/

Sr ratio and high MgO, Ni and Cr contents indicate that they were

generated from relatively primitive magmas. Ba, Cr and La/Sm ratios versus Rb suggest that fractional crystallization
of alkali basalts could have played a significant role in the formation of evolved rocks. Assimilation and fractional crystal-
lization modelling, as well as Rb/Zr, Th/Yb and Ta/Yb ratios clearly indicate that crustal contamination accompanied by
the fractional crystallization played an important role in petrogenesis of the trachyandesites. The small compositional
differences between magma types, isotopic composition, mineralogy and nonlinear trends on Harker diagrams also indi-
cate that magma mixing was not an essential process in the evolution of the Ahar magmas. Petrogenetic modelling has
been used to constrain sources. Trace element ratio plots and REE modelling indicate that the alkali basalts were generated
from a spinel-peridotite source via small degrees ( ~ 2.5%) of fractional melting.

Key words: Quaternary, Iran, NW Ahar, geochemistry, alkaline volcanism, crustal contamination.

549

QUATERNARY POST-COLLISION ALKALINE VOLCANISM: GEOCHEMICAL CONSTRAINTS (NW IRAN)

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2011, 62, 6, 547—562

(2010) the last phase of volcanic activity in this area oc-
curred in Quaternary. The oldest unit of this region is Creta-
ceous (?)

basement

metamorphic

rocks

(micaschist,

meta-diabase and amphibolite), that is exposed in a very lim-
ited area. These rocks are covered by the Upper Cretaceous
volcanic  and  flysch  type  sedimentary  rocks  (Fig. 1b).  The
Cenozoic magmatism started in the Paleocene and continued
in the Eocene with intensive volcanic activity that produced
widespread  intermediate  to  felsic  rocks.  In  the  Oligocene—
Miocene  large  granitoid  plutons  were  emplaced  and  this
caused  extensive  alteration  and  mineralization  (Mollaei
1993;  Mollaei  et  al.  2009).  The  Oligocene-Miocene  intru-
sions  mostly  consist  of  coarse-  to  medium-grained  grano-
diorite  and  monzonite,  with  local,  younger  diorite  and
gabbro plutons. More alkaline, nepheline-syenitic to monzo-
syenitic  bodies  occur  in  Kaleybar  and  Razghah  (in  NW  of
Iran) (Ashrafi 2009; Aghazadeh 2009; Tajbakhsh 2010). The
Quaternary  basaltic  and  trachyandesitic  rocks  unconform-
ably  cover  the  older  magmatic  units.  This  Quaternary  alka-
line volcanism in northwest Iran occurred after Late Miocene
calc-alkaline  magmatism  (Jahangiri  2007).  During  the  Late
Miocene  to  Quaternary,  the  Ahar-Arasbaran  region,  under-
went  regional  contraction,  shortening  first  in  the  N-NW  di-
rection  and  subsequently  in  the  NNE  direction.  The
NNE-oriented crustal shortening was accompanied by WNW
stretching  and  extension  and  associated  intensive  alkaline
magmatism  in  a  broad  zone  of  dextral  transtension  in  the
hinterland of the Arabia—Eurasia collision front (Mohajjel &
Fergusson  2000;  Sosson  et  al.  2005;  Masson  et  al.  2006;
Dilek et al. 2010; Jamali et al. 2010).

Fig. 2. A modified and simplified geological map (after Mehrpartou 1993) of the NW Ahar. The led circles show the sample locations.

Analytical techniques

A total of about 200 samples from Quaternary alkaline

rocks in the NW of Ahar were collected. One hundred twenty
thin  sections  were  studied  by  Polarized  microscope.  Fifteen
representative  samples  were  then  selected  for  whole-rock
chemical  analysis  (Table 1).  Samples  weighed  between
1—1.5 kg  before  crushing  and  powdering.  Whole-rock  major
elements were determined by X-ray fluorescence spectrometer
(XRF)  and  trace  and  rare  earth  elements  (REE)  were  deter-
mined by lithium borate fusion ICP-MS at the ALS Chemex
Laboratories in Vancouver, Canada.

Sr and Nd isotopic analyses were performed at the Institute

of  Geology  and  Geophysics  (IGG)  in  Beijing,  China.  Mass
analyses were performed with a multi-collector VG354 mass
spectrometer.  Rb,  Sr,  Sm  and  Nd  concentrations  were  mea-
sured  using  the  isotopic  dilution  method.

Sr/

Sr and

143

Nd/

144

Nd ratios were normalized against

Sr/

Sr = 0.1194

and

146

Nd/

144

Nd = 0.7219, respectively.

Sr/

Sr ratios were

adjusted to NBS-987 Sr standard = 0.710250 and

143

Nd/

144

ratios to La Jolla Nd standard = 0.511860. Uncertainties result-
ing from the concentration prior to isotopic dilution are ± 2 %
for Rb, ± 0.4—1 % for Sr and less than ± 0.5 % for Sm and Nd,
depending upon the concentration levels.

Petrographic studies

The volcanic rocks in the study area, according to mineral as-

semblages, can be divided into three sub-groups, based on the

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DABIRI, HASHEM EMAMI, MOLLAEI, CHEN, VOSOGI ABEDINI, RASHIDNEJAD OMRAN and GHAFFARI

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GEOLOGICA CARPATHICA, 2011, 62, 6, 547—562

study of 120 samples. (I) Olivine basalt with grey to greyish
brown colours, which displays vitrophyric, porphyritic and in-
tersertal textures. Plagioclase, olivine and clinopyroxene form
the main phenocryst phases in these basaltic rocks. The micro-
crystalline matrix is dominated by plagioclase, clinopyroxene
and olivine. Rare nepheline also occurs in the groundmass of
some olivine basalts; (II) Olivine trachybasalt to trachybasalt
with  porphyritic  and  trachytic  textures  occur.  These  samples
contain  plagioclase,  clinopyroxene,  biotite  and  olivine.  Their
groundmass  consists  of  plagioclase,  pyroxene,  apatite  and
opaque  minerals;  (III)  Amphibole  trachyandesites  are  dark
grey  to  black  and  have  a  trachytic,  porphyritic  and  microlithic
textures.  Plagioclase,  clinopyroxene,  amphibole  and  biotite  are

Sample Ah-124 Ah-125 Ah-138 Ah-139 Ah-129 Ah-131 Ah-133 Ah-115 Ah-116 Ah-132 Ah-141 Ah-103 Ah-104 Ah-118 Ah-27
Rock

type AB AB AB AB TB TB TB BTA

BTA

BTA TA TA TA TA

SiO

(wt. %)

48.40 45.60 47.71 46.60 48.68 49.50 50.50 52.32 53.10 51.04 51.90 56.13 53.90 56.69 54.70

TiO

1.96 3.16 2.94 2.31 1.62 1.74 1.52 1.07 1.02 1.21 0.95 1.02 0.67 0.71 0.49

15.09 15.50 14.97 15.73 15.96 15.50 17.40 18.05 18.50 15.00 16.45 18.90 18.63 18.55 19.40

8.93 9.34 9.05 9.65 9.40 8.40 8.60 6.89 7.25 8.22 7.98 4.56 5.70 5.06 5.61

MnO

0.15 0.14 0.12 0.22 0.14 0.13 0.12 0.15 0.14 0.11 0.15 0.14 0.11 0.07 0.07

MgO

7.31 8.08 8.30 8.40 6.07 5.69 4.60 3.32 2.28 3.89 4.50 1.75 2.78 1.14 1.82

CaO

9.44 9.96 8.30 9.13 9.22 8.63 8.78 8.37 6.20 7.80 7.47 5.32 6.43 4.20 5.40

3.66 2.40 2.56 2.61 4.20 4.22 4.10 4.60 5.02 4.33 3.64 6.36 6.20 5.09 6.09

0.97 1.56 1.48 1.58 1.95 1.60 1.36 2.76 3.10 2.87 2.25 3.04 3.36 2.73 2.77

0.33 0.46 0.39 0.32 1.00 0.86 0.93 0.62 0.64 1.16 0.59 0.47 0.37 0.27 0.23

LOI

0.49 1.50 2.20 1.27 1.08 2.10 0.89 1.05 1.06 2.27 3.08 1.49 1.27 1.59 1.09

Total

96.73 97.70 98.01 97.82 99.32 98.37 98.80 99.20 98.31 97.90 98.96 99.18 99.42 96.10 97.67

Cs (ppm)

1.09 0.60 0.32 0.11 1.23 0.49 0.43 1.46 2.16 0.33 0.38 2.31 1.84 3.00 2.01

35.2 33.3 37.5 34.6 40.6 39.5 40.0 43.0 45.6 44.8 44.0 54.6 51.7 57.6 49.7

335

363

520

371

707

473

568

874

1020

944

708

1058

1190

1118

1082

1.48 2.29 1.91 1.86 2.57 2.57 3.47 4.27 3.89 3.09 5.13 5.13 7.08 5.25 7.24

1.0 1.1 1.2 0.9 1.6 1.3 1.2 1.3 1.3 1.1 1.3 1.1 1.7 0.7 0.8

19.3 21.0 25.6 17.1 32.5 27.6 26.1 23.8 24.1 24.7 23.1 17.7 24.9 11.8 12.5

715

830

550

422

1430

1695

1445

1190

1300

1850

1450

2324

1604

1952

2180

11 8

268

260

249

253

207

253

204

189

136

168

158

160

154

4.2 4.1 3.7 2.5 4.5 3.8 3.5 4.5 4.5 4.0 5.7 4.2 5.4 3.2 3.3

19.3 17.4 14.2 21.6 18.8 15.8 15.6 20.2 20.8 11.7 28.0 15.5 14.2 13.0 10.1

185

186

218

268

190

212

199

182

171

203

176

107

320

330

347

296

291

254

209

153

109

161

155

35.4 42.1 28.7 30.7 39.5 45.9 25.7 23.7 21.1 29.1 22.4 14.3 20.4 14.3 15.3

266

244

286

215

185

174

181

159

186

177

162

106

130

121

124

130

118

142

44.8 50.1 43.0 50.0 63.5 56.3 42.4 42.4 50.1 44.2 75.0 46.0 52.7 30.5 36.0

37.8 58.0 53.7 29.5 97.5 111.5 103.5 93.8 108.5 115.0 128.0 93.2 129.8 104.8 81.3

5.34 7.11 5.69 3.97 14.50 12.95 11.70 10.30 11.90 12.80 14.50 9.27 9.97 7.43 6.46

22.7 33.2 26.2 18.1 57.1 50.0 44.9 39.9 44.9 48.3 56.2 33.0 36.7 23.1 22.8

10.57 11.39 8.63 9.40 13.72 11.92 8.40 8.71 9.46 8.66 13.11 9.16 9.94 5.69 6.12

1.82 1.91 2.26 1.55 2.37 2.21 2.02 1.97 2.12 1.82 2.75 1.70 1.63 1.15 0.98

5.93 6.46 7.03 4.46 7.86 7.08 6.38 6.45 6.90 5.89 9.13 6.02 5.85 3.95 3.31

0.76 0.76 0.81 0.69 0.89 0.82 0.74 0.81 0.85 0.61 1.19 0.79 0.78 0.52 0.39

3.56 3.65 3.48 4.17 4.11 3.62 3.48 3.94 4.16 2.66 5.71 4.18 3.28 2.66 2.05

0.66 0.65 0.60 0.83 0.71 0.62 0.61 0.74 0.81 0.44 1.04 0.82 0.79 0.50 0.39

1.80 1.86 1.65 2.41 1.96 1.64 1.71 2.16 2.27 1.23 2.96 2.46 2.34 1.46 1.12

0.23 0.23 0.18 0.32 0.24 0.18 0.19 0.27 0.30 0.14 0.37 0.31 0.33 0.19 0.13

2.73 2.91 2.50 2.50 3.40 2.89 2.00 1.91 2.15 2.00 3.00 1.90 2.10 1.20 1.40

0.34 0.28 0.27 0.37 0.22 0.17 0.18 0.29 0.31 0.14 0.37 0.26 0.17 0.20 0.16

Sr/

0.704463 0.704697 0.704670 0.704800 0.704921 0.704763

143

Nd/

144

0.512774 0.512742 0.512696 0.512702 0.512651 0.512649

2.7 2.0

1.1

1.2

0.3

0.2

Table 1: Representative whole-rock analyses of the Ahar Quaternary volcanic rocks. AB – alkali basalt, TB – trachybasalt, BTA – ba-
saltic trachyandesite, TA – trachyandesite.

ubiquitous phenocrysts. The groundmass consists of microlithes
of plagioclase, amphibole and biotite with minor clinopyroxene.

Olivine occurs as phenocrysts and microphenocrysts in the

basalt and trachybasalt. Some olivine phenocrysts are embayed
and olivine also occurs as resorbed phenocrysts in the olivine
basalts (Fig. 3a). There are reaction rims around olivine phe-
nocrysts. The reaction rims around the olivines are composed
of fine-grained orthopyroxene, plagioclase and Fe-Ti oxide.

Clinopyroxenes are found in all rock types as phenocrysts and

microphenocrysts. In some clinopyroxene phenocrysts, matrix
fills embayments and the others have embayed margins sug-
gesting resorption (Fig. 3b). Clinopyroxene also occurs in glo-
meroporphyritic aggregates with plagioclase and Fe-Ti oxides.

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DABIRI, HASHEM EMAMI, MOLLAEI, CHEN, VOSOGI ABEDINI, RASHIDNEJAD OMRAN and GHAFFARI

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GEOLOGICA CARPATHICA, 2011, 62, 6, 547—562

crysts. They typically have thin rims of fine-grained pyroxene
and Fe-Ti oxide (Fig. 3e). This feature probably reflects vola-
tile  loss  during  ascent  of  magma  in  conduits  (Rutherford  &
Hill  1993).  Occasionally,  amphiboles  breakdown  to  clinopy-
roxene,  plagioclase  and  Fe-Ti  oxides  in  trachyandesite
(Fig. 3f). In some amphibole phenocrysts, groundmass micro-
lithes fill embayments. The biotites, typically euhedral grains,
occur as elongated crystals surrounded by opaque grains at the
rim. Fe-Ti oxides have magnetite compositions, are subhedral
and are present mainly in association with mafic minerals and
disseminated in the groundmass.

Geochemistry

Major and trace elements

Major and trace elements analyses were carried out on fif-

teen samples (Table 1). The Quaternary volcanic rocks in
Ahar have a wide range of chemical composition with SiO

contents ranging between 45 % and 57 %, and have been
classified on the basis of their alkali and silica contents using
the total alkali—SiO

diagram (TAS) of Le Maitre et al.

(1989).  No  major  compositional  gap  or  bimodality  is  ob-
served; instead, all the samples lie along a well defined and
relatively  tight  trend  in  the  TAS  diagram  (Fig. 4).  On  this
diagram the composition of volcanic rocks is represented by
alkali  basalt,  trachybasalt,  basaltic  trachyandesite  and  tra-
chyandesite.  This  diagram  also  shows  that  all  samples  are
plotting in the alkaline field. In the Harker diagrams, as SiO

increases, Fe

, MgO, CaO and TiO

decrease, while K

and Al

increase (Fig. 5). Such negative and positive cor-

relations can be explained by removal of the ferromagnesian
phases such as olivine and pyroxene. Compatible trace ele-
ments such as Cr, Co, V and Zn show strong negative corre-
lation with increasing SiO

, whereas incompatible trace

elements  (e.g.  Ba,  Th)  correlate  positively  (Fig. 6).  These
major  and  trace  element  trends  are  broadly  consistent  with
fractional crystallization plagioclase + pyroxene + Fe-Ti ox-
ides + amphibole + biotite removal, all of which are present
as  phenocrysts  in  the  Quaternary  volcanic  rocks  in  Ahar.
Primitive  mantle-normalized  trace  elements  patterns  of  the
study area are characterized by a Nb—Ta trough and are en-
riched in incompatible trace elements (Fig. 7). The negative
Nb—Ta  anomaly  for  Ahar  lavas  is  consistent  with  a  melt
source that was metasomatized by Nb—Ta-depleted aqueous
fluids produced from a dehydrating slab with residual rutile.

Fig. 4.  Total  alkali-silica  diagram  (Le  Maitre  et  al.  1989)  for  the
NW  Ahar  Quaternary  volcanic  rocks.  Dividing  line  between  alka-
line and subalkaline fields after Irvine & Barager (1971). AB – al-
kali  basalt,  TB  –  trachybasalt,  BTA  –  basaltic  trachyandesite,
TA – trachyandesite.

Fig. 5. Selected major element variations against SiO

content.

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DABIRI, HASHEM EMAMI, MOLLAEI, CHEN, VOSOGI ABEDINI, RASHIDNEJAD OMRAN and GHAFFARI

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GEOLOGICA CARPATHICA, 2011, 62, 6, 547—562

Isotope geochemistry

Six samples have been analysed for Sr and Nd isotopes. Sr

and Nd isotope ratios determined in this study are presented in
Figure 8, and representative analyses and

values are listed

in Table 1. The Nd isotopic compositions of

Sr/

Sr ratios

range from 0.704463 to 0.704921;

143

Nd/

144

Nd ratios range

from 0.512649 to 0.512774. The

values range Nd from 0.2

to 2.7. There is a clear relationship between geochemistry type
and isotopic characteristics. In the conventional

143

Nd/

144

vs.

Sr/

Sr diagram (Fig. 8), the alkali basalts plot in the de-

pleted quadrant of the mantle array, whereas the trachyandes-
ites plot in the enriched side. Basaltic trachyandesites and
trachybasalts lie between the alkali basalts and trachyandesites
(Fig. 8). All the samples plot within the mantle array and close
to the field of BSE (Bulk Silicate Earth). This suggestion is
compatible with the

values of the rocks, because a positive

value of epsilon for volcanic rocks implies a magma derived
from an isotopically depleted source (e.g. Rollinson 1993).
Low

Sr/

Sr and high

143

Nd/

144

Nd and low Ba and Rb in

contents indicate a mantle source also for these rocks. The
higher

Sr/

Sr and the lower

143

Nd/

144

Nd isotope ratios of

the trachyandesites may be interpreted in terms of crust—mag-
ma interaction. Sr—Nd isotopic compositions were compared
with data of young volcanics from north Iran and east Turkey
(Fig. 8). The isotopic data of the Ahar Quaternary volcanic
rocks are similar to the isotopic data reported from the Dama-
vand Quaternary stratovolcano (Liotard et al. 2008; Mirnejad

et  al.  2010)  in  the  central  part  of  the  Alborz  magmatic  belt
(AMB),  Quaternary  volcanism  from  the  Iran/Turkey  border-
lands (Kheirkhah et al. 2009) and  Quaternary volcanic centers
in Eastern Anatolia (Buket & Temel 1998). The isotopic ratio
of  the  Lesser  Caucasus  alkaline  Quaternary  volcanic  rocks
(Lebedev  et  al.  2003,  2007),  Ararat  Quaternary  volcano
(Gülen 1984) and Neogene volcanic rocks of eastern Turkey
(Aydin et al. 2008) are different from the study rocks (Fig. 8).
The Ahar Quaternary volcanic rocks have high

Sr/

Sr and

low

143

Nd/

144

Nd compared to the Caucasus alkaline Quater-

nary volcanic rocks and Ararat Quaternary volcano and low

Sr/

Sr compared to the Neogene volcanic rocks of eastern

Turkey.

Discussion

Fractional crystallization

The new data reported in this study indicate that the Qua-

ternary  volcanic  rocks  in  Ahar  have  similar  petrographical
and  geochemical  features  and  define  typical  alkaline  trends
from alkaline basalts to trachyandesites. Major element vari-
ations  are  mainly  controlled  by  the  fractionation  of  olivine
and  clinopyroxene,  which  strongly  deplete  the  magma  in
MgO,  TiO

, Fe

, CaO and compatible trace elements

(e.g. Co, Cr, V and Zn) (Figs. 5, 6). Incompatible (Rb) ver-
sus incompatible (Ba) trace element variations are linear,

Fig. 8.

143

Nd/

144

Nd and

Sr/

Sr isotope variation diagram for the Ahar Quaternary

volcanic rocks. BSE (Bulk Silicate Earth) composition is from Hart et al. (1992).
Locations of depleted mantle (DM) and enriched mantles (EMI, EMII) are from
Zindler & Hart (1986). The samples from other Neogene alkaline volcanic suites
are also plotted for comparison, including the QVA (alkaline Quaternary volcanic
rocks, Ararat volcano; Gülen 1984), QVC (alkaline Quaternary volcanic rocks,
Lesser Caucasus; Lebedev et al. 2003, 2007), QVD (alkaline Quaternary volcanic
rocks, Damavand Volcano; Liotard et al. 2008; Mirnejad et al. 2010), QVEA
(Quaternary volcanic rocks, Eastern Anatolia; Buket & Temel 1998), QVIT (alka-
line Quaternary volcanic rocks, Iran/Turkey borderlands; Kheirkhah et al. 2009),
NVT (alkaline Neogene volcanic rocks, NE Turkey; Aydin et al. 2008) and QH
(Hocheifel volcanic rocks, Germany; Fekiacova et al. 2007).

Fig. 9. Cr (compatible element) and Ba (incompatible
element) against Rb for the Ahar Quaternary volcanic
rocks.

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with  trends  from  low  abundances  in  alkali  basalts
towards  higher  abundances  in  trachyandesites
(Fig. 9). Compatible (Cr) versus incompatible (Rb)
element  variations  form  curved  rather  than  linear
trends (Fig. 9). Normalized REE patterns form par-
allel trends, and LREE contents increase from alkali
basalts  to  trachyandesites  (Fig. 10).  La/Sm  data
points (Fig. 11) plot along a line, a feature restricted
to  the  process  of  fractional  crystallization  (Allegre
&  Minster  1978).  The  above-mentioned  character-
istics  show  that  the  Quaternary  volcanic  rocks  in
Ahar  evolved  predominantly  through  fractional
crystallization  of  the  petrographically  observed
phenocryst assemblage (olivine + plagioclase + cli-
nopyroxene  +  amphibole  +  biotite  +  Fe-Ti  oxides)
and  fractional  crystallization  is  the  dominant  pro-
cess for the Ahar rocks suite.

Role of crustal contamination

In order to constrain the role of crustal contami-

nation,  we  have  utilized  the  assimilation  and  frac-
tional  crystallization  (AFC)  model  of  DePaolo
(1981). The negative trend in the Sr-Nd isotope dia-
gram (Fig. 12) indicates that the magmas have been
affected by crustal contamination during their ascent
to  the  surface.  We  therefore  attempted  quantitative
modelling  of  AFC  using  the  equations  of  DePaolo
(1981). In AFC modelling, the primitive mafic end-
member  is  the  alkali  basalt  sample  Ah-124,  which
has a modal mineralogy of 8 % olivine, 1 % ortho-
pyroxene,  18 %  clinopyroxene,  53 %  plagioclase,
6 % alkali feldspar, and 5 % magnetite from CIPW
calculations (Table 2). It is further calculated from
the  CIPW  values  of  the  parent  mafic  end-member
(Ah-124)  that  the  bulk  distribution  coefficient  for
Sr is 1.12, and for Nd 0.10 (D

= 1.12; D

= 0.10).

The  upper  crust  has  been  selected  for  the  contami-
nant  end-member  for  the  AFC  modelling.  Upper
crustal  values  are  from  Veizer  &  Compston  (1974)
and  O’Nions  &  Hamilton  (1984).  The  ratios  of  the
rate  of  assimilation  to  the  rate  of  crystallization

Fig. 10. Chondrite-normalized REE diagram for the alkali basalts and tra-
chyandesites (normalized values after Nakamura et al. 1974).

Table 2: Data used in the calculations of AFC modelling.

values for:

Starting

composition*

Calculated bulk partition

coefficient (D

) **

Olivine Opx Cpx Plag Mt

Sr 715

0.98

0.014 0.04 0.06 1.83

0.00

Nd 22.7

0.15

0.006 0.03 0.31 0.081 1.00

Th 1.48

0.015

0.04

0.13 0.03 0.01

0.00

Ta 1.0

0.07

0.04

0.15 0.013 0.018 1.00

Yb 2.73

0.2

0.014 0.34 0.62 0.067 0.9

values are from Rollinson (1993) and Keskin (1994).

Abbrevations: K

— mineral/melt partition coefficient, Cpx — clinopyroxene,

Plag — plagioclase, Mt — magnetite.

* — mafic parental end-member, sample Ah-124.

** — Of sample Ah-124 (Ol — 8 %, Opx — 1 %, Cpx — 18 %, Plag — 53 %,

K-spar — 6 %, Mt — 5 %).

Fig. 11. La/Sm variations against Rb for the Ahar Quater-
nary volcanic rocks.

Fig. 12. AFC modelling for

Sr/

Sr versus

143

Nd/

144

Nd isotopic compositions

for upper crustal (UC) end-member. Upper crustal values are from Veizer &
Compston (1974) and O’Nions & Hamilton (1984). Variations in r (the ratio of
the rate of assimilation/rate of crystallization) are shown with tick marks.

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(r  values  in  Fig. 12)  are  from  0.1  to  0.9.  Some  samples  are
located along AFC trajectories. Alkali basalts exhibit negli-
gible  crustal  contamination  according  to  the  diagram,  since
they  are  located  along  the  r = 0.1  trajectory  (Fig. 12).  The
contamination  of  the  primitive  end-member  Ah-124  by  the
continental crust gives rise first to trachybasalts and basaltic
trachyandesites  and  then,  by  a  higher  degree  of  contamina-
tion, to trachyandesites.

We have also prepared AFC modelling for Th/Yb versus

Ta/Yb diagram. This diagram has been found to be useful in
the  determination  of  crustal  contamination  (Fig. 13).  Th  is
more  affected  than  Ta  and  Yb  during  crustal  contamination
processes.  Therefore,  rocks  with  crustal  contamination  show
high Th/Yb values (Wilson 1989). In this diagram, Yb is used
as  a  normalizing  factor  to  minimize  the  effects  of  fractional
crystallization  and  crystal  accumulation  (Pearce  1983).  The
composition of the upper crust has also been plotted on the
diagram. The fractional crystallization vector and AFC curve
(r = 0.4)  for  fractionation  of  a  crystal  assemblage  consisting
of  8 %  olivine,  1 %  orthopyroxene,  18 %  clinopyroxene,
53 %  plagioclase,  6 %  alkali  feldspar,  and  5 %  magnetite
from the Ah-124 sample are also plotted (Fig. 13). The parti-
tion coefficients used are given in Table 2. The alkali basalt
to  trachyandesite  lavas  of  the  Ahar  exhibit  a  consistent  dis-
placement  from  the  mantle  array  towards  higher  Th/Yb  val-
ues.  The  alkali  basalts  plot  close  to  the  mantle  array  field,
suggesting  minimal  crustal  contamination  (Fig. 14).  The  tra-
chyandesites  have  high  ratios  of  Th/Yb  (2.7—5.2).  This  sug-
gests  that  the  role  of  crustal  contamination  in  their  magma
genesis cannot be ruled out.

The LILE (e.g. Rb and K) and Zr are incompatible with re-

spect to the major crystallizing phenocryst assemblage (pla-
gioclase, pyroxene, Fe-Ti oxides) and ratio like Rb/Zr do not
significantly change by simple fractional crystallization of this
assemblage. Variations in these ratios are preferably related to

Fig. 13. Th/Yb vs. Ta/Yb diagram (after Pearce 1983) for the Ahar Quaternary
volcanic rocks. AFC – assimilation and fractional crystallization, C – crustal
contamination, PM – primordial mantle composition, MORB – Mid-Ocean
Ridge Basalt.

crustal  contamination  by  AFC  processes  (David-
son et al. 1987). Examination of the study volcanic
rocks  shows  that,  in  the  alkali  basalts,  trachyba-
salts  and  basaltic  trachyandesites,  there  is  no  sig-
nificant variation in the Rb/Zr ratio (Fig. 14). The
trachyandesites  have  a  wider  range  of  Rb/Zr  val-
ues,  which  indicate  that  significant  contamination
is  involved  in  the  evolution  of  these  samples.
However,  the  trachyandesites  have  higher  Sr  and
lower Nd isotope ratios, and have higher Th/Yb ra-
tios and wider ranges in Rb/Zr values that clearly
indicate  crustal  contamination,  which  has  played
an important role in the genesis of these rocks.

Magma mixing

Petrographic data provide evidence for magma

mixing  in  the  Quaternary  volcanic  rocks  in  Ahar.
Some  rocks  contain  disequilibrium  mineral  tex-
tures such as sieve textured plagioclases, and show
resorption  of  the  ferromagnesian  phases  such  as
olivine, pyroxene and amphibole. Fine-grained re-
sorption  zones  in  plagioclase  are  probably  caused
by  superheating,  as  described  by  Tsuchiyama

(1985). The clear overgrowth rims on the sieved cores demon-
strate that the reaction took place before crystallization of the
inclusion groundmass began. Phenocrysts which are reacted
and resorbed in the study area formed when their host mag-
ma  interacted  with  a  more  basic  one.  The  olivine  phenoc-
rysts  exhibit  normal  zoning  whereas  some  of  the
plagioclases are reversely zoned. These features may be gen-
erated by fractionation of plagioclase in a magma chamber at
depth,  with  a  sudden  influx  of  more  primitive  phenocryst-
poor magma. The result is continuous normal zoning of oliv-
ine  phenocrysts  and  reversed  zoning  of  the  previously
formed plagioclase phenocrysts as a result of the new liquid
composition  (e.g.  more  primitive).  Whole-rock  major  and
trace element chemistry is also an excellent method of deter-
mining mixing relationships (Reid et al. 1983; Srogi & Lutz
1997). Perfect mixing may be identified by linear trends for

Fig. 14. Rb/Zr variations against Rb for the Ahar Quaternary volca-
nic rocks.

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all elements in Harker diagrams, but nonlinear trends on
Harker variation diagrams are consistent with crystal frac-
tionation processes (Wall et al. 1987) (Figs. 5, 6).

Fig. 15.  (a)  Sm/Yb  versus  La/Yb  and    (b)  Sm/Yb  versus  La/Sm    diagrams
showing  the  melt  curves  obtained  from  fractional  and  batch  melting  equa-
tions of Shaw (1970). La, Sm and Yb concentrations of the spinel and garnet
peridotite  are  from  McDonough  (1990)  and  Sen  &  Leeman  (1991),  respec-
tively. Bulk partition coefcients are taken from Tables 3 and 4. Solid square
and  star  represent  starting  compositions  of  garnet  and  spinel  peridotite  at
0.1 % F, respectively.

Table 3: Data used in the batch and fractional melting calculations of spinel-
peridotite.

Spinel-peridotite

composition (K

)

Mineral/melt

partition coeficients

Bulk partititon

coeficients (D

)

Initial

concentration

Co (ppm)

Olivine Opx Cpx Spinel

(66 % Ol,

24 % Opx,

8 % Cpx,

2 % Spinel)

2.6

0.0067

–

0.056

0.01

0.0091

0.47

0.007

0.05 0.45

0.01

0.053

0.26

0.014

0.34

0.542

0.01 0.13

La, Sm and Yb concentrations are from McDonough (1990), modal mineralogy of
the spinel-peridotite are from Wilson (1989: p. 50) and mineral/melt partition
coeficients of the basaltic melts are from Fujimaki, Tatsumoto & Aoki (1984);
McKenzie & O’Nions (1991); Rollinson (1993: p. 108). Abbrevations: Opx —
orthopyroxene; Cpx — clinopyroxene; Ol — olivine.

It is very difficult to assess the extent of magma

mixing if the source was the same for all magmas.
However,  magma  mixing  is  not  believed  to  be  of
great importance in the evolution of Ahar magmas,
because: (1) the small compositional differences be-
tween magma types, (2) the identical isotopic signa-
tures of the erupted lavas, and (3) the domination of
normally  zoned  phenocrysts  (olivine  and  plagio-
clase)  over  the  occasional  reversely  zoned  plagio-
clases (4) unlinear trends in Harker diagrams.

Determination of source characteristics

Whole-rock REE content is mainly controlled by

source  composition  and  degree  of  partial  melting
and  as  such  it  has  been  widely  used  to  determine
the  origin  of  the  magmas,  and  the  degree  of,  and
variation  in  mantle  melting  (e.g.  Gurenko  &
Chaussidon  1995;  Johnson  1998;  Münker  2000;
Green  2006;  Zhao  &  Zhou  2007).  The  REE  are
moderately incompatible during melting of mantle
peridotite  according  to  their  partitioning  coeffi-
cient  (Johnson  1998),  and  thus,  their  concentra-
tions and ratios are not greatly affected by mantle
depletion  and  fluid  influx  (Pearce  &  Peate  1995;
Münker  2000).  Sm/Yb  ratios  can  be  used  to  con-
strain  the  source  mineralogy  of  the  alkaline  mag-
mas, since Yb is compatible with garnet. Thus, we
have  achieved  REE  modelling  of  the  alkali  basalt
samples  (Fig. 15).  In  REE  modelling,  we  use  the
fractional  and  batch  melting  equations  of  Shaw
(1970). La, Sm and Yb concentrations, mineral/melt
(K

) and bulk (D

) partition coeffcients and modal

mineralogy of the spinel-peridotite and garnet-peri-
dotite  are  reported  in  Tables 3  and  4.  The  plot  of
Sm/Yb versus La/Sm and La/Yb distinguishes be-
tween  melting  of  garnet-  and  spinel-peridotite
sources  (Fig. 15).  Partial  melting  of  a  spinel-peri-
dotite source produces melts with lower Sm/Yb ra-
tios  than  a  garnet-peridotite  source.  It  is  apparent
from Figure 15 that the alkali basalt clearly plots on
the  fractional  melting  curve  of  spinel-peridotite.
REE  modelling  indicates  that  the  alkali  basalts
formed by partial melting of spinel-peridotite sourc-
es via degree of partial melting ranging from ~ 1 %
to  ~ 3 %. In Table 5 – trace element contents, bulk
distribution  coeficients  and  results  obtained  from
the calculations of 1 % to 5 % fractional melting of
the  spinel-peridotite  are  reported.  The  results  ob-
tained  from  1 %  to  5 %  degree  of  partial  melting
modelling  were  compared  to  the  alkali  basalt  sam-
ples on the primitive mantle-normalized spidergram
(Fig. 16).  It  is  clear  in  Figure 16  that  the  trace  ele-
ment  pattern  obtained  from  the  2.5 %  fractional
melting  of  the  spinel-peridotite  sample  has  the

highest similarity to the alkali basalt samples. We conclude
that the alkali basalt samples were generated by low degree
partial melting ( ~ 2.5 %) of a spinel-peridotite source.

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Table 4: Data used in the batch and fractional melting calculations of garnet-peridotite.

Garnet-peridotite

composition (K

)

Mineral/melt

partition coeficients

Bulk partititon

coeficients (D

)

Initial concentration

Co (ppm)

Olivine Opx Cpx Garnet (63 % Ol, 30 % Opx,

2 % Cpx, 5 % Garnet)

1.73

0.0067

– 0.056 0.0016

0.0054

1.12

0.007

0.05 0.45

0.217

0.039

0.51

0.014

0.34 0.542

6.167

0.43

La, Sm and Yb concentrations are from Sen & Leeman (1991), modal mineralogy of the
garnet-peridotite are from Wilson (1989: p. 50) and mineral/melt partition coeficients of
the basaltic melts are from Irving & Frey (1978), Fujimaki, Tatsumoto & Aoki (1984);
Rollinson (1993: p. 108). Abbrevations: Opx — orthopyroxene; Cpx — clinopyroxene;
Ol — olivine.

Fig. 16. Primitive mantle normalized (Sun & McDonough 1989) spidergrams calcu-
lated from the spinel-peridotite sample (McDonough 1990) at 1 to 5 % fractional
melting, compared with the alkali basalt samples. Trace element concentrations and
bulk partition coefcient (D

) of spinel-peridotite are taken from Table 5. Modal min-

eralogy of the spinel-peridotite as in Table 3.

Geodynamic implications

NW Iran is in the central part of the Arabian

lithospheric  collisional  zone,  which  experi-
enced  N—S  shortening  and  E—W  extension
accompanied  by  intense  faulting,  strong
earthquakes  and  active  volcanism  (e.g.
Dewey  et  al.  1986;  Karakhanian  et  al.  1997;
Talebian & Jackson 2002; Karakhanian et al.
2004;  Copley  &  Jackson  2006).  This  region
was  affected  by  a  complex  tectonic  regime
from  the  Late  Paleocene—Early  Eocene
( engör  &  Kidd  1979;  Topuz  et  al.  2005;
Karsli  et  al.  2007;  Önal  &  Kaya  2007).  The
melt  generation  modelling  and  geochemical
results  presented  above  show  that  the  source
of the alkaline rocks is enriched in LILE and
LREE  relative  to  primitive  mantle  (PM)  and
depleted MORB mantle (DMM).

Three main geodynamic models have been

suggested  to  explain  the  melting  process  of
the  lithospheric  mantle  in  NW  Iran  and  SE
Turkey.  They  include  mantle  plume  (Ershov
& Nikishin 2004), partial lithospheric delami-
nation  (Pearce  et  al.  1990)  and  slab  breakoff
(Keskin  2003;  engör  et  al.  2003).  For  NW
Iran  and  the  northern  part  of  UDMA,  the
melting of mantle lithosphere by heat from a
mantle plume is improbable, because there is
no  evidence  for  a  mantle  plume  origin.  Ahar
Quaternary volcanic rocks have high

Sr/

and low

143

Nd/

144

Nd compared to rocks de-

rived from plumes (e.g. Quaternary Hocheifel
lavas  (QH))  (Fig. 8).  A  mantle  plume  would
also be expected to produce a dynamic uplift
over  an  area  1000—2000 km  in  diameter
(White  &  McKenzie  1989;  Hill  et  al.  1992;
Ritter & Christensen 2007). Furthermore, the
overall  volcanic  expression  in  NW  Iran  is
asymmetrical,  extending  in  a  NW—SE  trend
sub-parallel to the general trend of the orogen-
ic  belt.  Therefore,  a  possible  cause  of  the
melting of the lithospheric mantle beneath the
area can be explained by heat from asthenos-
pheric  upwelling  resulting  from  lithospheric
delamination  or  by  detachment  of  subducted
slab following collision. Both mechanisms in-
volve  ascent  of  asthenospheric  mantle  to  re-
place  the  sinking  material.  These  are  not
mutually exclusive explanations (Keskin et al.
2006;  Dokuz  2010).  A  partial  lithospheric
delamination  model  is  suggested  by  Pearce
et al. (1990) for volcanism in Eastern Anatolia
and recently by Liotard et al. (2008) for the
genesis  of  Quaternary  alkaline  volcanic
rocks  in  Damavand  volcano.  The  slab  brea-
koff model is proposed by Keskin (2003) and

engör et al. (2003) for genesis of collision

related Miocene to Quaternary volcanism in

Calculated composition

for fractional melting

Starting composition
(66 % Ol, 24 % Opx,

8 % Cpx, 2 % Spinel)

Spinel-peridotite

Bulk

partition

coeficients

)

1 %F 2.5 %F 3.5 %F 4.5 %F 5 %F

Rb 1.9

0.01

70.11 17.09 6.59 2.51 1.55

Ba 33

0.04

714.66 469.12 353.05 264.92 229.22

Nb 4.8

0.01

168.48 21.73 5.45 1.35 0.67

Nd 2.67

0.08

31.09 25.82 22.78 20.07 18.83

Zr 21

0.04

397.57 280.65 221.84 174.93 155.19

Sm 0.47

0.053

8.47 6.11 4.91 3.93 3.51

Eu 0.16

0.07

2.13 1.71 1.47 1.27 1.18

Dy 0.51

0.05

8.17 6.18 5.12 4.24 3.85

Y 4.4

0.12

33.27 29.84 27.73 25.75 24.80

Yb 0.26

0.13

2.90 2.43 2.16 1.91 1.80

0.043

0.06

0.66 0.51 0.42 0.35 0.32

Table 5: Data obtained from the 1 % to 5 % fractional melting calculations of the
spinel-peridotite (McDonough 1990) end-member.

Modal mineralogy of the spinel-peridotite as in Table 3. The mineral/melt partition coefcients
of the basaltic melts are from Fujimaki, Tatsumoto & Aoki (1984); McKenzie & O’Nions
(1991); Rollinson (1993: p. 108). Abbrevations: Opx – orthopyroxene; Cpx – clino-
pyroxene; Ol – olivine.

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Eastern Anatolia and recently by Ghasemi & Talbot (2006)
and Omrani et al. (2008) for Pliocene-Quaternary volcanic
rocks at UDMA in the Zagros orogeny.

The northern part of UDMA has experienced calc-alkaline

magmatism  during  the  Eocene  period  and  alkaline  and  ul-
trapotassic  magmatism  during  the  Quaternary  period
(Ahmadzadeh et al. 2010). Preliminary research indicates that
calc-alkaline magmatism during the Eocene is related to sub-
duction of Neo-Tethys oceanic crust beneath CIM. Opening of
the Red Sea and the Gulf of Aden and rotation of the Arabian
plate  has  been  responsible  for  oblique  convergence  between
the Arabian plate and CIM and the final closure of the Neo-
Tethys Ocean. The final closure of Neo-Tethys and collision
between the Arabian plate and CIM took place before or dur-
ing the Late Miocene (Berberian & Berberian 1981; Berberian
et  al.  1982;  Dargahi  2007).  In  the  northern  part  of  UDMA,
cessation of magmatism occurred after the main period of con-
vergence, probably controlled by rollback processes and sub-
sequent  breakoff  of  the  subducted  slab  (Ghasemi  &  Talbot
2006; Jahangiri 2007). After the calc-alkaline volcanism, an
extensional  transtensional  regime  was  developed  in  the
Oligocene-Miocene  period.  As  a  result  of  extensional  tran-
stensional regime, local volcanic activities occurred along the
main  dextral  faults,  like  the  north-Tabriz  dextral  fault.  The
volcanic activity along the north Tabriz dextral fault is repre-
sented  by  the  Late  Miocene  and  ultrapotassic  and  alkaline
mafic magmas with adakitic signatures during the Pliocene—
Quaternary (Ahmadzadeh et al. 2010).

These variations in the lava chemistry of the Cenozoic vol-

canic  rocks  (Eocene  to  Quaternary)  indicate  a  geochemical
progression from calc-alkaline to more alkaline compositions
over time and a spatial shift from north to south towards the
Arabian  plate.  Considering  the  temporal  and  spatial  relation-
ship between calc-alkaline, adakitic, ultrapotassic and alkaline
rocks,  the  northwestern  UDMA  is  a  special  case  of  subduc-
tion-related, rollback magmatism and was possibly related to a
slab breakoff (detachment) system. Slab breakoff leads to the
generation  of  a  shallow  thermal  perturbation  and  opening  of
an asthenospheric window that in turn caused partial melting
of the subduction metasomatized lithospheric mantle beneath
the  collision  zone  (Davies  &  von  Blanckenburg  1995).  The
findings  of  the  recent  northern  part  of  UDMA  (Taghizadeh-
Farahmand  2010)  and  eastern  Turkey  seismic  experiment
(Al-Lazki  et  al.  2003;  Gök  et  al.  2003;  Zor  et  al.  2003)  and
seismic velocity from the Zagros collision to UDMA and CIM
(Kaviani et al. 2007), along with the tomographic models, sug-
gest  that  velocity  difference  at  shallow  depth  is  due  to  higher
mantle  temperatures  and/or  higher  fluid  content  beneath  NW
Iran  and  eastern  Turkey.  These  observations,  combined  with
trace element and isotope characteristics of these volcanic se-
quences, suggest that their magmas were derived from partial
melting of subduction-metasomatized continental lithospheric
mantle in the spinel-peridotite field beneath the CIM.

Conclusions

The Ahar volcanic rocks range from alkali basalts to tra-

chyandesites and show a typical alkaline differentiation trend.

Major and trace element variations indicate fractional crystal-
lization.  Alkali  basalts  crystallized  from  relatively  primitive
magma  as  suggested  by  their  mineralogy,  geochemistry  and
trace element ratios. AFC modelling, as well as trace element
ratios indicate that crustal contamination played an important
role in petrogenesis of the trachyandesites. The small compo-
sitional  differences  between  magma  types,  identical  isotopic
signatures, the domination of normally zoned phenocrysts and
nonlinear trends on Harker diagrams also suggest that magma
mixing is not of great importance in the evolution of the Ahar
magmas. Alkali basalts were derived from a spinel-peridotite
mantle source via a small degree ( ~ 2.5 %) of partial melting.

Acknowledgments: We are grateful to Drs. Patrik Konečný,
Jaroslav Lexa and Ioan Seghedi for their constructive reviews
that significantly improved the quality of this paper. This arti-
cle is derived from a PhD Thesis entitled, “Geochemistry and
petrology of Quaternary mafic volcanic rocks from NW Ahar,
NW Iran”. The authors appreciate the support received from
the Islamic Azad University, Sciences and Researches Branch.

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