Petrography, geochemistry and geodynamic environmentof potassic alkaline rocks in Eslamy peninsula,

northwest of Iran

B Hajalilou1,∗, M Moayyed2,∗∗ and Gh Hosseinzadeh2

1Department of Geology, Payame Noor University, Tabriz, Iran.2Department of Geology, University of Tabriz, Tabriz, Iran.

∗e-mail: hajalilou@pnu.ac.ir bhshnaha@yahoo.com∗∗e-mail: m.moayyed@tabrziu.ac.ir

Eslamy peninsula, 360 km2 in area, is located in the eastern coast of Urmieh lake in the northwestof Iran. This peninsula is a complex stratovolcano with a collapsed center, which is elevated dueto later intrusions of sub-volcanic masses with trachytic to microsyenitic composition. The compo-site cone consists of a sequence of leucite tephrite, tephrite, leucite basanite, basanite and relatedpyroclastic rocks. Magmatic activities in the Eslamy peninsula begin with potassic alkaline to ultra-potassic and basic, silica-undersaturated shoshonitic rocks and they are followed by intrusions oflamprophyric dykes and end with acidic magmatism including trachytic, microsyenitic, syenitic andphonolitic domes. The original magma of the Eslamy peninsula rocks has a potassic alkaline nature(Roman type) rich in LREE and LILE and depleted of HREE. These characteristics suggest that theorigin of magma can be from deep mantle with a garnet lherzolite composition, a low partial meltingrate which has been contaminated by crustal materials in its way up. Fractional crystallization ofolivine, diopsidic clinopyroxene and leucite played an important role in the evolution of magmas.Scrutinizing the geodynamic environment of Eslamy peninsula rocks in discrimination diagramsindicates that these rocks must have been formed in a post-collision magmatic arc setting.

1. Introduction

Potassic igneous rocks are categorized as K-richcalc-alkaline rocks, subduction-related shoshonites,within-plate potassic rocks, orogenic ultrapotas-sic rocks, shoshonitic and alkaline lamprophyres(Morrison 1980; Muller and Groves 1997).K2O/Na2O molar ratio in potassic rocks is equalto 1 or a little more and their MgO contentis over than 3% (Peccerillo 1992; Foley et al1987). Ultrapotassic rocks have a K2O/Na2Omolar ratio greater than 2, with the amount ofMgO being lower than 3% (Foley et al 1987).Nevertheless, the term potassic is usually usedfor both potassic and ultrapotassic rocks. Theserocks are classified into four main groups namely,

lamproites, shoshonites and Roman-type potassic,kamafugites, and ultrapotassic rocks.

The following hypothesis have been put forwardregarding the petrogenesis of these rocks:

• Assimilation of carbonate rocks by basic magma(Rittman 1933; Peccerillo 1992).

• Local infiltration (Harris 1957).• Zone melting (Key and Gast 1973).• Mantle metasomatism (Menzies and Hawkes

1981; Peccerilo 1992; Roy et al 2004).

In general, it is believed that potassic magmascan not be produced by partial melting of themantle alone and the other factors like inhomoge-neous mantle sources metasomatically rich in LILEand LREE are required as well (Peccerillo 1992;

Keywords. Mineralogy; petrology; geochemistry; volcanology; geodynamics; Eslamy peninsula; Iran.

J. Earth Syst. Sci. 118, No. 6, December 2009, pp. 643–657© Indian Academy of Sciences 643

644 B Hajalilou et al

Foley et al 1987). Peccerillo (1992) believes thatthe volatiles, LILEs and LREEs are accumulatedin hydrous minerals such as phlogopite and apatitethat are found in the glimmeritic veins and layersbeneath the continental crust in the upper mantle.

Shoshonitic and ultrapotassic magmatism in theEslamy peninsula with the Pliocene (6.5–8 Ma) agehas been reported to occur in the eastern coast ofthe Urmieh lake (Moin-Vaziri et al 1991; Moradian1997, 2007). Several assumptions have been madewith regard to the petrogenesis of these rocks, someof which are as follows:

• Final stages of magmatism in the active conti-nental margin due to subduction of Neo-Tethysoceanic crust beneath the central Iran block(Moin-Vaziri 1985; Moin-Vaziri et al 1991).

• Magmatism related to continental rift setting(Amidi 1975; Emami 1981; Amidi et al 1984).

• Hot spot-related magmatism within a conti-nental crust (Berberian 1981; Berberian andBerberian 1981).

The evidence discussed in this study indicatesthat magmatism in the Eslamy peninsula musthave occurred in a post-collisional magmatic arc.

2. Geological setting

Eslamy peninsula is located in the eastern coast ofUrmieh lake (figure 1). This peninsula includes acomplex stratovolcano with gentle slope flanks anda collapsed caldera in the central part (Hajalilouand Moayyed 2005). Later intrusion of sub-volcanictrachytic to microsyenitic rocks is supposed to havecaused doming and an uplift in the central parts inthese sections (figure 2). These rocks are a part ofthe Tertiary–Quaternary magmatic zone in north-west of Iran. The Eslamy peninsula highlands havetheir own distinct morphotectonic features, andare separated from the Sahand volcanic rocks bya plain. The gravitational field in this area variesfrom −110 to −100 milligals and the thickness ofthe crust is about 42–43 km (Dehghani and Makris1983).

The Eslamy peninsula’s two main faults trendingNNW-SSE and ENE-WSW intersect one anotheralmost in the middle space (figure 2). Furthermore,aerial magnetometry data delineates an importantlineament trending NNE–SSW in the basal rocksof the peninsula. This lineament is presumablyan extension of either the Arax or the Apsheron–Palmira fault extended towards the western coastof the Caspian Sea. The lineament seems to havean important role in the tectonic evolution of thestudy area.

The Eslamy peninsula stratovolcano is com-posed of a sequence of leucite basanite to leucite

Figure 1. Location of Eslamy peninsula in Iran.

tephrite lavas and the related pyroclastic rocks(breccia and agglomerate). These rocks are cutoff by later dykes with composition of basa-nite and tephrite (figure 3a). The orientationof these dykes is WNW-ESE (figure 2) whichimplies the extensional mechanism of faults andfractures during later magmatic events of thepeninsula. These events have led to the uplift-ing of the older volcanic units (Hajalilou 2005,2006). Trachytic to microsyenitic plugs and lam-prophyric dykes intersect Pliocene volcanoclasticconglomerate (figure 3b).

3. Petrography

The igneous rocks from the Eslamy peninsula arecomposed of tephrite, basanite, lamprophyre, tra-chyte, syenite and ultramafic xenoliths, each ofwhich is taken up separately in some detail below.

3.1 Tephrites

Tephrites exhibit a porphyritic texture and theirdistinct phenocrysts are clinopyroxene and leucite.The major minerals of these rocks include euhedralto subhedral clinopyroxene (figure 4a) and idiomor-phic crystals of leucite. The chemical compositionof clinopyroxenes was identified as diopside to salite(Wo47 En48.5 Fs4.5 to Wo49.3 En36 Fs14.7) by EMPAanalysis (Moradian 1997). The analyses indicatedthat the amounts of MgO and CaO get reducedfrom center to margin in zonal diopside pheno-crysts, followed by an increase in the amounts ofFeO, Na2O, Al2O3, TiO2 and SiO2 are increasing.In all diopside phenocrysts the increase of Al2O3

and TiO2 is accompanied by a decrease in SiO2

(Moradian 1997). These crystals show sieve texture

Potassic alkaline rocks in Eslamy peninsula 645

Figure 2. Geological map of Eslamy peninsula.

(figure 4a). Modal data of the Eslamy peninsulaigneous rocks is summarized in table 1.

Leucites are the second most important mine-rals in tephrites and are seen as euhedral crys-tals of complex twinning with small needles ofapatite and rutile within them. This mineral isaltered to analcime and orthoclase. These crys-tals are low in Na2O; however, the margins ofphenocrysts are rich in Na2O which might as a

result of an alteration to nepheline and analcimefrom the margins of these phenocrysts. The Si/Alratio in phenocryst samples varies from 2.03 to2.06 (Moradian 1997). Minor minerals of theserocks include fewer amounts of plagioclase, sani-dine, olivine, biotite, apatite and opaque mineralswhich are located in hyaline matrix.

Abundance of clinopyroxene and leucite coupledwith the lack of hydrous minerals and plagioclase

646 B Hajalilou et al

Figure 3. (a) Tephritic-phonolitic dyke intersects volcano-clastic conglomerate. (b) Trachytic plug with lamprophyrichead intersects volcanoclastic conglomerate.

show that the crystallization of magma hashappened in dry and imbalanced conditions.These rocks basically display hyaloporphyritic tohyalomicrolitic porphyry texture.

3.2 Basanites

Basanites mainly consist of euhedral to subhe-dral clinopyroxene (figure 4b) with the composi-tion varying from diopside to salite (Wo47.5 En49.5

Fs3 to Wo49.2 En41 Fs9·8) which exhibit sieve tex-ture and normal zoning. Another major mineral ofthese lavas is euhedral crystals of leucite with acomplex twinning. The third most common mine-ral of basanites is euhedral olivine (figure 4b) withmodal amount of 10% to 15%. The compositionof these crystals ranges from Fo84 to Fo84.8 anddo not show any interaction margin. The presenceof CaO is higher than 0.1% and amount of TiO2,Al2O3, Cr2O3 and Ni is less than that. The diffu-sion coefficient of Mg and Fe elements in olivinecrystals in relation to matrix is 4% which refersto crystallization of these crystals in high pres-sure (Moradian 1997). These crystals are basicallyiddingsitised along crystalline fractures. Minorminerals of basanites are sanidine and magnetite(Hajalilou 2005). Some inclusions of rutile andapatite needles can be seen in leucite. Texture ofthese rocks is hyaloporphyritic to hyalomicroliticporphyry.

3.3 Lamprophyric dykes

Lamprophyric dykes cut the volcanic rocks(tephrites and basanites) and the related pyroclas-tics with a NW-SE trend and lie beneath trachytelavas. These rocks are characterized with euhe-dral and shiny phenocrysts of mica which cangrow up to 3 or 4 cm and show porphyiric tex-ture. The major minerals are euhedral to subhe-dral phenocrysts of zonal mica (figure 4c) whichare delimited in a fine grain matrix of alkalifeldsparwith ocellar texture and fine grain alterationproducts. Euhedral to subhedral clinopyroxenesare pseudomorphed by the alteration products (cal-cite and opaque minerals). Minor minerals consistof amorphous apatite phenocrysts (figure 4c) andopaque minerals like pyrrhotite and magnetite. Thebiotites composition of these dykes is phlogopite(Moayyed et al 2008).

Spider diagrams pattern for the phlogopite issimilar to the pattern for the whole rock but Rh,Ti, K, and Ba contents in the phlogopite are higherthan the entire rock and Zr, Nd, P, Sr, Ce, La, Nband Th contents are lower than those for the wholerock (Moayyed et al 2008).

3.4 Trachytes

Trachytes in the Eslamy peninsula are exposedin three main forms: lava, dyke and subvolcanicdomes. Porphyritic texture and sanidine mega-crysts which, in some cases, may be as long as 5 cmcan be seen in the samples belonging to dykes andsubvolcanic domes. Major minerals include sani-dine (figure 4d). The minor minerals are subhedralcrystals of clinopyroxene, mica, sphene, apatite andthe rarest is plagioclase. Megacrysts of sanidinearranged along the flow direction are present in thesamples showing microlitic porphyry texture. Thecomposition of sanidine in these rocks is Or62.8 toOr72.9, and they contain 0–0.15% TiO2, 0–1.77%MgO and 0–1.99% FeO. As SiO2 increases in sani-dine crystals, the amount of K2O grows larger inaccordance with it (Moradian 1997). In trachytelavas, biotite crystals are recognized by TiO2 andFeO assembly in their margins and their Mg/Mg+Fe+2 ratio is less than 0.67 (Moradian 1977). Theabsence of amphiboles in trachyte lava is a signof magma crystallization in dry situations. Thetextures of trachyte lavas are trachytic, felsiticand intergranular. In the samples, belonging todykes and subvolcanic domes, the main texture ismicrolitic porphyry.

3.5 Syenites

Syenite to microsyenite masses of Eslamy penin-sula, located in the center of this area, are injected

Potassic alkaline rocks in Eslamy peninsula 647

Figure 4. (a) Subhedral clinopyroxene with sieve texture and idiomorphic leucite with complex twinning in tephrites;(b) Euhedral clinopyroxene and olivine in basanite; (c) Subhedral phenocrysts of biotite and apatite in lamprophyric dykes;(d) Phenocrysts of sanidine and trachytic texture in trachyte; (e) Alkalifeldspar and clinopyroxene in syenite; (f) Phenocrystof phlogopite with clinopyroxene in mica clinopyroxenite (mantle xenoliths).

Table 1. Modal composition from the Eslamy peninsulaigneous rocks.

Minerals

Rocks CPX Oli. Lu. AFs. Plg. Bio.

Trachyte + − − + + +Syenite + − − + − +Lamprophyre + − − + − +Basanite + + + + + −Tephrite + − + + + +

into volcanic and pyroclastic rocks (tephrites,basanites and tuffs) and to the related pyro-clastics. The major minerals are subhedral phe-nocrysts of alkalifeldspar and clinopyroxenes,biotite (figure 4e), sphen, apatite and opaque min-erals are minor ones. The dominant texture of themass is granular to trachytoide.

3.6 Clinopyroxenites with mica(ultramafic xenoliths)

These xenoliths can be seen in leucite tephriteto leucite basanite dykes and lavas as circularto ellipsoidal forms. Their color in hand speci-men is olive to dark green. The major minerals inthese rocks are euhedral to subhedral clinopyro-xene, phlogopite and opaque (figure 4f). Phlogopiteshows kink banding. These rocks must have origi-nated as mantle xenoliths.

4. Analytical methods

Thirtyone specimens of various rock types werechosen to be analyzed for petrochemical andgeodynamic studies. These specimens were sent tothe Kansaran Binalood Company for XRF analysis(table 2). A Phillips PW-1480 X-Ray fluorescense

648 B Hajalilou et alTable

2.

Chem

icalco

mpo

sition

ofth

eEslam

ype

nin

sula

rock

s.

Sam

ple

Tep

h.1

Tep

h.2

Tep

h.3

Tep

h.4

Tep

h.5

Tep

h.6

Tep

h.7

Tep

h.8

Tep

h.9

*Tep

h.1

0*Tep

h.1

1*Tep

h.1

2*Tep

h.1

3*Tep

h.1

4

Majo

rel

emen

ts(w

t%)

SiO

245.8

647.8

148.6

147.9

748.7

449.5

150.2

148.6

150.6

347.8

148.6

147.9

449.0

147.0

1A

l 2O

312.9

412.8

713.6

13.6

312.1

314.1

114.7

611.2

515.2

312.8

13.5

712.7

713.0

112.3

4

Fe 2

Ot 3

10.5

9.1

98.9

68.7

39.1

710.6

79.0

58.8

38.2

29.2

68.9

88.9

69.7

10.1

4C

aO

12.9

11.7

910.7

411.5

111.8

112.0

110.3

311.5

210.3

711.8

10.8

211.8

11.9

810.9

4N

a2O

1.0

50.7

41.2

2.3

21.1

33.0

72.0

81.3

12.4

90.7

21.1

80.7

2.8

91.0

8K

2O

4.8

36.4

37.3

85.9

54.8

61.6

55.9

26.3

84.8

76.4

47.4

26.5

45.9

86.4

8M

gO

5.4

86.0

74.1

15.0

11

3.6

23.1

87.3

44.6

16.1

74.2

86.1

85.3

16.5

2M

nO

0.1

60.1

60.1

40.1

46

0.1

48

0.1

65

0.1

52

0.1

38

0.1

40.1

60.1

50.1

60.1

80.2

7T

iO2

1.5

11.1

51.1

91.0

21.2

1.1

21.0

61.0

71.0

81.1

51.2

41.1

21.0

81.2

1P

2O

51.6

61.2

21.2

81.3

81.6

1.0

81.0

12

1.0

76

0.9

97

1.2

41.2

81.3

21.2

11.5

1Tota

l96.8

997.4

397.2

197.6

66

91.7

88

97.0

25

97.7

54

97.5

44

98.6

37

97.5

597.5

397.4

9100.3

597.5

Min

or

elem

ents

(ppm

)

Y24

29

29

24

49

36

27

24

20

28

30

28

36

25

Nb

27

35

31

29

39

23

29

20

28

34

32

35

27

30

Ta

1.9

81.8

2.4

61.7

31.1

1.8

61.9

91.9

82.0

81.9

6B

a3694

2500

4100

2851

2890

2810

2803

3280

4230

1981

3560

1978

2810

2828

W10

57.4

84.7

64

48.6

28

36

130

165

64

44

18

12

10

Pb

41

39

35

41

35

46

28

28

48

38

36

32

28

29

La

55

96.6

490.6

262

87.8

877

55

69.2

110.7

82

66

85

78

52

Ce

82

154

151

88

157

122

112

117

173

142

112

148

132

112

Th

11

36.6

27.0

414

38.1

120

21

21.3

731.6

721

17

20

19

29

U1

3.2

33.1

74

3.6

83

66.0

67.3

12

32

38

Mo

74.3

2.3

72.8

68

3.5

36

46

64

S5

56

75

710

62

68

78

11

Cl

197

165

169

836

233

91

231

347

1318

160

168

164

91

189

V193

175

150

181

179

201

161

132

142

174

152

176

189

301

Cr

50

248

90.6

49

35.2

519

534

91.6

84

32

82

54

22

Co

24

40.2

237.2

921

35.5

927

19

44.7

136.4

519

18

17

27

23

Ni

39

52

21

31

41

15

22

90

29

54

32

59

48

52

Cu

153

109

83

100

86

30

82

42

35

110

85

108

58

216

Zn

70

66

95.4

63

65

81

65

64

102

75

62

54

64

84

Rb

108

303

279

123

651

276

163

205

96

192

186

188

212

154

Sr

820

1020

1160

885

925

1151

1006

701

1640

742

910

752

882

841

Zr

238

250

214

257

334

262

234

422

278

260

298

294

284

218

Sb

10.1

61

10.4

11

10.2

50.3

41

11

11

Sn

11

22

13

14

11

21

31

Cd

89

22

3B

i1

24

32

Potassic alkaline rocks in Eslamy peninsula 649A

g1

11

11

11

11

11

11

1N

d67

78

63

36

92

93

71

53

51

79

64

78

83

43

As

39

1.5

61.1

34

4.2

634

19

2.2

614.3

117

26

12

18

28

Ga

14

12

12

15

15

13

15

10

14

12

13

12

13

14

Yb

3.6

52.4

52.6

71.8

23.6

43.6

42.6

73.6

83.5

93.7

2H

f8.2

210.0

211.3

87.5

56.3

39

10

910

8Lu

0.5

30.4

40.5

50.2

90.3

9E

u2.8

83.6

83.4

22.7

53.0

4T

b2.0

21.6

41.7

51.7

21.6

2Sm

13.2

11.9

616.0

111.3

111.9

8N

d79

90

86

85

60

Sc

38.7

537.1

921.1

840.3

931.4

1C

s16.5

816.7

147.4

711.6

49.0

4

Sam

ple

Sy.

1Sy.

2Sy.

3Sy.

4*Sy.

5*Sy.

6*Sy.

7*Sy.

8*Sy.

9Lam

p.1

Lam

p.2

Lam

p.3

Lam

p.4

Lam

p.5

Lam

p.6

Lam

p.7

Lam

p.8

Majo

rel

emen

ts(w

t%)

SiO

262.4

259.3

456.8

556.5

459.3

861.9

862.4

57.8

563.1

853.1

352.5

338.2

943.0

447.4

842.6

652.9

351.7

8A

l 2O

315.0

215.1

213.8

617.3

15.1

15.0

215.0

213.8

15.0

814.4

713.1

58.8

89.1

312.3

411.1

313.4

813.5

8Fe 2

Ot 3

5.4

4.5

26.6

84.0

54.5

5.4

45.4

25.9

84.0

85.8

87.8

516.0

59.9

413.1

49.5

86.6

26.4

1C

aO

2.8

76.0

15.6

55.9

56.1

2.8

82.8

85.2

1.8

88.9

48.2

617.3

513.1

69.7

811.8

18.6

39.8

5N

a2O

2.7

40.9

1.3

10.9

31.2

62.7

2.7

41.8

21.9

20.8

51.6

80.4

80.3

1.0

33

0.7

1.4

5K

2O

8.7

18.2

18.6

39.4

28.1

78.8

8.7

18.6

39.4

47.8

46.9

82.3

95.4

96.5

56.9

18.0

47.4

1M

gO

1.2

1.3

83.7

61.4

61.4

41.2

71.2

22.8

80.9

83.8

34.4

610.7

712.7

85.6

46.7

4.3

44.0

3M

nO

0.0

70.0

76

0.1

20.0

70.0

80.0

70.0

70.1

20.0

90.0

97

0.1

19

0.1

70.1

20.2

60.1

40.1

07

0.1

02

TiO

20.7

76

0.6

72

0.9

70.5

70.6

70.7

80.7

80.9

70.6

80.8

51.0

61.8

82.1

71.1

21.4

31.1

41.0

1P

2O

50.2

90.6

90.7

20.5

60.6

90.3

20.3

20.7

80.2

11.0

50.9

83.0

12.1

81.1

51.0

16

1.1

51.1

1Tota

l99.4

96

96.9

18

98.5

596.8

597.3

999.2

699.5

698.0

397.5

496.9

37

97.0

69

99.2

798.3

198.4

994.3

76

97.1

37

96.7

32

Min

or

elem

ents

(ppm

)

Y30

28

31

23

40

82

30

31

34

26

25

19

22

25

28

27

27

Nb

73

39

39

31

40

68

73

48

57

28

23

55

30

28

35

37

Ta

2.3

1.8

12.3

83.1

42.8

42.4

82.9

41.7

8B

a2828

3140

2488

2160

1900

2814

2820

2470

1964

1414

3210

2974

3679

2244

2908

2372

2161

W97

100

61

108

63

96

97

60

40

61

80.1

37

751

253

69

Pb

43

59

40

38

60

44

43

40

44

35

53

84

18

40

36

38

La

52

80.7

650

80.3

148

53

52

50

54

43

82.4

43

33

68

45

44

45

Ce

112

134

75

126

60

110

112

102

117

99

138

68

64

137

85

77

96

Th

45

56.4

234

38.6

737

44

45

38

40

19

25.1

62

621

23

24

30

U10

14.6

119

12

910

10

19

12

10

7.0

11

48

97

12

Mo

15.5

65

3.7

21

11

16

4.8

97

84

44

S543

98

59

540

543

82

32

851

41

711

236

88

Cl

846

34

119

66

34

840

840

219

48

137

424

891

260

274

187

300

120

V86

93

138

74

94

88

88

132

79

114

143

288

164

301

159

126

131

650 B Hajalilou et alSam

ple

Sy.

1Sy.

2Sy.

3Sy.

4*Sy.

5*Sy.

6*Sy.

7*Sy.

8*Sy.

9Lam

p.1

Lam

p.2

Lam

p.3

Lam

p.4

Lam

p.5

Lam

p.6

Lam

p.7

Lam

p.8

Cr

22

121

72

259

30

21

22

38

589

37.2

779

59

150

138

82

89

Co

23

20.0

817

32.2

411

24

23

17

614

31.1

133

25

28

11

13

19

Ni

20

25

43

17

24

22

20

22

924

26

44

95

37

51

28

32

Cu

706

71

385

53

70

704

218

118

10

55

101

10

430

84

65

65

Zn

83

46

92

93.9

47

88

83

92

68

51

116

66

49

258

79

56

58

Rb

195

300

255

225

210

198

195

255

288

175

153

46

117

155

195

207

191

Sr

1206

156

1163

895

1288

1214

1207

1162

1218

751

949

450

483

851

531

843

864

Zr

586

637

391

308

437

568

586

432

490

293

317

100

49

208

279

364

364

Sb

11.2

21

0.9

11

11

11

20.6

71

11

21

1Sn

15

34

51

13

34

11

24

32

2C

d1

BD

11

1B

i1

11

11

Ag

11

11

11

11

11

11

11

11

1N

d35

62

29

21

63

37

44

31

28

51

46

77

32

35

38

30

44

As

40

3.7

637

8.4

14

42

40

32

28

53

12.6

915

25

55

31

531

Ga

18

20

17

19

21

19

18

17

21

13

14

99

13

15

20

14

Yb

1.6

2.1

61.6

1.4

32.8

82.5

82.1

53.4

2H

f13.1

10.4

10

13

24

19

17

8.8

3Lu

0.4

0.2

20.3

9E

u2.4

2.5

3.1

Tb

1.3

21.4

51.9

Sm

9.5

512.8

10.6

2N

d64

88

96

Sc

20.2

333.0

229.8

1C

s4.1

547.4

334.2

8

Sam

ple

Tr.

1Tr.

2Tr.

3Tr.

4Tr.

5Tr.

6Tr.

7Tr.

8*Tr.

9*Tr.

10

*Tr.

11

*Tr.

12

*Tr.

13

Majo

rel

emen

ts(w

t%)

SiO

264.2

564.9

254.0

460.3

458.4

60.4

663.6

761.7

964.9

56.6

459.3

60.3

61.7

Al 2

O3

16.5

416.9

17.1

615.0

115.3

15.4

214.3

916.5

16.8

818.0

215.1

215.0

115.8

Fe 2

Ot 3

3.6

32.3

46.0

14.2

45.5

84.6

36.1

14.2

72.3

45.4

44.5

4.1

44.2

CaO

0.6

51.4

46.1

75.0

44.2

4.8

21.6

63.4

51.4

45.5

85.8

85.0

43.5

8N

a2O

1.8

84.2

60.6

21.9

61.1

42.0

24.3

72.6

84.2

44.6

20.9

21.8

42.7

K2O

10.5

67.7

49.2

28.8

310.3

28.3

66.0

68.4

7.7

87.6

28.1

28.8

28.4

MgO

0.2

60.2

41.0

71.4

91.1

21.1

71.5

0.5

10.2

32.5

11.2

81.1

80.8

2M

nO

0.0

86

0.0

81

0.1

30.0

88

0.1

20.0

92

0.0

70.0

96

0.0

80.1

20.0

80.0

90.1

TiO

20.5

30.2

68

0.8

45

0.5

40.8

50.5

70.7

0.5

0.2

70.6

10.6

70.5

40.4

9P

2O

50.0

80.0

56

0.4

0.5

30.3

70.4

60.2

40.2

10.0

60.3

80.7

0.5

30.4

8Tota

l98.4

66

98.2

45

95.6

65

98.0

797.4

98.0

02

98.7

798.4

06

98.2

2101.5

496.5

797.4

998.2

7

Potassic alkaline rocks in Eslamy peninsula 651M

inor

elem

ents

(ppm

)

Y32

30

29

33

32

37

25

32

30

20

28

33

34

Nb

57

73

64

47

76

55

49

68

74

16

39

47

60

Ta

2.6

72.9

43.2

43.5

13.3

83.4

82.1

22.3

22.4

12.4

4

Ba

2210

1400

3025

1413

3727

2270

2310

2500

968

2308

1980

1490

1850

W57.1

180

56

129

74

144

100

168

147

752

88

92

Pb

69

101

60

42

33

69

112

69

102

47

59

42

62

La

75.5

3106

81

48

46

91.6

529.6

3109.3

65

28

48

52

65

Ce

125

154

161

99

98

142

114

160

78

27

59

99

128

Th

57.6

3109.9

40

49

49

75.7

658.8

899.2

679

44

36

49

67

U3.7

16.8

833

10

19

10.6

816.3

77.5

315

49

10

5

Mo

2.8

5.4

32

14.1

3.2

4.3

61

22

31

S9

885

98

10

179

11

884

12

911

Cl

48

1684

175

97

135

34

137

26

1680

175

36

97

26

V77

44

121

82

107

85

110

69

40

117

92

80

68

Cr

7.5

3.3

345

475.1

19.4

6.3

237

32

28

12

Co

7.1

812.4

213

12

12

19.0

219.0

215.6

19

21

11

10

47

Ni

46

917

17

88

56

18

25

17

5

Cu

10

9111

59

428

13

19

966

71

50

19

Zn

62

59.8

70

53

77

85.6

65.3

72.7

56

65

46

50

52

Rb

358

254

157

268

224

371

153

323

210

62

228

269

229

Sr

1380

1430

1331

1205

1341

1140

260

1750

1230

988

1280

1208

1218

Zr

395

789

531

557

798

580

537

687

838

534

440

557

688

Sb

0.6

50.6

61

11

0.6

81.3

40.7

14

BD

11

1

Sn

31

22

34

41

BD

BD

52

1

Cd

11

21

2

Bi

11

11

1

Ag

11

11

11

11

11

42

3

Nd

29

32

41

35

46

48

38

62

32

30

62

35

61

As

24.2

522.8

628

52

13

8.2

120.8

35.7

554

28

38

13

Ga

21

28

18

18

18

18

18

20

27

18

20

18

20

Yb

2.1

51.2

32.6

42.4

62.7

32.3

32.4

61.6

2.6

42.7

3

Hf

16.6

523.0

916.9

414.4

521.5

820

16

13

17

22

Lu

0.3

40.4

40.4

50.3

10.3

7

Eu

2.7

1.3

72.5

41.9

62.5

Tb

0.8

20.9

1.2

1.3

31.4

4

Sm

6.7

87.5

49.4

55.9

9.2

1

Nd

42

49

90

48

45

Sc

5.9

11.7

214.5

712.0

87.5

6

Cs

10.7

132

14.2

218.1

131.4

5

Tep

h:Tep

hrit

e,Sy

:Sy

enit

e,Tr:

Tra

chyt

e,Lam

p:Lam

prop

hyre

(∗:D

ata

from

Moa

yyed

etal

2008

).

652 B Hajalilou et al

Figure 5. Rock types of Eslamy peninsula in TAS diagram after Le Bas et al (1986).

Figure 6. Eslamy peninsula rocks plot in the shoshonite field in diagram of K2O vs. SiO2 (after Peccerillo and Taylor1976) and Th/Nb vs. Ta/Yb (after Pearce 1983).

was used for major and trace element analyses.The amounts of major oxides and 27 elementswere determined in these specimens as well.Furthermore, 14 specimens were selected for study-ing the behaviour of rare earth elements (REE).33-element analyses were performed using NeutronActivation Analysis (NAA) method. A minia-ture neutron source reactor (MNSR) operating in27 kW condition in Isfahan Nuclear Research Cen-ter was used for NAA. The error in the analyseswas about 1%. In addition to the above-mentionedsamples, the results of analyses included 15 samples

(Moayyed et al 2008) were used for drawing thegraphs and conclusions (table 2).

5. Geochemistry

Based on analytic data and the plot of alkaliesvs. silica (TAS) of the old volcanism in Eslamypeninsula, the samples lie within the field of basalt,trachy-basalt, tephrite and phonotephrite. Samplesrepresenting young magmatic activities were plot-ted within the trachyte, trachyandesite, phonolite,

Potassic alkaline rocks in Eslamy peninsula 653

Figure 7. Eslamy rocks plot in the group III of potassicigneous rocks (after Foley et al 1987).

Figure 8. Harker variation diagrams for Eslamy peninsula rocks (after Harker 1909).

trachyphonolite, syenite and syenodiorite fieldsand lamprophyre samples were represented in thefoidite, tephrite and trachyandesite fields (figure 5).

In general, based on the K2O/SiO2 dia-gram of Peccerillo and Taylor (1976) and theTh/Yb-Ta/Yb diagram of Pearce (1983), theoriginal magma of Eslamy peninsula rocks had ashoshonitic to ultrapotassic nature (figure 6a, b).The K2O/Na2O ratio in tephritic and basaniticrocks is always higher than 1, even reaching 4at times. These rocks have normative olivinesand leucites, rich in LILE and LREE. Theabove-mentioned qualities also exist in trachytes,phonolites, syenites and lamprophyres of the studyarea. In the CaO/Al2O3 diagram of Foley et al(1987) the rock types of Eslamy peninsula plot infield III (Roman type rocks, figure 7). Geochemicalinvestigation of minor and trace elements showsthese rocks to be rich in LIL. This characteristic is

654 B Hajalilou et al

Figure 9. Eslamy peninsula rocks plot in variation diagrams (a) mg #/Cr, (b) mg #/Ni, and (c) mg #/Co.

related to the role of liquid phases in magma gen-eration (Rollinson 1993). Depletion of HFSE is animportant feature in Roman type rocks that existin Eslamy peninsula rocks.

Harker diagram was used for studying the majoroxides vs. silica variations. Investigation of thesediagrams showed that there is a geochemical simi-larity between all rock types of the peninsula(figure 8).

CaO, MgO, Fe2O3, TiO2 and MnO decrease withSiO2 increasing. The similarities between TiO2 andFe2O3 decline in relation to ilmenite, magnetite andtitanomagnetite crystallization. The sharp declinein MgO vs. silica (under 50% of silica) show olivine(in early stage) and diopside (in latter stages) crys-tallization. There is no distinctive variation forK2O and Na2O vs. silica. This case may indi-cate crustal contamination in Eslamy peninsularocks. High amounts of K2O in mafic rocks revealthat crystallization of leucite has happened indry conditions. Ca rich plagioclases are absent inEslamy peninsula rocks so intense decreases in CaOand subsequent increases in Al2O3 was in relationto diopside crystallization. The replacement of ironby manganese in olivine and pyroxene caused aslow decrease in MgO vs. silica.

The investigation of mg#/Ni diagram showedthe fractional crystallization of olivine in magma.Dispersion of samples in mg#/Cr and mg#/Co isresponsible for crustal contamination (figure 9).

The ratio of (Ba/La)n and (Th/Nb)n in Eslamypeninsula rocks are between 1.29 to 10.95 and 3.35

to 23.06. These characteristics prove the crustalcontamination on the petrogenesis of ultrapotassicrocks in Eslamy peninsula (Taylor and McLennan1985). Al2O3/TiO2 ratio in the primitive mantle(PM) is about 27.75, in upper mantle it is 22and the average of this ratio in Eslamy peninsulais 19.2 (63.1–4.21), so this amount shows crustalcontamination of magma that originated from themantle. Thus the ratio of Zr/Nb and Rb/Sr isabout 14.82 and 0.031in the primitive mantle(PM), but it is 9.09 and 0.123 in the continentalcrust (Taylor and McLennan 1985). Variations ofZr/Nb and Rb/Sr in Eslamy peninsula ratios arefrom 6.9 to 33.4 (10.8 average) and 0.06 to 1.92(0.26 average). The low ratio of Zr/Nb and highratio of Rb/Sr in relation to primitive mantle, pointto the role of continental crust in Eslamy peninsulamagmatism.

Scrutinizing the major and trace elementsbehaviour in the Eslamy peninsula rocks showsthat fractional crystallization and segregation ofolivine, clinopyroxene and leucite are the main fac-tors controlling the evolution of the magmas. Theexistence of a large amount of leucite in basani-tes and tephrites reveals that the correspondingmagmas are solidified in low water pressure oreven in dry conditions. Probable contamination bycrustal rocks and magma mixing were among theother factors in magmatic evolution of the studiedrocks. High Nb/Ta and Zr/Hf ratios (Dupuy et al1992; Rudnick et al 1993; Furman and Graham1999; Foley et al 2002) in the lamprophyres studied

Potassic alkaline rocks in Eslamy peninsula 655

Figure 10. Spider diagrams normalized to the (a) MORB,(b) PM, and (c) REE pattern normalized to MORB (datafor MORB and PM from Sun and McDonough 1989).

indicate enrichment process for the source regionprior to partial melting and crustal contaminationor differential crystallization (Moayyed et al 2008).The above-mentioned ratios are controlled by mag-matic processes such as partial melting, crystalli-zation and rutile and amphibole metasomatism inthe mantle (Ionov et al 1997; Foley et al 2000,2002; Tiepolo et al 2001). High REE/HFSE ratiofor the Eslamy lamprophyres such as high Eu/Ti

may indicate a carbonatitic metasomatism as well.Non-existence of negative anomaly for Eu showsthat the mechanism of fractional crystallizationand plagioclase separation does not play any sig-nificant role in Eslamy peninsula magmatism. Highamounts of Th and U in the Eslamy rock units showpossible contamination by the middle to uppercrust (Taylor and McLennan 1985). To elucidatethe nature of the Eslamy peninsula lamprophyres,they are compared with typical alkaline (SpanishCentral System) and calc-alkaline lamprophyres(Orejana et al 2006).

The study of spider diagrams which were plot-ted for REE and normalized to MORB andPM indicates that these elements have the samebehaviour in basic, intermediate and acidic rocksof the peninsula and display a general nega-tive slope (figure 10a, b, c). This characteristicsuggests a co-magmatic origin for the studiedrocks and also is demonstrative of great depthand a high CO2/H2O ratio. Most of these fea-tures are attributed to the origin of these rocksfrom a metasomatised mantle (Guo et al 2004).The absence of amphibole in peninsula rocks canexplain the negative anomaly for HREE (Rollinson1993). The positive anomaly for Th, Rb, K andBa, is similar to Roman type and may reflectcrustal contamination in magma evolution andlow ratio melting in enriched mantle (Taylorand McLennan 1985; Wilson 1989; Rollinson1993).

The negative anomaly for Ta, Nb and Ti canshow the role of subducted liquids in mantlemetasomatism (Rollinson 1993). The negativeanomaly of P in peninsula is an important indexfor high potassic post collision rocks (Muller andGroves 1997).

6. Geodynamic environment

Tectonic setting of the shoshonitic and ultrapotas-sic rocks of the Eslamy peninsula were investigatedusing the diagram proposed by Muller and Groves(1997) (figure 11) and it was deduced that potassicand ultrapotassic magmatism of the Eslamy penin-sula has occurred in a post-collision magmatic arc(figure 11).

This study shows that, despite the former modelsfor magmatism in the Eslamy peninsula, this geo-logical event is neither related to subduction ofNeo-Tethys beneath the central Iranian plate, nordid it occur in a continental rift zone. It couldbe suggested that the combination of fault dis-placements and their trend distribution relativeto the maximum stress applied to the studiedarea, had an important role in post-collision mag-matism of the Eslamy peninsula. Evidence to

656 B Hajalilou et al

Figure 11. Ce/P2O5–Nb*50–Zr*3 diagram for separation ofpotassic rocks interrelation with post collision arc (PAP) andactive continental margin (CAP) after Muller et al (1992)with position of Eslamy peninsula rocks.

suggest this can be found in the fact that thereare a large number of fault systems in the cen-tral Iranian block and in the northwest of Iranand also considering the oblique pressure dueto the convergence of the Iranian continentalcrust and the Arabian plate. The fore-mentionedhaving been caused by the spreading of the RedSea.

7. Conclusions

Eslamy peninsula is a complex stratovolcano witha collapsed caldera which is intruded by later lam-prophyres, trachytes, phonolites and syenites. Theolder magmatic activities include tephrite, basa-nite and the related pyroclastic rocks whereas theyounger events tend to be acidic terms.

Sieve texture and normal zoning in clinopyrox-enes and the existence of abundant amounts ofleucites in tephritic and basanitic lavas demon-strate that magma mixing, assimilation followedby a quick pressure decrease during ascent werethe main factors in the evolution of relatively drymagmas of the Eslamy peninsula.

The magmas that produced rocks of the penin-sula must have had a shoshonitic to ultrapotas-sic nature (Roman type) and had most likely beengenerated from partial melting of garnet lherzoliticmantle with low partial melting ratio in a highCO2/H2O condition, probably. Investigation ofHarker diagrams showed that there is a geochemi-cal similarity between all rock types of Eslamypeninsula. These magmas are presumed to havebeen contaminated by crustal materials duringrising up toward the surface. Variation of K2O,

Na2O vs. silica and mg �= /Cr, Co and the ratiosof (Ba/La)n, (Th/Nb)n, Al2O3/TiO2, Zr/Nb andRb/Sr show the crustal contamination in Eslamypeninsula rocks. Fractional crystallization ofolivine, diopsidic clinopyroxene and leucite playedan important role in the evolution of magmas.

Existence of a large amount of leucite inbasanites and tephrites reveals that the corres-ponding magmas are solidified in low water pres-sure or even dry conditions. High REE/HFSE ratiofor the Eslamy lamprophyres such as high Eu/Timay indicate a carbonatitic metasomatism as well.

Spider diagrams of REEs imply that all rocksin peninsula are co-magmatic and general nega-tive slope along with high LREE and low HREEanomalies suggest for a garnet lherzolite sourceand partial melting in high CO2/H2O conditions.LREE concentrations in the lamprophyre dykesand plugs reflect the existence of garnet as a residueof the melting (Polat et al 1997). The negativeanomaly for Ta, Nb and Ti can show the role ofsubducted liquids in mantle metasomatism.

Shoshonitic and ultrapotassic magmatism ofEslamy peninsula is supposed to have occurredin a post-collisional tectonic setting (Muller andGroves 1997) without any relation to Neo-Tethyansubduction or continental rifts.

Acknowledgements

The authors would like to thank the Payame NoorUniversity for financial support. We are thankfulto Dr A A Clagari, Dr M Moazzen, M Hoseinpourand M Hajialilu for their valuable suggestions.

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MS received 11 September 2008; revised 6 July 2009; accepted 17 July 2009