Post on 11-Jan-2023
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