Petrology of the Izmir-Karaburun Volcanic Area (West Turkey)
F. INNOCENTI and R. MAZZUOLI Institute of Mineralogy and Petrology, University of Pisa, Italy
Abstract The I z m i r - K a r a b u r u n region is located on the West coast of Turkey. In this area volcanic rocks of the late Miocene-Pliocene age outcrop. On the basis of the collected petrographic and geochemical data it has been possible to subdivide these rocks in to three series: a) calc-alkaline series of Karaburun-Koca dagI z m i r (quantitatively the most important). This series is formed by Iatiteandesites-dacitcs-rhyodacites, b) Silicic series of Izmir-Lebedos, mainly constituted by alkali rhyolitic rocks, c) Urla series, formed by alkali trachytes and alkali rhyolites, associated with scarce basic lavas of hawaiitic type. A different genesis is assumed for these series. In a first phase the latite-andesitic m a g m a was formed by a partial melting in the lower crust or in the upper mantle. Afterwards a subcrusial magma with alkali basaltic affinity rose slowly through the crust forming an intermediate reservoir and differentiating p r e d o m i n a n t l y towards alkali trachytic terms. Finally silicic m a g m a of Izmir-Lebedos was formed by an anatectic process. It is possible that the fusion has been favoured by the presence of basic m a g m a in the upper crust.
Introduction The Izmir-Karaburun volcanic area is situated on the West coast of Turkey. The study of volcanism of this area is part of a programme of volcanological and petrological investigations on the post-orogenic volcanism of West and Central Anatolia carried out by the International Laboratory of Volcanological Researches of the Italian Council of Researches and the Institute of Mineralogy and Petrology of the University of Pisa with the support of the Mineral Research and Exploration Institute of Turkey (M.T.A.). In this paper new petrological and geochemical data on the calc-alkaline rocks of Izmir region
84 are presented. The purpose of this study is to investigate the origin of this rock series and its relationships to the other magmatic rocks outcropping in the investigated area.
Outlines of Geology and Volcanology The investigated area is located South of Izmir Gulf; it is bounded on the East by the Izmir-Lebedos lineament and extends westwards up to the Egean Sea with the Karaburun peninsula (Fig. 1). The geology of this area has recently been described (Ar,~TUNA, 1962; KALAFATt~IOGLU,1961 ; URC~N, 1967); the rocks formations range in age from Devonian to Neogene. Outcrops of the paleozoic basement occur in the Karaburun peninsula and extend southwards to Kirindag (SW of Ermegan dag). The basement is overlain by a mesozoic carbonaceous series. Cretaceous flysch formations outcrop in a horst structure located SW of Izmir. The horst stretches roughly N-S and is bordered by two neogenic basins emplaced along its eastern and western flanks (Fig. 1). According to AKARTUNA (1962) the Neogene of this area is of continental facies and consists mainly of uppermiocenic deposits (Dacian or nearly Dacian). The volcanic rocks occur in this area in five well differentiated zones. The oldest volcanic products are represented by a complex of andesitic lava flows overlying the paleozoic basement in the Karaburun peninsula. The rocks constituting the lava flows are mostly dark and massive except at the contact with different units, where they are scoriaceous and red coloured because of fumarolization processes. The lava formations are locally overlain by neogenic sediments containing thin conglomeratic layers bearing r o u n d e d fragments of the underlying volcanites (N of Karaburun village). In the southern part of the region the volcanic formations occupy two broad areas (Koca dag massif and Alaqati massif). These formations constist of lava domes and small lava flows of latite-andesitic (Alaqati) or of dacitic-rhyodacitic composition (Koca dag). The outer parts of the domes are generally autobrecciated, and volcanic breccias with elements ranging in size from a few centimetres to one metre, are particularly abundant at the boundaries between one dome and another. Small rhyodacitic domes without internal structure and with the outer parts m o r e glassy than the inner ones, have also been observed (i.e., series of domes occurring near Hildir k6y). At the
m
85
contact with the sedimentary basement some extrusive domes enclose large fragments of carbonaceous rocks carried during the uprising and emplacement. These fragments occur as brecciated and weakly metamorphosed lenses of marbles alternating with volcanic materials.
b o
AEGEAN
f
Is
~l
SEA
AEGEAN SEA
IZMIR
AEGEAN SEA o L
~
zo I Km LEOEDO$ GULF
F10. 1 - Geological sketch m a p of I z m i r - K a r a b u r u n area w i t h location of the analysed samples (after KALAFT(~IOGLU, 1961, a n d AKATUNA, 1962, modified). 1: Palaeozoic Series; 2: Mesozoic Carbonatic Series; 3: Cretaceous Flysch; 4: Neogenic Sediments; 5: Quaternary Alluvium; 6: Rhyolitic Lava Flows a n d Lava Domes (generally with o u t e r perlitic parts); 7: Alkali-trachytic a n d Alkalirhyolitic Lava Domes with S u b o r d i n a t e Hawaiitic Lava Flows; 8: Calc-alkaline Series (a = dacitic a n d rhyodacitic lava flows and lava domes; b = latiteandesitic lava flows a n d lava domes).
The neogenic deposits at the contact with the lava domes are generally undisturbed and not uplifted. In some areas (i.e., domes N of Hildir k6y and Ala~ati) the upper-miocenic deposits contain layers of conglomerate with volcanic elements. The good preservation of
m
86
w
volcanic structures and the relatively scarcity of volcanic products in the upper-miocenic series suggest that the emplacement of the volcanites of Karaburun, Alaqati and Koca dag areas, took place during or immediately before Miocene. Also in the Izmir-Lebedos and Urla areas the volcanism is characterized by domes with minor lava flows. In the latter zone the most basic products of the whole region have been found, represented by flows of hawiitic composition. The miocenic sedimentary formations appear locally displaced by lava extrusion; in the Urla area (Iskele kSy) the neogenic deposits have been clearly uplifted by dome uprising. The age of emplacement of these volcanites is therefore mainly postmiocenic (1). The emplacement of domes, sometimes associated with lava flows, along the eastern flank of the Seferihisar tectonic high has given rise to a volcanic range of particular interest. The domes and the lava flows are mainly of alkali rhyolitic composition. The outer shells of domes are perlitic whereas perlitic textures are lacking within the inner parts constituted of glassy, massive lava. The lava flows exhibit frequently volcanoclastic structures with coarse glassy blocks cemented by finer glassy fragments. Sometimes in the marginal parts of the volcanic range, thin layers constituted by small glassy fragments derived from erosion and remotion of external portions of domes and lava flows outcrop. This fact suggests that sedimentation in brackish or lacustrine environment was taking place during the emplacement of volcanic formations. It seems therefore possible that hydration processes producing the outer perlitic parts of silicic domes have been favoured by the particular environment of emplacement (continental environment with lakes and lagoons) (AKARTUNA, 1962; CHESTERMAN, 1957). Moreover, it is to be noted that sedimentary levels composed with glassy volcanic materials occur also along the internal side of the massif. This occurrence suggests a paleogeographic picture with a series of small intravolcanic lakes which were subsequently filled with clastic materials mainly derived from the perlitic aureole of the domes.
(~) Preliminary results on the K / A t ages of volcanic rocks of I z m i r - K a r a b u r u m area carried out b y S, BORSI a n d G. FERRA~ (personal c o m m u n i c a t i o n ) confirm these observations ( K a r a b u r u m , Alagati and Koca dag massifs: 16-21 m.y.; Urla a n d IzmirLebedos: 11.5-12.5 m.y.).
87 N Petrography
Nomenclature The classification of the studied rocks has been made on the basis of the diagram proposed by STRECKEISEN (1967) using the normative alkali feldspars/plagioclase/quartz ratios. Together with the K-feldspar also the sodic plagioclase with composition from An0 to An~2, has been included in ~, A ,~. The application of the Streckeisen diagram to the effusive rocks classification leads to a semplification of their nomenclature, but it appears rather critical with regard to the calc-alkaline rocks owing to the remarkable restriction of the andesite field. In fact many rocks usually described as andesites fall in the latite-andesite field of the Streckeisen diagram because of their relatively high potassium content which produces high normative ,, or ,, content (i.e., see PICHLER and ZEIL, 1969). On the basis of the field occurrence and taking into account the chemical and petrographic characters, the volcanites of the IzmirKaraburun area can be assigned to three petrographically and, as we shall see later, genetically distinct groups. These will now be described briefly.
Karaburun-Koca dag-Izmir Series This series is the most important of the investigated area from a quantitative point of view. It represents a typical calc-alkaline suite Q
Fro. 2 - Distribution of normative Q:A:P ratios of Karaburun-Koca dag-Izmir series plotted on the Streckeisen triangle.
containing terms ranging from latite-andesites to dacites and rhyodacites. The values of the normative Q : A : P ratios of the samples of this series are reported in Fig. 2. Latite-andesites are the predominant
88
D
rock type but they show strongly variable chemical compositions (SiO, ranging f r o m 55 to 62 %). The most basic units of the suite were found in K a r a b u r u n massif which is entirely constituted by latite-andesitic rocks. Rocks with the same composition and probably with the same age, outcrop in the near Chios island (BESENECKERe t al., 1968; PARASKEVOPOULOS,1958). The usual texture of these rocks is porphyritic, but aphyric textures also occur. Olivine (2Ha = 84-85°, Fa 34-36 %), frequently with iddingsite rim, and pyroxene of diopsidic composition (c/X7 = 38-42°, 2V v = 52°) are the most widespread microphenocrysts; rare zoned plagioclase crystals exhibit a labradoritic composition with oscillatory zoning (An 71-56 %). Microphenocrysts of orthorombic pyroxene are scarce, but this mineral is abundant together with plagioclase (An 66-52 %), ore minerals and minor clinopyroxene in the pilotaxitic groundmass. Orthopyroxene occurs also as reaction rim a r o u n d olivine phenocrysts. In this series lavas markedly enriched in mafic minerals are also found with the phenocrysts represented only by olivine and clinopyroxene. The petrographic observations indicate that the first stages of crystallization were characterized by segregation of olivine and clinopyroxene in cotectic relation; orthopyroxene then formed by reaction of olivine with liquid, followed by plagioclase and opaque oxides. The latite-andesitic rocks occurring in the Ala~ati, Izmir and, to a lesser extent, in the Koca dag massifs show a saturation degree higher than the samples of the K a r a b u r u n massif. In fact they are all ~ quartz bearing ,, rocks, and the value of D. I. (THORTON and TUTTLE, 1960) is usually higher than 55. Also their mineralogy is different from the paragenesis observed in Karaburun rocks. Olivine is lacking and horneblende is a c o m m o n constituent; also biotite, although more rare than horneblende, occurs. The plagioclase is the dominant mineral; it is rhytmically zoned, its composition ranging from An 62 to An 45 %. Only rarely, more calcic cores are present (i.e., An 75 % in the sample K50). Two pyroxenes are commonly present although their relative abundances are very variable. In the Alagati massif rocks, where horneblende is more widespread, the clinopyroxene (cA'( = 41 °, 2V v = 54°) is less abundant than orthopyroxene. The latter shows zoning with outer parts enriched in iron (cores 2V~ = 58-60 °, rims 2V~ = 63-66°). The orthopyroxene is very scarce in the Izmir rocks and it is frequently mantled by clinopyroxene. As mentioned above, phenocrysts of horneblende (c/X7 = 5-7°, 2V~z = 70 -74°) are widespreadingly diffused within these rocks; they show pleochroism from
- -
89
- -
brown to dark green; the rims are darkened c o m m o n l y by opaque minerals. Biotite is rather rare in latite-andesites; its occurrence was recognized in some samples of the Izmir rocks (i.e., T1 and T89). Microphenocrysts of ore minerals also occur. The groundmasses are generally glassy or cryptocrystalline. The dominant rock types of the Koca dag massif are dacitic and rhyodacitic in composition. These rocks are m o r e scarcely represented in the Izmir and Ala~ati (Hildir domes) areas, where they are associated with quartz bearing latite-andesites. The mineralogical assemblage of these rocks is quite similar to that of latite-andesites; plagioclase (An 56-48 %) is the dominant mineral with less a b u n d a n t hypersthene (2V~ = 58-60°). Clinopyroxene is very scarce or lacking. Horneblende is rather abundant and it shows the same optic characters previously described. Biotite occurrence is c o m m o n ; it is particularly a b u n d a n t in silica rich rock types. Rare rounded and corroded grains of quartz have been found.
The Urla Series The Urla series consists mainly of alkali trachytes and alkali rhyolites with subordinate basic lava flows. These latter exhibit porphyric texture with phenocrysts of pale yellow clinopyroxenes (2Vv = 58°, c&~( = 41-42°), subordinate olivine (2H~ = 88°, Fa = 25 %) with iddingsitic rims, and strongly zoned plagioclase (core 82-86 % An, intermediate zones 76-66 % An, outer shells 50-45 % An). In the groundmass, with intersertal texture, microlites of zoned plagioclase (64-42 % An) are associated with fine grained olivine, clinopyroxenes and ore minerals with scarce glass. The petrographic features indicate for these rocks an alkali basaltic affinity; they can be classified as hawaiites for the moderate color index, the composition of normative plagioclase, associated with relatively high alkalis, Na20 : K20 > 2, and low MgO contents (MACDONALD,1960). The alkali trachytes are characterized by a mineralogical assemblage consisting of zoned anorthoclase (2Va = 49 ° in the cores and 43 ° in the marginal zones) and of alkaline amphibole of riebeckitic type, mainly in the groundmass ; the quartz is subordinate ; sodic plagioclase is very scarce and it is generally found at the core of anorthoclase crystals. In the rhyolitic rocks the mineralogical assemblage is constituted by crystals of m o r e or less sodic sanidine [2V~ = 34-38 °, O.A.P.
B
90
--
~ ( 0 1 0 ) ] , acid zoned plagioclase (An 32-20 %) f r e q u e n t l y w i t h sanidine rim and generally opacitized biotite. All these rocks have porphyritic texture w i t h prevalently trachytic groundmass.
Izmir-Lebedos Series The rhyolitic rocks of Izmir-Lebedos area exhibit generally vitrophyric t e x t u r e ; they contain scarce phenocrysts of quartz and sanidine [ 2 V , = 10-24°, O.A.P. / / ( 0 1 0 ) ] ; the plagioclase (oligoclase) is very scarce. The g r o u n d m a s s is very o f t e n perlitic a n d contains generally small plates of biotite; sometimes it appears recrystallized, showing spherulitic or m i c r o g r a n o p h y r i c textures w i t h irregular zones of globular quartz.
Petrochemistry
Analytical Methods The chemical analyses were performed employing different techniques; standard procedures based on gravimetric (SiO2), colorimetric (Fe, Ti, P) and volumetric (A1, Ca) methods were used. Alkalis, Mn and Mg determinations were made using a Perkin-Elmer Mod. 303 Atomic Absorption (A.A.) Spectrophotometer, following the analytical procedures described in CIoNI et aL (1971). Trace elements analyses also were made with the A.A. spectrophotometry: Cu, Li, Rb contents were determined using the addition method; Sr was determined in presence of 1% La to suppress Al and P molecular interferences; Zn determinations were made using routine procedure; Ni and Co were determined in organic solvent after complexation with ammonium pyrrolidine dithio. carbamate (APDC) and extraction with metyl isobutyl ketone (MIBK) (CIoNI et al., 1971).
Major E l e m e n t s Chemical analyses and n o r m s of the rocks of K a r a b u r u n - K o c a dag-Izmir area are r e p o r t e d in Table 1. The samples have been listed w i t h increasing values of differentiation index, calculated after THOR~TOM and TUXTLE (1960) (D.I. = n o r m a t i v e Q + o r + a b + n e + l c + k s ) . The data relative to the Urla and Izmir-Lebedos areas have been r e p o r t e d in Table 2.
91
--
TABLE 1 - Chemical analyses and C.I.P.W. norms of the rocks of Izmir-Koca dag-Karaburun area.
K83
K87
K85
K84
K86
T 89
K64
SiO~
53.53
55.37
56.94
57.01
57.51
59.43
60.85
A1203
14.06
16.74
16.77
18.25
17.37
14.67
15.94
Fe~O3
3.74
2.90
1.43
6.02
5.37
2.96
2.57
FeO
3.41
3.48
4.54
0.39
1.00
2.64
2.50
MnO
0.13
0.11
0.12
0.i1
0.09
0.11
0.09
MgO
8.96
6.63
4.85
3.10
3.03
3.90
3.48
CaO
8.12
7.44
6.89
7.04
7,26
6.52
6.02
NazO
2.60
3.08
3.17
3.63
3.60
2.73
3.37
KzO
2.52
1.98
2.20
2.22
2.12
3.56
2.85
TiOz
0.92
0.87
0.84
0.81
0.78
0.77
0.66
P2Os
0,39
0.36
0.24
0.20
0.21
0.39
0.23
L.O.I.
1.17
1.35
1.94
1.42
1.50
2.03
1.09
99.55
100.31
99.93
100.20
99.84
99.71
99.65
Q
2.3
5.7
7.7
9.7
11.1
13.4
14.0
or
14.9
11.7
13.0
13.1
12.5
21.0
16.8
ab
22.0
26.1
26.8
30.7
30.4
23.1
28.5
an
19.3
17.3
20.0
3.5
C
.
26.0 .
25.0 .
27.0 .
.
25.0 .
.
l wo
7.7
3.6
3.2
2.4
4.0
5.2
~ en
6.3
2.7
2.0
2.1
3.5
4.1
2.7
fs
0.5
0.5
1.0
--
--
0.6
0.5
I en
16.0
13.8
10.I
5.6
4.1
5.6
6.0
fs
1.4
2.3
5.0
--
--
0.8
1.1
mt
5.4
4.2
2.1
--
1.3
4.3
3.7
il
1.7
1.7
1.6
1.1
1.5
1.5
1.3
ap
0.9
0.9
0.6
0.5
0.5
0.9
0.5
hm
--
--
--
6.0
4.5
--
--
di
hy
K 83 = m a f i c l a t i t e - a n d e s i t e W K a r a b u r u n . K 87 - K 85 - K 84 - K 86 = q u a r t z - b e a r i n g l a t i t e - a n d e s i t e s S-W K a r a b u r u n . T 8 9 = q u a r t z - b e a r i n g a n d e s i t e K a d i f e c a l e ( I z m i r ) . K 64 --- q u a r t z - b e a r i n g l a t i t e - a n d e s i t e E r m e g a n Da.
m
92
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Continued: T~ILE 1 - Chemical analyses and C.I.P.W. n o r m s of the rocks of Izmir-Koca dag-Karaburun area. K95
TI
K65
K60
K50
K99
K63
SiOz
61.07
59.97
60.61
61.91
61.85
60.78
62.08
A1203
I6.27
15.77
17.20
16.38
17,04
16.62
16.42
Fe20~
1.93
4.28
2.83
2.27
3.22
3.05
2.74
FeO
2.97
1.58
2.49
2.59
1.86
1.96
1.92
MnO
0.11
0.13
0.12
0.11
0.08
0.12
0,!0
MgO
3.36
2.88
2.67
2.76
2.36
2.72
2,72
CaO
5.74
6.23
5.82
5.49
5.60
5:71
5.43
Na20
3.38
328
3.58
3.19
3.40
3,53
3.34
K20
2.99
3.33
3.07
3.23
2.71
3,09
3.03
TiO2
0.63
0.93
0.69
0.65
0,72
0.80
0.57
P~Os
0.21
0.32
0.18
0.20
0.16
0.28
0.15
L.O,I.
0,94
1.27
1.12
1.45
1.12
0.95
1.49
99.60
99.97
100.38
100.23
100.12
99.61
99.99
O
13.3
13.7
12.8
15.9
17.4
14.2
16.7
or
17.7
19.7
18.1
19.1
16.0
18.3
17.9
ab
28.6
27.7
30.3
27.0
28.8
29.9
28,2
an
20,4
20.4
20.9
C
di
hy mt
.
18.5 .
2I .8 .
20.8 .
.
23,2 .
.
l wo
2,8
4.3
2.5
2.1
1.5
2,6
2.1
en
1.9
3.7
1.8
1,5
1.3
2.2
1.7
fs
0.7
0.4
0.4
en
6,5
3.4
4.8
5.4
4.6
4.6
5.0
fs
2.3
--
1.0
1.6
--
--
0.4
2.8
2.8
4.1
3,3
4.2
4.4
4.0
-
-
-
-
-
-
0.1
il
1.2
1.8
1.3
1.2
1.4
1.5
1.1
ap
0.5
0.8
0.4
0.5
0.4
0.7
0.4
hm
--
2.3
--
--
0.3
--
--
K 95 = quartz-bearing latite-andesite N Hildir. T 1 - - q u a r t z - b e a r i n g latite-andesite N Izmir (Karsiyeka). K 65 = quartz-bearing latite-andesite Ermegan Da. K 60 = quartzbearing latite-andesite N Ermegan Da. K 50 = dacite S Balikliova. K 99 = quartz-bearing latite-andesite S. Ala~ati. K 63 -- quartz-bearing latite-andesite S Ermegan Da. 10
- -
93
w
Continued: TABLE 1 - Chemical analyses and C.I.P.W. n o r m s of the rocks of Izmir-Koca dag-Karaburun area. K 54
K 55
K 51
K 100
K 53
K 61
K 59
K 58
SiO,
62.M
62.83
62.70
63.45
63.43
66.17
65.87
65.45
AI20~
17.13
I6.41
16.98
16.53
I6.98
15.64
16.14
16.55
Fe, O~
2.66
2.85
2.28
4.33
3.73
2.71
1.82
1.57
FeO
1.84
1.58
2.09
0.60
0.95
0.84
0.90
1.15
MnO
0.08
0.10
0.08
0.08
0.06
0.06
0.05
0.06
MgO
2.18
1.86
1.58
1.58
1.23
1.37
0.96
0.99
CaO
4.96
5.41
5.12
4.84
4.63
4.05
3.54
3.53
Na20
3.35
3.54
3.80
3.28
3.60
3.53
2.99
3.56
I(20
2.94
3.10
3.08
3.24
3.16
3.35
4.72
4.28
TiO,
0.69
0.62
0.68
0.62
0.73
0.50
0.50
0.51
P,O5
0.19
0.19
0.18
0.41
0.18
0.14
0.21
0.16
1.40
1.03
1.01
1.01
1.03
1.12
2.29
2.05
99.76
99.52
99.58
99.97
99.71
99.48
99.99
99.86
Q
18.3
17.8
16.4
20.5
19.4
23.0
22.0
19.8
or
17.4
18.3
18.2
19.1
18.7
19.8
27.9
25.3
ab
28.3
29.9
32.1
27.7
30.4
29.9
25.3
30.1
an
23.0
19.7
20.2
20.8
20.8
16.9
16.2
16.5
L.O.I.
c
di
.
.
.
.
.
I wo
0.i
2.4
en
0.1
2.1
fs
--
--
0.3
.
en
5.3
2.5
2.7
3.7
fs
0.2
.
1.7
0.2
1.2
0.2
0.4 0.3 .
.
.
2.7
0.9
--
---
0.8
--
--
2.6
2.4
2.5
.
0.2
--
0.7
mt
3.9
3.6
3.3
0.4
1.1
1.5
1.6
2.3
il
1.3
1.2
1.3
1.2
1A
1.0
1.0
1.0
ap
0.5
0.5
0.4
1.0
0.4
0.3
0.5
0.4
--
0.4
--
4.1
2.9
1.7
0.7
--
hm
.
.
.
0.1
.
K 54 - K 5 5 = dacites Koca Da. K 51 = quartz-bearing latite-andesite Veli Da. K 100 = dacite G6ztepe ( h m i r ) . K 53 = dacite Veli Da. K 61 = dacite Hildir. K 59 = rhyodacite S Barbaros. K 58 = rhyodacite N-E Barbaros. 11
m
TAaLE 2 - Chemical
analyses and
94
C.I.P.W.
n o r m s o f Urla a n d
I z m i r - L e b e d o s areas.
T 92
K 165
K 79
K 76
K 93
T 83
K 91
T 86
T 91
SiO2
48.48
49.03
67.15
70.69
72.91
73.58
74.16
74.50
74.48
AI20~
16.77
16.44
16.77
15.15
1Z48
11.97
12.60
11.68
11,26
FezO3
2.85
3.49
1.47
0.98
0.78
0.89
0.87
0.76
0.63
FeO
6.89
6.36
0.93
0.34
0.29
0.35
0.09
0.33
0.28
MnO
0.19
0.I7
0,07
0.03
0.06
0.04
0.08
0.04
0.09
MgO
5.15
5.40
0.04
0.28
0.10
0.05
0.07
0.07
0.03 0.84
CaO
9.79
8.71
0.46
1.30
0.79
0.98
0.66
0.83
Na20
3.27
3.41
6.72
4.79
1.90
3.22
3,31
2,26
3.37
K20
1.40
1.56
5.18
5,04
6.13
5.39
5.02
5.29
4.92
TiO2
1.72
1.63
0.26
0,35
0.07
0.09
0.07
0.11
0.04
P205
0.34
0.30
0.04
0.11
0.02
0.10
0.03
0.04
0.I0
L.O.I.
2.73
3.18
0.69
0.69
3.97
3.04
2.72
3.91
3.56
99.58
99.68
99.61
9935
99.50
99.70
99.68
99.82
99.60
Q
--
--
7.6
20.8
36.6
32.8
34.3
33.8
35.0
or
8.3
9.2
30.6
29.8
36.2
31.8
29.7
31.6
29.1
ab
27.7
28.8
56.8
40.5
16.1
27.2
28.0
27.2
28.5
an
27.0
24.9
0.3
5.0
3.8
2.3
3.1
2.4
1.1
c
.
wo
--
--
l wo
8.1
en
4.8
t fs
1.3
--
0.6
--
--
0.4
--
--
0.7
--
0.6
0.8
6.8
0.3
0.3
--
0.1
--
0.I
0.2
4.3
0.1
0.3
--
0.1
--
0.1
2.9
2.1
0.2
.
en
1.3
4.2
--
fs
0,8
2.0
.
.
.
.
.
.
.
fo
4.7
3.5
.
.
.
.
.
.
.
fa
3.2
1.8
.
.
.
.
.
.
.
mt
4.1
5.1
2,1
0.2
0.9
di
hy
.
.
.
.
0.4
. 0.2
. --
. 0.2
1.0
0.1 0.1
0.3
--
--
1.0
0.9
il
3.3
3.1
0.5
0,7
0.1
0.2
0.1
0.2
0.1
ap
0.8
0.7
0.1
0.3
0.1
0.2
0.1
0.2
0.2
hm
--
--
2.1
0.9
0.I
0.2
0.6
0.2
--
T 92 = Hawaiite. Urla - K 165 = H a w a l i t e . S. E a s t o f Urla (Ovacik) - K 79 = Alkalitrachyte. N. West of U r l a - K 76 = Alkali-rhyolite. N. West of Urla - K 93 = Rhyolite N. E a s t Yeni K/Sy - T 83 = Alkali rhyolite. S. West of C u m a o v a s i - K 91 = Alkali rhyolite. S. West of K u n e r (Keller) - T 86 = Alkalirhyolite. S. West of Yeni Ktiy - T 91 = Alkali rhyolite. S o u t h of K u n e r . 12
m 95 m The rocks of the Karaburun-Koca dag-Izmir series represent a suite with a calc-alkaline character (the Peacock index of these rocks is 59.5). A remarkable feature of this series is the constant relatively high K20 content, even in the most basic terms of the suite. While gradual variations can be observed throughout the latite-andesite-dacites-rhyoI1-
MalO •
TiO~
KzO 7
1. -
s
"ma
o,
=~Os ' Fe 0
,
~0 e
•
~
,..
.
2
q~.
s-
s MgO
4 Ha=(]
....
:, o~:~
•.
1,
}. .e CaO 7o
e
A"
SJO) im
~
70
so
~0
D.I, Fro.
3 -
sa
Ja
D.I.
30
J
Major oxide variations. D . I . = Differentiation index after Thornton and Tuttle; o = Karaburun-Koca dag-Izmir series; + = Urla series; • = Izmir-Lebedos series.
dacites suite, a sharp break results between rhyodacites and rhyolites of the Izmir-Lebedos area. In some of the most acid rocks normative corundum was obtained; this is most probably due to secondary processes such as weak leaching of alkalis from the groundmass glasses. By plotting the major elements contents against the D.I., a continous variation trend from latite-andesites to dacites and rhyodacites is clearly shown (Fig. 3). 13
96
SiO2 content shows a progressive increase in the D.I. interval from 39 to 75; a sharp gap exists between D.I. values of 75 and 90; this is probably due to differences in the origin of the three series, and not to an incomplete sampling. CaO, MgO and TiO2 contents show a gradual decrease with increasing D.I. The total iron decreases very slightly in the latite-andesites with low D.I., while decreases sharply in the m o r e acid terms (see also Fig. 4). The sum of alkalis increases with increasing D.I., but only the K20 shows a continuous increasing over the whole D,I. field; K20
F
A
M
NazO
~0
FIG. 4 - A (Na20 + K~O) - F (FeO + I"e20~) - M (MgO) a n d Na20-K20-CaO d i a g r a m s f o r t h e volcanites of I z m i r K a r a b u r u n area. The s y m b o l s are the s a m e as in Fig. 3.
Na20 shows initially a progressive enrichment (D.I. 39 to 55), afterwards it remains practically constant. A1203 vs. D.I. shows a remarkable spreading ; however it is possible to recognize a roughly constant trending of the alumina distribution except for an initial increase at the lowest D.I. values. Among the high D.I. rocks (D.I. ~ 90), striking differences, particularly with respect to Na20 and A120~ contents, have been found between the rhyolites of Lebedos and the most advanced rocks of Urla. Both these elements are in fact of particularly low concentration in the perlitic alkali rhyolites of Lebedos and their Na20 content is quite comparable with that occurring in rocks of the latite-andesiterhyodacite series. Some suggestions on the variation trends are offered by AFM 14
--
97
and Na20-K20-CaO diagrams of Fig. 4, where the gap between the rocks of Izmir-Lebedos series and calc-alkaline series is clearly shown. For comparison the trends of two orogenic series, representing two extreme cases of variability, have been drawn in AMF diagram. The Karaburun-Koca dag-Izmir series defines a trend that remarkably approaches the Cascades trend, with only some differences in the early crystallisation stages. However this discrepancy is largely covered by the variability, sometimes very wide, of the orogenic suites (LOWDER and CARM~CHAEL, 1970). The variation diagrams also suggest some considerations about the minerals involved in the differentiation of the main calc-alkaline series. The first stages of differentiation were dominated by the segregation of either iron oxides and mafic minerals such as olivine and calcic pyroxene. The crystallisation of these minerals produced a weak variation in iron and an increasing of Na20 and K20 contents, associated with a decrease of MgO, TiO2, CaO in the residual liquid. The further stages of differentiation were characterized by crystallisation of plagioclase never strongly calcic and hypersthenic orthopyroxene with minor clinopyroxene. The crystallisation of these minerals may have proceed together with segregation of iron oxides; the resulting chemical variations mainly consist of a progressive enrichment in SiO2 with a strong decrease of CaO, MgO and total iron. With regard to the alkalis, K20 increases while Na20 is practically constant. Trace E l e m e n t s The data relative to the trace elements distribution are given in Table 3. The contents of these elements are plotted against the D.I. in the diagrams of Fig. 5. The trace elements distribution p a t t e r n relative to the main calc-alkaline series suggests the following considerations: Cu and Zn decrease as D.I. increases. The contents of these elem e n t are comparable with the values observed in other calc-alkaline series_(BA~R, 1968; SIEGERS et al., 1969). The remarkable decrease of Cu in first stages of differentiation suggests an early segregation of this element into a sulphur phase. Cu/Fe ratio also decreases with increasing D.I. whereas Z n / F e ratio does not exhibit striking variations, but only a slight increase in correspondence of dacitic and rhyodacitic terms of the series. These differences between the trend of Cu/Fe and Zn/Fe ratios are due to the m a j o r similarity in 15
B
98
- -
TABLE 3 - Trace elements in Izmir-Karaburun volcanic rocks (in ppm). (Rock Nos. as in Table 1 and 2). Co
Cu
K83
36
64
K87
29
63
K85
26
40
K84
22
24
K86
22
T89
22
K64
Li
Ni
Rb
Sr
Zn
17
161
109
880
80
14
102
88
639
90
20
80
84
648
80
16
61
76
658
75
27
8
63
82
676
80
15
15
35
137
670
83
16
22
11
31
100
509
80
K95
19
27
16
26
95
520
66
T1
17
32
16
21
130
754
70
K65
16
20
14
18
93
536
65
K60
16
23
14
19
100
536
62
K50
14
17
12
14
107
520
70
K99
17
8
12
15
115
607
83
K63
16
21
21
24
111
502
61 73
K54
14
15
10
20
128
429
K55
16
15
13
18
130
431
69
K51
15
6
19
21
108
435
69
KI00
15
20
17
17
146
563
70
K53
10
22
19
9
124
413
71
K61
13
9
29
23
134
367
60
K59
10
15
17
11
175
438
58
K58
7
15
31
7
176
429
54
T92
34
24
14
29
50
574
181
K165
26
23
23
16
79
561
115
K79
2
7
79
4
354*
K76
6
--
18
8
168
176
18"
106 51
K93
3
7
5
6
197
28
41
T83
1
6
23
3
216"
3*
34
K91
3
2
46
7
420*
9*
36
T86
I
6
11
4
175"
17"
43
T91
2
8
22
3
282*
3*
38
* determinations carried out by isotopic dilution at the Laboratory of Nuclear Geology of the University of Pisa. 16
m 99 m size and electronegativity of Zn +2 than Cu +2 with respect to Fe+2; the Zn-O bond being more covalent than Fe-O bond (TAYLOR, 1965), this accounts of the slight enrichment in Zn +2 with respect to Fe +2 in the latest stage of crystallisation. Co and Ni decrease with increasing of D.I., but while Co decrease is rather uniform through the whole D.I. interval, Ni distribution pattern shows a steep decrease in the first stages of differ-
°
eO
*
Cu a¢o.
I,o
7~
•
.°
1oo #
-lzo
.-° o
Sr
Z:
.so
too • 4.*
Rb
580
.;~uo
I *~
1to
*
o
*
NI io
• ~,a
A
w.
C
.ia g'o
,?
~o
u• o.~
t,o
~'*
°
D.I.
D.L
Fie,. 5 - T r a c e e l e m e n t s variations• T h e s y m b o l s are the s a m e as in Fig. 3.
entiation in relation also to the higher crystal field stabilization energy in octahedral co-ordination of this ion with respect to Co2÷ (Bt;RNS, 1970)• The Ni content is rather high in the basic terms and drops to values as low as about 20 ppm in the Iati'te-andesites with high D.I. The Co concentrations closely approach those observed in other calc-alkaline series (BAKER, 1968; TAYLOR et al., 1969a, 1969b); Ni/Co ratio is major than one, while it is usually minor than one in many other orogenic series (TAYLORet al., 1969a). As the crystallisation proceeds the Ni/Co ratio follows a decreasing trend typical of a fractional crystallisation process. Li does not show striking variations during initial and intermediate stages of differentiation; only in the rocks with high D.I. values, 17
--
100
--
an increase in the Li content is observed. Li/Mg ratio increases regularly with the proceeding of the crystallisation as predicted by a process of fractional crystallisation. Rb and Sr concentrations are remarkably high. High Sr abundance is not u n c o m m o n in calc-alkaline series; on the contrary the Rb contents of these rocks are strikingly higher than those commonly found in other orogenic series. Only rocks of the Chilean Andes andesite formation yielded values of Rb content, which although characterized by a large variation range, are comparable to those recorded on the Karaburun series (SIEGERS et al., 1969). The high Rb content obviously reflects in the relatively low values of K/Rb ratio which shows an average value of 228 in latiteandesitic rocks. The geochemistry of silicic rocks of Izmir-Lebedos series is clearly distinctive with respect to the rocks of the main latite-andesitic series. The absolute abundances of Zn, Cu, Ni, Co and particularly Sr are low. This could be explained if a residual genesis is assumed for these rocks, but the low concentrations of Rb and Li are inconsistent with this hypothesis; in fact Rb and Li contents are similar to those of the rocks of Karaburun-Koca dag-Izmir series. Also K/Rb ratio, although variable, results generally higher than the mean value characterising the latite-andesitic series. Li and Rb distribution is discrepant with that expected for rocks derived from a differentiation by crystallisation and this indicates a different genesis of these rocks with respect to the calc-alkaline series, in line with the conclusions previously suggested by the trends of major elements. Also the rocks of Urla do not set in the latite-andesitic trend; so as an example, the Urla hawaiites (T92, K165) show remarkably higher Zn and lower Ni, Co, Rb contents than the rocks of Karaburun series characterized by similar values of D.I. Thus also for the Urla rocks no genetical relationships with the calc-alkaline series may be assumed. Summary
and
Conclusions
Field evidences and geochemical and petrographic data suggest a grouping of the volcanic rocks occurring in the investigated area into three distinct series: a) Karaburun-Koca dag-Izmir calc-alkaline series, consisting of a latite-andesite, dacite, rhyodacite suite; 18
101
b) Urla series, mainly constituted of alkali trachytic rocks with minor alkali rhyolites and hawaiites; c) Izmir-Lebedos silicic series, represented by rhyolites and alkali rhyolites. The Izmir-Lebedos silicic rocks can be related neither to the calc-alkaline series, owing to the existence of a striking break between the distribution of major and trace elements of these two series, nor to the alkali trachyte-alkali rhyolite series of Urla; in fact the rhyolitic rocks occurring in Urla show significant mineralogical and petrological differences with respect to the Izmir-Lebedos rhyolites. As a residual origin for this series is to be discarded mainly on account of the low content of some trace elements such as Rb and particularly Li, an independent genesis by means of a partial crustal melting process can be proposed. The peculiar distribution of trace elements could, in this way, be related to the types of minerals involved in the anatectic melting. On the contrary the petrographic and geochemical features of the Urla series suggest a derivation from a subcrustal magma of alkali basaltic affinity. In the investigated area the basic products are scarce and are respresented by slightly differentiated lavas of hawaiitic composition. The absence of true alkali basalts and the abundance of differentiated products suggest a slow transit of subcrustal magma through the crust with a probable formation of an intermediate reservoir in the crust. The slow uprising of the basic magma can be related to the physical conditions of the crust in this area in the late Mioceneearly Pliocene. In fact in this period the geothermal gradient was probably so high to determine a plastic behaviour of the crust; this is also indicated by the partial melting process which originated the silicic volcanism of Izmir-Lebedos during the same time. The genesis of calc-alkaline series of Karaburun-Koca dag-Izmir is rather difficult to postulate. Any hypotheses must however take into account the following considerations: Relationships between this series and basaltic rocks are lacking. In fact in western Anatolia no extensive amount of basic rocks is found which could represent the parent magma of the great volume of andesites outcropping in this region. The only important recent basic formation is represented by the Kula volcanics (WASHINGTON, 1894, 1900) which is located about 100 km East of Izmir. But the Kula basic volcanites consist of undersaturated alkaline rocks so that a genetic relationship between them and calc-alkaline series seems 19
- -
102
- -
very unlikely. Other small outcrops of basaltic rocks occur (i.e. in Urla area), but they are commonly associated to their differentiation products, which exhibit strikingly different features with respect to the latite-andesitic rocks. The high potassium and rubidium contents and the low K/Rb ratio in the whole series, similar to the average value accepted for the continental crust. In addition the value of Rb/Sr ratio is also relatively high in the most basic terms of the series (Rb/Sr = 0.12-0.20). On the basis of these considerations it seems very improbable that an origin of calc-alkaline rocks through a fractional crystallisation process of basalt under oxidasing conditions (OSBORN, 1959) could be achieved. Also an origin by a contamination process between basic magma and crustal material (Kuno, 1967), is to be rejected for the impossibility to characterise the parent magma and for the absence of data on the possible assimilated products and because of a lack of petrographic evidences of such a process. Then a primary latiteandesitic magma can be envisaged; its production may be related either to a process of partial melting in the lower crust, or to one or two stage process in the mantle (O'HARA, 1968; GREEN and RINGWOOD, 1968). The petrochemical data do not permit to discard one of the two hypotheses; however mainly because of the low K/Rb and high Rb/Sr ratios the hypothesis of a partial melting in the lower crust is to be preferred. Concluding on the basis of the available data, the picture of the magmatic evolution of Izmir-Karaburun area can be outlined as follows: 1) Production of a latite-andesitic magma probably by partial melting in the lower crust. This magma ascended towards the surface and poured out during the early Miocene originating a typical calcalkaline suite mainly by fractional crystallisation processes. 2) Production of subcrustal magma of alkali-basaltic type, genetically distinct from the calc-alkaline series. However it is not to be excluded that the production of the latite-andesitic magma, contributing to the upper mantle instability, may have favoured the formation of the basaltic magma. This latter rose through the crust and, forming an intermediate reservoir, differentiated mainly towards alkali-trachytic products. 3) The formation of a basic reservoir within the upper crust probably caused an increase in the already high geothermal gradient.
20
- -
103
- -
This thermal anomaly favoured the production of the anatectic melt which originated the rocks of Izmir-Lebedos series. 4 ) As s o o n a s f a v o u r a b l e tectonic conditions were realized ( a b o u t 11-12 m i l l i o n y e a r s a g o ) t h e d i f f e r e n t i a t e d p r o d u c t s o f t h e sub-crustal magma and the anatectic melt ascended to the surface pouring out along the flanks of Seferihisar horst.
References AK~TUNa, M., 1962, On the Geology of lzmir-Torbali-Seferihisar-Urla district. M.T.A. Bull., vol. 59, p. 1-18. BAKER, P. E., 1968, Petrology of Mt. Misery Volcano, St. Kitts, West Indies. Lithos, vol. 1, p. 124-150. BESE~ECKER, H., DURR, S., /-IERGET, G., JACOBSHAGEN,V., KAUFFMANN, G., LUOTKE, G., ROTH, W., TIEXZE, K. W., 1968, Geologie yon Chios (Agiiis). Geologica et Paleontologica, vol. 2, p. 121-150. BURNS, R. G., 1970, Mineralogical Applications of Crystal Field Theory. Cambridge, 224 pp. CHESTERMAN, C. W., 1957, Volcanic Lightweight Aggregates of Western United States. Congr. Geol. Int., Seccion I, vol. 1, p. 205-229, Mexico. CIoNI, R., I~OCENTI, F., MAZZUOLI,R., 1971, Chemical Analyses and S o m e Trace E l e m e n t Data on S t a n d a r d Silicate Rocks. Chem. Geol., vol. 7, p. 19-23. GREEN, T. H., RINGWOOD, A. E., 1968, Genesis of Calc-alkaline Igneous R o c k Suite. Contr. Min. and Petrol., vol. 18, p. 105-162. KALAFAT(}IOGLU,A., 1961, A Geological S t u d y in the K a r a b u r u m Peninsula. M.T.A. Bull., vol. 56, p. 40-49. KuNo, H., 1967, Igneous Rock Series. Chemistry of the Earth's Crust II, p. 113-128. LOWDER, G. G., CARMICHAEL, I. S. E., 1970, The Volcanoes and Caldera of Talasea, N e w Britain: Geology and Petrology. Geol. Soc. Am. Bull., vol. 81, p. 17-31. MACDONALD,G. A., 1960, Dissimilarity of Continental and Oceanic Rock Types. J. Petrol., vol. 1, p. 172-177. O'HARA, M. J., 1968, The Bearing of Phase Equilibria Studies on the Origin and Evolution of Basic and Ultrabasic Rocks. Earth Sc. Rev., vol. 4, p. 6%686. OSBORN, E. F., 1959, Role of Oxygen Pressure in the Crystallisation and Differentiation of Basaltic Magma. Am. J. Sci., vol. 257, p. 609-647. PARASKEVOPOULOS,G. M., 1958, Uber den C h i m i s m u s u n d die provinzialen Verhiiltnisse der terti~iren u n d quat~irnaren Ergussgesteine des iig~iischen R o u m e s und der benachbarten Gebiete. Tscherm. Min. Petr. Mitt., vol. 6, p. 13-72. PICHLER, I-I., ZEIL, W., 1969, Andesites of the Chilean Andes. Proc. Symp. on Andesites,
Univ. Oregon, p. 165-174. SIEGERS, A., PICr~L~R, H., ZZIL, W., t969, Trace E l e m e n t Abundances in the ,~ Andesite ,, Formation of N o r t h e r n Chile. Geochim. et Cosmocbim. Acta, vol. 33, p. 882-887. STRECKEISEN, A. L., 1967, Classification and N o m e n c l a t u r e of Igneous Rocks. N. Jb. Miner. Abh., vol. 107, p. 144-240.
21
J
104
- -
TAYLOR, S. R., 1965, The Application of Trace Element Data to Problems in Petrology. Phys. Chem. Earth, vol. 6, p. 133-213. - - , 1969, Trace Element Chemistry oI Andesites and Associated CaIc-alkaline Rocks. Proc. Syrup. on Andesites, Univ. of Oregon, p. 43-63. - - , KAYE, M., WHITE, A. J. R., DUNCAN, A. R., EWART, A., 1969a, Genetic Significance of Co, Cr, Ni, Sc and V Contents o[ Andesites. Geochim. et Cosmochim. Acta, vol. 33, p. 275-286. - - , CAPP, A. C., GRAHAM, A. L., 1969b, Trace Element Abundances in Andesites. II: Saipan, Bouganville and Fiji. Contr. Min. and Petrol., vol. 23, p. 1-26. THORNTON, C. P., TUTTLE, O. F., 1960, Chemistry of Igneous Rocks. I: Differentiation Index. Am. J. Sci., vol. 258, p. 664-684. URGON, T,, 1967, Geological Work of Urla-lzmir Region for the Geothermal Survey. Preliminary Report. M.T.A. Report, Ankara. WASHINGTON, H. S., 1894, On the Basalts o[ Kula. Am..I. Sci., vol. 47, p. 114-123. - - , 1897, On Igneous Rocks [rom Smyrna and Pergamon. Am. J. Sci., vol. 3, p. 41-50. - - , 1900, The Composition o[ Kulaite. 3. Geol., vol. 8, p. 610-620.
371anuscript received Feb. 1971
22
