International Journal of Geosciences, 2011, 2, 214-226 doi:10.4236/ijg.2011.23023 Published Online August 2011 (http://www.SciRP.org/journal/ijg) Copyright © 2011 SciRes. IJG An Example for Arc-Type Granitoids along Collisional Zones: The Pertek Granitoid, Taurus Orogenic Belt, Turkey Sevcan Kürüm1*, Bünyamin Akgül1, Ayten Öztüfekçi Önal2, Durmuş Boztuğ2, Yehudit Harlavan3, Melek Ural1 1University of Fırat, Engineering Faculty, Department of Geleogy, Elazığ, Turkey 2University of Tunceli, Engineering Faculty, Department of Geleogy, Tunceli, Turkey 3Geological Survey of Israel, Jerusalem, Israel E-mail: *skurum@firat.edu.tr Received April 5, 2011; revised June 8, 2011; accepted July 14, 2011 Abstract The Pertek granitoid consisting dominantly of diorite, quartz diorite, quartz monzodiorite, tonalite and lesser granite, adamellite and syenite, is considered to form the easternmost continuation of the Central Anatolian Crystalline Complex. Diorite and monzonites of this granitoid complex are cut by the granitic dykes. The Pertek granitoid, in the study area, is found in the Permo-Triassic Keban metamorphic sequence along intru- sive and tectonic contacts. Along the intrusive contacts metasomatic mineralizations are common. Granitoids are, depending on the mineralogical composition, low-, middle- high-K subalkaline features. Major oxide- SiO2 variation diagrams show that fractionation (particularly plagioclase, hornblend, pyroxene and olivine fractionation) played an important role on the granitoid formation during a continuous crystallization process. Distribution of the samples from the Pertek granitoid in the tectonic setting diagrams, and their chondrite- and primordial mantle-normalized trace element patterns resemble to the of arc-type granitoids. Trace element and rare earth element compositions indicate that the magma, from which the Pertek granitoid crystallized, derived from a mantle that was enriched by the fluids derived from the subducted slab, however this magma was contaminated by the crust during its intrusion. These geochemical characteristics are also supported by the field observations. The field and geochemical characteristics of the Pertek Granitiod suggest that they are similar to the other granitoids cropping out in the central and eastern Anatolia and they form the lateral continuation of the same magmatic belt. Keywords: Pertek, Tunceli, Island Arc, Granitoid, Geochemistry 1. Introduction E-SE Anatolia Orogenic Belt was formed along the colli- sion zone between Afro-Arabic and Aurasian plates during the Middle Miocene [1,2]. Palaeozoic-Mesozoic platform- type carbonates, supra-subduction zone ophiolites and granitoids are found together and form the tectono- magmatic unites of this belt. Isotopically dated granitoids of this belt yield a Cretaceous-Eocene age [3,4,2]. These granitoids are considered to be formed along the south- ern Neo-Tethyan subduction in the larger-scale Neo- Tethyan Conversion System and expose in three different areas. From west to east, in the collision zone, Afşin- Elbistan (Kahramanmaraş), Doğanşehir (Malatya) and Baskil-Keban (Elazığ) granitoids have been studied in detail and results have been published [5-17,3,18]. The Pertek granitoid, in a similar fashion to the other granitoids along this belt, show intrusive contacts with the Palaeozoic-Mesozoic Keban metamorphics (Keban platform-type carbonates). Platform-type carbonates were thrust onto the granitoids by the Eocene aged and younger tectonic activity to form the tectonic contact observed between the granitoids and the older metamorphic se- quence [19]. Both the basement units and the Pertek Granitoid, in the study area, are overlain by the Teriary marine sediments, terrestrial volcanic rocks and equiva- lent terrestrial sediments [20] (Figure 1). In this study, field occurences, petrographical and geo-
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 215 Figure 1. Location map of the study area and Geological map of the Pertek granitoid (simplified) [21]. chemical characteristics of the Pertek granitoid are documented for the first time. Results of this study will discuss the tectonic setting and source of the magmatic rocks in the area and contribute to the understanding of the geological evolution of the region. This contribution would also explain to the future researchers that using only geochemical data in order to evaluate the geological evolution of the region may result in erroneous inter- pretations. 2. Analytical Techniques The geological maps [21] covering the area where Pertek granitoid crops out were used in this study and they were revised whenever needed. Samples were taken from different rock units in relatively fresh parts of the units. Of those, 45 samples were examined under polirizan microscope. Totally 34 samples were geochemically an- alysed 29 of them in ACME Laboratories (Canada) and 5 of them in ACTLAB (Canada) and their major element oxide, trace element and rare earth element contents were determined. 3. Regional Geology SE Anatolian Orogenic Belt was controlled by the opening of southern branch of the Neo-Tethys Ocean from Late Triassic to Early Cretaceous between the Keban Paltform and Pütürge metamorphics [22] and following northward subduction under the Keban Plate during Senomanian- Turonian. Yazgan and Chessex [8] suggested that Eastern Tauride tectonism developed as an arc-continent collision between Keban and Arabic microcontinents that started in Late Cretaceous-Early Mastrichtian and continued until Early Eocene. Magmatic rocks observed in this orogenic belt formed along an arc that developed on oceanic and continental crust in Malatya Province and westward [22,6]. A number of researchers [8,1,9,12,4,14] documented that this magmatic belt consists of calc- alkaline volcanic and plutonic rocks. Palaeozoic-Mesozoic Keban metamorphics form the oldest units in the study area. The Keban metamrophics consist of marble, chalk schist and amphibolites and bound the magmatic rocks along their northern side (Figure 1) in the studey area. Kipman [23], suggested that the Keban metamorphics are Jurassic-Early Creta- ceous in age and metamorphosed under low P-T con- ditions. Yazgan [22] on the other hand suggested that the platform-type carbonates in this metamorphic sequence metamorphosed under gren schist methamorphism con- ditions during Senomanian along the subducion zone. Özgül and Turşucu [24] also suggested green schist conditions for the metamrophism of the Keban meta- morphics supporting Yazgan’s view [22]. Some resear- chers [6,9] on the other hand proposed that the arc magmatism caused the metamorphism. Intrusive contact between the arc magmatics and metamorphics and mine- ralizations along this intrusive contact has been pre- viously documented by various researchers. [22,10,18, 25]. The Pertek granitoid crops widely crop out in the northern and southern part of the Keban Dam to the north of Elazığ. The Pertek granitoid is overlain by the Eocene-Oligocene marine sediments and Miyo-Pliocene
S. KÜRÜM ET AL. 216 terrestrial volcanic and sedimentary sequences. 4. Field Characteristics The Pertek pluton crops out widely along two opposite sides of the Keban Dam Lake situated to the North of Elazığ, therefore appears like two different plutons in the field. In this study is focused on the northern side of the dam lake (Figure 1) where the magmatic rocks consist of diorite-gabbro, quartz diorite, tonalite, monzonites and cross-cutting dykes of acidic composition. These diffe- rent units are not indicated in geological map, however diorites crop out widely along the study area, whreas tonalites have wide outcrops in western parts of the study area. Monzonites, on the other hand, volumetrically do- minates the outcrops to the south of Pertek. In the field, diorites are weathered, medium-grained, competent, dark gray-black in appearence and form a smooth topography. Tonalites consist of large quartz crystals, less amount of mafic minerals and more mafic microgranular enclaves (MME). To the west of Pertek, close to the carbonates of the surrounding metamorphic association, strong hydrothermal alteration and oxidi- zation in mafic minerals are common. Prolonged amphi- boles which are found along the intrusive contacts may indicate a skarn zone. Presence of skarn metamorphism in the region has previously been noted by Altunbey and Çelebi [25]. Mafic microgranular enclaves, preserved in the main pluton, are generally rounded and ellipsoidal in shape and reach up to 50 cm in diameter. Dioritic main body is cross cut by the harder, felsic, fine grained, acidic and strongly altered porphyres that are exhumed widely in the north of Pertek and its thickness vary from a few meters to few hundreds meters. In the southeastern part of Pertek, close to the Keban Dam Lake, monzonites are less altered then the other magmatic lithologies. Monzonites are easily distinguished in the field because of containing pink K-feldspar crystals which display lengths from a few milimeter to a few centimeters. Mon- zonites are not mappable in scale and generally found as small stocks cutting diorites and tonalites in the lower parts and a few tens of meter-thick dykes, in the upper parts. At the 30th km of Pertek-Tunceli highway, in a valley, up to 3 m-thick, hard, NW-SE-trending, almost vertical aplite dykes are also found in the upper part of the magmatic body. In the uppermost part of these dykes cataclastic enclaves are commonly found. The Kırkgeçit formation cropping out in the study area is represented by sandstone-mudstone alternation and channel-fill conglomerates [19]. The Late Miocene-Plio- cene aged Karabakır formation which is dominated by the pyroclastic rocks and lava flows in the study area, forms the youngest unit and crops out in the N-NW part of the study area. The thrust fault along which the Keban metamorphics are found tectonically overlying the Pertek magmatics, form the main tectonic structure in the study area (Figure 1). [19] suggested that this approximetely 10° north dipping fault is Late Cretaceous - Late Palaeocene in age. NW-SE trending strike-slip fault which is observed in the west of Pertek, is another significant tectonic structure in the area (Figure 1). 5. Petrography Petrographically the Pertek granitoid consists of quartz diorite, tonalite-granite/granodiorite, monzonite, diorite/ gabbro. Samples are dominantly plotted in quartz diorite, diorite quartz monzodiorite and tonalite areas in nomen- clature diagram [26] and only one sample is found in granite, ademellite and syenite areas respectively (Figure 2). Places of the samples in the geochemical nomen- clature diagrams are in accordance with the petrographic nomenclature. Sample PR-20 is plotted in the geoche- mical nomenclature diagram in granite area, PR-31 in syenite area and PR-26 in ademellite area and they are found in Streckeisen [27] triangle diagram in monzo- granite area. Diorites and quartz diorites are fine to medium grained granular and poikilitic in texture and are dominated by plagioclase and hornblende crystals. In some of the samples hornblends are greater in amount than the pla- gioclases. Plagioclases in diorites commonly show une- quilibrium textures of oscillatory zoning and polysyn- thetic twinning indicating open system processes like magma mixing [28]. Subhedral or skeleton shaped horn- blends with green pleocroism are commonly chloritized. Poikilitic texture is characterized in hornblends by pla- gioclase and opaque mineral inclusions. In some horn- blende crystals relic pyroxenes are observed indicating that hornblends were formed by uralitization in pyro- xenes. Tonalite, granite and granodiorites are coarse grained hypidiomorphic granuler in texture. Plagioclase, quartz, amphibole, K-feldspar, apatite, zircon, sphene and opaque minerals form the mineral association. Plagioclases are the dominant felsic minerals and show albite twinning, zoneing and overgrowth texture. Quartz crystals are vary- ing in size, unhedral and show wavy extinction. Amphi- boles show green pleochroism. Chloritization and opaci- tation in amphiboles and argillic alteration in K-feldspars are the common alteration types. Sphenes are found as coarse idiomorph cystals and apatites as acicular crystals in accessory phase. Zircon is rarely observed. In monzonites plagioclase, amphibole, quartz and K- feldspar form the main mineral phase. Amphiboles with Copyright © 2011 SciRes. IJG
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 217 Figure 2. QP plot [26] for samples from the Pertek granitoid. slight, pale gren pleochroism are rarely found as coarse crystals but commonly as pseudomorphic acicular crystals. Chloritization is the common alteration type. Sample PR-31 is distinguishable from the remaining sample even as hand specimen. Large amount of perthitic K-feldspar crystals give a pink color to the syenites in hand specimen. The main minerals forming the rock are perthitic K-feldspars. Quartz content of the Syenites is low. 6. Geochemistry Whole rock geochemical composition of 34 samples from the Pertek granitoid is given in Table 1 and results are plotted in total alkalies-Silica (Figure 3(a)) and AFM (Figure 3(b)) diagrams. All samples, except for syenite (PR 31), are gathered in subalkaline area in total alkalies- silica diagram. Diorite/gabbro and quartz diorite samples are mostly tholeiitic-high Mg and other samples are calk-alkaline in nature. In AFM diagram quartz monzo- diorites and granites are found in high K area and other samples are found in low K area. According to Shand index samples are metaluminous in character (A/CNK= –0.5 - 1; A/NK < 1) and I-type in nature (A/CNK < 1.1) [29]. The I-type nature of the samples is in accordance with the mafic mineral assemblage. In Harker-type variation diagrams, it is distinguished that the Pertek granitoid evolved from a single magma phase during continuous normal fractional crystallization stage. During this crystallization stage mineral fractio- nation did not develope in diorites, less developed in quartz diorites and well developed in tonalites. Addi- tionally, while, depending on the mafic composition, enrichment in FeO*, MgO, CaO 2 and Ti2O ratios is observed in diorites (Figure 4(b), (c), (d), (g)); enrich- ment in Na2O ratio are observed depending on the K- feldspar (Figure 4(e)) in tonalites and quartz monzo- granites. In the chondrite-normalized spider diagams (Figure 5(a), (c), (e)), diorites and quartz diorites show similar patterns (Figure 5(a), (c)). In both groups, some of the samples are depleted in LREEs and others are enriched. In these diagrams, in some of the diorite and quartz diorite samples, depletion in LREEs is more significant than the others. In these samples depletion in HREEs is also more distinguishable compared to the others. In de- pleted LREEs samples a significant enrichment of Eu is observed. In addition to the similar REE patterns of diorite and quartz diorite samples, a concave pattern from the enriched LREEs to depleted HREEs is observed (Figure 5(a), (c), (e)). The REE composition of samples indicate a fractionation processes in these rocks [30]. In the Primordial mantle-normalized spider diagrams (Figure 5(b), (d), (f)) diorites and quartz diorites show two different patterns in LILEs (K, Rb, Ba, Th) (Figure 5(b), (d)). An enrichment in LILEs in the other rock groups, on the other hand, is clear (Figure 5(f)). Signi- ficant enrichment in LILEs may indicate an E-MORB or within plate setting for the basic rocks [31]. In the acidic rocks, however, enrichment in LILEs may indicate either crustal contamination [32] or enrichment by fluids derived from the oceanic crust [33]. In these diagrams, Nb show
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 218 Table 1. Major (%) and trace element (ppm) contents of the Pertek granitoides. Sample Symbol PR1 ♦ PR29 ♦ PR32 ♦ PR2 ■ PR3 ■ PR5 ■ PR8 ■ PR9 ■ PR10 ■ PR13 ■ PR15 ■ PR16 ■ PR19 ■ PR25 ■ PR27 ■ PR28 ■ PR30 ■ SiO2 56.11 63.14 62.94 48.26 44.40 46.2246.4346.8046.34 44.95 46.60 48.1247.65 54.89 49.98 50.85 56.68 Al2O3 13.73 17.84 17.69 17.36 16.44 16.5021.7817.9314.73 17.29 14.24 15.5314.70 17.86 18.05 20.33 17.69 Fe2O3 7.09 4.13 4.58 11.44 11.24 8.665.645.8012.877.54 8.82 7.547.46 7.24 10.10 7.09 6.85 MgO 3.52 1.16 1.25 6.24 7.45 8.866.6710.847.8411.5112.279.9911.46 4.31 5.60 4.50 3.14 CaO 7.79 4.36 4.70 11.08 12.6 15.7315.5915.1314.1912.6913.3113.8814.80 7.99 9.66 10.95 7.07 Na2O 2.86 4.85 4.47 2.18 2.21 1.391.491.241.36 1.45 1.41 1.731.25 4.10 2.64 2.97 4.12 K2O 2.67 3.18 3.10 0.49 0.52 0.12 0.070.050.10 0.10 0.19 0.110.07 1.42 1.22 0.90 2.40 TiO2 0.32 0.28 0.30 0.84 0.58 0.420.160.181.42 0.36 0.43 0.340.36 0.52 0.72 0.47 0.48 P2O5 0.10 0.09 0.09 0.06 0.06 0.02<0.01<0.010.03 0.01 0.02<0.010.01 0.08 0.09 0.06 0.11 MnO 0.16 0.09 0.007 0.18 0.19 0.160.110.10 0.16 0.12 0.180.14 0.13 0.13 0.15 0.12 0.13 LOI 5.5 0.7 0.6 1.6 4.6 1.7 1.9 1.7 1.2 3.7 2.2 2.3 1.7 1.3 1.5 1.5 1.1 Total 99.84 99.80 99.78 99.74 99.78 99.79 99.8499.7999.71 99.78 99.75 99.7899.73 99.78 99.70 99.79 99.76 K2O/P2O5 26.70 35.33 34.44 8.17 8.67 6.007.005.003.33 10.00 9.5011.001.00 17.75 13.56 15.0021.82 A/CNK 0.51 0.59 0.59 0.56 1.07 0.49 1.271.090.94 1.21 0.96 0.990.91 1.32 1.34 1.37 1.30 A/NK 2.48 2.22 2.34 6.50 6.02 10.9313.9613.9010.0911.158.908.4411.14 3.24 4.68 5.25 2.71 Ni (ppm) <20 21 <20 22 <20 62 41 78 41 148133109196 22 78 <20<20 Sc 7 5 4 35 26 52 41 40 57 27 37 58 51 16 31 26 10 Cs 2.1 2.8 1.2 0.1 0.8 0.1 <0.1<0.10.2 0.1 0.2 0.2 0.3 2.0 3.2 5.9 1.0 Ga 14.8 16.8 16.6 16.4 14.5 12.8 13.910.315.3 11.8 10.0 12.110.5 17.3 17.1 16.3 16.8 Hf 3.5 4.6 4.1 1.7 0.9 0.7 0.3 0.3 0.6 0.5 0.6 0.3 0.3 2.7 2.2 1.7 3.0 Sn 1 1 <1 <1 <1 1 <1 <1 <1 <1 <1 4 <1 1 <1 1 1 Ba 361 835 1019 137 98 23 14 8 9 12 20 13 7 471 512 288713 Rb 77.8 88.2 79.8 6.0 16.1 2.4 1.0 1.0 1.11.4 6.4 1.2 1.1 48.3 24.8 19.665.0 Sr 243 464 548 257 289 193222174226 150 179156 145 487 467 677 631 Nb 9.9 17.6 11.6 3.1 3.2 0.8 0.2 0.2 0.2 0.5 0.5 0.2 <0.1 7.8 8.6 8.810.6 Zr 124.6 190.0 184.9 60.9 32.4 15.68.5 3.6 19.1 14.8 17.87.9 8.5 112.0 76.2 59.3130.4 Ta 0.5 1.4 1.1 0.2 0.2 <0.1<0.1<0.1<0.1<0.1<0.1<0.1<0.1 0.3 0.8 0.8 0.6 Th 4.5 19.6 11.3 1.8 0.7 0.2 <0.2<0.2<0.2<0.2<0.2<0.2<0.2 10.2 3.7 6.89.0 U 1.9 3.9 3.4 0.8 0.4 0.1 0.1 <0.1<0.10.1 0.2 <0.1<0.1 3.1 1.8 2.8 3.9 V 44 38 51 374 247 239150115715 115 160185197 151 317 151 116 W 50.5 3.3 2.0 <0.5 37.1 5.1 1.8 1.1 <0.56.1 1.7 3.3 <0.5 1.5 <0.5 3.3 1.1 Y 21.5 16.0 11.7 14.1 14.8 12.04.7 4.4 12.17.6 9.1 7.6 9.7 11.9 17.1 11.6 12.9 La 14.5 28.0 17.6 5.8 6.1 1.4 0.6 0.5 0.8 1.0 2.3 0.6 0.5 17.2 12.8 10.620.4 Ce 27.9 47.1 31.9 12.5 12.9 3.7 1.2 0.9 2.42.7 3.9 1.4 1.5 25.8 25.2 18.7 31.3 Pr 3.42 5.00 3.54 1.61 1.78 0.630.180.160.44 0.45 0.53 0.270.28 2.75 3.06 2.27 3.35 Nd 12.9 16.9 12.4 7.0 7.3 3.6 1.1 0.8 2.9 2.4 2.7 1.7 2.0 10.6 12.0 8.711.0 Sm 2.73 2.74 2.14 1.75 1.73 1.09 0.360.361.08 0.74 0.88 0.620.85 1.91 2.61 1.86 2.11 Eu 0.98 0.72 0.68 0.62 0.68 0.440.220.250.57 0.37 0.39 0.350.47 0.61 0.82 0.58 0.78 Gd 3.05 2.42 1.88 2.17 2.19 1.57 0.570.631.77 1.02 1.22 1.041.36 2.01 2.73 1.88 2.25 Tb 053 0.44 0.36 0.40 0.40 0.30 0.120.130.33 0.21 0.26 0.220.27 0.35 0.47 0.37 0.40 Dy 3.39 2.59 1.96 2.38 2.51 1.890.850.782.16 1.24 1.47 1.361.71 1.97 2.83 2.11 2.31 Ho 0.72 0.51 0.41 0.51 0.52 0.440.180.160.46 0.28 0.34 0.300.36 0.41 0.58 0.41 0.46 Er 2.05 1.73 1.34 1.48 1.53 1.27 0.500.461.34 0.74 0.99 0.830.99 1.32 1.66 1.23 1.45 Tm 0.35 0.33 0.26 0.23 0.24 0.190.080.070.20 0.14 0.180.140.15 0.23 0.25 0.22 0.26 Yb 2.29 2.10 1.54 1.55 1.52 1.210.500.461.24 0.75 0.91 0.780.93 1.43 1.66 1.25 1.59 Lu 0.34 0.36 0.26 0.23 0.23 0.190.070.060.18 0.12 0.150.120.13 0.24 0.25 0.21 0.26 Ba/Nb 36.46 47.44 87.84 44.19 30.63 28.75 70.0040.0045.00 24.00 40.00 65.0077.78 60.38 59.53 32.73 67.26 La/Nb 1.46 1.59 1.52 1.87 1.91 1.75 3.002.504.00 2.00 4.60 3.005.56 2.21 1.49 1.20 1.92 La/Ta 29.0 20.0 16.0 29.0 30.5 14.06.7 6.3 11.4 11.1 25.67.5 5.0 57.3 16.0 13.3 34.0 Zr/Nb 12.59 10.80 15.94 19.65 10.13 19.5042.5018.0095.529.60 35.6039.50 94.44 14.36 8.86 6.7412.30 Nb/U 5.21 4.51 3.41 3.88 8.00 8.00 2.002.002.00 5.00 2.502.004.00 2.52 4.78 3.14 2.72 Rb/Sr 0.32 0.19 0.15 0.02 0.06 0.01 0.000.010.01 0.01 0.04 0.010.01 0.10 0.05 0.03 0.10 ♦;quartz monzodiorite, ■,diorite, ▼;quartz diorite, ●; tonalite, ○;granite, □;adamellite, ▲;syenite
S. KÜRÜM ET AL.219 Figure 3. Major element geochemical discrimination diagrams of the Pertek granitoid. (a) Total alkalis vs silica [47]; dividing line between alkaline and subalkaline fields [48] (b) AFM triangular diagram [47]. Figure 4. Major oxides vs. SiO2 variation diagrams for rock samples from the Pertek granitoid. Copyright © 2011 SciRes. IJG
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 220 Figure 5. (a) Chondrite (b-c) PRIM normalized spider diagrams for the Pertek granitoid. (PRIM and Chondrite normalizing values after [49]). 7. Petrogenesis a significant negative anomaly whereas Sr show, parti- cularly in diorites and quartz diorites, a strong positive anomaly. Ti, in all different lithologies but parti- cularly in tonalites, show a strong negative anomaly (Figure 5(f)). Medium and heavy REEs (Sm-Lu) are depleted in all rock types. When all the geochemical characteristics of the geographically close and minera- logically similar diorites are taken into consideration, this significant difference observed in spider diagrams do not seem to be caused by fractionation or fractional crystallization from a single magma source. Mixing of two different magma sources may explain these geoche- mical chracteristics [30]. Fractional crystallization processes during crystallization of the Pertek granitoid is defined in Harker type major oxides-silica diagrams (Figure 4). In these diagrams a negative correlation in FeO*, MgO, CaO, Ti2O ve MnO ratios and a positive correlation in Na2O and K2O ratios with the increasing SiO2 indicate the fractional crystalli- zation. Particularly MgO ratios of 3% - 14 % in diorites and quartz diorites indicate that olivine and pyroxene played important role during the fractionation phase. In the other rock groups amphiboles accompanied olivine and pyroxene during fractionation. This fractionation
S. KÜRÜM ET AL.221 could be defined also in LILE and HFSE vs silica dia- grams (Figure 6). For example, in quartz and quartz diorites Rb and Ba contents increase with the increasing silica (Figure 6(a) and (b)) indicating assimilation- fractional crystallization processes. Similarly in Sr-SiO2, Y-Rb variation diagrams (Figure 6(c) and (d)), amphi- bole and bio- tite effect in diorites, quartz diorites and tonalites is clear. Samples from the Pertek granitoid are plotted in che- mical affinity diagram of Debon Le Fort [26] (Figure 7) (I, II, III are peraluminous, IV, V, VI are metaluminous in character), our samples in this diagram are plotted in areas of IV and V indicating metaliminous-cafemic cha- racter. However some samples including diorites, are found in leucogranites area. Autochthonous or intrusive granitoids of peraluminous character are related to the crustal source in collisional or post collisional tectonic setting. Metaluminous more basic rocks, on the other hand, are related to crust-mantle (hybrid) source in collisional or post collisional tectonic setting. Debon Le Fort [26] noted that aluminous magma suites generally were formed by the partial melting of sialic material and cafemic suites may evolve from mantle or, more com- monly, a hybrid magma of mantle-sialic material mixing. Debon Le Fort [26] suggests cafemic character of magma suites indicate depletion in mantle source. Ni composition is an important indicator in plutonic rocks in order to determine if the source was primitive or originated from depleted mantle. In tonalites and quartz monzodiorites of the Pertek granitoid, Ni composition varies from 15 to 24 ppm indicating that their source was not primitive mantle but may be a fractionally crysta- llized depleted mantle [34]. However, in diorites Ni ratio varies from 18 to 178 ppm and in quartz diorites from 17 to112 ppm (Table 1) indicating that the more basic rocks might have evolved from primitive mantle. In addition to that, most of the acidic and basic samples are gathered in an area between MORB and subduction melt areas in La/Nb-Ti variation diagram (Figure 8(a)). In Th/Yb- Ta/Yb variation diagram they are found in subduction zone and N-type MORB areas and effect of fractional crystallization could be defined in diagram (Figure 8b). In the Zr/Yb-Nb/Yb diagram (Figure 8c) diorites are found in an area between depleted mantle (DM) or Oceanic Island Basalt (OIB) areas. Quartz diorites, in the same diagram, are gathered in Enrich-Ocean Ridge Basalt Figure 6. (a-c) Rb, Ba and Sr vs. silica semi-logarithmic variation diagrams of Pertek granitoid. (d) Y vs Rb. AFC; assimilation-fractional crystallisation, opx; orthopyroxene, cpx; clinopyroxene, amp; amphibole, plg; plagioclase, bio; biotite, K-feld; K-feldspar, hb; hornblende, gt; garnet, zr; zircon, ol; olivine. Copyright © 2011 SciRes. IJG
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 222 Figure 7. Chemical trends representing the main magma associations of the Pertek granitoid in the A-B characteri- stic minerals diagram [26]. I, II, III and IV, V, VI regions represent the peraluminous and metaluminous domains. Bi; biotite, mu; muscovite, hb; hornblende, opx; orthopyroxene, cpx; clinopyroxene, ol; olivine, ALUM; aluminous, ALCAF; aluminocafemic, CAFEM; cafemic association. (E-MORB) area, and tonalites are found between DM and E-MORB areas. All samples are plotted in volcanic arc granitoid area in Nb-Y and Rb-Y/Nb variation dia- grams (Figure 9). In Sm/Yb-Ce/Sm diagram, diorites are found in MORB area, and the others are in between MORB-OIB areas. Pearce et al. [35] noted that gathering in these areas might be caused by subduction zone en- richments of crustal contamination. Distribution of sam- ples from the Pertek granitoid in Rb/Y-Nb/Y and Ba/Nb- La/Nb diagrams (Figure 10(a)-(c)) also show a crustal contributions into the magma. As mentioned above, increasing in Rb/Sr and K2O/ P2O5 ratios with increasing SiO2 is a clear indicator of crustal contamination (Table 1) [36]. However, this con- tamination should be considered with the assimi- lation-fractional crystallization (AFC) and partial melting [37]. Low La/Ta ratio also indicates crustal contami- nation [31]. When these interpretations are taken into consideration, these La/Ta ratios in diorites (La/Ta = 19.1), quartz diorite ((La/Ta = 20.7) and quartz monzo- diorite (La/Ta = 21.7) indicate effects of crustal contami- nation for these groups but tonalites (La/Ta = 38.7). In some diagrams, given above, Pertek granitoid show similar geochemical composition to the mantle wedge. Considerably high Ba/Nb (11-139) and Zr/Nb (6-79) ratios (Table 1) indicate that these rocks were subjected to a mantle-sourced depletion [38]. Similarly, except for syenite (PR-31) and one quartz diorite sample, La/Nb ratios are higher than 1 and this also indicates that these groups evolved from a lithospheric mantle source [39]. It Figure 8. (a) La/Nb vs. Ti (ppm) [35]. (b) Th/Yb vs. Ta/Yb, [35] and (c) Zr/Yb vs. Nb/Yb plots of the rock samples from the Pertek granitoides. SMZ; subduction zone magmatites, MORB; Ocean Ridge Basalt, OIB; Ocean Island Basalt, FC; Fractional Crystallisation, DM; Depleted Mantle, N, E- MORB; Normal - Enrich Ocean Ridge Basalt. is widely accepted that in subcontinental lithospheric mantle-sourced magma La/Nb is higher (La/Nb > 1) than asthenospheric mantle-sourced ones (La/Nb < 1) [39]. In Pertek granitoid samples La/Nb ratio varies from 1, 2 to 4, 6 indicating a lithospheric melt. However, some re- searchers also suggest that relative depletion in Nb and Ta might be caused by interaction between subconti- nental litfospheric and astenospheric melts [40].
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 223 Figure 9. (a) Nb – Y and (b) Rb - Y+Nb [50] geotectonic discrimination diagrams for the Pertek granitoid. Syn COLG; Syn-Collisional Granitoid, WPG; Within-Plate Granitoid, VAG; Volcanic-Arc Granitoid, ORG; Ocean-Ridge Granitoid. Figure 10. (a) Sm/Yb vs. Ce/Sm, (b) Rb/Y vs. Nb/Y [35], (c) Ba/Nb vs. La/Nb [51] plots of the rock samples from the Pertek granitoid. 8. Discussion and Conclusions The NW-SE-trending Pertek granitoid consists of dio- rites, quartz diorites, quartz monzodiorites, tonalites and crosscutting aplites and monzonitic dykes that were all formed in similar tectonic setting. Large amount of mafic microgranuler enclaves are found in quartz diorites, tonalites and monzonites. All these rocks, except for a sample (PR-31) taken from syenites, are sub-alkaline; diorites and quartz diorites are tholeiitic and others are calc-alkaline in nature and all of them are evolved from a single phase magma during a normal crystallization process. Major element-silica variation characteristics show that fractionation particularly plagioclase, horn- blend, pyroxene and olivine played an important role on their formation during a continuous crystalliation period.
S. KÜRÜM ET AL. Copyright © 2011 SciRes. IJG 224 Table 2. The general features of the granitoides in the E-SE Anatolia. Rocks Magma type Tectonic setting Age Göksun-Afşin Granodiorite and granitic [4] Calc-alkaline [4] Volcanic Arc [4] 85.76±3.17-77.49±1.91 [4] Doğanşehir Amphibole gabbro, diorite, quartz diorite, tonalite, granodiorite [43, 44] I-type, peralüminus, calc-alkaline [43, 44] Volcanic arc [43,44] Compatible with the Baskil, Göksun-Afşin and Keban [4] Baskil Granite, granodiorite, tonalite, quartz monzonite, diorite, gabbro, aplite, diabase [2,16], granophyric, granite porphyre, granodiorite porphyre, microdiorite, quartz microdiorite, quartz diorite-porphyre, orbicular gabbro [2] I-type [13], metalüminus, peralüminus [2,16], calc-alkaline [2] ± tholeiitic Magmatic arc [14,45] Ensimatic ısland arc [3, 14] Volcanic arc granitoid [2] Granitoid=81.5±1.1 [2] Diabase=78 my [16] Granite=76 ±2.5 – 78.5±2.5 my [8] Keban Tonalite, quartz diorite, gabbro, dacite, andesite, basalt [9,6,17] Tonalites;calc-alkaline, I-type, metalüminus, peralüminus Diorite-gabbros; tholeiitic, M-type, metalüminus [17] Volcanic Arc [17] Tonalite=59.77 ± 1.2 -75.65 ± 1.5 Diorite= 84.76 + 1.8 [17] Pertek Diorite, quartz diorite, Q.monzodiorite, tonalite, granite, syenite I-type, metalüminus, Q.monzodiorite and tonalite; calc-alkaline, Diorite and Q.diorite; calc-alkaline and tholeiitic Volcanic Arc Granitoid 68.6±5.6 Chontrite and pimordial mantle-normalized patterns of diorite and quartz diorites show two different path indicating that mantle-sourced magma that later formed the Pertek granitoid was enriched by fluids derived from the oceanic crust in an arc setting, and contaminated by continental crust. This result is supported by both the petrographic and geochemical evidences that magma formed in an arc setting, enriched by magmatic fluids derived from a subducted oceanic crust, injected into the crust and contaminetd in this crustal environment. The repeated modifications in subcontinental litho- spheric mantle by dehidration in subduction zones and accretionary prism sediments included by subcontinental lithospheric mantle [41] caused a relative depletion in Ti, Nb and Ta and an enrichment in Ba. The fact that the rocks are concentrated in classical sedimentary and granulite areas may indicate the same thing as well. Significant negative Nb and Ti anomalies in Pertek gra- nitoid are probably caused by its subduction sediment content. Negative Ti anomaly may also indicate apatite and Fe-Ti oxides played important role on petrogenesis [42]. In the geological map of MTA [21], the Cretaceous magmatic rocks cropping out to the N and NE of Elazığ are defined as “ophiolites” and “unclassified magmatic rocks”. The Pertek granitoid crops out in a part of this region and when our conclusions are compared with the other granitoids cropping out in the region, it is seen that they display similar characteristics (Table 2). Thus, it might be concluded that the Pertek granitoid is the east- ern continuation of Elbistan (Kahramanmaraş), Doğan- şehir (Malatya), Baskil and Keban (Elazığ) granitoids. The future petrographic and geochemical studies on the cross-cutting acidic dayks would contribute in under- standing if the magmatism was bimodal in nature or not. In order to clarify the problems, related to the place and importance of the Pertek granitoid within the context of geotectonic evolution of the region, additional studies are needed along with the detailed geochemical studies we presented in this article. We continue studying isotop geochronology and isotop geochemistry of the Pertek granitoid in accordance with our purpose. 9. Acknowledgements The authors gratefully acknowledge a grant from the University of Fırat, Project number FUBAP-1109 (Fırat University Scıentific Research Projects Unıt). 10. References [1] Y. Yılmaz, E. Yiğitbaş and S. C. Genç, “Ophiolitic and Metamorphic Assemblages of Southeast Anatolia and Their Significance in the Geological Evolution of the Orogenic Belt,” Tectonics, Vol. 12, No. 5, 1993, pp. 1280-1297. doi:10.1029/93TC00597 [2] T. Rızaoğlu, O. Parlak, V. Höck, F. Koller, W. E. Hames and Z. Billor, “Andean Type Active Margin Formation in the Eastern Taurides: Geochemical and Geochronological Evidence from the Baskil Granitoid, SE Turkey,” Tecto- nophysics, Vol. 473, No. 1-2, 2009, pp.188-207. doi:10.1016/j.tecto.2008.08.011 [3] T. Rızaoğlu, O. Parlak and F. İşler, “Geochemistry and Tectonic Setting of the Kömürhan Ophiolite in Southeast Anatolia,” 5th International Symposium on Eastern Medi- terranean Geology, Thessaloniki, 14-20 April 2004, p. 285. [4] O. Parlak, “Geodynamic Significance of Granitoid Mag- Matism in the Southeast Anatolian Orogen: Geochemical
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