Middle Eocene high-K acidic volcanism in the Princes’ Islands (İstanbul) and its geodynamic implications

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They show high-K calc-alkaline affinity. On primitive-normalized spider diagrams, negative anomalies of Ba, Nb, Sr, P, and Ti and positive anomalies of Pb are noteworthy. Their chondrite-normalized REE patterns are characterized by strongly fractionated patterns with demonstrative negative Eu anomaly, whereby middle REE are not fractionated relative to the heavy REE. These geochemical features suggest a fractionating mineral assemblage of feldspar, apatite, and biotite without significant involvement of garnet. The Lutetian rhyolites of the Princes’ Islands are a part of the Middle Eocene magmatic associations of the West Pontides, related to collision of the Menderes-Taurus block with the Pontides.

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Nội dung Text: Middle Eocene high-K acidic volcanism in the Princes’ Islands (İstanbul) and its geodynamic implications

Turkish Journal of Earth Sciences Turkish J Earth Sci (2020) 29: 208-219 http://journals.tubitak.gov.tr/earth/ © TÜBİTAK Research Article doi:10.3906/yer-1905-19 Middle Eocene high-K acidic volcanism in the Princes’ Islands (İstanbul) and its geodynamic implications Fatih ŞEN* Institute of Graduate Studies in Sciences, İstanbul University, Vezneciler, İstanbul, Turkey Received: 26.05.2019 Accepted/Published Online: 03.10.2019 Final Version: 02.01.2020 Abstract: The rock assemblages of the Princes’ Islands, which are located to the south of mainland İstanbul, are regarded as parts of the Lower Paleozoic quartz sandstones, although they were initially considered as volcanic rocks by Swan in 1868. They differ from quartz sandstones by their vesicular texture and are devoid of any stratigraphic layering. Their mineral constituents are plagioclase (30%–35%), feldspar (35%–40%), and quartz (20%–25%), corresponding to rhyolite. The crystallization age of the rhyolites is 45.66 ± 0.84 Ma on the basis of the U-Pb zircon data. They show high-K calc-alkaline affinity. On primitive-normalized spider diagrams, negative anomalies of Ba, Nb, Sr, P, and Ti and positive anomalies of Pb are noteworthy. Their chondrite-normalized REE patterns are characterized by strongly fractionated patterns with demonstrative negative Eu anomaly, whereby middle REE are not fractionated relative to the heavy REE. These geochemical features suggest a fractionating mineral assemblage of feldspar, apatite, and biotite without significant involvement of garnet. The Lutetian rhyolites of the Princes’ Islands are a part of the Middle Eocene magmatic associations of the West Pontides, related to collision of the Menderes-Taurus block with the Pontides. Key words: İstanbul, quartz sandstone, rhyolite, Middle Eocene, West Pontides 1. Introduction 2004; Karslı et al., 2010; Kaygusuz et al., 2011; Arslan et The Tethys Ocean, which began to subduct under al., 2013). Laurasia during the late Paleozoic-early Mesozoic (Topuz It is stated that Eocene magmatism is not present in et al., 2018), was completely consumed during the Eocene the western section of the İstanbul-Zonguldak Tectonic along the İzmir-Ankara-Erzincan suture (İAES) (Şengör Unit (İZTU), except for the Armutlu-Almacık zone (e.g., and Yılmaz, 1981). Destruction of the Tethys Ocean is Gülmez et al., 2013). In this study, I present new U-Pb associated with collision of the Pontides with the Kırşehir zircon age and geochemical data for volcanic rocks from block (KB) and the Menderes-Taurus block (MTB) along the Princes’ Islands, located in western section of the İZTU, the İAES (e.g., Okay and Tüysüz, 1999; Espurt et al., 2014). with the aim of shedding light on the Eocene geodynamic The models explaining the Eocene tectonic setting evolution. of the Pontides are a matter of debate. The suggested models include: (a) an arc-related environment (Yılmaz 2. Geological setting et al., 1981, 2001; Ercan et al., 1995; Robinson et al., 1995; The study area is located in the İZTU, forming the western Delaloye and Bingöl, 2000; Köprübaşı et al., 2000; Okay part of the Pontides, to the east of the Rhodope-Strandja and Satır, 2006; Ustaömer et al., 2009; Eyüboğlu et al., zone and to the north of the Sakarya zone (Figure 1). The 2010, 2011), (b) a postcollisional environment (Harris İZTU includes Ordovician to Carboniferous sedimentary et al., 1994; Genç and Yılmaz, 1997; Arslan et al., 2006; rocks, which unconformably overlie metamorphic rocks of Kaygusuz and Öztürk (2015), (c) a postcollisional setting Proterozoic age (e.g., Yiğitbaş et al., 1999). In the western comprising slab break-off (Altunkaynak, 2007; Keskin section of the İZTU, these sequences are locally intruded et al., 2008; Gülmez et al., 2013), (d) postcollisional by a Late Permian magmatic body (e.g., Yılmaz, 1977). All extension (Topuz et al., 2005, 2011; Kürkçüoğlu et al., these rocks are unconformably overlain by Permo-Triassic 2008; Kaygusuz et al., 2011; Temizel et al., 2012; Arslan siliciclastic and carbonate rocks (Türkecan and Yurtsever, et al., 2013; Aslan et al., 2014; Yücel et al., 2014), and (e) 2002; Özgül, 2012). The western part of the İZTU lithospheric delamination (Köprübaşı and Aldanmaz, was probably above sea level during Jurassic and early * Correspondence: senfatih81@gmail.com 208 This work is licensed under a Creative Commons Attribution 4.0 International License.
ŞEN / Turkish J Earth Sci 24 27 30 + 42 ++ Eocene-Oligocene N Black Sea ++ + + + Haskovo ++ v v v vv v + ++++ v v vvv v v vv v v v ++ + v + + + ++ + + + +++ v v v vvv v vv v v + vv v v v Edirne ++ + v vv vv v vv v vv v vv v v v + ++ ++ + v v v v v v ++++ + + v v v v v v v vv v vv v vv Eocene ++ + + ++ + + ++ v v v vv v v v v v v v v v v v v vv v v +++ + v + v vv vv v v v +++ v + v v v İstanbul vv v v + ++ ++ + + v + ++ + + v ++ v vv vv v v v Tekirdağ Figure 2 v Düzce 41 + v vv v vv v v v Kavala v v v v v vv v v v v vv v v v v Princes’ Kocaeli vv v v vvv v v v vv v v Bolu vvv vv v + v Islands vv vv v Sakarya v v v Thasos v v v vv v v Apulia + v v v v v v ++ v+ vv v Thessaloniki Rhodope-Strandja + ++ + v v vv v ++ Karabiga + Zone v vv v v v v Lapseki + Biga + Bursa v v +++ + Karyes Çanakkale vv v v v v Gönen Bilecik ++ + + + ++++ ++ + v v vv Çan v v + v v v v v v vv + + +++ vvv vv + + v vvv v + Pontides + + +++ ++ + v v vv v v v vv v Oligocene volcanic rocks 40 v v v v vv + + ++ Bayramiç v v + v v v vv v BULGARIA BLACK SEA v vv v +++ ++ GEORGIA Ezine v vv ++++ + Oligocene plutonic rocks Study Area Edremit vv Balıkesir + +++ + v + + ++ E EC İZTU T S ARMENIA RSZ RE N v vv v v G I E v v v vv v Eocene-Oligocene volcanic rocks O D SZ İAES v v vv v IRAN ANKARA İAES KB MTB Menderes-Taurus P + + +++ IT S BZ S Block + ++ + + ++ + + + + Eocene-Oligocene plutonic rocks 39 MTB + + + ++ AEGEAN IRAQ v v v vv Eocene-Oligocene SEA v v v v Eocene volcanic rocks SYRIA v vv v v MEDITERRANEAN sedimentary rocks v v v v 0 100 + +++ + + + +++ Eocene sedimentary rocks ++ + Eocene plutonic rocks + + + + + + + km Figure 1. Distribution of the Middle-Late Eocene plutonic and volcanic rocks in the West Pontides. Red box shows the location of the study area. Inset shows the main continental blocks and suture in Turkey (modified from Moix et al., 2008; Gülmez et al., 2013; Elmas et al., 2016). RSZ: Rhodope-Strandja zone, İZTU: İstanbul-Zonguldak Tectonic Unit, SZ: Sakarya zone, KB: Kırşehir block, MTB: Menderes-Taurus block, AP: Arabian platform, İAES: İzmir-Ankara-Erzincan suture; ITS: Inner-Taurus suture, BZS: Bitlis-Zagros suture. Cretaceous times. Upper Cretaceous-Paleocene sequences the Ordovician sandstones are thrust over the Devonian sit on the older rock units with major unconformity carbonate rocks. This thrust is regarded as the southerly (e.g., Tüysüz et al., 2004). Additionally, there are local extension of the Maltepe-Beykoz nappe on the mainland granodiorite intrusions of Late Cretaceous age (Öztunalı of İstanbul (Seymen, 1995; Çılgın, 2006). To the north of and Satır, 1975). The Paleozoic sedimentary rocks are Heybeli Ada and northeast of Büyük Ada, Carboniferous thrust over the Upper Cretaceous volcanosedimentary clastic rocks, which comprise sandstone, mudstone, and rocks and Paleocene sedimentary rocks to the north of minor limestone, are juxtaposed with Ordovician quartz İstanbul from south to north (Türkecan and Yurtsever, sandstones by large normal faults (Çılgın, 2006; Özgül, 2002). 2012) (Figure 2). The Middle Eocene magmatic and volcanic rocks Felsic volcanic rocks, the topic of this study, extend in the Armutlu-Almacık zone are represented by basic roughly in the NW-SE direction and cover approximately to intermediate volcanic rocks, dykes-sills, and coeval 4 km2 (Çılgın, 2006) (Figure 2). They mostly crosscut granites. The volcanic rocks exhibit a continuous trend the Ordovician quartz sandstones (Swan, 1868). The from basalt to dacite. The Middle Eocene magmatic- felsic volcanic rocks, which show strong alteration on volcanic assemblages show subduction components and the Princes’ Islands, are distinguished from the Paleozoic display tholeiitic to low-K subalkaline affinities (e.g., quartz sandstones by their vesicular texture and massive Kürkçüoğlu et al., 2008; Gülmez et al., 2013). appearance (Figure 3). The discussion about these volcanics has a history of 3. Geology of the Princes’ Islands 150 years. The first person who dealt with these rocks was The geology of the Princes’ Islands is represented Swan (1868). His observations from Prinkipo to Antigoni, by Ordovician to Carboniferous sedimentary rocks the initial names for Büyük Ada and Burgaz Ada, (Ketin, 1953; Çılgın, 2006; Özgül, 2012) (Figure 2). The respectively, were as follows: (a) The units are similar to the Ordovician quartz sandstones are the dominant lithology quartz sandstones observed on all of the islands; however, on the islands (Figure 2). To the southwest of Büyük Ada, feldspar and quartz minerals in the rocks show euhedral there is a roughly N-S directed thrust zone along which crystal forms unlike those in sedimentary rocks. (b) The 209
ŞEN / Turkish J Earth Sci 29°3'0''E 29°5'30''E Thrust fault 40°55'00''N Alluvium 40°55'00''N Quaternary Debris flow N Strike-slip fault 32 Lutetian Rhyolite 12 Normal fault 14 22 Sandstone-mudstone Carboniferous Strike and dip and minor limestone 33 of bedding 22 20 23 Devonian Limestone Contact Fold axis KINALI ADA Ordovician Quartz sandstone sample BURGAZ ADA KAŞIK ADASI HEYBELİ ADA FS-Brg-1 50 24 41 42 28 32 30 23 FS-Brg-2 BÜYÜK ADA FS-Brg-4 -+ 17 42 FS-Brg-3 46 26 60 28 -+ Yalı FS-Hyb-1 FS-Hyb-2 FS-Hyb-4 FS-Hyb-3 40 33 FS-Ba-1 FS-Ba-2 35 20 42 28 28 23 33 14 30 40 Marmara Sea 43 27 24 24 30 37 50 48 24 15 22 30 SEDEF ADASI 55 20 50 40°50'30''N 44 44 50 40°50'30''N 22 33 24 57 0 1 29°3'0''E 29°6'30''E km Figure 2. Geological map of the Princes’ Islands (modified from Çılgın, 2006). unstratified rocks are different from the quartz sandstones (1981). In contrast, the rocks were described as altered described as Paleozoic based on their vesicular textures. quartz sandstones belonging to the Paleozoic sequence by (c) The joint systems observed in these two rock groups Ketin (1953), Kaya (1973), and Özgül (2012). are distinct. Swan (1868) stated that they are volcanic rocks and described them as trachyte according to their 4. Petrography mineral composition. The rocks were also determined as The felsic volcanic rocks have aphanitic and porphyritic felsic volcanics by von Hochstetter (1870) and Önalan textures. Plagioclase-oligoclase (30%–35%), alkali 210
ŞEN / Turkish J Earth Sci Vesicular textures a Vesicular textures b sanidine quartz c d Figure 3. Outcrop photographs of the Middle Eocene volcanic rocks on the Princes’ Islands. a–b) Vesicular texture in volcanic rock (35T 0672950/4527259; 0678845/4525 752); c) euhedral quartz and sanidine crystals in rhyolite, roughly resembling detrital grains in sandstone (35T 0677620/4525497); d) massive rhyolite (35T 0676570/45265 15). feldspar-sanidine (35%–40%), and quartz (20%–25%) under a binocular microscope. The U-Pb zircon ages were are the main phenocrysts (Figure 4). Amphibole, biotite, determined by LA-ICP-MS at the Geological Institute of zircon, and apatite are conspicuous accessory minerals. the Bulgarian Academy of Sciences in Sofia. Details of the Plagioclase forms euhedral to subhedral crystal forms and analysis technique were given by Peytcheva et al. (2015). rarely displays polysynthetic twinning. Sanidine crystals Special care was taken in the selection of the samples also exhibit euhedral to subhedral forms. The felsitic for geochemical analysis. Ten samples were selected groundmass displays sericitization, saussuritization, and prepared for geochemical analyses at the Sample chloritization, kaolinization, and oxidation. The volcanic Preparation Laboratory of İstanbul University. The altered rocks of the Princes’ Islands are rhyolite according to their surfaces of each sample were cleaned and the sample was mineral assemblage. prepared for geochemical analysis by crushing in a jaw crusher and grounding in an agate ball mill. 5. Analytical methods All samples were analyzed by ICP-ES and ICP-MS at Zircon grains were separated from host minerals by heavy ACME Labs (Vancouver, Canada). ICP-ES was used for liquids after crushing, grinding, sieving, and cleaning at major oxides, Ba and Sc, and Cu, Zn, and Ni. Other trace the Mineral Extraction Laboratory of İstanbul University elements and rare earth elements (REEs) were analyzed by for radiometric age dating. Zircons were extracted from ~1 ICP-MS. Major elements have a detection limit of 0.01%. kg of the freshest rhyolite and large zircon grains of ~63– Trace elements have a detection limit between 0.01 and 200 µm were taken for analysis after being handpicked 1 ppm. Major and trace elements were measured from 211
ŞEN / Turkish J Earth Sci a cathodoluminescence (CL) images of the zircon grains selected from the rhyolites are given in Figure 5. The zircon grains have oscillatory zoning and sector zoning, and are transparent, dark brown, stumpy, and euhedral Ser to prismatic, ranging in size from 100 to 200 µm (Figure Pl 5). The CL images of zircon grains support a magmatic Sa origin. U and Th concentrations of sample FS-Brg-2 range from 166.5 to 431.8 and 83.8 to 369.6, and Th/U ratios are Sa scattered from 0.45 to 0.86 (Table 1). Sixteen zircon grains define a concordia age of 45.66 ± 0.84 Ma (2σ, MSWD = 2) (Figure 6). Based on the morphological and geochemical features of the zircons, FS-Brg-4 500 µm the age is interpreted as the age of igneous crystallization for rhyolites of the Princes’ Islands. b 7. Geochemistry SiO2 and Al2O3 contents of rhyolites range from 70.06% to 73.04% and from 12.69% to 15.74%, respectively. K2O/ Chl Qtz Na2O ratios are in the range of 0.33 to 0.38 (Table 2). LOI values are consistent with advanced alteration, as observed petrographically, and range from 3.6 to 8.1. They have Sa moderate Sr values, ranging from 129 to 139 ppm. Ba values are in the range of 124–142 ppm. Zr abundances are also relatively high, varying from 213 to 234 ppm. The ASI value ranges from 1.31 to 1.99 (Table 2), similar to that of S-type granite. Due to the small outcrop area of FS-Hyb-3 the rhyolites (~4 km2) and restricted SiO2 values, there is 250 µm no significant trend in major-trace element fractionation Figure 4. Thin section micrographs showing textural features diagrams. of the rhyolites in the Princes’ Islands. a) Euhedral sanidine The analyzed samples fall into the rhyolite field in the (Sa) and plagioclase (Pl) crystals in a groundmass consisting Nb/Y–Zr/Ti diagram of Pearce (1986) (Figure 7a) and the of quartz, plagioclase, feldspar. and secondary sericite (FS- high-K calc-alkaline field of the classification diagram of Brg-4). b) Highly strained quartz (Qtz) grains showing undulose extinction and formation of subgrains, sanidine crystals (sample Hastie et al. (2007) (Figure 7b). FS-Hyb-3). On the primitive mantle-normalized element concentration diagram (Figure 8a), the rhyolites of the Princes’ Islands display negative anomalies in Ba, Nb, Ce, P, and Ti and positive anomalies in K, Nd, Zr, and Y. They aliquots samples of 0.2 g following LiBO2 fusion and HNO3 show depletion in Nb relative to Ce. This means that all acid digestion. One gram of sample split was ignited for 2 samples of rhyolites contain subduction components. h at 1000 °C and then cooled in a desiccator and weighed The rhyolites have similar REE patterns and show a with the difference in weight represented as percent loss on prominent enrichment in LREEs (those from La to Nd), ignition (% LOI). Calibration, verification standards, and MREEs (from Sm to Ho), and HREEs (from Er to Lu) reagent blanks were added to the sample sequence. The with respect to the chondrite values of Boynton (1984) elemental concentrations of the samples were acquired (Figure 8b). Negative Eu anomalies (Eu/Eu* = 0.67–0.90) using the CANMET standards (i.e. SY-4, STD SO-17) at in the rhyolites are related to negative Ba, Nb, Sr, P, and Ti ACME Labs, and USGS standards (i.e. W-2, AGV-1, G-2, anomalies, suggesting crystallization of plagioclase, apatite, GSP-2, BCR-2) were applied as known external standards. and biotite without significant involvement of garnet and The analytical accuracy was better than ±3%. alkali feldspar. In addition, chondrite-normalized La/Yb and Gd/Yb ratios of rhyolites range from 3.56 to 5.04 and 6. Geochronology of rhyolites in Princes’ Islands from 1.23 to 1.51, respectively. One sample (FS-Brg-2) was selected for LA-ICP-MS U-Pb zircon dating. The results of the analysis are given in Table 1. 8. Discussion Selected zircon grains are transparent and light- The rocks defined as Paleozoic quartz sandstones (e.g., brown under binocular microscope. Representative Özgül, 2012) are, in fact, volcanic rocks as initially 212
ŞEN / Turkish J Earth Sci Table 1. Results of zircon LA-ICP-MS age determination of rhyolites of the Princes’ Islands. U Th Pb Th/U Isotope ratios Age (Ma) Spot name (ppm) (ppm) (ppm) ratio 206Pb/238U 1SE Pb/ U 1SE 207 235 Rho Pb/238U 2S 206 Pb/235U 2S 207 Rhyolite Brg-2-1 167.9 83.8 4.59 0.50 0.0075 0.00032 0.051 0.015 0.091 48.2 2 42 14 Brg-2-2 196 88 15.8 0.45 0.0072 0.00032 0.057 0.014 0.029 46.7 2.7 52 16 Brg-2-3 239.5 142.1 5.37 0.59 0.00718 0.00032 0.053 0.016 0.064 46.2 2.1 50 13 Brg-2-4 166.5 86.2 6.68 0.52 0.00732 0.00029 0.052 0.012 0.036 46.3 2.1 43 14 Brg-2-5 221.8 153.4 12.5 0.69 0.00694 0.00038 0.053 0.018 0.069 47 1.8 46 11 Brg-2-6 283.5 176.4 38.9 0.62 0.00711 0.00026 0.053 0.0098 0.017 44.5 2.4 47 17 Brg-2-7 431.8 369.6 10.9 0.86 0.00693 0.00025 0.048 0.0093 0.029 42.1 1.5 44 8.7 Brg-2-8 324 197.9 58.6 0.61 0.00701 0.00029 0.054 0.013 0.015 45.6 1.6 50 9.3 Brg-2-9 311.9 213.3 65.4 0.68 0.00775 0.00039 0.061 0.017 0.016 44.5 1.6 45 8.9 Brg-2-10 325 240 51.2 0.74 0.00722 0.00027 0.0492 0.0099 0.092 45 1.8 49 12 Brg-2-11 186.7 104.1 41.3 0.56 0.00718 0.00031 0.049 0.012 0.041 49.8 2.5 52 15 Brg-2-12 297.2 234 57.9 0.79 0.00685 0.00025 0.0434 0.0097 0.030 49 2.1 128 15 Brg-2-13 296.8 173 50.3 0.58 0.00707 0.00037 0.052 0.015 0.141 46.3 1.7 47 9.6 Brg-2-14 229.6 155.6 60.5 0.68 0.00719 0.00039 0.047 0.015 0.015 46.1 2 45 12 Brg-2-15 278.8 233.1 18.6 0.84 0.00695 0.00031 0.046 0.013 0.043 44 1.6 40 9.3 Brg-2-16 221.4 151.3 34.1 0.68 0.00741 0.00033 0.049 0.017 0.175 45.4 2.4 46 14 Brg-2-17 232.8 145.2 32.3 0.62 0.00702 0.0002 0.0472 0.006 0.008 46.2 2.5 42 14 Brg-2-18 216.1 118.3 35.7 0.55 0.00738 0.0003 0.058 0.013 0.147 44.7 2 41 12 Brg-2-19 168.4 87.9 42.6 0.52 0.00728 0.00042 0.056 0.017 0.037 47.5 2.1 43 15 FS-Brg-2 Brg-2-20 574 344 41.3 0.60 0.00764 0.00032 0.142 0.017 0.081 45.1 1.3 46 5.8 Brg-2-21 223.7 113.9 27.8 0.51 0.00655 0.00024 0.0472 0.0092 0.061 47.4 1.9 52 12 described by Swan (1868). They crosscut Ordovician The temporal and spatial equivalences of the rocks, quartz sandstones (Swan, 1868; Çılgın, 2006) and are which are associated with the consumption process of rhyolite as defined by their petrography and geochemistry. the Tethys Ocean, are confined to a narrow belt along The crystallization age of the rhyolites is Lutetian on the the İAES (Keskin et al., 2008; Gülmez et al., 2013). The basis of U-Pb zircon age data. The Lutetian rhyolites with Lutetian rhyolites were not formed during a lithospheric their high-K calc-alkaline affinity are a part of the Middle delamination process, because the mentioned rocks Eocene magmatic and volcanic associations in the West should be observed along the N-S directional line in a Pontides (Figure 1) (e.g., Kürkçüoğlu et al., 2008; Gülmez wide geography, covering the İAES and the KB with the et al., 2013). MTB. The fact that the Lutetian rhyolites include subduction In the West Pontides, the final phase of the collision signatures does not necessarily indicate that they were is described as Chattian (Elmas et al., 2016). The Kazdağ formed in an arc-setting because the KB collided with the core complex, accepted as the beginning of the extensional Pontides in the Paleocene–Eocene transition (Hippolyte tectonic regime in Western Anatolia, started during the et al., 2010; Espurt et al., 2014) and the MTB was added latest Oligocene (c. 22–19 Ma; Okay and Satır, 2000). The to the Pontides during the middle Ypresian (Akbayram et collision related to the destruction of the Tethys Ocean al., 2016). There is a difference of about 5 million years in lasted ~25 million years. Therefore, the Lutetian rhyolites the collision of these continental blocks to the Pontides. In of the Princes’ Islands formed in a syncollisional instead short, the arc has been inactive since the middle Ypresian of postcollisional setting. in the West Pontides. Therefore, subduction components The Middle Eocene magmatic and volcanic rocks in in the Lutetian rhyolites were inherited from the former the Armutlu-Almacık zone, ranging in age from Ypresian subduction-influenced mantle domain. to Priabonian (c. 50–36 Ma; Kürkçüoğlu et al., 2008; 213
ŞEN / Turkish J Earth Sci Brg-2-4 46.7 ± 2.7 Brg-2-3 Brg-2-5 46.3 ± 2.1 48.2 ± 2 Brg-2-2 Brg-2-1 47 ± 1.8 46.2 ± 2.1 42.1 ± 1.5 44.5 ± 2.4 45 ± 1.8 44.5 ± 1.6 45.6 ± 1.6 Brg-2-6 Brg-2-7 Brg-2-9 Brg-2-8 Brg-2-10 Brg-2-13 49.8 ± 2.5 Brg-2-14 49 ± 2.1 46.3 ± 1.7 46.1 ± 2 Brg-2-1 1 Brg-2-12 Brg-2-18 46.2 ± 2.5 44.7 ± 2 Brg-2-17 Brg-2-15 44 ± 1.6 47.5 ± 2.1 Brg-2-16 Brg-2-19 45.4 ± 2.4 45.1 ± 1.3 47.4 ± 1.9 Brg-2-20 Brg-2-21 FS-Brg-2 200 um Figure 5. Representative CL images of dated zircon grains from sample FS-Brg-2. The red circles mark the analyzed domains. data -point error el lipses are 2 s 0.0 095 Concord ia Age = 45 .66 ± 0.84 Ma 60 FS-Brg-2 MSW D(of concordance) = 2.0, Probability (of concordance) = 0.15 n = 21 0.0085 50 206 Pb/ 238 U 0.0 075 0.0 065 40 0.0 055 0.0 0 0.0 2 0.0 4 0.0 6 0.0 8 0.1 0 0.1 2 207 Pb/ 235 U Figure 6. U-Pb concordia diagram for the dated zircons from sample FS- Brg-2. The ‘n’ symbol represents the number of spots. 214
ŞEN / Turkish J Earth Sci Table 2. The results of whole-rock major (wt.%), trace (ppm), and rare earth elements (REE) (ppm) geochemical analysis of rhyolites of the Princes’ Islands, including coordinates of all samples. The dated sample is represented in bold font. Rhyolites f Burgaz Ada Rhyolites of Heybeli Ada Rhyolites of Büyük Ada Sample FS-Brg-1 FS-Brg-2 FS-Brg-3 FS-Brg-4 FS-Hyb-1 FS-Hyb-2 FS-Hyb-3 FS-Hyb-4 FS-Ba-1 FS-Ba-2 0673404 / 0673799 / 0673901 / 0673098 / 0673098 / 0673098 / 0673098 / 0673098 / 0673098 / 0673098 / Coordinates 4528110 4527561 4527048 4527352 4527352 4527352 4527352 4527352 4527352 4527352 SiO2 72.04 71.23 70.06 70.56 72.32 71.08 70.96 72.46 73.04 71.28 TiO2 0.38 0.37 0.34 0.31 0.36 0.38 0.31 0.34 0.39 0.36 Al2O3 15.32 14.68 14.03 13.09 12.69 14.56 13.67 14.81 14.36 15.74 Fe2O3 2.03 2.66 3.45 3.39 3.74 3.05 2.95 3.41 2.51 2.94 MnO 0.06 0.03 0.05 0.08 0.01 0.06 0.02 0.05 0.05 0.04 MgO 1.21 1.27 1.18 1.14 1.16 1.19 1.17 1.13 1.23 1.29 CaO 1.64 1.72 1.51 1.34 1.96 1.87 1.36 1.84 1.63 1.57 Na2O 3.81 3.93 3.62 3.64 3.45 3.63 3.57 3.91 3.74 3.61 K2O 1.23 1.15 1.33 1.44 1.51 1.63 1.21 2.37 1.27 1.38 P2O5 0.13 0.11 0.11 0.12 0.14 0.13 0.13 0.12 0.13 0.12 Cr2O3 0.001 0.002 0.002 0.003 0.001 0.003 0.004 0.002 0.001 0.003 LOI 5.2 5.2 6.3 6.1 5.6 5.3 8.1 4.8 4.8 3.6 Sum 97.85 97.15 95.68 95.11 97.34 97.58 95.35 100.44 98.35 98.33 Sc 8.00 7.00 8.00 6.00 6.00 8.00 4.00 6.00 9.00 6.00 V 16.00 14.00 17.00 15.00 16.00 16.00 14.00 17.00 16.00 18.00 Cr Co 5.80 5.20 6.40 7.20 4.10 5.60 5.90 6.30 5.10 4.60 Ni 3.00 4.00 2.00 1.00 5.00 1.00 3.00 4.00 1.00 3.00 Zn 62.00 64.00 61.00 60.00 65.00 74.00 81.00 52.00 60 65 Ga 17.10 17.30 17.60 18.20 17.10 16.60 16.80 18.30 16.90 17.10 Rb 37.00 35.00 39.00 41.00 35.00 38.00 42.00 38.00 38.00 40.00 Sr 135.00 129.00 134.00 13200 131.00 134.00 139.00 137.00 130.00 137.00 Y 44.00 43.00 42.00 45.00 41.00 43.00 48.00 47.00 43.00 40.00 Zr 218.00 215.00 225.00 213.00 220.00 229.00 234.00 232.00 221.00 215.00 Nb 9.00 7.00 8.00 10.00 7.00 9.00 7.00 8.00 8.00 10.00 Th 5.10 5.30 5.20 5.10 5.30 5.20 5.20 5.10 5.30 5.60 Cs 0.90 0.70 0.80 0.80 0.90 0.70 0.80 0.70 0.90 0.70 Ba 135.00 132.00 128.00 124.00 142.00 130.00 127.00 129.00 130.00 138.00 Pb 8.20 8.60 8.20 8.60 8.10 8.30 8.60 8.40 8.10 8.70 Ta 0.57 0.51 0.57 0.53 0.53 0.54 0.53 0.54 0.55 0.58 Hf 5.20 5.40 5.30 5.30 5.50 5.50 5.30 5.40 5.10 5.30 U 1.50 1.60 1.70 1.60 1.60 1.50 1.60 1.60 1.50 1.50 La 24.00 26.00 24.00 23.00 27.00 23.00 21.00 24.00 23 22.00 Ce 36.00 42.00 45.00 38.00 39.00 36.00 39.00 36.00 34.00 36.00 Pr 4.55 4.68 4.75 4.58 4.69 4.57 4.61 4.64 4.63 4.71 Nd 23.40 25.60 27.10 22.30 27.60 24.60 27.30 21.40 22.10 24.90 Sm 5.30 5.90 7.50 6.30 6.90 5.40 5.20 5.90 5.10 5.80 Eu 1.40 1.40 1.50 1.60 1.50 1.40 1.70 1.50 1.30 1.50 215
ŞEN / Turkish J Earth Sci Table 2. (Continued). Gd 6.10 6.20 6.10 6.10 6.50 6.40 6.20 6.30 6.20 6.40 Tb 1.10 1.30 1.20 1.00 1.10 1.30 1.20 1.00 1.30 1.10 Dy 6.45 7.52 7.50 6.30 6.24 6.52 6.30 6.47 6.41 5.49 Ho 1.39 1.34 1.54 1.36 1.57 1.63 1.32 1.37 1.61 1.54 Er 4.25 4.12 4.38 4.21 4.68 4.34 4.38 4.69 4.21 4.19 Tm 0.64 0.63 0.74 0.57 0.78 0.53 0.57 0.65 0.52 0.61 Yb 3.68 3.92 3.97 3.75 3.92 3.92 3.97 3.21 3.31 3.69 Lu 0.65 0.63 0.69 0.78 0.71 0.63 0.64 0.69 0.64 0.75 ASI 1.44 1.35 1.38 1.31 1.16 1.30 1.41 1.19 1.36 1.53 Eu/Eu* 0.75 0.70 0.67 0.78 0.68 0.72 0.91 0.75 0.70 0.75 100 (a) (b) alkali rhyolite 0.500 phonolite High-K and Shoshonitic FS-Brg-2 10 rhyolite dacite trachyte te onoli riph teph Zr/Ti (ppm) FS-Brg-2 y- trach site 0.050 Th (ppm) ande 1 CA site ande ndesite s a lt ic a ba IAT foidite rhyolites in Burgaz Ada 0.005 alkali 0.1 B BA/A DR/R basalt basalt rhyolites in Heybeli Ada rhyolites in Büyük Ada Pearce (1996) 0.001 dated samples Hastie et al. (2007) 0.01 0.01 0.10 1.00 10.00 70 60 50 40 40 20 10 0 Nb/Y (ppm) Co (ppm) Figure 7. Classification diagrams of the rhyolites from the Princes’ Islands. a) Nb/Y–Zr/Ti diagram after Pearce (1986); b) Co–Th diagram after Hastie et al. (2007). B: Basalt; BA/A: basaltic andesite and andesite; D/R: dacite and rhyolite; IAT: island-arc tholeiite; CA: calc-alkaline; H-K: high-K series. 1000 100 (a) rhyolites in Burgaz ada (b) rhyolites in Burgaz ada rhyolites in Heybeli ada rhyolites in Heybeli ada Sample/REE chondrite Rock/Primitive Mantle rhyolites in Büyük ada rhyolites in Büyük ada 100 10 Sun and McDonough (1989) Boynton (1984) 10 1 Cs Rb Ba Th U Nb K La Ce Pb Pr Sr P Nd Zr Sm Eu Ti Dy Y Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 8. a) Primitive mantle-normalized multi-element diagrams, b) chondrite-normalized REE diagrams for the rhyolites in the Princes’ Islands. 216
ŞEN / Turkish J Earth Sci Gülmez et al., 2013 and references therein), occurred Lutetian based on the U-Pb age data. (c) The Lutetian in an extensional setting (e.g., Kürkçüoğlu et al., 2008). rhyolites of the Princes’ Islands in the İZTU formed Late Ypresian N20°W trending basaltic andesite dykes in a syncollisional setting based on the data of regional cross-cutting the İZTU from east to west formed in an geological correlation. (d) Lutetian rhyolites of the Princes’ extensional setting (Şen, 2019). On the whole, the Lutetian Islands form a part of the Middle Eocene magmatic rhyolites of the Princes’ Islands formed in an extensional volcanic province in the Armutlu-Almacık zone. setting during the ongoing collision. Acknowledgments 9. Conclusions The author thanks Serdal Karaağaç and Ümitcan Erbil for Based on my field observations and analytical data, the discussions during the preparation of the manuscript. 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