208
http://journals.tubitak.gov.tr/earth/ © TÜBİTAK
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
* Correspondence: senfatih81@gmail.com
1. Introduction
The Tethys Ocean, which began to subduct under Laurasia during the late Paleozoic-early Mesozoic (Topuz et al., 2018), was completely consumed during the Eocene along the İzmir-Ankara-Erzincan suture (İAES) (Şengör and Yılmaz, 1981). Destruction of the Tethys Ocean is associated with collision of the Pontides with the Kırşehir block (KB) and the Menderes-Taurus block (MTB) along the İAES (e.g., Okay and Tüysüz, 1999; Espurt et al., 2014).
The models explaining the Eocene tectonic setting of the Pontides are a matter of debate. The suggested models include: (a) an arc-related environment (Yılmaz et al., 1981, 2001; Ercan et al., 1995; Robinson et al., 1995; Delaloye and Bingöl, 2000; Köprübaşı et al., 2000; Okay and Satır, 2006; Ustaömer et al., 2009; Eyüboğlu et al., 2010, 2011), (b) a postcollisional environment (Harris et al., 1994; Genç and Yılmaz, 1997; Arslan et al., 2006; Kaygusuz and Öztürk (2015), (c) a postcollisional setting comprising slab break-off (Altunkaynak, 2007; Keskin et al., 2008; Gülmez et al., 2013), (d) postcollisional extension (Topuz et al., 2005, 2011; Kürkçüoğlu et al., 2008; Kaygusuz et al., 2011; Temizel et al., 2012; Arslan et al., 2013; Aslan et al., 2014; Yücel et al., 2014), and (e) lithospheric delamination (Köprübaşı and Aldanmaz,
2004; Karslı et al., 2010; Kaygusuz et al., 2011; Arslan et al., 2013).
It is stated that Eocene magmatism is not present in the western section of the İstanbul-Zonguldak Tectonic Unit (İZTU), except for the Armutlu-Almacık zone (e.g., Gülmez et al., 2013). In this study, I present new U-Pb zircon age and geochemical data for volcanic rocks from the Princes’ Islands, located in western section of the İZTU, with the aim of shedding light on the Eocene geodynamic evolution.
2. Geological setting
The study area is located in the İZTU, forming the western part of the Pontides, to the east of the Rhodope-Strandja zone and to the north of the Sakarya zone (Figure 1). The İZTU includes Ordovician to Carboniferous sedimentary rocks, which unconformably overlie metamorphic rocks of Proterozoic age (e.g., Yiğitbaş et al., 1999). In the western section of the İZTU, these sequences are locally intruded by a Late Permian magmatic body (e.g., Yılmaz, 1977). All these rocks are unconformably overlain by Permo-Triassic siliciclastic and carbonate rocks (Türkecan and Yurtsever, 2002; Özgül, 2012). The western part of the İZTU was probably above sea level during Jurassic and early
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
Received: 26.05.2019 Accepted/Published Online: 03.10.2019 Final Version: 02.01.2020
Cretaceous times. Upper Cretaceous-Paleocene sequences sit on the older rock units with major unconformity (e.g., Tüysüz et al., 2004). Additionally, there are local granodiorite intrusions of Late Cretaceous age (Öztunalı and Satır, 1975). The Paleozoic sedimentary rocks are thrust over the Upper Cretaceous volcanosedimentary rocks and Paleocene sedimentary rocks to the north of İstanbul from south to north (Türkecan and Yurtsever, 2002).
The Middle Eocene magmatic and volcanic rocks in the Armutlu-Almacık zone are represented by basic to intermediate volcanic rocks, dykes-sills, and coeval granites. The volcanic rocks exhibit a continuous trend from basalt to dacite. The Middle Eocene magmatic-volcanic assemblages show subduction components and display tholeiitic to low-K subalkaline affinities (e.g., Kürkçüoğlu et al., 2008; Gülmez et al., 2013).
3. Geology of the Princes’ Islands
The geology of the Princes’ Islands is represented by Ordovician to Carboniferous sedimentary rocks (Ketin, 1953; Çılgın, 2006; Özgül, 2012) (Figure 2). The Ordovician quartz sandstones are the dominant lithology on the islands (Figure 2). To the southwest of Büyük Ada, there is a roughly N-S directed thrust zone along which
the Ordovician sandstones are thrust over the Devonian carbonate rocks. This thrust is regarded as the southerly extension of the Maltepe-Beykoz nappe on the mainland of İstanbul (Seymen, 1995; Çılgın, 2006). To the north of Heybeli Ada and northeast of Büyük Ada, Carboniferous clastic rocks, which comprise sandstone, mudstone, and minor limestone, are juxtaposed with Ordovician quartz sandstones by large normal faults (Çılgın, 2006; Özgül, 2012) (Figure 2).
Felsic volcanic rocks, the topic of this study, extend roughly in the NW-SE direction and cover approximately 4 km2 (Çılgın, 2006) (Figure 2). They mostly crosscut
the Ordovician quartz sandstones (Swan, 1868). The felsic volcanic rocks, which show strong alteration on the Princes’ Islands, are distinguished from the Paleozoic quartz sandstones by their vesicular texture and massive appearance (Figure 3).
The discussion about these volcanics has a history of 150 years. The first person who dealt with these rocks was Swan (1868). His observations from Prinkipo to Antigoni, the initial names for Büyük Ada and Burgaz Ada, respectively, were as follows: (a) The units are similar to the quartz sandstones observed on all of the islands; however, feldspar and quartz minerals in the rocks show euhedral crystal forms unlike those in sedimentary rocks. (b) The
Düzce Sakarya Kocaeli Tekirdağ Bursa Bilecik Balıkesir Ezine Bayramiç Çan Biga Gönen Karabiga Edremit Kavala Thasos Karyes Thessaloniki Haskovo Edirne ++ + + +++ + + + ++ + ++ + + + ++ ++ + + ++++ ++ + + + ++++ + +++++++ + + + + + + + ++ +++ + + + + ++++ + ++ + + + + + + +++++ + + + ++++ + ++ + +++ + ++++++++++ ++ ++ + + + + v v vv v vvv vvvv + v v v v v v v v v v v v v v vv v vvv v vvv v v v v v v v v v v v v v v v v v v v v v v v v vv v v v v vv vv v v v v vv vvvvvv v vv v v v v v vvvvv vvv v v vv v v v v v v v v v v v v v v v v v v v v v v v v v v v v v vvv v v v vv v v v v vv v v v v v v v vv v vvv v v vv v v vv v v v v v v v v v v vv v vvvv ++ ++ ++++++++ + + + + + v v v vvvvvv v v v vvv v v vv vv v v vv vvv vvvv vv v vvv v v vv v v v v v v vv vvv v v v v v vv vvv vv vv v v 24 27 30
N
Çanakkale Lapseki 0 100 km Apulia Menderes-Taurus Block Pontides Rhodope-Strandja Zone GEORGIA IRAN IRAQ SYRIA GREECE BULGARIA İZTU ANKARA MEDITERRANEAN AEGEAN SEA RSZ İAES İAES KB ITS BZS MTB MTB BLACK SEA ARMENIA SZ P O N T I D E S Study Area Figure 2 Princes’ Islands İstanbul + Bolu v v v v v 42 41 40 39 Eocene-Oligocene Eocene Black SeaEocene-Oligocene volcanic rocks Eocene-Oligocene plutonic rocks
++ + ++ +++ ++ ++++++ + + + +
Eocene volcanic rocks Eocene plutonic rocks v v v vvv v v v v v vvv vvvv
Oligocene volcanic rocks Oligocene plutonic rocks
+ v ++ + + +++ +++++++ +++ ++ v v vvv v v vvv vv v v v + v + v v vvv vvv vvv vvv + + ++ + + + + + + ++ ++ ++ + +
Eocene sedimentary rocks Eocene-Oligocene sedimentary rocks
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.
unstratified rocks are different from the quartz sandstones described as Paleozoic based on their vesicular textures. (c) The joint systems observed in these two rock groups are distinct. Swan (1868) stated that they are volcanic rocks and described them as trachyte according to their mineral composition. The rocks were also determined as felsic volcanics by von Hochstetter (1870) and Önalan
(1981). In contrast, the rocks were described as altered quartz sandstones belonging to the Paleozoic sequence by Ketin (1953), Kaya (1973), and Özgül (2012).
4. Petrography
The felsic volcanic rocks have aphanitic and porphyritic textures. Plagioclase-oligoclase (30%–35%), alkali
Figure 2. Geological map of the Princes’ Islands (modified from Çılgın, 2006).
BÜYÜK ADA Yalı km 24 22 57 33 50 44 20 22 50 55 44 33 37 15 30 24 5024 30 24 27 30 33 14 40 28 20 42 2328 35 40 FS-Ba-2 FS-Ba-1 SEDEF ADASI Marmara Sea + -+ -28 26 17 46 23 42 32 43 48 FS-Hyb-1 FS-Hyb-2 FS-Hyb-3 FS-Hyb-4 HEYBELİ ADA BURGAZ ADA 28 60 42 30 50 24 41 FS-Brg-1 FS-Brg-4 FS-Brg-2 FS-Brg-3 20 23 22 12 22 14 32 KINALI ADA KAŞIK ADASI 40°55'00''N 29°3'0''E 29°6'30''E 29°3'0''E 40°50'30''N 40°50'30''N 40°55'00''N 29°5'30''E 0 1
N
Sandstone-mudstone and minor limestone Carboniferous Quartz sandstone Ordovician Limestone Devonian Alluvium Quaternary Debris flow Rhyolite Lutetian Thrust fault Strike-slip fault Normal fault33 Strike and dip of bedding Contact Fold axis sample
feldspar-sanidine (35%–40%), and quartz (20%–25%) are the main phenocrysts (Figure 4). Amphibole, biotite, zircon, and apatite are conspicuous accessory minerals. Plagioclase forms euhedral to subhedral crystal forms and rarely displays polysynthetic twinning. Sanidine crystals also exhibit euhedral to subhedral forms. The felsitic groundmass displays sericitization, saussuritization, chloritization, kaolinization, and oxidation. The volcanic rocks of the Princes’ Islands are rhyolite according to their mineral assemblage.
5. Analytical methods
Zircon grains were separated from host minerals by heavy liquids after crushing, grinding, sieving, and cleaning at the Mineral Extraction Laboratory of İstanbul University for radiometric age dating. Zircons were extracted from ~1 kg of the freshest rhyolite and large zircon grains of ~63– 200 µm were taken for analysis after being handpicked
under a binocular microscope. The U-Pb zircon ages were determined by LA-ICP-MS at the Geological Institute of the Bulgarian Academy of Sciences in Sofia. Details of the analysis technique were given by Peytcheva et al. (2015).
Special care was taken in the selection of the samples for geochemical analysis. Ten samples were selected and prepared for geochemical analyses at the Sample Preparation Laboratory of İstanbul University. The altered surfaces of each sample were cleaned and the sample was prepared for geochemical analysis by crushing in a jaw crusher and grounding in an agate ball mill.
All samples were analyzed by ICP-ES and ICP-MS at ACME Labs (Vancouver, Canada). ICP-ES was used for major oxides, Ba and Sc, and Cu, Zn, and Ni. Other trace elements and rare earth elements (REEs) were analyzed by ICP-MS. Major elements have a detection limit of 0.01%. Trace elements have a detection limit between 0.01 and 1 ppm. Major and trace elements were measured from
b
d
quartz Vesicular textures Vesicular texturesc
sanidinea
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).
aliquots samples of 0.2 g following LiBO2 fusion and HNO3 acid digestion. One gram of sample split was ignited for 2 h at 1000 °C and then cooled in a desiccator and weighed with the difference in weight represented as percent loss on ignition (% LOI). Calibration, verification standards, and reagent blanks were added to the sample sequence. The elemental concentrations of the samples were acquired using the CANMET standards (i.e. SY-4, STD SO-17) at ACME Labs, and USGS standards (i.e. W-2, AGV-1, G-2, GSP-2, BCR-2) were applied as known external standards. The analytical accuracy was better than ±3%.
6. Geochronology of rhyolites in Princes’ Islands 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.
Selected zircon grains are transparent and light-brown under binocular microscope. Representative
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 to prismatic, ranging in size from 100 to 200 µm (Figure 5). The CL images of zircon grains support a magmatic 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 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, the age is interpreted as the age of igneous crystallization for rhyolites of the Princes’ Islands.
7. Geochemistry
SiO2 and Al2O3 contents of rhyolites range from 70.06% to 73.04% and from 12.69% to 15.74%, respectively. K2O/ 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 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 the rhyolites (~4 km2) and restricted SiO
2 values, there is
no significant trend in major-trace element fractionation diagrams.
The analyzed samples fall into the rhyolite field in the Nb/Y–Zr/Ti diagram of Pearce (1986) (Figure 7a) and the high-K calc-alkaline field of the classification diagram of Hastie et al. (2007) (Figure 7b).
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 show depletion in Nb relative to Ce. This means that all samples of rhyolites contain subduction components.
The rhyolites have similar REE patterns and show a prominent enrichment in LREEs (those from La to Nd), MREEs (from Sm to Ho), and HREEs (from Er to Lu) with respect to the chondrite values of Boynton (1984) (Figure 8b). Negative Eu anomalies (Eu/Eu* = 0.67–0.90) in the rhyolites are related to negative Ba, Nb, Sr, P, and Ti anomalies, suggesting crystallization of plagioclase, apatite, and biotite without significant involvement of garnet and alkali feldspar. In addition, chondrite-normalized La/Yb and Gd/Yb ratios of rhyolites range from 3.56 to 5.04 and from 1.23 to 1.51, respectively.
8. Discussion
The rocks defined as Paleozoic quartz sandstones (e.g., Özgül, 2012) are, in fact, volcanic rocks as initially
FS-Hyb-3 Qtz Sa Chl a FS-Brg-4 Pl Sa Ser Sa 500 µm 250 µm b
Figure 4. Thin section micrographs showing textural features of the rhyolites in the Princes’ Islands. a) Euhedral sanidine (Sa) and plagioclase (Pl) crystals in a groundmass consisting of quartz, plagioclase, feldspar. and secondary sericite (FS-Brg-4). b) Highly strained quartz (Qtz) grains showing undulose extinction and formation of subgrains, sanidine crystals (sample FS-Hyb-3).
described by Swan (1868). They crosscut Ordovician quartz sandstones (Swan, 1868; Çılgın, 2006) and are rhyolite as defined by their petrography and geochemistry. The crystallization age of the rhyolites is Lutetian on the basis of U-Pb zircon age data. The Lutetian rhyolites with their high-K calc-alkaline affinity are a part of the Middle Eocene magmatic and volcanic associations in the West Pontides (Figure 1) (e.g., Kürkçüoğlu et al., 2008; Gülmez et al., 2013).
The fact that the Lutetian rhyolites include subduction signatures does not necessarily indicate that they were formed in an arc-setting because the KB collided with the Pontides in the Paleocene–Eocene transition (Hippolyte et al., 2010; Espurt et al., 2014) and the MTB was added to the Pontides during the middle Ypresian (Akbayram et al., 2016). There is a difference of about 5 million years in the collision of these continental blocks to the Pontides. In short, the arc has been inactive since the middle Ypresian in the West Pontides. Therefore, subduction components in the Lutetian rhyolites were inherited from the former subduction-influenced mantle domain.
The temporal and spatial equivalences of the rocks, which are associated with the consumption process of the Tethys Ocean, are confined to a narrow belt along the İAES (Keskin et al., 2008; Gülmez et al., 2013). The Lutetian rhyolites were not formed during a lithospheric delamination process, because the mentioned rocks should be observed along the N-S directional line in a wide geography, covering the İAES and the KB with the MTB.
In the West Pontides, the final phase of the collision is described as Chattian (Elmas et al., 2016). The Kazdağ core complex, accepted as the beginning of the extensional tectonic regime in Western Anatolia, started during the latest Oligocene (c. 22–19 Ma; Okay and Satır, 2000). The collision related to the destruction of the Tethys Ocean lasted ~25 million years. Therefore, the Lutetian rhyolites of the Princes’ Islands formed in a syncollisional instead of postcollisional setting.
The Middle Eocene magmatic and volcanic rocks in the Armutlu-Almacık zone, ranging in age from Ypresian to Priabonian (c. 50–36 Ma; Kürkçüoğlu et al., 2008;
Table 1. Results of zircon LA-ICP-MS age determination of rhyolites of the Princes’ Islands.
Spot name U(ppm) Th (ppm) Pb (ppm) Th/U ratio Isotope ratios Age (Ma)
206Pb/238U 1SE 207Pb/235U 1SE Rho 206Pb/238U 2S 207Pb/235U 2S Rhyolite FS-B rg-2 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 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
46.2 2.1± Brg-2-3 Brg-2-4 46.3 2.1± Brg-2-5 47 1.8± 44.5 2.4± 42.1 1.5± Brg-2-6 Brg-2-7 Brg-2-8 45.6 1.6± 44.5 1.6± Brg-2-9 Brg-2-10 45 1.8± Brg-2-12 49 2.1± Brg-2-13 46.3 1.7± Brg-2-14 46.1 2± Brg-2-15 Brg-2-16 44 1.6± 45.4 2.4± Brg-2-17 46.2 2.5± 44.7 2± Brg-2-18 Brg-2-19 Brg-2-20 47.5 2.1± 45.1 1.3± 48.2 2± Brg-2-1 Brg-2-1 1 49.8 2.5± 200 mu
FS-Brg-2
46.7 2.7± Brg-2-2 Brg-2-21 47.4 1.9±Figure 5. Representative CL images of dated zircon grains from sample FS-Brg-2. The red circles mark the analyzed domains.
0.0055 0.0065 0.0075 0.0085 0.0095 0.00 0.02 0.04 0.06 0.08 0.10 0.12
data -point error el lipses are 2 s
207Pb/235U 206Pb/ 238 U 60 50 40 FS-Brg-2 Concord ia Age = 45 .66 0.84 Ma MSW D(of concordance) = 2.0, Probability(of concordance) = 0.15
±
n = 21
Figure 6. U-Pb concordia diagram for the dated zircons from sample FS-Brg-2. The ‘n’ symbol represents the number of spots.
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.
Sample Rhyolites f Burgaz Ada Rhyolites of Heybeli Ada Rhyolites of Büyük Ada
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 Coordinates 0673404 /4528110 0673799 /4527561 0673901 /4527048 0673098 /4527352 0673098 /4527352 0673098 /4527352 0673098 /4527352 0673098 /4527352 0673098 /4527352 0673098 /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
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 Table 2. (Continued). 1000 100 10 1 Cs Rb Ba Th U Nb K La Ce Pb Pr Sr P Nd Zr Sm Eu Ti Dy Y Yb Lu Rock /Primitive Mantle
Sun and McDonough (1989)
(a) rhyolites in Burgaz ada
rhyolites in Heybeli ada rhyolites in Büyük ada
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Boynton (1984)
10
100
Sample/REE chondrite
(b) rhyolites in Burgaz ada
rhyolites in Heybeli ada rhyolites in Büyük ada 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.
Figure 8. a) Primitive mantle-normalized multi-element diagrams, b) chondrite-normalized REE diagrams for the rhyolites in the Princes’ Islands. 0.01 0.10 1.00 10.00 0. 00 1 0. 00 5 0. 05 0 0. 50 0 Pearce (1996) Zr/T i (ppm) Nb/Y (ppm) alkali rhyolite rhyolite dacite trachyte phonolite andesite basaltic andesite trachy-andesite tephriphonolite
basalt alkalibasalt
foidite FS-Brg-2 (a) (b) 70 60 50 40 40 20 10 0 0.01 0.1 1 10 100 Hastie et al. (2007) Co (ppm) Th (ppm)
High-K and Shoshonitic
CA
B BA/A DR/R
FS-Brg-2
rhyolites in Burgaz Ada rhyolites in Heybeli Ada rhyolites in Büyük Ada dated samples
Gülmez et al., 2013 and references therein), occurred in an extensional setting (e.g., Kürkçüoğlu et al., 2008). Late Ypresian N20°W trending basaltic andesite dykes cross-cutting the İZTU from east to west formed in an extensional setting (Şen, 2019). On the whole, the Lutetian rhyolites of the Princes’ Islands formed in an extensional setting during the ongoing collision.
9. Conclusions
Based on my field observations and analytical data, the main conclusions are as follows: (a) The studied rocks defined as Paleozoic quartz sandstones are, in fact, rhyolites. (b) The crystallization age of these rhyolites is
Lutetian based on the U-Pb age data. (c) The Lutetian rhyolites of the Princes’ Islands in the İZTU formed in a syncollisional setting based on the data of regional geological correlation. (d) Lutetian rhyolites of the Princes’ Islands form a part of the Middle Eocene magmatic volcanic province in the Armutlu-Almacık zone.
Acknowledgments
The author thanks Serdal Karaağaç and Ümitcan Erbil for discussions during the preparation of the manuscript. He thanks Volume Editor Aral Okay, and Gültekin Topuz and one anonymous referee for their thoughtful reviews and constructive comments on his manuscript.
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