2022 | 75/2 | 249–267 | 11 Figs. | 4 Tabs. | www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society 1. INTRODUCTION Mt. Papuk, situated at the southern edge of the Pannonian basin in northern Croatia (Fig. 1a), is characterized by a complex geo- logical evolution that comprises several orogenic events (JAMIČIĆ, 1983; BALEN et al., 2006, 2013; HORVÁTH et al., 2010). These events led to a variety of rocks and complexes such as granitoids and metamorphic complexes of pre-Variscan, Va- riscan and Alpine ages. Together with Late Permian–Jurassic sedimentary rocks, these complexes are part of the Tisia Mega- Unit and are surrounded by Neogene and Quaternary sedimen- tary rocks and sediments of the Pannonian basin (JAMIČIĆ, 1983, 1988; PAMIĆ et al., 1988; PAMIĆ & LANPHERE, 1991a). In addition to the rocks of the Tisia Mega-Unit and those of the Pannonian basin, there are relatively small occurrences of volca- nic rocks in the vicinity of the town of Voćin (JAMIČIĆ & BRKIĆ, 1986; JAMIČIĆ et al., 1987, 1989; JAMIČIĆ, 1989; PAMIĆ, 1991). Among them are rocks of the Senonian basalt- rhyolite formation (PAMIĆ, 1997), outcropping at Mt. Papuk near Voćin known as the Voćin volcanic mass (PAMIĆ, 1991). These rocks are difficult to distinguish from similar-looking Miocene volcanic rocks in northern Croatia. Based on micropalaeontolo- gical records and geological relationships (JAMIČIĆ & BRKIĆ, 1986; JAMIČIĆ et al., 1987, 1989; JAMIČIĆ, 1989; BELAK et al., 2000), it is concluded that the Miocene rocks are related to the evolution of the Pannonian basin. The age of the Voćin vol- canic rocks is questionable, because only K-Ar dating on associ- ated basalts (72.8–51.7 Ma, PAMIĆ, 1991) and basalt cores from Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) and the relationship to the Sava Zone Petra Schneider1,*, Dražen Balen1, Joachim Opitz2 and Hans-Joachim Massonne2 1 University of Zagreb, Faculty of Science, Department of Geology, Horvatovac 95, 10000 Zagreb, Croatia; (*corresponding author: pschneider@geol.pmf.unizg.hr), (drbalen@geol.pmf.unizg.hr) 2 Universität Stuttgart, Institut für Mineralogie und Kristallchemie (closed), Azenbergstraβe 18, 70174 Stuttgart, Germany; (opitz.joachim@web.de, h-j.massonne@imi.uni-stuttgart.de) doi: 10.4154/gc.2022.19 Abstract The Rupnica geosite, a key locality of the UNESCO-protected Papuk Geopark in northern Croa- tia, is well-known for an excellent exposure of columnar jointing in volcanic rock. This rock is defined as an albite rhyolite that comprises almost pure albite phenocrysts within a fine-grained matrix composed of microphenocrysts of albite, quartz and devitrified volcanic glass. Primary accessory minerals are clinopyroxene, apatite, zircon and magnetite. Haematite, apatite and anatase were found as inclusions in zircon. The albite rhyolite is characterized by a highly sili- ceous, peraluminous, oxidized (ferroan), dry, alkali-calcic to alkalic composition, with low CaO, MgO, and MnO contents and high FeOT/(FeOT+MgO) ratios. Normalized trace element contents display positive anomalies of K, Pb, and Zr as well as negative anomalies of Nb, P, Ti, Ba and Eu, together with an enrichment of light rare-earth elements (REE) relative to heavy REE. Zircon from the rhyolite of Rupnica is characterized by ratios of Th/U=1.13 and Zr/Hf=55 and contents of HfO2=1.04 wt. % typical for an early-stage igneous zircon crystallized from a dry high-tem- perature magma in a deep magma chamber. Apatite REE patterns show enrichment of light REE over heavy REE and a pronounced Eu anomaly, typical for apatite from granitoids formed in an oxidizing environment. The magma is of A-type and was generated at high temperatures at 800–900 °C by partial melting of lower- to mid-crustal rocks. The age of the albite rhyolite of Rupnica is Late Cretaceous at 80.8±1.8 (2σ) Ma, according to U-Pb dating of zircon, coeval with geochemically similar igneous rocks of Mt. Požeška Gora and Mt. Kozara within the Sava Zone. šnajder i borojević drillholes across the Sava depression (83.4–32 Ma, PAMIĆ, 1997) are available. The similar petrography and appearance of the Voćin and Miocene volcanic rocks, as well as the lack of reliable dating led to the above-mentioned age controversies, which also led to different views on the petrogenesis and geodynamic setting of the Voćin rocks. The Rupnica locality is a key outcrop of the Voćin volcanic rocks with an excellent exposure of columnar jointing (BALEN & PETRINEC, 2014), and is the first protected geosite, i.e. “Geo- logical Monument of Nature”, in Croatia. The exposed rocks are albite and aegirine-albite rhyolites (TAJDER, 1956, 1960). Al- though these rocks are exposed in a part of the Tisia Mega-Unit, they do not belong to it because volcanic rocks cross-cut through the rocks of the Tisia Mega-Unit (JAMIČIĆ & BRKIĆ, 1986). Intense magmatic activity also took place in the Late Cretaceous within the adjacent geotectonic unit called the Sava (-Vardar) Zone (PAMIĆ, 1993) or Sava suture zone (SCHMID et al., 2008, 2020). The timing of geological processes in this zone and the geochemical features of volcanic rocks also show similarities to the characteristics of the Voćin volcanic rocks at the Rupnica lo- cality. For this reason, we re-evaluated the petrographic and geo- chemical signatures of the albite rhyolite of Rupnica and deter- mined the trace and isotopic geochemistry of zircon and apatite to unravel and reconstruct the origin, evolution and especially the age of this rock. Albite rhyolite is a type of acidic high-temperature volcanic rock, which compared to ordinary rhyolite, has high alkali con- Article history: Manuscript received September 15, 2021 Revised manuscript accepted April 19, 2022 Available online June 23, 2022 Keywords: zircon, apatite, rhyolite, Cretaceous, Papuk Geopark, Sava Zone G eo lo gi a C ro at ic a Geologia Croatica 75/2250 tents (with Na predominating over K) and shows low concentra- tions of Ca and Mg (TAJDER, 1953, 1960; BALEN & PETRI- NEC, 2014). Moreover, albite rhyolite is often subjected to various alteration processes with zircon being the only remaining pri- mary magmatic and unaltered mineral suitable for dating. In ad- dition, the determination of minor and trace elements in zircon and apatite can provide further geochemical information on magma evolution and petrogenesis. Our U-Th-Pb zircon dating, which is an improvement of previous age estimates, opens the link to the occurrence of igneous rocks with similar geochemis- try and age in the vicinity of the Rupnica site. 2. GEOLOGICAL SETTING 2.1. Tisia Mega-Unit The geology of Mt. Papuk is dominated by the Tisia (also Tisza, Tisa) Mega-Unit. This complex and composite unit is regarded Figure 1. Simplified maps of the Dinaride-Alpine-Pannonian region showing: (a) the mountain belts and Pannonian basin and (b) major structural units after SCHMID et al. (2008, 2020). Map modified after LUŽAR-OBERITER et al. (2012). (c) Mt. Papuk geological map (after JAMIČIĆ & BRKIĆ 1986; JAMIČIĆ et al. 1987, 1989; JAMIČIĆ 1989; CROATIAN GEOLOGICAL SURVEY 2009). The position of the study area is marked by the rectangle and circled stars. Legend: 1 – metamorphic rock complex (Precambrian); 2 – progressive metamorphic series (Ordovician-Devonian); 3 – metamorphic rock complex (Ordovician-Devonian); 4 – granitic rocks (Or- dovician-Devonian); 8 – Variscan/Hercynian semi-metamorphic complex (Devonian-Permian); 13b – clastic sedimentary deposits (Late Permian); 14 – clastic sedi- mentary deposits and carbonates (Early Triassic); 15 – carbonate deposits (Middle Triassic); 27 – limestones (Jurassic); 44 – clastic sedimentary deposits and carbona- tes (Miocene, M2,3); 46 – “litavac” (bioclastic beech carbonate) and clastic sedimentary deposits with volcanic rocks (Miocene, M4); 47 – carbonate clastic deposits (Miocene, M5,6); 48 – clastic sedimentary rocks and coal (Miocene, M7); 52 – clastic deposites (Plio-Quaternary); 54a – loess (Pleistocene); 58b – alluvial deposits (Holocene); α – andesites and rhyolites (Miocene, M3,4). G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 251 as a continental fragment which rifted and drifted away from Eu- rope in the Middle Jurassic as a consequence of kinematically linked opening of the easternmost branch of the Alpine Tethys Ocean (Ceahlau-Severin Ocean) (SCHMID et al., 2020). The fi- nal emplacement of the Tisia Mega-Unit into the present-day con- figuration took place during the Palaeogene and Miocene, i.e. after its internal structuring, which mainly occurred during a Cretaceous orogeny (SCHMID et al., 2020). Only small parts of this unit are exposed in rare isolated and rather small so-called inselbergs within the Pannonian basin, such as the Mecsek and Villany Mts. of Hungary, the northern Apuseni Mts. in Romania and the Slavonian Mts. in Croatia (Fig. 1b). The Slavonian Mts. include the Mt. Papuk area where pre-Variscan, Variscan and Al- pine igneous and metamorphic rocks crop out (Fig. 1c; BALEN et al., 2015, 2018; BIŠEVAC et al., 2010; HORVAT et al., 2018; SLOVENEC et al., 2020). 2.2. Sava Zone The western branch of the Neotethys Ocean was closed through convergence of the Adria microplate (Dinarides) and Europe (Ti- sia). This convergence caused the formation of a suture zone named the Sava-Vardar Zone (PAMIĆ, 2002), Sava Zone or Sava suture zone (SCHMID et al., 2008, 2020). The Sava Zone is a complex belt comprising ophiolites and related igneous, meta- morphic and sedimentary rocks, including Cretaceous to Eocene deep water sediments and flysch. Late Cretaceous ophiolites rep- resent the structurally lowermost unit of the Sava Zone. This zone runs from Zagreb towards Belgrade, and then further to the south through the Vardar Zone into Greece (Fig. 1b; SCHMID et al., 2008; USTASZEWSKI et al., 2010). The northwestern end of the Sava Zone close to Zagreb sharply turns into the SW-NE strike of the Mid-Hungarian fault zone and is further buried below the Cenozoic cover of the Pannonian basin (SCHMID et al., 2020). The formation age of the Sava Zone ranges from the Cretaceous to the Early Palaeogene until the final collision of the Dinarides with the Tisia Mega-Unit (PAMIĆ, 2002). The relatively rare late Mesozoic and Cenozoic igneous rocks within the Sava Zone are related to magmatism along the Europe-Adria suture zone. Known occurrences of these rocks (Fig. 1b) are in northern Bos- nia (Mts. Kozara, Prosara and Motajica), northern Serbia (Mt. Fruška Gora) and eastern Croatia (Mts. Požeška Gora and Moslavačka Gora) (e.g. SCHMID et al., 2008). 2.3. Senonian basalt-rhyolite formation In part of the Slavonian Mts. PAMIĆ (1997) described a Senoni an basalt-rhyolite formation including A-type granites. Rocks of this formation crop out in the areas of Mt. Požeška Gora (with the only known surface occurrence of A-type granite at the Gradski Vrhovci locality; PAMIĆ, 1987; PAMIĆ & LANPHERE, 1991a) and Mt. Papuk. The volcanic rocks at the latter locality, the so- called Voćin volcanic mass (PAMIĆ, 1997), are situated at the northern slopes of Mt. Papuk, near the town of Voćin, and include the rocks from the Rupnica locality. The Voćin volcanic mass consists of basalts, rhyolites and pyroclastic rocks, covers an area of ~10 km2 (PAMIĆ, 1991), and penetrates the igneous, metamor- phic and sedimentary rocks of surrounding complexes (Fig. 1c). PAMIĆ (1991) proposed a Late Cretaceous age for the volcanic rocks in the immediate area of Voćin, while the volcanic and py- roclastic rocks in the wider area were considered to be Miocene in age (JAMIČIĆ et al., 1987, 1989; BELAK et al., 2000). The whole-rock K-Ar dating at 72.8‒51.7 Ma presented in PAMIĆ (1991) was conducted on basalts. The older ages were obtained on relatively fresh basalts, whereas the younger ones resulted from the study of altered basalts (spilites). Younger ages were in- terpreted as a consequence of a loss of radiogenic Ar, possibly during the younger volcanic activity in the area, which also pro- duced spatially associated basalts. Furthermore, K-Ar dating was performed on basalt cores from drillholes across the Sava depres- sion (PAMIĆ, 1997) with ages between 83.4 and 32 Ma. 2.4. A-type granite of Mt. Požeška Gora The A-type granite of Mt. Požeška Gora (PAMIĆ, 1987; PAMIĆ et al., 1988/89; PAMIĆ & LANPHERE, 1991b) has been reinves- tigated in detail by BALEN et al. (2020), who confirmed a Late Cretaceous age (83.6±1.5 Ma) by U-Th-Pb dating on zircon. This recent study revealed the significance of this rather small granite body because it marks the activation of deep faults in an exten- sional tectonic environment at the suture zone, where the subduc- tion of the Adria plate under the European plate took place. Therefore, this A-type granite indicates the local tectonic transi- tion from compression to extension. The idea of a connection be- tween the Late Cretaceous (Senonian) volcanic masses at Mt. Požeška Gora and Mt. Papuk was already postulated by PAMIĆ (1997). Therefore, it is of interest to compare the geochemical features of rhyolite at the Rupnica site, its accessory minerals and the crystallization age of zircon, with the same features of the A- type granite from Mt. Požeška Gora. 2.5. Miocene volcanic rocks A detailed description of volcanic rocks from the northwestern part of Mt. Papuk (including Voćin and its surroundings) can be found in LUGOVIĆ (1983), where an overview of the age con- straints based on earlier reports is given. In these historical pa- pers (STUR, 1861/62; KOCH, 1919; POLJAK, 1939), besides de- tails on field relationships, the prevailing opinion is that these rocks are of Miocene age. In the Basic Geological Map of Croatia M 1:300,000 (CRO- ATIAN GEOLOGICAL SURVEY, 2009) volcanic rocks at Voćin and its surroundings are described as andesites and rhyolites of Miocene age (Fig. 1c), as it was postulated in the Basic Geologi- cal Map of SFRY 1:100.000, sheets Orahovica and Daruvar (JAMIČIĆ & BRKIĆ, 1986; JAMIČIĆ et al., 1987, 1989; JAMIČIĆ, 1989). The contact of the Voćin volcanic rocks with the Triassic and Late Cretaceous deposits is described as tectonic. According to the interpretation in the above mentioned explana- tory notes, the volcanic activity was accompanied by sedimentary processes related to the evolution of the Pannonian basin. 3. ANALYTICAL METHODS 3.1. Whole-rock chemistry From 20 collected homogeneous samples at the Rupnica geosite, 3 samples plus 1 used in BALEN & PETRINEC (2014) were se- lected for whole-rock geochemistry. These samples were crushed in a jaw crusher, powdered in an agate mill, and analysed at the Bureau Veritas Commodities Canada Ltd. (Vancouver) by induc- tively coupled plasma mass spectrometry (ICP-MS; trace ele- ments including rare-earth elements (REE)) and inductively cou- pled plasma emission spectrometry (ICP-ES; major elements). Powders were air-dried and sieved through a 0.125 mm stainless- steel screen. The sample preparation included the splitting of 0.2 g rock powder each for LiBO2/Li2B4O7 fusion for ICP-ES and ICP-MS. Natural rocks of known composition and pure quartz were used as reference materials. The analytical accuracy was G eo lo gi a C ro at ic a Geologia Croatica 75/2252 Table 1. Results of the whole-rock analyses of major (wt. %) and trace (ppm) elements with characteristic element ratios and zircon saturation temperatures (ZST) after WATSON & HARISSON (1983) and GERVASONI et al. (2016) for selected samples of rhyolite of Rupnica. The compositions were determined with ICP-MS and ICP-ES. Sample 1 is from BALEN & PETRINEC (2014). Major elements (wt. %) Sample 1 RUP Sample 2 Rupnica 3 Sample 3 Rup4 Sample 4 Rup7 d.l. (wt. %) MIN MAX Mean SiO2 66.41 66.83 69.5 68.27 0.01 66.41 69.50 67.75 TiO2 0.45 0.42 0.41 0.41 0.01 0.41 0.45 0.42 Al2O3 16.7 15.61 15.35 15.53 0.01 15.35 16.70 15.80 Fe2O3 3.87 3.72 3.53 4.22 0.04 3.53 4.22 3.84 MnO 0.03 0.07 0.05 0.04 0.01 0.03 0.07 0.05 MgO 0.53 0.48 0.27 0.38 0.01 0.27 0.53 0.42 CaO 0.36 1.48 0.35 0.36 0.01 0.35 1.48 0.64 Na2O 5.6 5.29 5.27 5.22 0.01 5.22 5.60 5.35 K2O 3.41 2.91 3.47 3.23 0.01 2.91 3.47 3.26 P2O5 0.12 0.11 0.1 0.11 0.01 0.10 0.12 0.11 LOI 2.40 2.90 1.60 2.10 0.01 1.60 2.90 2.25 Total 99.88 99.82 99.9 99.87 99.82 99.90 99.87 Trace elements (ppm) (ppm) As 3.2 1.2 1.4 8.5 0.5 1.2 8.5 3.575 Au (ppb) 0.3 1.9 32.4 28.1 0.5 (ppb) 0.3 32.4 15.7 Ba 548 459 492 512 1 459 548 503 Be 4 2 2 3 1 2 4 2.75 Co 1.3 2.7 0.8 2.8 0.2 0.8 2.8 1.9 Cs 0.4 <0.1 0.5 0.7 0.1 0.4 0.7 0.5 Cu 1.3 16.2 7.3 14.7 0.1 1.3 16.2 9.9 Ga 20 21 18 16 0.5 16.4 20.8 18.6 Hf 9.0 9.5 7.6 7.9 0.1 7.6 9.5 8.5 Mo 0.6 0.6 0.5 0.5 0.1 0.5 0.6 0.6 Nb 26 27 22 25 0.1 22 27 25 Ni 1.5 2.9 0.9 2.3 0.1 0.9 2.9 1.9 Pb 3.7 8.4 11.0 14.6 0.1 3.7 14.6 9.4 Rb 45 44 55 52 0.1 44 55 49 Sb <0.1 0.2 0.5 0.4 0.1 0.2 0.5 0.4 Sc 7 7 6 7 1 6 7 7 Sn 4 4 4 4 1 4 4 4 Sr 134 175 129 117 0.5 117 175 139 Ta 1.7 1.7 1.6 1.4 0.1 1.4 1.7 1.6 Th 9.4 9.8 8.8 7.7 0.2 7.7 9.8 8.9 U 2.0 2.1 2.0 2.1 0.1 2.0 2.1 2.1 V 11 17 12 14 8 11 17 13.5 W 1.5 2.0 1.3 1.5 0.5 1.3 2.0 1.6 Y 32 37 29 32 0.1 29 37 32 Zn 59 70 48 66 1 48 70 61 Zr 354 386 329 339 0.1 329 386 352 La 29 33 29 18 0.1 18 33 27 Ce 63 60 55 49 0.1 49 63 57 Pr 6.6 6.9 6.6 4.4 0.02 4.4 6.9 6.1 Nd 25 27 26 17 0.3 17 27 24 Sm 5.6 5.7 5.6 4.1 0.05 4.1 5.7 5.3 Eu 1.4 1.4 1.3 1.0 0.02 1.0 1.4 1.3 Gd 5.9 6.4 5.1 5.2 0.05 5.1 6.4 5.6 Tb 1.1 1.1 0.9 0.9 0.01 0.9 1.1 1.0 Dy 6.0 6.4 5.8 5.6 0.05 5.6 6.4 5.9 Ho 1.2 1.4 1.2 1.1 0.02 1.1 1.4 1.2 Er 3.6 4.2 3.2 3.4 0.03 3.2 4.2 3.6 Tm 0.6 0.6 0.5 0.5 0.01 0.5 0.6 0.5 Yb 3.4 3.9 3.3 3.5 0.05 3.3 3.9 3.5 Lu 0.5 0.6 0.5 0.6 0.01 0.5 0.6 0.5 G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 253 controlled using internal geological reference materials, the com- positions of which are comparable to the rocks in this study (STDGS311-1, STD GS910-4, STD DS10, STD OREAS45EA, STD SO-19). Detection limits are shown in Table 1. Reference materials were certified in-house by analysis with CANMET Certified Reference Materials. Loss on ignition (LOI) was deter- mined by weight difference before and after 4 hours ignition at 1000 °C. Geochemical data and diagrams are recalculated and handled with the GCDkit software (JANOUŠEK et al., 2006). 3.2. Scanning electron microscopy Zircon was separated from the rhyolite (sample Rupnica 3) by a standard procedure of extraction from the host rock (crushing of the rock, sieving, heavy-liquid separation with sodium polytung- state and magnetic separation) and analysed using scanning elec- tron microscopy at the Slovak Academy of Sciences, Earth Sci- ence Institute, Laboratory of electron microscopy in Banska Bystrica, in order to detect the external morphology of individual zircon grains. The analyses were performed with a JEOL JSM- 6390LV equipped with a secondary electron detector for imaging and an acceleration voltage of 20 kV. The specimens were coated with gold. 3.3. Raman spectroscopy Separated zircon grains were also analysed with the aid of micro- Raman spectroscopy in order to characterize the inclusions in zircon. This spectroscopy was performed at the Slovak Academy of Sciences, Earth Science Institute, Laboratory of vibration spectroscopy in Banska Bystrica with a Horiba Jobin-Yvon LabRam HR 800 spectrometer equipped with a Czerny-Turner monochromator, 600 grooves per mm grating, and a Peltier- cooled charge-coupled device detector coupled to an Olympus BX41 microscope with a long working distance 100×/0.8 objec- tive. Zircon crystals were irradiated by a He–Ne (633 nm) laser with a power of ~3 mW. A frequency-doubled Nd:YAG (532 nm) laser was only used for verifying possible luminescence effects. The Rayleigh line (0 cm-1) and emission bands of Ne glow lamps were used for calibration. Wave-number accuracy and lateral reso lution were better than 0.8 cm−1 and 1 µm, respectively. The spectral resolution was ~3.6 cm−1 (red spectral range). The spec- tra of the unknown phases were collected in the range of 60–4000 cm−1 to additionally cover the region of OH-stretching bands. 3.4. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) Isotopic concentrations of selected elements in zircon were de- termined by LA-ICP-MS. Analyses were performed at the Insti- tut für Mineralogie und Kristallchemie, Universität Stuttgart (Germany), using an AGILENT 7700 mass spectrometer after laser ablation with a CETAC LSX-213 laser system. The diameter of the ablated spots was 25 µm. The laser energy was set to 100 % of the maximum (100 % = 4 mJ at a spot diameter of 150 µm) at a laser pulse frequency of 10 Hz and 330 (for elemental con- centrations) or 375 (for dating) laser pulses per analysis. A mixed He and Ar gas flow with 500 ml/min and 800 ml/min, respec- tively, served as carrier of the ablated material into the ICP-MS system. Zircon grains separated from the rhyolite were mounted in an epoxy resin and polished approximately to their centres. The details of the data evaluation methods and corrections are given in BALEN et al. (2020). 3.4.1. Zircon chemical analysis Glass standards for the determination of elemental concentrations in zircon were the following: DLH7 and DLH8 from P&H Devel- opments Ltd. and NIST612 and NIST610 from National Institute of Standards and Technology, USA. The validity of the calibra- tion, data evaluation, and reproducibility were checked with the Sample 1 RUP Sample 2 Rupnica 3 Sample 3 Rup4 Sample 4 Rup7 MIN MAX Mean MI 0.87 0.87 0.92 0.91 0.87 0.92 0.89 A/CNK 1.24 1.08 1.19 1.23 1.08 1.24 1.19 A/NK 1.29 1.32 1.24 1.29 1.24 1.32 1.28 K2O/Na2O mol 0.40 0.36 0.43 0.41 0.36 0.43 0.40 Ba/Rb 12.1 10.6 9.0 9.8 9.0 12.1 10.4 10000·Ga/Al 2.2 2.5 2.2 2.0 2.0 2.5 2.2 Zr/Hf 39 41 43 43 39 43 42 Y/Ho 26 27 25 28 25 28 26 (La/Yb)N 5.75 5.70 5.92 3.47 3.47 5.92 5.21 (La/Sm)N 3.26 3.64 3.26 2.76 2.76 3.64 3.23 (Gd/Yb)N 1.40 1.32 1.25 1.20 1.20 1.40 1.29 Ce/Ce* 1.10 0.96 0.96 1.33 0.96 1.33 1.08 Eu/Eu* 0.74 0.71 0.74 0.66 0.66 0.74 0.71 Σ REE 152 159 142 115 115 159 142 M 1.33 1.50 1.33 1.27 1.27 1.50 1.36 TWH (°C) 866 860 858 867 858 867 863 G 8.20 7.81 8.98 8.51 7.81 8.98 8.38 TG (°C) 789 778 798 790 778 798 789 d.l. = detection limit; LOI = loss on ignition; MI (mafic index) = FeOT/(FeOT+MgO); A/CNK = Al2O3/(CaO+Na2O+K2O) in mol%; A/NK = Al2O3/(Na2O+K2O); M (cation ratio) = (Na+K+2Ca)/Al·Si; G = (3·Al2O3+SiO2)/(Na2O+K2O+CaO+MgO+FeO) in molar proportions; TWH and TG − Zircon saturation temperatures after WATSON & HARISSON (1983) and GERVASONI et al. (2016), respectively. Table 1. continued. G eo lo gi a C ro at ic a Geologia Croatica 75/2254 Ta bl e 2. C he m is tr y of z irc on fr om th e rh yo lit e of R up ni ca d et er m in ed b y LA -IC P- M S w ith c ha ra ct er is tic e le m en t r at io s a nd d et ec tio n lim its (d .l. ). El em en ta l m as s c on ce nt ra tio ns a nd d et ec tio n lim its a re g iv en in p pm . T i-i n- zi rc on te m pe ra - tu re w as c al cu la te d fo r s el ec te d gr ai ns a ft er W AT SO N e t a l. (2 00 6) . b .d .l. – b el ow d et ec tio n lim it. El em en t G ra in 1 a G ra in 2 a G ra in 3 a G ra in 4 a G ra in 5 a G ra in 6 a G ra in 7 a G ra in 8 a G ra in 9 a G ra in 1 0a G ra in 1 1a G ra in 1 2a G ra in 1 3a G ra in 1 4a d. l. M IN M AX M ea n M ed ia n Ba 0. 7 1. 0 0. 9 0. 8 1. 3 5. 0 0. 9 1. 5 1. 0 1. 6 1. 7 4. 2 13 .1 3. 9 0. 4 0. 7 13 2. 7 1. 4 Ca 20 14 0 12 59 2 88 71 b. d. l. 14 40 9 34 73 0 27 97 8 15 07 9 15 17 4 32 29 1 62 27 37 44 41 19 25 62 4 77 0 37 44 34 73 0 16 99 8 15 07 9 Cr 3. 5 3. 8 2. 1 2. 7 3. 2 3. 6 2. 0 3. 5 3. 9 3. 6 3. 0 2. 9 3. 9 2. 1 2 2. 0 3. 9 3. 1 3. 3 Fe 65 2 42 6 75 1 32 3 35 6 45 18 21 19 68 3 27 0 95 4 38 9 34 7 20 06 76 3 33 27 0 45 18 10 40 66 7 G a 1. 1 b. d. l. b. d. l. b. d. l. 1. 1 2. 6 1. 3 3. 1 0. 6 1. 1 1. 5 b. d. l. 1. 0 1. 3 0. 4 0. 6 3. 1 1. 5 1. 2 H f 97 91 72 83 11 51 1 93 48 91 13 78 34 94 05 11 34 2 76 46 74 47 94 11 64 36 77 71 86 35 0. 3 64 36 11 51 1 87 84 88 74 M n 52 28 24 5. 9 45 10 3 13 7 53 67 78 28 17 52 77 2 5. 9 13 7 55 52 N b 9. 0 4. 4 7. 6 9. 9 15 28 8. 5 25 13 7. 9 13 9. 0 8. 0 7. 4 0. 04 4. 4 28 12 9. 0 P 82 80 65 39 34 02 91 1 10 09 7 12 97 2 13 34 6 96 97 68 84 14 37 2 25 29 31 82 25 92 12 59 0 14 8 91 1 14 37 2 76 71 75 82 Pb 4. 2 2. 3 5. 6 10 7. 2 8. 9 5. 0 11 5. 1 3. 6 6. 5 12 11 7 3. 5 0. 2 2. 3 11 7 14 6. 1 Si 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 15 14 00 12 23 15 14 00 15 14 00 15 14 00 15 14 00 Sn 1. 0 b. d. l. b. d. l. b. d. l. b. d. l. 2. 0 1. 3 b. d. l. 1. 0 1. 0 1. 2 b. d. l. b. d. l. b. d. l. 0. 8 1. 0 2. 0 1. 2 1. 1 Sr 23 14 6. 6 1. 6 18 35 31 17 12 29 12 4. 5 4. 4 27 0. 1 1. 6 35 17 16 Ta 2. 8 1. 2 2. 1 2. 4 3. 3 2. 8 2. 6 5. 2 2. 7 1. 3 3. 3 1. 8 2. 0 1. 9 0. 04 1. 2 5. 2 2. 5 2. 5 Th 40 5 10 7 30 2 42 5 79 9 87 1 53 9 14 11 55 8 27 2 71 5 33 7 35 0 34 8 0. 1 10 7 14 11 53 1 41 5 Ti 78 15 2 34 19 21 49 0 41 38 21 60 5 10 8 55 26 89 2 19 60 5 12 7 48 U 40 0 13 7 29 1 38 0 66 7 53 6 46 6 95 8 50 5 28 2 58 8 34 2 33 6 32 0 0. 1 13 7 95 8 44 3 39 0 V 0. 6 0. 6 0. 2 0. 3 0. 1 1. 6 0. 9 0. 3 0. 2 0. 7 0. 2 0. 3 0. 6 0. 3 0. 2 0. 1 1. 6 0. 5 0. 3 Y 36 25 11 78 36 56 37 10 61 54 44 65 35 70 59 97 52 23 31 27 49 20 35 77 23 15 29 75 0. 2 11 78 61 54 38 92 36 41 Zn 7. 9 13 23 26 2 9. 9 29 15 14 7. 5 22 13 61 6 16 89 7. 3 2 7. 3 16 89 19 5 14 Zr 45 21 14 43 23 94 48 84 23 52 53 78 48 04 23 44 67 24 49 17 55 50 89 04 48 15 39 45 31 72 48 65 56 43 88 20 45 12 41 46 76 46 8 43 23 94 52 53 78 47 17 92 47 40 34 La 63 23 17 3. 5 75 11 9 99 63 54 95 89 20 14 73 0. 06 3. 5 11 9 58 63 .0 Ce 14 9 72 58 25 20 7 37 2 25 2 23 6 13 4 22 3 24 8 61 37 17 7 0. 08 25 37 2 16 1 16 3 Pr 20 7. 6 5. 3 1. 5 23 52 40 30 14 29 34 6. 3 3. 7 25 0. 03 1. 5 52 21 21 N d 12 3 39 32 14 13 9 25 7 17 2 17 0 76 12 8 17 4 29 21 12 7 0. 26 14 25 7 10 7 12 5 Sm 44 13 22 17 80 71 49 77 44 45 68 19 19 40 0. 29 13 80 43 44 Eu 5. 5 1. 7 3. 9 2. 7 9. 9 7. 8 6. 0 8. 3 6. 3 5. 1 6. 8 2. 7 3. 2 4. 4 0. 07 1. 7 9. 9 5. 3 5. 3 G d 11 4 27 94 86 23 5 15 6 12 9 22 7 15 7 10 0 16 4 80 69 89 0. 22 27 23 5 12 3 10 7 Tb 32 9. 0 28 28 65 40 36 59 47 28 42 24 22 27 0. 03 9. 0 65 35 30 D y 39 5 11 0 29 1 34 1 69 3 40 3 36 9 55 8 52 7 32 8 53 4 25 4 24 9 33 9 0. 23 11 0 69 3 38 5 35 5 H o 14 3 46 12 7 12 7 21 9 15 1 12 9 18 2 19 0 11 7 16 7 89 86 11 8 0. 04 46 21 9 13 5 12 8 Er 64 1 22 9 67 0 59 3 86 9 65 2 57 0 88 4 78 7 53 3 74 1 40 0 37 1 49 5 0. 11 22 9 88 4 60 2 61 7 Tm 12 6 47 14 1 11 4 15 9 12 3 12 1 17 7 15 3 10 3 14 5 82 71 10 1 0. 05 47 17 7 11 9 12 2 Yb 11 20 44 4 11 22 94 4 13 77 98 3 10 71 15 17 12 39 87 4 12 35 71 1 58 5 87 7 0. 29 44 4 15 17 10 07 10 27 Lu 22 2 87 22 6 18 1 27 7 17 0 20 3 30 2 21 4 15 9 22 4 13 6 11 2 17 0 0. 04 87 30 2 19 2 19 2 Su m R EE 31 96 11 55 28 36 24 79 44 27 35 57 32 46 44 90 36 42 27 69 38 70 19 14 16 62 26 62 11 55 44 90 29 93 30 16 Su m o xi de s ( w t % ) 10 0. 44 95 .3 8 10 2. 78 10 5. 75 10 4. 28 10 3. 44 10 8. 24 10 8. 54 10 3. 36 10 3. 38 10 2. 04 94 .6 2 96 .5 7 10 4. 01 94 .6 2 10 8. 54 10 2. 35 10 3. 37 H fO 2 11 54 7 85 88 13 57 4 11 02 4 10 74 7 92 39 11 09 2 13 37 6 90 17 87 82 11 09 8 75 90 91 64 10 18 4 75 90 13 57 4 10 37 2 10 74 7 Y 2 O 3 46 03 14 95 46 43 47 11 78 15 56 70 45 34 76 16 66 33 39 72 62 48 45 43 29 40 37 78 14 95 78 15 50 33 46 43 Th /U 1. 01 0. 78 1. 04 1. 12 1. 20 1. 62 1. 16 1. 47 1. 11 0. 97 1. 22 0. 99 1. 04 1. 09 0. 78 1. 62 1. 13 1. 10 Zr /H f 46 59 42 56 53 57 52 45 63 61 52 68 58 54 42 68 55 55 .2 N b/ Ta 3. 2 3. 7 3. 7 4. 0 4. 5 10 .0 3. 3 4. 8 4. 8 6. 3 4. 0 5. 0 4. 0 3. 9 3. 2 10 4. 7 4. 0 Ce /C e* 1. 01 1. 31 1. 47 2. 63 1. 20 1. 14 0. 96 1. 31 1. 17 1. 02 1. 09 1. 31 1. 24 1. 00 0. 96 2. 63 1. 27 1. 19 Eu /E u* 0. 24 0. 28 0. 26 0. 22 0. 22 0. 23 0. 23 0. 19 0. 23 0. 23 0. 20 0. 21 0. 27 0. 23 0. 19 0. 28 0. 23 0. 23 La N /Y b N 0. 04 0. 03 0. 01 0. 00 0. 04 0. 08 0. 06 0. 03 0. 03 0. 07 0. 05 0. 02 0. 02 0. 06 0. 00 0. 08 0. 04 0. 04 La N /S m N 0. 90 1. 11 0. 49 0. 13 0. 59 1. 05 1. 27 0. 51 0. 77 1. 33 0. 82 0. 66 0. 46 1. 15 0. 13 1. 33 0. 80 0. 80 G d N /Y b N 0. 08 0. 05 0. 07 0. 07 0. 14 0. 13 0. 10 0. 12 0. 10 0. 09 0. 11 0. 09 0. 10 0. 08 0. 05 0. 14 0. 09 0. 09 Ti -in -z irc on (° C) 80 1 81 2 81 2 83 1 80 1 83 1 81 4 81 2 G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 255 reference materials Diorite (DRN) and Zinnwaldite (ZW-C) from Service d’Analyses des Roches et des Minéraux du CNRS. Rela- tive elemental concentrations were calculated from the abun- dance of the corresponding isotopes, assuming natural isotopic distributions and individual calibration factors, which were de- termined under the same experimental conditions. Absolute el- emental concentrations were calculated on the basis of the known absolute elemental concentration of an internal reference element. For zircon chemical analysis, the following isotopes were monitored: 28, 29Si, 31P, 42, 44Ca, 45Sc, 49Ti, 51V, 52Cr, 55Mn, 56, 57Fe, 59Co, 60Ni, 66Zn, 71Ga, 88Sr, 89Y, 90, 91Zr, 93Nb, 118Sn, 137Ba, 139La, 140Ce, 141Pr, 146Nd, 147, 149Sm, 151, 153Eu, 157Gd, 159Tb, 161, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, 175Lu, 177, 178Hf, 181Ta, 208Pb, 232Th and 238U. All elemental concentrations were calculated relative to Si=15.14 wt. %, a value which is taken as an internal reference value in zircon, because Si is least likely to be replaced by other elements in the zircon structure. Therefore, the mean value of Si, as derived from the isotopes 28, 29Si, was set to 151,400 ppm. The calculated elemental concentrations are presented in Table 2. The concentrations of elements, which are usually not incorporated in zircon, were either very near to the detection limit or clearly elevated and therefore ascribed to inclusions in zircon. 3.4.2. Apatite chemical analysis Through the process of zircon separation with sodium polytung- state, grains of apatite were also successfully separated due to their relatively high specific gravity. Separated grains were used for chemical analysis of apatite, for which the same set of isotopes were monitored as for the chemical analyses of zircon. All elemental concentrations were calculated relative to P=18.25 wt. %, a value which is taken as a reference value in ap- atite, with the assumption that P is hardly replaced by some other elements in the apatite structure. Therefore, the P concentration, derived from the isotope 31P, was set to 182,500 ppm. The calcu- lated elemental concentrations are summarized in Table 3. The Figure 2. (a) Columnar jointing of albite rhyolite at the Rupnica geosite; person as scale; (b) plain-polarized transmitted-light photomicrograph of a typical micro- fabric of the rhyolite of Rupnica taken from a thin section of the Rupnica 3 sample; (c) backscattered electron image displaying the texture of the rhyolite of Rupni- ca. The centre of the image shows an albite phenocryst. G eo lo gi a C ro at ic a Geologia Croatica 75/2256 Ta bl e 3. C he m is tr y of a pa tit e fro m th e rh yo lit e of R up ni ca d et er m in ed b y LA -IC P- M S w ith c ha ra ct er is tic e le m en t r at io s a nd d et ec tio n lim its (d .l. ). El em en ta l m as s c on ce nt ra tio ns a nd d et ec tio n lim its a re g iv en in p pm . b .d .l. – b el ow d et ec - tio n lim it. El em en t G ra in 1 G ra in 2 G ra in 3 G ra in 4 G ra in 5 G ra in 6 G ra in 7 G ra in 8 G ra in 9 G ra in 1 0 G ra in 1 1 d. l. M IN M AX M ea n M ed ia n Ba 4. 9 7. 0 5. 2 6. 8 5. 1 4. 0 4. 8 5. 8 6. 1 5. 9 7. 5 0. 49 4. 0 7. 5 5. 7 5. 8 Ca 44 96 19 44 62 72 37 94 87 43 10 69 40 33 60 37 48 70 34 77 09 41 74 05 40 70 31 42 12 31 44 04 66 93 6 34 77 09 44 96 19 41 07 74 41 74 05 Co b. d. l. 0. 31 0. 21 0. 25 0. 35 b. d. l. b. d. l. 0. 36 0. 66 0. 22 0. 20 0. 20 0. 20 0. 66 0. 32 0. 28 Cr 3. 9 3. 0 2. 2 2. 3 2. 4 2. 4 4. 3 3. 1 4. 3 2. 8 3. 0 1. 9 2. 2 4. 3 3. 1 3. 0 Fe 31 89 32 67 14 23 14 59 b. d. l. b. d. l. 65 25 84 42 7 b. d. l. 11 14 32 67 13 78 94 3 G a 11 17 17 12 6. 7 12 11 11 14 17 12 0. 35 6. 7 17 13 12 H f 0. 41 8. 1 0. 65 0. 24 0. 37 1. 5 b. d. l. 1. 1 2. 2 0. 83 0. 24 0. 22 0. 24 8 1. 6 0. 74 M n 75 0 84 4 89 2 85 1 79 3 10 22 72 1 81 7 10 66 10 16 80 1 1. 6 72 1 10 66 87 0 84 4 N b 1. 2 1. 1 0. 14 0. 09 12 0. 06 0. 10 0. 26 2. 0 5. 4 b. d. l. 0. 06 0. 06 12 2. 3 0. 70 P 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 18 25 00 12 5 18 25 00 18 25 00 18 25 00 18 25 00 Pb 2. 5 3. 6 2. 1 2. 2 3. 6 1. 1 1. 7 1. 9 2. 3 3. 0 2. 0 0. 20 1. 1 3. 6 2. 4 2. 2 Sc b. d. l. 2. 0 3. 5 1. 6 2. 5 2. 4 b. d. l. b. d. l. 2. 0 b. d. l. b. d. l. 1. 6 1. 6 3. 5 2. 3 2. 2 Si 41 93 49 16 46 87 49 14 44 82 32 34 30 81 39 87 72 67 50 76 42 33 12 39 30 81 72 67 45 52 44 82 Sn 1. 1 b. d. l. b. d. l. b. d. l. 2. 1 b. d. l. 1. 8 b. d. l. b. d. l. 1. 1 b. d. l. 0. 97 1. 1 2. 1 1. 5 1. 4 Sr 38 6 38 2 37 9. 9 39 6 52 6 42 0 29 8 45 8 38 7 50 1 43 0 0. 09 29 8 52 6 41 5 39 6 Ta 0. 04 0. 04 b. d. l. b. d. l. 0. 36 0. 05 b. d. l. b. d. l. 0. 07 0. 11 b. d. l. 0. 03 0. 04 0. 36 0. 11 0. 06 Th 15 24 25 15 12 15 12 12 19 21 11 0. 07 11 25 16 15 Ti 14 6 16 2 14 23 14 59 3. 6 b. d. l. 65 25 84 42 7 3. 3 3. 2 3. 3 25 84 48 9 10 5 U 5. 8 8. 5 9. 5 5. 7 4. 6 5. 9 5. 0 4. 9 8. 6 8. 0 3. 8 0. 09 3. 8 9. 5 6. 4 5. 8 V 3. 2 3. 5 0. 9 3. 3 5. 0 0. 3 3. 4 7. 6 8. 2 2. 4 7. 5 0. 21 0. 3 8. 2 4. 1 3. 4 Y 10 29 16 17 13 46 10 19 69 3 95 1 95 4 98 0 11 72 15 30 10 52 0. 12 69 3 16 17 11 22 10 29 Zn 5. 1 12 8. 1 10 9. 8 7. 1 5. 9 11 29 34 8. 3 2. 9 5. 1 34 13 10 Zr 47 47 8 38 13 18 18 3 9. 1 42 17 4 57 12 0. 47 9. 1 47 8 97 42 La 76 6 12 65 12 76 89 1 53 9 85 4 71 7 76 7 11 94 12 31 96 9 0. 07 53 9 12 76 95 2 89 1 Ce 17 50 30 89 29 01 22 58 13 39 21 34 17 93 18 05 27 72 29 09 21 49 0. 10 13 39 30 89 22 63 21 49 Pr 23 1 45 0 37 9 32 5 19 6 28 2 24 6 26 3 35 6 40 3 27 5 0. 07 19 6 45 0 31 0 28 2 N d 11 39 19 21 19 01 15 82 96 2 14 17 12 54 12 54 17 91 21 06 12 29 0. 49 96 2 21 06 15 05 14 17 Sm 27 1 49 5 44 4 34 4 25 1 37 5 31 3 31 1 41 4 52 8 29 8 0. 41 25 1 52 8 36 8 34 4 Eu 34 49 43 45 56 53 32 41 44 54 41 0. 10 32 56 45 44 G d 28 4 45 8 41 3 33 4 28 8 32 5 27 1 30 9 40 3 42 8 32 0 0. 45 27 1 45 8 34 9 32 5 Tb 41 59 68 44 39 42 40 45 57 63 47 0. 05 39 68 50 45 D y 21 6 35 7 41 9 27 0 20 7 20 9 22 2 21 2 34 6 35 5 25 4 0. 25 20 7 41 9 27 9 25 4 H o 42 63 75 50 38 36 47 40 66 66 48 0. 06 36 75 52 48 Er 10 2 15 1 18 0 12 6 87 88 11 1 99 16 0 14 7 11 0 0. 12 87 18 0 12 4 11 1 Tm 12 17 23 15 10 11 12 12 19 17 12 0. 04 10 23 15 12 Yb 56 93 10 3 79 47 57 61 60 88 83 61 0. 28 47 10 3 72 61 Lu 6. 9 11 12 10 5. 3 7. 6 6. 9 7. 5 11 10 8. 0 0. 06 5. 3 12 8. 7 8. 0 Su m R EE 49 51 84 79 82 36 63 73 40 64 58 92 51 25 52 23 77 23 84 00 58 21 40 64 84 79 63 90 58 92 Su m o xi de s ( w t % ) 10 6. 42 10 6. 27 96 .6 8 10 3. 98 10 0. 33 95 .7 7 91 .6 8 10 1. 84 10 1. 86 10 2. 83 10 5. 09 91 .6 8 10 6. 42 10 1. 16 10 1. 86 Sr /Y 0. 38 0. 24 0. 28 0. 39 0. 76 0. 44 0. 31 0. 47 0. 33 0. 33 0. 41 0. 24 0. 76 0. 39 0. 38 Ce /C e* 1. 00 0. 99 1. 00 1. 01 0. 99 1. 05 1. 03 0. 97 1. 02 0. 99 1. 00 0. 97 1. 05 1. 01 1. 00 Eu /E u* 0. 37 0. 31 0. 30 0. 41 0. 63 0. 47 0. 33 0. 41 0. 33 0. 35 0. 41 0. 30 0. 63 0. 39 0. 37 La N /Y b N 9. 20 9. 15 8. 36 7. 65 7. 80 10 .0 9 7. 93 8. 65 9. 11 9. 95 10 .6 4 7. 65 10 .6 4 8. 96 9. 11 La N /S m N 1. 78 1. 61 1. 81 1. 63 1. 35 1. 43 1. 44 1. 55 1. 81 1. 47 2. 04 1. 35 2. 04 1. 63 1. 61 G d N /Y b N 4. 08 3. 97 3. 24 3. 43 4. 99 4. 60 3. 59 4. 17 3. 68 4. 14 4. 20 3. 24 4. 99 4. 01 4. 08 La /S m 2. 8 2. 6 2. 9 2. 6 2. 1 2. 3 2. 3 2. 5 2. 9 2. 3 3. 2 2. 1 3. 2 2. 6 2. 6 Y/ ƩR EE 0. 21 0. 19 0. 16 0. 16 0. 17 0. 16 0. 19 0. 19 0. 15 0. 18 0. 18 0. 15 0. 21 0. 18 0. 18 C e /T h 11 5 13 1 11 8 15 1 11 0 14 3 15 5 15 2 14 3 14 0 20 2 11 0 20 2 14 2 14 3 G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 257 concentrations of elements, which are usually not incorporated in apatite (such as Co, Cr, Ni, Sc, Sn, Ta and V) were either only slightly above or below the detection limit. 3.4.3. Zicon age-dating For zircon dating and isotopic corrections with LA-ICP-MS, 3 natural zircon reference materials were used: FC1 (1099.0±0.6 Ma; PACES & MILLER, 1993), Peixe (564±4 Ma; DICKINSON & GEHRELS, 2003 and 558±2.7 Ma; SHAULIS et al., 2010), and Plešovice (337.13±0.37 Ma; SLÁMA et al., 2008). The following ions were measured: 202Hg, 204(Hg+Pb), 206Pb, 207Pb, 208Pb, 232Th, 235U, 238U, and 254(238U16O). The method and corrections used for data evaluation are described in detail in BALEN et al. (2020). By dating these 3 references as unknowns, using the aforemen- tioned method and corrections, the obtained concordia ages plot- ted in a 206Pb/238U vs. 207Pb/235U diagram (FC1=1104.3±5.9 Ma, MSWD=0.5, n=8; Peixe=564.8±4.1 Ma, MSWD=0.2, n=6; Plešovice=335.6±3.7 Ma, MSWD=0.2, n=4) coincide with their literature values. 4. RESULTS 4.1. Outcrop and rock description The Rupnica locality is a small abandoned quarry in the north- western part of Mt. Papuk within the Papuk Nature Park. It is a key geosite of the Papuk Geopark protected under the UNESCO supervision, and is well-known for its columnar jointing devel- oped in albite rhyolite (Fig. 2a). The site is located near the town of Voćin (Fig. 1c, coordinates: 45.6049º N, 17.5320º E). BALEN & PETRINEC (2014) investigated the phenomenon of columnar jointing in detail, conducting a non-destructive statistical analy- sis of the geometric distribution of columns combined with pe- trography, geochemistry and the geology of the geosite. These authors suggested that the albite rhyolite formed via rapid cooling of a (sub)surface acidic lava body. The albite rhyolite of the Rupnica locality and its variations (aegirine-albite and anorthoclase-aegirine rhyolite) are described as volcanic rocks, the chemical composition of which are not sig- nificantly affected by hydrothermal alteration or other types of Figure 3. Comparison of the rhyolite of Rupnica, Mt. Požeška Gora granite and acidic effusive rocks from the northern part of Mt. Kozara: (a) QAP modal composi- tion diagram after STRECKEISEN (1974, 1978) for both volcanic and plutonic rocks: Q – quartz; A – alkali feldspar; P – plagioclase; 2 – alkali-feldspar trachyte/Q-rich granite; 3 – alkali-feldspar rhyolite/alkali-feldspar granite; 4 – rhyolite/syenogranite; 8 – Q-alkali-feldspar trachyte/Q-alkali-feldspar syenite. Classification and dis- crimination diagrams based on major elements after (b) DE LA ROCHE et al. (1980), and (c–e) FROST et al. (2001) and FROST & FROST (2011). Geochemical data for the acidic effusive rocks from the northern part of Mt. Kozara are from USTASZEWSKI et al. (2009) and CVETKOVIĆ et al. (2014). G eo lo gi a C ro at ic a Geologia Croatica 75/2258 secondary processes (TAJDER, 1956, 1960). The rhyolites are leucocratic and light-grey to greenish in colour with porphyritic texture and phenocrysts of feldspar (albite). Detailed petrographic descriptions of albite rhyolite and its variations can be found in TAJDER (1956, 1960) and BALEN & PETRINEC (2014). Albite contains 98.1−99.9 % albite component (BALEN & PETRINEC, 2014) and occurs as phenocrysts (up to 30 vol. % of the rock) and as microliths in the fine-grained groundmass (Fig. 2b−c) together with a devitrified volcanic glass (up to 10 vol. %). Magnetite, ap- atite, zircon and in places alkali clinopyroxene (aegirine-augite) occur as accessory minerals, while kaolinite, illite, smectite, chlorite and calcite are secondary minerals. Haematite, apatite and anatase are found additionally as inclusions in zircon (see section 4.3.2. Inclusions in zircon). 4.2. Whole-rock geochemistry The rhyolite of Rupnica (Table 1, Fig. 3) is characterized by: (1) relatively high siliceous compositions (SiO2 up to 69.5 wt. %), (2) high abundance of alkalies (K2O+Na2O between 8.2 and 9.0 wt. % with K2O up to 3.5 wt. %), (3) relatively high K2O/Na2O molar ratios (0.36–0.43), (4) high Al2O3 (15.4–16.7 wt. %, molar A/CNK ratios = Al2O3/(CaO+Na2O+K2O) of 1.08–1.24, A/NK ratios = Al2O3/(Na2O+K2O) of 1.24–1.32), (5) low CaO (0.35–1.5 wt. %), MgO (0.27–0.53 wt. %), and MnO (<0.07 wt. %), and (6) rela- tively high Fe2O3 contents (3.5–4.2 wt. %); thus, the FeOT/ (FeOT+MgO) ratios (0.87–0.92) are high. These parameters indi- cate that the studied rocks are peraluminous, ferroan and alkali- calcic to alkalic (Fig. 3c–e). In the primitive mantle-normalized element plot (Fig. 4a), the analysed rhyolite samples display positive anomalies of K, Pb, and Zr and relatively pronounced negative anomalies of P, Ba, Eu, Nb and Ti. Chondrite-normalized data of REE reveal an en- richment of light REE (LREE) relative to heavy REE (HREE) with (La/Yb)N, (La/Sm)N and (Gd/Yb)N of 3.47–5.92, 2.76–3.64, and 1.20–1.40, respectively (Fig. 4b). Eu/Eu* parameters are be- tween 0.66 and 0.74, whereas Ce/Ce* ranges between 0.96 and 1.33. The sum of REE is around 142 ppm. Contents of Y and Yb are around 32 ppm and 3.5 ppm, respectively. The data presented for the major elements are in the good agreement with previous data from TAJDER (1956, 1960) and PAMIĆ (1991) for rhyolite of Rupnica. 4.3. Accessory minerals analyses 4.3.1. Zircon external morphology The population of zircon analysed for external morphology con- sists of 65 grains which are 50‒110 μm long and 25‒55 μm wide. Aspect ratios range from 1.4:1 to 3.3:1, with the median value of 2.3:1. Such ratios, the colourlessness, high transparency and bire- fringence are usually characteristic of early crystallized zircon in a granitic magma (HOSKIN & SCHALTEGGER, 2003). Around 40 % of the examined zircon population is partially dissolved, so the external morphology could not always be clearly defined. The rest of the separated zircon, i.e. grains with recognizable external morphology, was carefully examined. Their external morphology is defined by {100} prisms and {101} > {211} bipyramids. After PUPIN’s (1980) zircon typology, types J4 (50 %), J3 (30 %), J5 (10 %) and J2 (<10 %) are present (Fig. 5). According to PUPIN & TURCO (1972) and PUPIN (1980), such morphologies are conside- red to characterize zircon crystallized from high-temperature magmas with lower crust or upper mantle origin. 4.3.2. Inclusions in zircon Zircon grains are very rich in inclusions. Even dozens of them can occur in a single zircon grain and therefore represent potential material for further detail research. The inclusions vary in shape; some of them are euhedral and needle-like, but all are smaller than 10 μm. Raman bands of zircon (at 202, 212, 225, 356, 392, 438, 972–974 and 1005–1008 cm−1, strongest at 356, 972–974 and 1005–1008 cm−1, after FREZZOTTI et al., 2012), despite the con- focal mode, are very intense, making the identification of included phases difficult. So far, inclusions of haematite (bands at 223, 290, 409, 498, 609 and 1313 cm−1, strongest at 290 and 409 cm−1, after FREZZOTTI et al., 2012), apatite (bands at 432, 449, 581, 592, 608, 965, 1042, 1053 and 1081 cm−1, strongest at 965 cm−1; char- acteristic for F-apatite after HURAI et al., 2015; bands at 3100– 3800 cm−1 characteristic for O-H were not detected) and anatase (143, 195, 395, 514 and 638 cm−1, strongest at 143 and 638 cm−1, after FREZZOTTI et al., 2012) were detected (Fig. 6). 4.3.3. Zircon geochemistry For zircon geochemistry, 14 grains were successfully analysed with LA-ICP-MS. The results, together with basic statistical parameters and characteristic elemental ratios, are presented in Table 2. Zircon from the rhyolite of Rupnica shows variable Figure 4. Comparison of the rhyolite of Rupnica, Mt. Požeška Gora granite and rhyolite from the northern part of Mt. Kozara: (a) primitive mantle whole-rock incompatible trace element patterns after SUN & MCDONOUGH (1989) and (b) whole-rock chondrite-normalized patterns of REE after BOYNTON (1984). References for Mt. Kozara are the same as in Fig. 3. G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 259 U (137–958, mean 443 ppm) and Th (107–1411, mean 531 ppm) contents, with Th/U ratios between 0.78 and 1.62 (mean 1.13), typical for igneous zircon (HOSKIN & SCHALTEGGER, 2003; KIRKLAND et al., 2015). The compositional range of the determined REE patterns (Fig. 7a) is characteristic for zircon from granitoids (BELOU- SOVA et al., 2002a; HOSKIN & SCHALTEGGER, 2003) with significant rise of contents from Sm to Lu and total contents of REE between 1155 and 4490 ppm (mean 2993 ppm). A positive Ce anomaly (mean 1.27) indicates oxidized magma conditions, as does the finding of haematite as a primary inclusion in zircon. 4.3.4. Zircon U-Th-Pb dating The results of dating on 20 zircon grains from the Rupnica local- ity, selected on the basis of euhedral shape and elemental ratios (such as Th/U), are presented in Table 4 and in a concordia dia- gram in Fig. 8. Zircon yielded a concordia age of 80.8±1.8 (2σ) Ma and a mean square weighted deviation (MSWD) of 0.8. The zircon ages determined from the individual calibrated quotients of isotopic intensities 206Pb/238U, 207Pb/235U and 208Pb/232Th are 80.0±2.1, 82.7±3.3 and 81.7±1.8 Ma, respectively, with errors given as 2σ values. The MSWD values of 0.76, 0.45 and 1.00, re- spectively, suggest a single zircon generation. Table 4. Individual elemental and isotopic concentrations and ages of zircon from the rhyolite of Rupnica obtained from calibrated isotopic ratios of 206Pb/238U, 207Pb/235U, and 208Pb/232Th. Elemental concentrations of Pb refer to the sum of the Pb isotopes. Grain Elemental concentrations Isotopic concentrations (ppm) Si (wt. %) Zr (wt. %) Th (ppm) U (ppm) Pb (ppm) Th/U 204Pb 206Pb 207Pb 208Pb 1b 15.14000 47.13930 495.67 492.20 7.64 1.01 0.004 5.13 0.36 2.14 2b 15.14000 42.77307 328.12 343.58 7.41 0.96 0.024 4.39 0.60 2.40 3b 15.14000 46.23996 785.15 667.36 12.81 1.18 0.034 8.07 0.78 3.93 4b 15.14000 44.05930 221.57 279.74 4.89 0.79 0.052 3.28 0.30 1.26 5b 15.14000 43.30943 825.65 696.89 14.78 1.18 0.033 8.75 1.11 4.89 6b 15.14000 44.56110 404.35 517.83 9.19 0.78 0.013 6.50 0.55 2.12 7b 15.14000 43.86399 444.66 443.50 8.04 1.00 0.005 5.56 0.41 2.05 8b 15.14000 47.62453 770.86 705.22 13.30 1.09 0.001 9.00 0.66 3.65 9b 15.14000 48.44948 1552.14 917.59 18.77 1.69 0.012 12.21 0.70 5.85 10b 15.14000 45.80696 525.60 493.64 8.70 1.06 0.000 5.98 0.44 2.28 11b 15.14000 45.34541 828.67 684.20 11.90 1.21 0.017 8.40 0.41 3.08 12b 15.14000 44.69870 785.57 659.58 14.01 1.19 0.018 9.02 0.90 4.07 13b 15.14000 50.44010 524.08 476.65 10.30 1.10 0.058 6.30 0.79 3.15 14b 15.14000 48.10264 458.37 448.63 7.66 1.02 0.022 5.11 0.44 2.09 15b 15.14000 48.20173 964.95 718.38 13.46 1.34 0.023 8.23 0.82 4.38 16b 15.14000 43.88730 2157.05 1263.47 24.03 1.71 0.010 15.30 0.83 7.88 17b 15.14000 49.07538 386.88 281.20 5.82 1.38 0.026 3.62 0.34 1.83 18b 15.14000 49.54529 933.63 691.47 14.00 1.35 0.014 8.30 0.80 4.89 19b 15.14000 49.07977 396.54 360.44 7.04 1.10 0.016 4.73 0.42 1.87 20b 15.14000 48.50643 419.63 426.19 7.52 0.98 0.019 5.01 0.38 2.12 Grain Isotopic ratios Age (Ma) 206Pb/238U 1σ 207Pb/235U 1σ 208Pb/232Th 1σ 206Pb/238U 1σ 207Pb/235U 1σ 208Pb/232Th 1σ 1b 0.01160 0.00061 0.07659 0.00536 0.00421 0.00018 74.3 3.9 74.9 5.1 85.1 3.6 2b 0.01214 0.00063 0.08326 0.02146 0.00449 0.00066 77.8 4.0 81.2 20.1 90.9 13.3 3b 0.01228 0.00069 0.08622 0.01491 0.00410 0.00019 78.7 4.4 84.0 13.9 82.8 3.9 4b 0.01185 0.00041 0.07631 0.01193 0.00433 0.00041 75.9 2.6 74.7 11.3 87.6 8.3 5b 0.01221 0.00100 0.08209 0.01861 0.00412 0.00027 78.2 6.4 80.1 17.5 83.3 5.4 6b 0.01287 0.00132 0.08643 0.01170 0.00404 0.00018 82.4 8.4 84.2 10.9 81.7 3.6 7b 0.01310 0.00088 0.08697 0.00913 0.00407 0.00019 83.9 5.6 84.7 8.5 82.3 3.9 8b 0.01296 0.00087 0.09118 0.01000 0.00429 0.00012 83.0 5.6 88.6 9.3 86.7 2.5 9b 0.01383 0.00095 0.09191 0.00627 0.00385 0.00011 88.6 6.1 89.3 5.8 78.0 2.3 10b 0.01243 0.00042 0.08519 0.00735 0.00385 0.00020 79.6 2.7 83.0 6.9 77.8 4.1 11b 0.01319 0.00081 0.08792 0.00330 0.00397 0.00023 84.5 5.1 85.6 3.1 80.4 4.7 12b 0.01366 0.00109 0.09348 0.02380 0.00399 0.00054 87.5 6.9 90.7 22.1 80.7 10.9 13b 0.01332 0.00086 0.08398 0.01203 0.00393 0.00020 85.3 5.5 81.9 11.3 79.5 4.0 14b 0.01147 0.00124 0.07905 0.01466 0.00373 0.00028 73.5 7.9 77.3 13.8 75.6 5.7 15b 0.01178 0.00182 0.07547 0.01261 0.00368 0.00026 75.5 11.6 73.9 11.9 74.4 5.2 16b 0.01294 0.00101 0.08967 0.00631 0.00390 0.00017 82.9 6.4 87.2 5.9 78.9 3.4 17b 0.01322 0.00092 0.08653 0.01349 0.00392 0.00023 84.7 5.9 84.3 12.6 79.2 4.6 18b 0.01277 0.00073 0.08081 0.00622 0.00434 0.00015 81.8 4.6 78.9 5.8 87.7 3.1 19b 0.01351 0.00071 0.08925 0.01587 0.00372 0.00027 86.5 4.5 86.8 14.8 75.3 5.4 20b 0.01192 0.00069 0.07766 0.00590 0.00420 0.00024 76.4 4.4 75.9 5.6 84.9 4.9 Weighted average (Ma) 80.0 82.7 81.7 Error 2σ (Ma) 2.1 3.3 1.8 MSWD 0.76 0.45 1.00 G eo lo gi a C ro at ic a Geologia Croatica 75/2260 4.3.5. Apatite geochemistry For apatite geochemistry, 11 grains were successfully analysed with LA-ICP-MS (Table 3). REE patterns (Fig. 7b) with total con- tents of REE between 4064 and 8479 ppm (mean 6390 ppm) dis- play a negative slope according to the relative enrichment of the LREE, with a (La/Yb)N mean ratio of 9.0, which is typical for apatite from granitoids (BELOUSOVA et al., 2002b). Pronounced negative Eu anomalies with a mean of 0.39 were determined. This mean is close to the average for apatite from granitoid rock types (BELOUSOVA et al., 2002b). 4.4. Geothermometry A zircon saturation temperature (ZST) was calculated after WAT- SON & HARRISON (1983) and GERVASONI et al. (2016), using whole-rock Zr concentrations (Table 1). A negative SiO2-Zr co- variation occurs in the whole-rock data for the rhyolite of Rup- nica. Therefore, ZrSiO4 saturation during early magmatic crys- tallization is assumed (SCHILLER & FINGER, 2019). Calculated temperatures are within a narrow range of 858‒867 ºC (mean 863 ºC) using parameters from WATSON & HARRISON (1983), in- dicating a high-temperature environment. Calculations with the model by GERVASONI et al. (2016), which is considered to give more reliable values, yielded lower temperatures of 778‒798 ºC (mean 789 ºC), but these would still correspond to a high-tempera- ture environment. The Ti-in-zircon temperature after WATSON et al. (2006) was calculated for selected grains that are characterized by rela- tively low Ti contents, i.e. analyses that exclude Ti-rich inclusions (Table 2). Calculated temperatures are 801‒831 ºC (mean 814 ºC) with a precision of ±5 ºC (WATSON et al., 2006). These temper- atures fit the range of the calculated ZST and are only slightly lower than the ZST after WATSON & HARRISON (1983). Such a temperature difference is common for samples with M (cation ratio) = (Na+K+2Ca)/Al·Si <1.9 (FU et al., 2008; Fig. 9). The apatite saturation temperature (AST) calculated after HARRISON & WATSON (1984) for metaluminous to slightly peraluminous systems is 900 ºC. As apatite generally crystallizes over a relatively restricted interval within 60‒100 ºC of the AST (PICCOLI & CANDELA, 1994, 2002), the calculated AST would imply crystallization of apatite prior to crystallization of zircon (corroborated by apatite inclusions in zircon) or during zircon crystallization. Because ZST and AST are based on the whole- rock analysis and not on glass separates, the calculated tempera- tures are considered to represent maximum ones (KIRKLAND et al., 2015). 5. DISCUSSION 5.1. Whole-rock geochemistry and comparison with an A-type granite at Mt. Požeška Gora The whole-rock geochemistry in this paper was intended to pro- vide the geochemical environment for zircon and apatite crystal- lization in the studied rocks. However, whole-rock geochemistry presented here shows noticeable similarities with the A-type granite of Mt. Požeška Gora, despite the limited number of ana- lysed samples. PAMIĆ (1997) associated the Voćin volcanic rocks with those at Mt. Požeška Gora. It was assumed that (sub-)volcanic rocks from both localities have a similar age and are therefore as- sociated to a unique Senonian basalt-rhyolite formation, although the volcanic rocks at Mt. Požeška Gora also comprise A-type granite. PAMIĆ (1997) suggested a connection of these masses Figure 5. (a) Typical external morphologies of zircon from the rhyolite of Rupnica. (b) Morphologies and types of investigated zircon grains shown on the modified zircon typology diagram after PUPIN (1980). G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 261 and a Late Cretaceous age based on petrography, geochemistry and mineralogical features of the samples. In addition, the rather arguable age data of K-Ar dating on basalts from Voćin (72.8‒51.7 Ma; PAMIĆ, 1991) and the application of the Rb-Sr isochron method to granite and rhyolite from Mt. Požeška Gora (71.5±2.8 Ma; PAMIĆ et al., 1988) were used to support this connection. The latter age was recently revised by LA-ICP-MS dating of zir- con to 83.6±1.5 Ma by BALEN et al. (2020). The zircon age fits geological relations to the surrounding sedimentary rocks. When comparing mean values of whole-rock major element contents of granite from Mt. Požeška Gora (BALEN et al., 2020, PAMIĆ, 1987) and rhyolite of Rupnica (Table 1), the following similar mean values were found: (1) highly siliceous composi- tions (69.9 and 67.75 wt. % SiO2, respectively); (2) enrichment in alkalies (K2O+Na2O content: 8.68 and 8.60 wt. %); (3) relatively high K2O/Na2O molar ratios (0.56 and 0.40); (4) high Al2O3 con- tents (15.3 and 15.8 wt. % Al2O3; A/CNK ratio = 1.21 and 1.19; A/NK ratio = 1.27 and 1.28); (5) low contents of CaO (0.28 and Figure 6. (a) Plain-polarized transmitted-light photomicrograph of a zircon grain rich in inclusions. Arrows indicate the analytical spots for Raman spectrometry and detected inclusions. Magnification 1000x. Ap – apatite; Ats – anatase; Hem – haematite. (b) Raman spectra of anatase, apatite and haematite inclusions in zir- con. Spectra were compared with data given by FREZZOTTI et al. (2012) and HURAI et al. (2015). G eo lo gi a C ro at ic a Geologia Croatica 75/2262 0.64 wt. %), MgO (0.07 and 0.42 wt. %), and MnO (<0.08 wt. %); (6) relatively high Fe2O3 contents (3.30 and 3.84 wt. %); (7) high FeOT/(FeOT+MgO) ratios (0.98 and 0.89). According to the listed parameters, both the Mt. Požeška Gora granite and the rhyolite of Rupnica refer to peraluminous, oxidized, ferroan, and alkali- calcic to alkalic magmas (Fig. 3c–e). Trace element contents in both the granite from Mt. Požeška Gora (BALEN et al., 2020) and the rhyolite of Rupnica are also similar (Fig. 4). In the primitive mantle-normalized element plots (Fig. 4a) both rock types display positive anomalies of K, Pb, and Zr and relatively pronounced negative anomalies of high field strength elements (HFSE), P, Ba and Eu. The main differences concern the contents of Cs, U and Th. Whole-rock Zr/Hf ratios are also similar (mean: 39 for granite and 42 for rhyolite) and fall in the range for the average continental crust (PUPIN, 2000). Chondrite-normalized data of REE (Fig. 4b) reveal an enrichment of LREE relative to HREE with pronounced negative Eu anoma- lies (mean: 0.46 for granite and 0.71 for rhyolite) and minor pos- itive Ce anomalies (mean: 1.01 for granite and 1.08 for rhyolite). The mean sum of REE is 165 ppm for the granite and 142 ppm for the rhyolite. REE patterns of the rhyolite of Rupnica do not show the tet- rad effect implying the absence of a significant H2O content in the melt (MCLENNAN, 1994). Instead, according to the Zr/Hf (39–43) and Y/Ho (25–28) ratios, the element distribution is CHARAC (CHArge and RAdius Controlled, BAU, 1996). Pat- Figure 7. (a) Chondrite-normalized patterns of REE in (a) zircon and (b) apatite grains separated from the rhyolite of Rupnica using normalizing factors after BOYNTON (1984). Result of the whole-rock (WR) analysis of sample Rupnica 3, from which zircon and apatite grains were separated (thick line), is given for com- parison. (c) HfO2 versus Y2O3 diagram after PUPIN (2000). Fields 1–2 are specific domains for anorogenic rocks, fields 5–6: orogenic rocks, fields 3–4 both types of rocks.1b – hypersolvus alkaline granite/rhyolite; 1d – hypersolvus alkaline granite/rhyolite or silica over/under-saturated alkaline/peralkaline syenite/tra- chyte; 2 – subsolvus alkaline granite/rhyolite. For other fields see the reference. (d) Chondrite-normalized patterns of REE after BOYNTON (1984); comparison of zircon grains from Mt. Požeška Gora granite and the rhyolite of Rupnica. Figure 8. U-Pb concordia diagram for zircon from the rhyolite of Rupnica. Error ellipses relate to 1σ errors. Weighted average ages, errors and MSWD values are given in Table 4. Figure 9. Boxplot of temperature ranges for different geothermometers: 1 – apa- tite saturation temperature (AST) after HARRISON & WATSON (1984); 2 – zircon saturation temperature (ZST) after WATSON & HARRISON (1983); 3 – Ti-in-zircon after WATSON et al. (2006); 4 – ZST after GERVASONI et al. (2016). G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 263 terns of incompatible trace elements (Fig. 4a and 4b), trace ele- ment ratios (Table 1), apparent enrichments in LREE together with intermediate-to-low contents of HFSE (except Hf and Zr), variable abundances of large ion lithophile elements (LILE), and negative Eu anomalies (Fig. 4b) point to crustal sources of the corresponding magmas. According to the geochemistry in respect to reference mate- rials (BOYNTON 1984; SUN & MCDONOUGH,1989), standard geotectonic classification diagrams and classification of granitic rocks by WHALEN et al. (1987), EBY (1990, 1992) and KING et al. (1997), the rhyolite of Rupnica shows A-type features (Figs. 10 and 11), which are relatively high contents of HFSE (Ga, Nb, Ta, Th, U, Y, Zr); significantly enriched LILE compared to primi- tive mantle, high FeO* (>1 wt. %), K and total contents of REE, 10000 × Ga/Al ratios of 2.0−2.5, and low MgO, CaO, Cr, Ni, Sr and Ba contents. Furthermore, the temperature characteristics for magmas forming the albite rhyolite of Rupnica and the granite of Mt. Požeška Gora are similar. Both rocks originated from hot (ca. 800–900 ºC), dry and oxidized magmas generated at lower- to mid-crustal levels. An inhomogeneous source at such depth can be expected (KEMPTON et al., 1990; BUROV et al. 2007), where tonalitic to granodioritic crust produces peraluminous alkali-cal- cic to calc–alkalic granitic melts (PATIÑO DOUCE 1997; FROST & FROST, 2011) by a low degree of partial melting at higher pressures (see SKJERLIE & JOHNSTON, 1993, for mag- nesian tonalite at pressures ≥ 10 kbar). A relatively fast ascent to (sub)surface levels of the A-type magma led to rhyolite with glass in the matrix at Rupnica. 5.2. Chemical compositions of zircon and apatite and their petrogenetic significance Normalized patterns of REE in zircon, not contaminated by in- clusions, demonstrate the igneous nature by negative Eu anoma- lies and enrichment of HREE (Fig. 7a) with generally high sums Figure 10. Diagrams to discriminate A-type granitoids after WHALEN et al. (1987). I, S, and A denote I-, S-, and A-type granites, respectively. FG – fraction- ated felsic granites; OTG – unfractionated M-, I-, and S-type granites. Figure 11. (a) Geotectonic discrimination diagram after BATCHELOR & BOWDEN (1985), (b) geotectonic discrimination diagrams for granites after PEARCE et al. (1984) and PEARCE (1996) and (c) after HARRIS et al. (1986). VAG – volcanic arc granites, WPG – within-plate granites, syn-COLG – syn-collision granites, ORG – ocean-ridge granites, post-COLG – post-collision granites, GCTS – granites from collisional tectonic setting. G eo lo gi a C ro at ic a Geologia Croatica 75/2264 of REE. The positive Ce and significantly negative Eu anomalies are typical for zircon from granitoids especially for those with 65‒70 wt. % of SiO2 (BELOUSOVA et al., 2002a). A less develo- ped Eu anomaly accompanied by an enhanced Hf content in zircon indicates co-crystallization of zircon and plagioclase (SŁODCZYK et al., 2016). Relative enrichment in HREE over medium REE and apatite and a Ti-phase detected by Raman spec- troscopy as inclusions in zircon suggest the co-crystallization of these phases (HOSKIN et al., 2000). In the Rupnica samples, ap- atite also occurs as individual grains, which combined with AST values point to early crystallization of the apatite prior to or si- multaneous with zircon. Chemical compositions of zircon (e.g. Hf, Th, U) define it as an early crystallized mineral formed in a deep magma chamber at relatively high and constant temperatures (WANG et al., 2010; KIRKLAND et al., 2015). According to WANG et al. (2010), an early-stage zircon is characterized by high Zr/Hf ratios (~39; compared to late-stage zircon ~29) and low Hf concentrations (~1.35 wt. % HfO2 compared to 1.85 wt. % for the late-stage), which fit the chemistry of the studied zircon (mean Zr/Hf=55, HfO2=1.04 wt. %). Zircon of Rupnica has Hf concentrations of 6436‒11511 ppm (mean 8784 ppm), which are characteristic of highly-evolved mag- mas (BELOUSOVA et al., 2002a). According to PUPIN (2000), whole-rock and zircon Zr/Hf ratios are indicative of magmatic fractionation of a granitic melt. A decrease of these ratios in zir- con from mantle-derived plagiogranites (median 60−70), through hypersolvus alkali granites, alkali syenites and hybrid calc-alka- line granitoids to the lowest values in peraluminous granites and migmatites (median 35−37) was noted by PUPIN (2000). In other words, the higher this ratio the higher is the mantle input in the generated magma. For the studied zircon, the Zr/Hf ratio is on ave rage 55, which points to a chemical mantle contribution to the magma. This view is supported by BALEN et al. (2020) who sug- gested a potential influence from a mantle source on the magma forming the A-type granite of Mt. Požeška Gora based on Zr/Hf ratio, morphology of zircon and inclusions therein. Furthermore, the Zr/Hf ratio of zircon crystallizing from a water-undersaturated melt is higher than the whole-rock Zr/Hf ratio (ERDMANN et al., 2013; BREITER & ŠKODA, 2017), which is valid for the rhyolite of Rupnica (mean whole-rock Zr/Hf ratio = 42). Zircon grains extracted from the Mt. Požeška Gora granite and the rhyolite of Rupnica also show similar geochemical sig- natures (Fig. 7d) with mean zircon Zr/Hf ratios of 55 and 53, re- spectively, and Th/U ratios of 0.74 and 1.13, respectively. These signatures point to a magma origin by partial melting of material from mid- to lower-crustal levels (HOSKIN & SCHALTEGGER, 2003). The high-temperature environment determined here by ZST, Ti-in-zircon and AST (789–863, 814 and 900 °C, respectively) was also found for the early crystallization of the studied acces- sory minerals in the Mt. Požeška Gora granite (BALEN et al., 2020) with ZST of 830‒950 ⁰C (mean 873 ⁰C). Furthermore, zir- con morphologies after PUPIN (1980) with D and J5 type prevail- ing in Mt. Požeška Gora granite and J4 and J3 in the rhyolite of Rupnica also suggest a high-temperature environment which is typical for an I- and/or an A-type granitic melt. Zircon crystal- lized from a magma which originated in the lower crust, but con- tributions from an upper mantle source should not be excluded due to the external zircon morphology (PUPIN & TURCO, 1972; PUPIN, 1980) and zircon Zr/Hf ratios (PUPIN, 2000). This crys- tallization occurred in a deep magma chamber at relatively con- stant temperature > 800 ⁰C (WANG et al., 2010; KIRKLAND et al., 2015). The amplitude of Eu anomalies in apatite generally increases toward more fractionated rocks and is controlled by the crystal- lization of feldspar (BELOUSOVA et al., 2002b). Contents of Mn are expected to be relatively high in apatite crystallized from a magma under reduced conditions (BELOUSOVA et al., 2002b, reported Mn contents of 0.1–1 wt. %). Moreover, BELOUSOVA et al. (2002b) demonstrated that there is an excellent correlation between contents of REE in apatite and the oxidation state of the magma. Apatite from more oxidized granitic melts shows lower Y/ƩREE and higher La/Sm and Ce/Th ratios than apatite from less oxidized rocks, regardless of the overall degree of fractiona- tion of the magma Following such relations, the apatite from Rup- nica with Y/ƩREE= 0.18, La/Sm=2.6 and Ce/Th=142 crystallized in an oxidizing environment. This environment is also confirmed by primary inclusions of haematite in zircon from the rhyolite of Rupnica and the red granite from Mt. Požeška Gora (BALEN et al., 2020). 5.3. Implications on the regional setting Considering the afore-mentioned characteristics of the whole rock and the accessory minerals therein, it can be assumed that the magmas forming the Mt. Požeška Gora granite and the rhyo- lite of Rupnica have the same origin. Thus, the rhyolite of Rup- nica should be considered as a part of an igneous suite that in- truded not only the Sava Zone, but also the adjacent Tisia Mega-Unit. This also concerns the Mt. Požeška Gora granite to- gether with the Mt. Prosara leucogranite (82.68±0.13 Ma; PAMIĆ & INJUK, 1988; PAMIĆ & LANPHERE, 1991b; USTASZE- WSKI et al., 2009) and Late Cretaceous acidic rocks from Mt. Moslavačka Gora (82±1 Ma; STARIJAŠ et al., 2010; BALEN & BROSKA, 2011; BALEN & PETRINEC, 2011), but also basic rocks from the latter locality which show upper mantle isotopic signatures (109±8 and 83±9 Ma; BALEN et al., 2003). Also rhy- olites from the northern part of Mt. Kozara (USTASZEWSKI et al., 2009; CVETKOVIĆ et al., 2014), located in northern Bosnia and Herzegovina south of the Slavonian Mts. (Figs. 1 and 3), can be included in the comparison. These rhyolites with a mean zir- con 206Pb/238U age of 81.60±0.12 Ma (USTASZEWSKI et al., 2009) are part of a bimodal magmatic association. Mafic rocks of the same age occur and, according to geochemistry (normal- ized patterns of REE), originated from the same magma source as the acidic rocks. USTASZEWSKI et al. (2009) placed these rocks into an intra-oceanic environment (island-arc, ocean island or mid-ocean ridge setting), based on Sr and Nd isotopes. CVETKOVIĆ et al. (2014) focused more on the acidic rocks of the bimodal association from the northern part of Mt. Kozara and confirmed the close petrogenetic link between basic and acidic rocks. Furthermore, these authors revisited the basic suite and concluded that the entire ophiolite slice from the northern part of Mt. Kozara could represent the remnant of an anomalous ridge segment (similar to present day Iceland). Cogenetic acidic mag- mas most probably originated through the obduction-induced par- tial melting of hydrated oceanic crust. These voluminous magmas were emplaced as subaerial high-temperature rhyodacite-rhyolite. Discrimination diagrams after BATCHELOR & BOWDEN (1985) place rhyolites from the northern part of Mt. Kozara to- gether with the rhyolite of Rupnica and the Mt. Požeška Gora granite in an anorogenic or postorogenic environment, whereas rhyodacites from Mt. Kozara point to a somewhat different envi- ronment (Fig. 11a). Rhyolite of Rupnica and the Mt. Požeška G eologia C roatica Schneider et al.: Dating and geochemistry of zircon and apatite from rhyolite at the UNESCO geosite Rupnica (Mt. Papuk, northern Croatia) ... 265 Gora granite plot into the within plate or, less clearly, into the volcanic arc field (Fig. 11b) of the discrimination diagrams after PEARCE et al. (1984), whereas the rhyolite of Rupnica can be discriminated from the Mt. Požeška Gora granite (within-plate setting vs. volcanic arc setting, Fig. 11c) in the Rb-Hf-Ta diagram by HARRIS et al. (1986). According to HfO2 vs. Y2O3 contents (7590‒13574 ppm HfO2, mean 10372 ppm; 1495‒7815 ppm Y2O3, mean 5033 ppm), which are directly connected to the contrasting Hf and Y contents in zircon of orogenic and anorogenic rocks (PUPIN, 2000), zircon from the rhyolite of Rupnica crystallized from a hypersolvus or subsolvus alkaline granitic magma of anorogenic origin (Fig. 7c). According to the data presented here and those by BALEN et al. (2020) discussed above, the rhyolite of Rupnica with a zir- con U-Pb age of 81 Ma is related to the magmatism within the Sava Zone, i.e. the collisional environment between the Adria and Tisia microplates, and in the adjacent Tisia Mega-Unit. This col- lision with Adria as a subducted plate caused hot mantle to rise, leading to local extensional rift processes in the suture zone. The subsequent crustal extension caused a fast extrusion of rhyolitic magmas to the (sub)surface. The igneous rocks of the Banatitic Magmatic and Metallo- genetic Belt (BMMB, BERZA et al., 1998) of Late Cretaceous age (ZIMMERMAN et al., 2008; overview in ILINCA et al., 2011), known as banatites, extend to the Balkan-South Car- pathian orogenic belt in southeastern Europe. Although the pe- trology of the banatites is extremely diverse, geochemical data (trace elements and isotope composition) point to subduction re- lated magmas with sources in the upper mantle or even lower crust (ILINCA et al., 2011). For the formation of the BMMB a slab rollback model is plausible (ZIMMERMAN et al., 2008). The rhyolite of Rupnica and the Mt. Požeška Gora granite share their age with those of banatites and therefore could represent the westernmost occurrences of the BMMB, as has been previously suggested by ILINCA et al. (2011). This opens a new link and possible extension of research in the future, because the relation- ship between the BMMB and the igneous rocks, which penetrated the Sava Zone and Tisia Mega-Unit in the south-western part of the Panonnian basin, is currently far from clear. 6. CONCLUSION The chemical compositions of zircon, apatite, and whole-rock, as well as the petrography of the rhyolite of Rupnica indicate that the magma forming this rock originated from partial melting of mid- to lower-continental crust at temperatures > 800 °C. The compressional tectonics of the Adria microplate towards Europe and the closure of the Neotethys Ocean caused the opening of lo- cal extensional zones. In such a tectonic environment, the mag- mas of the rhyolite of Rupnica were generated. These local ex- tensional zones acted as pathways for the rapid ascent of hot, dry, and oxidized acidic magmas to (sub)surface levels in the Late Cretaceous at ca. 81 Ma. The rhyolite of Rupnica and the granite from Mt. 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