© Author(s) 2025. CC Atribution 4.0 License Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia Petrografija in geotermobarometrija kremenovega diorita s Pohorja Tim SOTELŠEK1, Simona JARC1, Andreja PAJNKIHER2 & Mirijam VRABEC1* 1University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Geology, Aškerčeva cesta 12, SI-1000 Ljubljana, Slovenia; e-mail: tim.sotelsek@ntf.uni-lj.si; simona.jarc@ntf.uni-lj.si; *corresponding author: mirijam.vrabec@ntf.uni-lj.si 2ELEA IC projektiranje in svetovanje, Dunajska cesta 21, SI-1000 Ljubljana, Slovenia; e-mail: andreja.pajnkiher@gmail.com Prejeto / Received 5. 9. 2025; Sprejeto / Accepted 21. 11. 2025; Objavljeno na spletu / Published online 10. 12. 2025 Key words: quartz diorite, “cizlakite”, petrography, clinopyroxene geothermobarometry, amphibole geothermobaromery, amphibole–plagioclase thermometry, Pohorje Mountains Ključne besede: kremenov diorit, “čizlakit”, petrografija, klinopiroksenova geotermobarometrija, amfibolova geobarometrija, amfibol–plagioklaz termometrija, Pohorje Abstract The mineral composition and pressure–temperature conditions of Pohorje quartz diorite were investigated to reconstruct crystallization sequence and integrate the results with previous data on the Pohorje igneous complex, providing insights into its petrogenesis. Pohorje quartz diorite has phaneritic texture and is medium- to coarse-grained. The major minerals include light green clinopyroxene, dark green amphiboles, and white feldspars; the first two give the rock its characteristic colour. The proportion of dark- to light-colored minerals is approximately 4:1. Clinopyroxene predominates and correspond to diopside (XCa = 0.47–0.51, XMg = 0.41–0.49, XFe = 0.05–0.09). Amphiboles are Ca-amphiboles and are divided into two types: Type I amphiboles occur as single grains with distinctive core and rim zones, whereas Type II amphiboles replace clinopyroxene grains. Type I amphibole cores are classified as magnesiohornblende, tschermakite, edenite, pargasite, or magnesiohastingsite; Type I amphibole rims are classified as magnesiohornblende and actinolite; and Type II amphiboles are classified as magnesiohornblende. The dominant feldspars are oligoclase to andesine (XAb = 0.61–0.73), often replaced by potassium feldspar orthoclase. Minor minerals include quartz, biotite group minerals, apatite group minerals, titanite, epidote group minerals (allanite), and magnetite, while secondary minerals comprise chlorite group minerals and calcite. Various thermometers and barometers were applied to reconstruct the crystallization history of the quartz diorite and link it to the evolution of the host granodiorite intrusion. Thermobarometric data indicate that clinopyroxene in the quartz diorite, which is considered the earliest cumulate product from basaltic melts, crystallized under the highest P–T conditions (840–905 °C; 6.70–7.70 kbar), consistent with petrographic evidence. Subsequent crystallization of Type I amphibole cores occurred at 675–730 °C and 6.45–6.50 kbar, conditions comparable to those of the less evolved granodiorite, suggesting coeval formation. Later stages involved the formation of Type I amphibole rims at 585–640 °C and ~2.00 kbar, Type II amphiboles at 615–680 °C and 2.59–2.79 kbar, and biotites at 670–690 °C, associated with the emplacement of more evolved granodiorite at shallower crustal levels. Izvleček Proučili smo mineralno sestavo in tlačno-temperaturne pogoje nastanka pohorskega kremenovega diorita, z namenom določitve zaporedja kristalizacije posameznih mineralov. Dobljene rezultate smo povezali z objavljenimi podatki o pohorski granodioritni intruziji, kar omogoča dodaten vpogled v petrogenzo kremenovega diorita. Pohorski kremenov diorit ima faneritsko strukturo in je srednje do debelozrnat. Glavne minerale predstavljajo svetlozeleni klinopirokseni in temnozeleni amfiboli, ki dajo kamnini značilno barvo, ter beli glinenci. Razmerje med temnimi in svetlimi minerali je približno 4:1. V kamnini prevladuje klinopiroksen, ki ustreza diopsidu (XCa = 0,47–0,51, XMg = 0,41–0,49, XFe = 0,05–0,09). Amfiboli so Ca-amfiboli in jih lahko razdelimo na dve vrsti: amfiboli tipa I se pojavljajo kot posamezna zrna z značilno različno sestavo jedra in robnih delov, medtem ko amfiboli tipa II nadomeščajo zrna klinopiroksenov. Jedra amfibolov tipa I pripadajo magnezijski-rogovači, tschermakitu, edenitu, pargasitu ali magneziohastingsitu; robni deli amfibolov tipa I pripadajo magnezijski-rogovači in aktinolitu; amfiboli tipa II so po klasifikaciji vsi magnezijska-rogovača. Med glinenci prevladujejo plagioklazi sestave oligoklaz do andezin (XAb = 0,61–0,73), ki so pogosto nadomeščeni z ortoklazom. Med manj zastopanimi minerali se pojavljajo kremen, biotiti, apatiti, titanit, minerali epidotove skupine (allanit) in magnetit, od sekundarnih mineralov so prisotni kloriti in kalcit. Da bi rekonstruirali zgodovino kristalizacije kremenovega diorita in ga povezali z razvojem glavnega granodioritnega intruziva smo uporabili različne geotermometre in geobarometre. Rezultati geotermobarometrije kažejo, da so klinopirokseni v kremenovem dioritu, ki velja za najzgodnejši kumulat bazaltnih talin, kristalili pri najvišjih P–T pogojih (840–905 °C; 6,70–7,70 kbar), kar je skladno s petrografskimi dokazi. Sledila je kristalizacija jeder amfibolov tipa I, ki je potekala pri 675–730 °C in 6,45–6,50 kbar, kar ustreza pogojem kristalizacije manj razvitega granodiorita in nakazuje njihov sočasni nastanek. Kasnejše faze so vključevale nastanek robnih delov amfibolov tipa I pri 585–640 °C in ~2,00 kbar, amfibolov tipa II pri 615–680 °C in 2,59–2,79 kbar, ter biotitov pri 670–690 °C in so povezane z intruzijo bolj razvitega granodiorita v višje nivoje skorje. Article GEOLOGIJA 68/2, 269-286, Ljubljana 2025 https://doi.org/10.5474/geologija.2025.012 270 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC Introduction Quartz diorite, in the past also known as “ci- zlakite” is an intrusive igneous rock. It consists of dark green amphiboles, light green pyroxene, white feldspars and quartz, with minor biotite group minerals (in continuation biotite), titanite, epidote group minerals (allanite), apatite group minerals (in continuation apatite), chlorite group minerals (in continuation chlorite), calcite and opaque minerals, mainly magnetite. In Slovenia, it occurs in only one location – on Pohorje, near the village of Cezlak, forming large enclave within granodiorite host rock. In the past, both granodio- rite and quartz diorite were extracted. The quarry of quartz diorite had a significant economic val- ue for the natural stone industry and at the same time represents an important natural heritage site (ARSO, 2018). The first studies of the igneous rocks of Pohorje were carried out by Benesch (1917). He drew atten- tion to a smaller outcrop of “green stone”, analysed it and described it as quartz hornblende augite di- orite, and thus classified it as diorite. Dolar-Man- tuani (1935) analysed samples of quartz diorite, which were subsequently named by Nikitin & Kle- men (1937) as tylaite, a rock with a transitional composition between gabbro and peridotite. Niki- tin & Klemen (1937) described quartz diorite more precisely as a quartz hornblende augite diorite containing 70–80% mafic minerals (hornblende, augite, biotite, apatite, titanite) and 20–30% sal- ic minerals (quartz, plagioclases). As the existing name was not suitable, Nikitin (1939) carried out a detailed classification and defined the rock as a separate igneous rock according to the CIPW sys- tem, which he named “cizlakite” after the village of Čizlak (now Cezlak). Rock was considered as a product of the early gravitational differentiation during crystallization of granodioritic magma (Nikitin & Klemen, 1937; Nikitin, 1939; Faninger, 1965). Later investigations confirmed the character- istic mineral composition with dominant augite, hornblende and an anorthite component in the plagioclases between 34 and 52% (Dolar-Mantu- ani, 1935, 1940; Nikitin, 1939; Faninger, 1973). Faninger (1973) suggested that quartz diorite is a product of hybridisation of ultramafic magma with magma from the Pohorje main igneous rock, while Dolenec et al. (1987) concluded, that quartz diorite is classified as a gabbroic rock based on the isotopic composition of oxygen. Činč (1992) showed that quartz diorite was formed by fraction- al crystallization of tholeiitic magma and that the samples fall into the gabbro or quartz gabbro field according to Streckeisen’s classification. Dolenec (1994) determined the Miocene age of the quartz diorite (18.7 ±0.7 Ma) using the radiometric K–Ar method, confirming that it is slightly older than granodiorite, which Nikitin (1939) had already surmised. Poli et al. (2020) claimed that mixing and fractional crystallization were responsible for the formation of rocks from the Pohorje Igneous Complex (PIC) including granodiorite, tonalite and quartz diorite. The geodynamic sequence in- volves mantle metasomatism, crustal thickening, and mantle melt production in response to tectonic events. The objective of this study is to characterize the mineral composition of quartz diorite and to recon- struct the crystallization sequence and pressure– temperature conditions using optical microscopy, cold cathodoluminescence, electron microprobe analysis, and geothermobarometric calculations. The results are integrated with previously pub- lished data on the Pohorje igneous complex to pro- vide a more comprehensive understanding of its petrogenesis. Geological setting Pohorje is part of the Eastern Alps, which con- sist of Cretaceous nappes, collectively known as the Austroalpine nappes, or Austroalpine for short. The Eastern Alps include Kobansko, Pohorje, the northern Karawanke, and Strojna. The Pohorje Mountains are bounded to the west and southwest by the Labot Fault, which separates them from the Southern Alps; to the north, the Ribnica trough separates them from the lithologically similar structures of Strojna and Kozjak; and to the east and southeast, they sink beneath the Plio–Qua- ternary sediments of the Pannonian Basin (Fig. 1) (Mioč, 1978; Mioč & Žnidarčič, 1989). The sequence of Cretaceous nappes in Pohor- je begins with the structurally deepest Pohorje nappe, composed of medium to high metamor- phic rocks. This is followed by two further nappes, namely the first, structurally higher nappe with low-grade metamorphic rocks, mainly schists and phyllites, and the second nappe composed of clas- tic sedimentary rocks (Janák et al., 2004). The en- tire sequence is overlain by Miocene sediments of the Pannonian Basin (Fodor et al., 2003, 2008). The metamorphic rocks from the Pohorje nappe are mainly gneisses, and, less commonly, micaschist, containing lenses of eclogite, amphi- bolite, marble, quartzite, and a somewhat larger ultrabasic body with remnants of garnet peridotite (Hinterlechner-Ravnik, 1971, 1973; Hinterlech- ner-Ravnik & Moine, 1977; Hinterlechner-Ravnik 271Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia et al., 1991a, b) (Fig. 1a). These rocks underwent intracontinental subduction during the Creta- ceous orogeny, descending to depths over 100 km (Janák et al., 2004). At these depths, they experi- enced ultrahigh pressure metamorphic conditions at pressures up to 4.0 GPa and temperatures of 750–940 °C (e.g., Vrabec et al., 2012; Janák et al., 2015). The Pohorje nappe is folded into an antiform (Pohorje antiform; Kirst et al., 2010), with an axis trending east–southeast to west–northwest. Its central part is occupied by the Pohorje Igneous Complex (Poli et al., 2020), which intruded met- amorphic rocks during the Miocene (ca. 18 Ma; Zupančič, 1994; Altherr et al., 1995; Fodor et al., 2008; Trajanova et al., 2008). The PIC compris- es three main rock groups: (1) granodiorite, to- nalite (GDT), and quartz diorite; (2) dacite dykes and stocks intruding both metamorphic rocks and GDT, particularly in western Pohorje, togeth- er with porphyritic microgranodiorite (DAMG); and (3) andesitic dykes (AD), which mainly cut metamorphic rocks and less commonly GDT (Poli et al., 2020). Magmatic activity in the PIC occurred in multiple pulses (Poli et al., 2020). The f irst pulse (ca. 20 Ma) involved the ascent of small mafic magma batches to middle-crustal level chambers, where cumulus processes pro- duced the quartz diorite body. During the second pulse (ca. 18 Ma, 6.2 kbar), hybridized magmas rose into middle-crustal level chambers and crys- tallized to form less evolved GDT that enclosed the earlier quartz diorite. Continued magma–fel- sic interaction during the third pulse (ca. 17 Ma, 4.2 kbar) generated more evolved GDT, with chamber depths decreasing in response to rapid uplift. The fourth pulse (ca. 16 Ma, 2–3 kbar) was characterized by magmas that evolved through mixing and fractional crystallization (MFC), as- cended into subvolcanic-level chambers, and were emplaced as Ga-rich DAMG dykes and sheet-like intrusions. The f ifth pulse (ca. 17 Ma) introduced small batches of mantle-derived melts into mid- dle-crustal levels, producing dykes and crosscut- ting intrusions of Ga-poor DAMG. In the f inal stages of crystallization, residual granitic melts (~20%) intruded GDT and quartz diorite as aplitic and pegmatitic bodies, cutting the main intrusion in multiple directions; these late-stage intrusions occur both at the pluton margins and, locally, within the surrounding metamorphic rocks (Poli et al., 2020). Fig. 1. (a) Simplified geological map showing the position of the quartz diorite body (modified after Mioč & Žnidarčič, 1977). (b) Present-day view of the Cezlak II quarry. (c) Close-up of a quarry wall section, where pegmatite veins clearly cutting through the quartz diorite (marked with a blue rectangle in panel b). (d) Elongated amphibole crystals (up to 5 cm) visible within the pegmatite vein (marked with a red rectangle in panel c). 272 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC Sotelšek (2019) determined pressures and tem- peratures of granodiorite intrusion using conven- tional amphibole and biotite geothermobarome- ters. Calculated pressures decrease from southeast to northwest from 6.6 kbar to 2 kbar, suggesting that the intrusion was tilted after emplacement. Temperatures follow the same decreasing trend from 724 °C in the southeast to 670 °C in the northwest. Materials and methods Samples and sample preparations Available fresh rock samples were collected in the abandoned Cezlak II quarry (Fig. 1b), from which 19 thin sections were prepared. The sam- ples, thin sections, and corresponding labels are presented in Table 1. Optical microscopy Polished thin sections were examined with a Nikon Eclipse E200 optical polarising microscope. A Nikon DS-Fi1 camera and the NIS-Elements Ba- sic Research software were used for photo docu- mentation of individual areas under parallel and crossed polars. A method of point counting was used to determine the relative proportions be- tween minerals in thin sections. Between 400 and 600 points were counted per sample, depending on the grain size and texture. Optical cathodoluminescence with cold cathode Cathodoluminescence (CL) imaging was per- formed on polished thin sections of selected sam- ples in order to examine mineral textures, zoning, and phase relations. The measurements were con- ducted using a CITL 8200 Mk3 cold-cathode CL stage attached to an Olympus BH2 petrographic microscope. Analytical conditions were kept sta- ble, with a vacuum of ~0.05–0.1 mbar, an acceler- ating voltage of 14–15 kV, and a beam current of 200–300 μA. Images were captured using a digital camera under constant operating parameters to ensure comparability between minerals. With this meth- od, clear distinction between potassium feldspar, plagioclases, quartz, amphiboles, and accesso- ry phases such as apatite, was possible based on their characteristic luminescence colours. Lumi- nescence colours were used qualitatively to recog- nize textural features and were processed only for brightness and contrast adjustment, without mod- ification of the original colour information. Electron microprobe analyses (EPMA) with wavelength dispersive spectroscopy (WDS) Electron microprobe analyses (EPMA) with wavelength dispersive spectroscopy (WDS) were carried out using a CAMECA SX-100 mi- croprobe, operating at an electron acceleration voltage of 15 kV, a beam current of 20 nA, and a peak counting time of 20 s. All analyses were spot measurements using an electron beam with cross-section of 5 μm. Raw counts were correct- ed using a PAP routine. A total of 45 amphibole grains, 30 clinopyroxene grains, 30 plagioclase grains, 20 potassium feldspar grains, and 3–5 grains of minor mineral phases were measured. Within individual grains 4–6 spot measurements were conducted. The contents of the following oxides were mea- sured: SiO2, TiO2, Al2O3, Cr2O3, Na2O, K2O, FeO, MnO, MgO, and CaO, using the following stan- dards: LiF for F, albite for Na, orthoclase for Si, orthoclase for K, Al2O3 for Al, NaCl for Cl, wol- lastonite for Ca, TiO2 for Ti, fayalite for Fe, rhodo- nite for Mn, forsterite for Mg, Cr for Cr, and Ni for Ni. The chemical composition of minerals — in- cluding clinopyroxene, amphiboles, plagioclases, biotite, potassium feldspar, quartz, chlorite, and Table 1. List of quartz diorite samples from Cezlak II quarry. Sample number Sample description Thin section number C1 Quartz diorite C1-1 C2 Quartz diorite C2-1 C3 Quartz diorite C3-1, C3-2, C3-3, C3-4 C4 Quartz diorite in contact with pegmatite vein C4-1 C5 Quartz diorite in contact with pegmatite vein C5-1, C5-2 C6 Quartz diorite in contact with pegmatite vein C6-1, C6-2 C7 Quartz diorite in contact with pegmatite vein C7-1, C7-2, C7-3 C8 Quartz diorite in contact with pegmatite vein C8-1, C8-2, C8-3 C9 Quartz diorite C9-1 C10 Quartz diorite C10-1 273Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia epidote group minerals — was determined on sam- ples C1-1, C3-1, C4-1, C7-3, and C8-3. Content of Fe2+ and Fe3+ in amphiboles and pyroxene was determined by stoichiometric cal- culations. The presented ferric iron content in amphiboles was estimated based on averaged nor- malization to 15 cations excluding Na, K ((15eNK + 15eK)/2) (Yavuz & Döner, 2017). Where needed, the normalizations were recalculated considering the required calculation steps for the specific ther- mobarometer. The calculation of ferric iron in py- roxene was determined as the average of Fe3+ con- tent calculated using the models of Droop (1987) and Papike et al. (1974). All iron in other minerals was considered as Fe2+. Geothermobarometric calculations Pressures and temperatures are key parameters for determining the emplacement sequence of plu- tons. To constrain the pressure and temperature conditions of quartz diorite crystallization, we applied several geothermobarometers, which are listed in Table 2. For geothermobarometric calculations in- volving amphiboles, understanding the specific site-related reactions within the amphibole struc- ture can provide valuable insight. A substitution analysis is commonly used to check for the major substitution types. A Tschermak molecule substi- tution is thought to be a function of temperature and pressure (Anderson and Smith, 1995; Ham- marston and Zen, 1986; Helz, 1982). Al-Tscher- mak exchange is pressure sensitive and can be written as C(Mg,Fe) + TSi = VIAl + IVAl, where Al in tetrahedral coordination (IVAl) replaces TSi and Al in octahedral coordination (VIAl) replaces Mg and Fe in C sites. Ti-Tschermak exchange is a tem- perature-sensitive coupled substitution, where CTi replaces BMg, which leads to TSi being replaced by IVAl. At higher temperatures it can be expressed as BMg + TSi = CTi + IVAl. Another temperature sen- sitive substitution is edenite substitution written as Avacancy + TSi = A(Na + K) + IVAl, where higher A(Na + K) is accommodated by the exchange of TSi with IVAl (Helz, 1982; Hammarstrom & Zen, 1986; Anderson & Smith, 1995). Plagioclase substitu- tion can also play an important role in the content of IVAl in amphiboles as variations in albite and anorthite components in coexisting plagioclase can affect Al incorporation at the T site (Blundy & Holland, 1990; Holland & Blundy, 1994) and can be expressed as BNa + TSi = BCa + IVAl. Results Macroscopic description Quartz diorite has phaneritic structure and is medium- to coarse-grained with a grain size of up to 8 mm (Figure 2a,b). It is heterogeneous both in grain size and in the proportion of indi- vidual minerals. It consists of dark green amphi- boles, light green pyroxene, white feldspars, and greyish quartz. Visually, the green colour domi- nates, which is due to the main minerals, pyrox- ene 4–7 mm in size, and amphiboles up to 8 mm in size. The ratio between the proportion of mafic and salic minerals determined using picture anal- ysis of scanned polished hand specimens is about 4:1 in most cases. Samples are often intersected by pegmatite veins (Fig. 1c,d and Fig. 2c,d). The pegmatite is uniform and medium-grained with a grain size of up to 5 mm. It contains white feld- spars, greyish quartz, a small amount of elongated green amphibole minerals occasionally reaching 5 cm in length, calcite and rare beryl. Table 2. Selected geothermobarometers and their calibrations applied to calculate the P–T conditions of quartz diorite crystallization. Geothermobarometer Estimated uncertainty Reference Abbreviation Clinopyroxene barometer ± 1.70 kbar Nimis & Ulmer (1998) NU98 Clinopyroxene barometer ± 1.10 kbar Nimis (1999) N99 Fe2+–Mg exchange Clinopyroxene thermometer Not reported Dal Negro et al. (1982) DN82 Fe2+–Mg exchange Clinopyroxene thermometer Not reported Molin & Zanazzi (1991) MZ91 Fe2+–Mg exchange Clinopyroxene thermometer Not reported Bertrand & Mercier (1985) BM85 Al-in-Amphibole barometer ± 0.6 kbar Schmidt (1992) S92 Al-in-Amphibole barometer ± 0.6 kbar Anderson & Smith (1995) AS96 Amphibole–Plagioclase thermometer ± 30 °C Blundy & Holland (1990) BH90 Amphibole–Plagioclase thermometer ± 30 °C Holland & Blundy (1994) HB94 Ti-in-Amphibole thermometer ± 25 °C Otten (1984) O84 Biotite thermometer ± 23 °C Luhr et al. (1984) L84 Biotite thermometer ± 24 °C Henry et al. (2005) H05 274 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC Fig. 2. Close-up of the polished surface of a quartz diorite hand specimens. (a) The prevailing green colour of the rock is a result of the com- bination of pale green clinopyroxene and dark green amphiboles. (b) Amphibole replacing pyroxene is forming an uralitic structure. The white minerals are feldspars, and the grey mineral (lower left corner) is quartz. (c, d) Samples are often cut by pegmatitic veins, composed of quartz, feldspars and common elongated amphibole grains. The lower border of each picture measures 12 cm. Fig. 3. (figure caption on next page) 275Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia Petrography and mineral chemistry Under the optical microscope, the rock exhib- its a heterogeneous texture. Clinopyroxene is the dominant mineral, accounting for approximately 35–40% of the rock (Fig. 3). The average grain size of clinopyroxene is 3.4 mm, with the largest crys- tals reaching 7.6 mm. Amphiboles are the second most abundant mineral phase, comprising up to 30% of the sample. Plagioclases makes up 10–15% of the rock, with an average grain size of 1.63 mm and maximum grains reaching 5.6 mm. Potassi- um feldspar (i.e., orthoclase) represents about 10% of the quartz diorite; its average grain size is 1.57 mm, with the largest grains measuring up to 5.2 mm. Minor mineral phases include quartz, biotite, titanite, apatite, magnetite, and epidote group minerals (allanite) with average grain sizes rang- ing from 0.08 mm (apatite) to 1.1 mm (quartz). Together, these minerals account for 10–15% of the sample. Secondary minerals identified include chlorite, and calcite. The remaining microscopic and microchemical characteristics are described below for individu- al minerals. Representative mineral analyses are presented in Table 3. Fig. 3. Microphotographs of quartz diorite. (a) An idiomorphic, twinned clinopyroxene grain surrounded by smaller clinopyroxene and an- hedral quartz grains. Sample C7-3. (b) Amphibole replaces clinopyroxene in an irregular patchy pattern (upper right). Clinopyroxene grains form small clusters enclosed in plagioclase, producing a poikilitic texture. Sample C7-3. (c) Amphibole replacing clinopyroxene completely envelops the grain, producing an uralitic texture. Sample C7-3. (d) An idiomorphic amphibole grain is surrounded by quartz, plagioclase and orthoclase grains. Sample C6-2. (e) Clinopyroxene, quartz and biotite grains enclosed in plagioclase with polysynthetic twins forming a poikilitic texture. Amphibole is visible in the upper-left corner. Sample C8-3. (f) Potassium feldspar (orthoclase) replacing plagioclase forms a myrmekitic texture at their contact. Small apatite inclusions in plagioclase are clearly visible. Sample C3-1. (g) Inclusions of biotite and magnetite occur within amphibole. Sample C5-2. (h) Idiomorphic titanite and amphibole grains surrounded by orthoclase. Sample C10-1. (i) A large allanite grain. Sample C8-3. Abbreviations: Aln–Allanite, Amp–amphiboles, Bt–biotite, Cpx–clinopyroxene, Kfs–potassium feldspar (orthoclase), Mag–magnetite, Pl–plagioclases, Qz–quartz, Ttn–titanite. Crossed polars (a–e, h, i); parallel polars (g); cathodolu- minescence (f). Table 3. Representative microprobe analyses of the main mineral phases identified in quartz diorite. Analyses (in wt%) include amphiboles (Amp), clinopyroxene (Cpx), plagioclases (Pl), potassium feldspar (Kfs), biotite (Bt), chlorite (Chl), and epidote (Ep). Amp IC – Type I am- phibole core, Amp IR – Type I amphibole rim, Amp II – Type II amphibole. Elements in the lower part of the table are calculated values per formula unit, based on the corresponding number of oxygens. An. No. denotes the analysis number. Sample C3-1 C4-1 C4-1 C7-3 C4-1 C7-3 C4-1 C7-3 C3-1 C4-1 C7-3 C7-3 C3-1 C1-1 Mineral Amp IC Amp IC Amp IR Amp IR Amp II Amp II Cpx Cpx Pl Pl Kfs Bt Chl Ep An. No. 12 5 6 4 4 3 2 2 10 9 6 8 5 10 SiO2 44.36 44.35 53.12 51.91 51.91 50.69 54.04 54.23 63.13 61.03 64.36 36.36 28.31 36.94 TiO2 0.99 1.01 0.21 0.30 0.60 0.71 0.24 0.11 0.27 0.00 0.11 2.72 0.05 1.08 Al2O3 10.91 12.71 4.78 5.30 6.04 6.50 1.92 1.42 22.84 25.00 18.91 14.14 19.13 21.76 Cr2O3 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.42 0.00 0.00 0.07 0.00 1.40 FeO 13.69 9.31 6.64 7.13 6.77 7.90 3.38 3.35 0.10 0.11 0.07 21.38 18.66 10.62 MnO 0.50 0.15 0.21 0.17 0.20 0.14 0.12 0.11 0.12 0.02 0.06 0.25 0.39 0.13 MgO 11.63 14.32 18.69 17.97 18.03 17.25 15.36 15.58 0.01 0.00 0.01 11.81 19.61 0.22 CaO 12.21 12.20 12.61 12.67 12.81 12.42 24.05 24.08 4.48 6.25 0.04 0.01 0.09 23.24 Na2O 1.17 1.80 0.49 0.49 0.56 0.55 0.39 0.32 7.52 7.92 0.88 0.07 0.02 0.01 K2O 1.25 0.60 0.26 0.29 0.27 0.39 0.00 0.00 0.35 0.36 14.76 9.83 0.03 0.01 BaO 0.00 0.25 0.00 0.04 0.05 0.06 0.01 0.00 0.00 0.03 1.49 0.00 0.00 0.00 Total 96.77 96.70 97.01 96.27 97.23 96.62 99.49 99.18 99.22 100.73 100.67 96.63 86.29 95.41 Oxygens 23 23 23 23 23 23 6 6 8 8 8 22 28 12.5 Si 6.56 6.39 7.48 7.39 7.31 7.23 1.98 1.99 2.81 2.70 2.98 5.56 2.29 3.08 Ti 0.11 0.11 0.02 0.03 0.06 0.08 0.01 0.00 0.01 0.00 0.00 0.32 0.00 0.07 Al 1.90 2.16 0.79 0.89 1.00 1.09 0.08 0.06 1.20 1.30 1.03 2.54 1.83 2.14 Cr 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.09 Fe3+ 0.51 0.55 0.18 0.21 0.21 0.23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe2+ 1.18 0.58 0.63 0.64 0.61 0.72 0.10 0.10 0.00 0.00 0.00 2.74 1.26 0.74 Mn 0.06 0.02 0.03 0.02 0.02 0.02 0.00 0.00 0.00 0.00 0.00 0.04 0.03 0.01 Mg 2.56 3.07 3.92 3.82 3.79 3.67 0.84 0.85 0.00 0.00 0.00 2.70 2.37 0.03 Ca 1.93 1.88 1.90 1.93 1.93 1.90 0.94 0.95 0.21 0.30 0.00 0.00 0.01 2.08 Na 0.34 0.50 0.13 0.14 0.15 0.15 0.03 0.02 0.65 0.68 0.08 0.02 0.00 0.00 K 0.24 0.11 0.05 0.05 0.05 0.07 0.00 0.00 0.02 0.02 0.87 1.92 0.00 0.00 Ba 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total 15.41 15.38 15.14 15.12 15.15 15.15 3.99 3.99 4.91 5.00 4.97 15.82 7.79 8.24 276 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC Clinopyroxene They occur in hypidiomorphic to idiomorphic forms. They often occur as simple twins (Fig. 3a). In some places, idiomorphic pyroxene grains are clustered in one area (Fig. 3b). They are often overgrown by amphiboles (Fig. 3c), which is a re- sult of the uralitization process. They correspond in composition to diopside (Fig. 4) and have val- ues of XCa = 0.47–0.51, XMg = 0.41–0.49, and XFe = 0.05–0.09. Amphiboles Two types of amphiboles can be distinguished. Type I amphibole occurs as xenomorphic individ- ual grains (Fig. 5a) and only rarely form hypid- iomorphic (Fig. 5b) to idiomorphic shapes (Fig. 3d). Their average size is approximately 4.15 mm. In Type I amphibole core and rim parts have slightly different composition (Fig. 5c). The av- erage core/rim compositions are as follows: XCa = 0.31/0.30, XMg = 0.44/0.56, XFe = 0.25/0.14, and Ti = 0.11/0.03 atoms per formula unit (apfu). Biotite inclusions are very common in Type I amphibole. Type II amphibole replaces clinopyroxene grains (Figs. 3d and 5b), sometimes forming uralitic tex- ture (Fig. 3e). Their average composition corre- sponds to XCa = 0.30, XMg = 0.55, XFe = 0.15, and Ti = 0.06 apfu. According to the nomenclature of Leake et al. (1997) all amphiboles are calcic (BCa>1.5 apfu; with an average Ca content of 1.9 apfu). Type I amphibole cores are classified as magnesiohorn- blende, tschermakite, edenite, pargasite, or mag- nesiohastingsite. Type I amphibole rims are clas- sified as magnesiohornblende and actinolite. All Type II amphibole grains belong to magnesiohorn- blende (Fig. 6). Based on their Al content, amphiboles can be grouped into two distinct clusters, as shown in the graphs in Figure 7. Amphiboles with higher Al content correspond to Type I amphibole cores, while those with lower Al content belong to Type I amphibole r ims and Type II amphibole grains. A positive correlation of Al in T sites with A(Na + K) for both groups indicates the importance of the edenite exchange (Fig. 7a). Only a slight positive correlation between I VAl and CTi indi- cates that the Ti-Tschermak exchange substitu- tion is not signif icant (Fig. 7b). Calcium at the B site shows a slightly positive correlation in the Type I amphibole r ims and Type II amphibole grains and a slightly negative one in the Type I amphibole cores; however, the plagioclase ex- change is insignif icant in both cases (Fig. 7c). The Al-Tschermak substitution is ref lected in Fig. 4. Classification of clino- pyroxene grains in a trian- gular diagram, following Pol- dervaart & Hess (1951). 277Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia Fig. 5. Backscattered electron images of quartz diorite. (a) Type I amphibole grains are often heavily replaced. Together with plagioclase, quartz, and potassium feldspar (orthoclase), they form a paragenesis suitable for Al-in-amphibole barometry. Biotite grain in the centre is partly chloritized (darker parts). Sample C7-3. (b) A large clinopyroxene grain is partly replaced by Type II amphibole. Type I amphibole is hypidiomorphic and has different core and rim compositions. A large plagioclase grain is enveloping numerous smaller clinopyroxene grains forming a poikilitic texture. Sample C4-1. (c) Type I amphibole grains with well-distinguished core (pale–IC) and rim (dark–IR) parts, clinopyroxene, plagioclase, small titanite, and an apatite grain next to plagioclase are visible. Sample C8-3. (d) A large titanite inclusion in clinopyroxene, Type I amphibole, and Type II amphibole replacing clinopyroxene grains. Sample C7-3. Abbreviations: Amp–amphiboles, Bt–biotite, Cpx–clinopyroxene, Kfs–potassium feldspar (orthoclase), Pl–plagioclases, Qz–quartz, Ttn–titanite. Fig. 6. The composition of Type I and Type II amphibole is shown in the calcic amphibole classification diagram (adapted from Leake et al., 1997). Type I amphibole cores, however, no correlation is observed (Fig. 7d). the relationship between V IAl and I VAl and shows a good positive correlation in the Type I amphi- bole r ims and Type II amphibole grains. In the 278 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC Fig. 7. Site occupancies and exchange mechanisms in amphiboles: (a) edenite exchange, (b) Ti–Tschermak exchange, (c) plagioclase ex- change, and (d) Al–Tschermak exchange. Note that scales on the x- and y-axes are not equal. Minor mineral phases Quartz occurs in all samples. It typically oc- curs as small grains, with larger individual crys- tals observed only occasionally. The average grain size is 1.1 mm, and the largest measured grain is 6 mm. Quartz makes up 5–10% of the total rock. It occurs as small inclusions in minerals but mostly forms xenomorphic grains filling the spaces be- tween larger crystals (Figs. 3a and 5a). Biotite is also present among the femic minerals, but in sub- ordinate amounts not exceeding 3%. The average grain size is 0.67 mm, and the largest measured grain is 0.84 mm. It is brown in colour and exhib- its strong pleochroism. It occurs in hypidiomor- phic grains. Biotite most frequently appears as in- clusions in amphiboles (Fig. 3g), or as individual grains (Fig. 5a). It is partly replaced by chlorite (Fig. 5a). Accessory mineral phases include apatite, ti- tanite, and epidote group minerals. Titanite is present as idiomorphic grains (Figs. 3h and 5d). The average grain size is 0.74 mm, and the largest measured grain is 1.4 mm. It usually accounts for 1–2% of the total rock. It often occurs as an in- clusion in plagioclases, orthoclase, clinopyroxene, and amphiboles (Fig. 5c). Apatite occurs as small Feldspars Plagioclases are usually quite homogeneous; however, in some grains, zoning and polysynthetic twinning (Fig. 3e) can be recognised. Occasion- ally, a poikilitic texture is present, where grains of other minerals, such as clinopyroxene, quartz, and biotite, are enclosed within larger plagioclase grains (Fig. 3b). A myrmekitic texture at the boundary between plagioclase and orthoclase may also be observed, formed as a result of reaction between these two minerals (Fig. 3f ). Plagioclases are intermediate in composition, with X Ab = 0.61– 0.73, corresponding to the feldspar series from ol- igoclase to andesine (Fig. 8), with a low proportion of orthoclase (up to ~2.56 mol%). Potassium feldspars are represented by ortho- clase commonly forming characteristic perthitic structure. It mostly fills the spaces between the femic minerals. In some places, orthoclase grains replace plagioclases (Fig. 3f ). The measured com- position of potassium feldspar shows 85.43– 91.72 mol% orthoclase, 8.12–14.32 mol% albite, and 0.16–0.32 anorthite. Some potassium feld- spar grains contain BaO, with an average content of 1.49 wt%. 279Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia grains; the average grain size is 0.08 mm, while the largest measured grain is 0.13 mm. Apatite grains account for up to 1% of the total rock. They occur as rod-shaped grains, often as inclusions in plagioclases, and orthoclase (Fig. 3f ). Epidote group minerals (most probably allanite) are very rare and enriched in REEs (Fig. 3i). Magnetite occurs as small grains included in amphiboles, of- ten accompanied by biotite (Fig. 3g). Secondary minerals are abundant in more in- tensely differentiated and/ or metasomatically al- tered samples and are mainly chlorite replacing biotite and amphibole grains (Fig. 5a) and calcite replacing clinopyroxene and feldspar grains. Geothermobarometry Data selection and validation for geothermobarometric calculations Nimis (1995) developed a crystal-structure– based clinopyroxene barometer. This calibration is restricted to C2/c clinopyroxene crystallized from basaltic melts. Because the alumina content of the parental magma strongly inf luences clinopyrox- ene chemistry, it is not applicable to high-alumina magmas. Later revision by Nimis and Ulmer (1998) produced a new calibration valid only for clinopy- roxene that satisfy the following conditions: (Ca + Na) > 0.5 apfu, Mg/(Mg + Fe2+) > 0.7, and Al2O3/ SiO2 (wt%) < 0.375 (i.e., Al₂O₃ < 18 wt%). All investigated clinopyroxene grains are clas- sified as diopside, which belongs to the C2/c space group, therefore meeting the crystal-structure cri- terion. Furthermore, all the measured clinopyrox- ene grains satisfy the chemical restrictions. (Ca + Na) contents vary between 0.9 and 1.0, Mg/(Mg + Fe2+) values are 0.8–0.9 and Al2O3/SiO2 rang- es from 0.012 to 0.039. Therefore, we find all the measurements to meet the requirements for apply- ing geothermobarometric calculations. The amphibole composition varies not only with pressure, temperature and coexisting miner- al assemblage, but also with oxygen fugacity ( fO2) in melt, which controls the Fe# and Fe3+/FeTOT ra- tios. Spear (1981) and Anderson & Smith (1995) classify Fe# values in the range from 0 to 0.6 as high, between 0.6 and 0.8 as medium, and 0.8 to 1 as low oxygen fugacity. Low fO2 favours the insertion of Fe2+ in the amphibole lattice, which promotes the substitution of Mg by Al during the Tschermak exchange. A low oxygen fugacity therefore leads to high contents of aluminium in amphibole. Therefore, Anderson & Smith (1995) recommends using only amphiboles with Fe# ≤ 0.65. On the other hand, a high fO2 leads to a pre- ferred incorporation of Fe3+ into the lattice, which Fig. 8. Composition of feld- spars shown in the classifi- cation diagram of orthoclase (Or), albite (Ab), and anorthite (An) (adapted from Deer et al., 2001). 280 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC preferably substitutes Al, thus keeping the content of aluminium in amphibole low. Anderson & Smith (1995) recommend using amphiboles with Fe3+/ FeTOT ratio ≥ 0.25, while Schmidt (1992) sets this ratio at ≥ 0.2. Presence of accessory minerals can, according to Ishihara (1977), suggest conditions of oxygen fugacity. Magnetite and titanite in igne- ous rocks point to a high oxygen fugacity, while il- menite indicates a low oxygen fugacity. In general, amphibole crystallizing under high fO2 gives bet- ter and more reliable geothermobarometry results than those growing under low fO2 as experimen- tal calibrations were carried out under medium to high oxygen fugacity (Stein & Dietl, 2001). Measured amphibole grains in our case show different ratios of Fe3+/FeTOT and Fe#, which can be seen in Figure 9. All grains have Fe# well below 0.65, which according to Spear (1981) and Ander- son & Smith (1995) indicates high oxygen fugacity. Fe3+/FeTOT ratio of all grains are within the recom- mended values apart from grains Amp6 (sample C8-3, analysis no. 10) and Amp8 (sample C8-3, analysis no. 16). Therefore, these measurements are excluded from further calculations. However, it is important to stress that the Fe3+ content is based on stoichiometric calculations and not on direct measurements of the amount of Fe3+ and Fe2+ in amphiboles. In addition, magnetite and titanite were found as accessory minerals, which point to high fO2 as well, suggesting the overall suitability of the measured amphibole samples for geother- mobarometry. The empirical biotite thermometer equa- tion of Henry et al. (2005) is strictly valid only for XMg = Mg/(Mg + Fe) = 0.275–1.000 and Ti = 0.04–0.60 apfu calculated on the basis of 22 oxygen atoms, with temperatures in the range 480–800 °C. All our measured biotite grains meet the required criteria (XMg = 0.496–0.799 and Ti = 0.16–0.34 apfu, so we were able to apply the ther- mometer. Clinopyroxene thermobarometry Results of thermobarometric calculations of clinopyroxene are presented in Table 4, where pressures and temperatures of all considered sam- ples are shown, as well as averages and standard deviations of individual thermobarometers. Cal- culated crystallization temperatures using the pressure-uncorrected thermometers of Dal Negro et al. (1982) and Molin & Zanazzi (1991) yielded values of approximately 900 °C. Pressure-depend- ent thermometer of Bertrand & Mercier (1985), calculated at 7 kbar results in lower temperatures, averaging around 842 °C, though with standard deviation of 61 °C. Pressures of crystallization based on barometer of Nimis (1999) result in an average of 7.73 kbar. Temperature corrected barometer of Nimis & Ul- mer (1998) at 900 °C on average shows 6.73 kbar. Standard deviations in calculated pressures are 0.94 and 0.79 kbar for Nimis (1999) and Nimis & Ulmer (1998), respectively. Positions of thermoba- rometers calculated for the representative clinopy- roxene grain Cpx9 (sample C4-1, analysis no. 5) in the P–T diagram are shown in Figure 10. Amphibole thermobarometry Results of thermobarometric calculations using the above-listed thermometers and barometers applied to selected amphiboles are summarized in Table 4. Type I amphibole cores crystallized at av- Fig. 9. Ratios of Fe2+/FeTOT plotted against Fe# [Fe2+/ (Fe2+ + Mg)] for analysed amphiboles. Amp6 (sam- ple C8-3, analysis no. 10) and Amp8 (sample C8-3, analysis no. 16) fall outside the recommended values, so we excluded them from further calculations. 281Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia Table 4. Temperatures T(°C) and pressures P(kbar) calculated for selected clinopyroxene, amphibole and biotite grains. The applied geother- mobarometers are listed in Table 2, along with their corresponding abbreviations. The assumed pressure for the calculation of temperatures with the BM85 thermometer was 7.0 kbar. The assumed temperature for the calculation of pressures with the NU98 barometer was 900 °C. Grain An. No. Sample T(DN82) T(BM85) T(MZ91) P(NU98) P(N99) Clinopyroxene Cpx2 8 C8-3 907 750 906 6.75 7.05 Cpx3 3 C8-3 897 835 904 6.54 7.21 Cpx4 5 C8-3 901 854 905 5.51 6.82 Cpx6 18 C8-3 897 883 904 5.86 7.33 Cpx7 10 C7-3 899 918 904 7.38 8.43 Cpx8 11 C7-3 907 848 906 6.42 7.86 Cpx9 5 C4-1 903 930 906 8.27 9.18 Cpx10 4 C1-1 901 818 905 8.07 8.63 Cpx12 12 C1-1 909 746 907 5.76 7.04 Average 902 842 905 6.73 7.73 Standard deviation 4 61 1 0.94 0.79 T(O84) T(BH90) T(HB94) P(S92) P(AS95) Grain An. No. Sample T(L84) T(H05) Type I amphibole core Biotite Amp2 3 C8-3 669 673 634 6.16 6.23 Bt1 11 C8-3 697 698 Amp 4 5 C8-3 654 674 671 6.33 6.56 Bt2 12 C8-3 674 673 Amp10 18 C8-3 672 673 659 6.47 6.50 Bt3 8 C7-3 638 677 Amp13 10 C7-3 632 695 804 6.69 7.12 Bt4 9 C7-3 658 694 Amp14 11 C7-3 638 668 773 5.60 5.93 Bt5 12 C7-3 651 685 Amp17 5 C4-1 676 688 842 7.26 7.25 Bt6 13 C7-3 695 697 Amp20 4 C1-1 699 664 803 5.56 5.25 Amp22 3 C3-1 711 719 775 7.44 6.86 Amp23 12 C3-1 677 678 654 6.04 6.02 Amp24 13 C3-1 716 705 709 7.44 6.76 Average 675 684 732 6.50 6.45 669 687 Standard deviation 28 18 75 0.70 0.61 24 11 Type I amphibole rim Amp3 4 C8-3 586 605 587 2.08 2.18 Amp5 7 C8-3 599 624 707 2.81 3.03 Amp9 17 C8-3 578 615 587 2.49 2.60 Amp12 4 C7-3 583 591 664 1.22 1.20 Amp18 6 C4-1 571 575 596 0.77 0.61 Amp21 11 C1-1 593 624 696 2.67 2.87 Average 585 606 640 2.01 2.08 Standard deviation 10 20 56 0.83 0.97 Type II amphibole Amp1 2 C8-3 600 616 575 2.67 2.88 Amp7 15 C8-3 607 610 691 1.92 2.08 Amp11 3 C7-3 636 613 649 2.19 2.36 Amp15 3 C4-1 643 629 730 3.57 3.78 Amp16 4 C4-1 621 601 688 1.76 1.92 Amp25 16 C1-1 622 634 758 3.45 3.72 Average 622 617 682 2.59 2.79 Standard deviation 17 12 64 0.77 0.81 282 Tim SOTELŠEK, Simona JARC, Andreja PAJNKIHER & Mirijam VRABEC erage temperatures of 675 °C, 732 °C, and 684 °C calculated by equations of Otten (1984), Holland & Blundy (1994), and Blundy & Holland (1990), respectively. The latter two thermometers are pressure-corrected using pressures derived from Schmidt (1992) and thus considered more relia- ble. Average pressures at the time of equilibrium are calculated to be 6.50 kbar and 6.45 kbar based on barometers of Schmidt (1992) and tempera- ture-corrected Anderson & Smith (1995), respec- tively. Type I amphibole rims show temperatures of 585 °C, 640 °C, and 606 °C based on calibrations of Otten (1984), Holland & Blundy (1994), and Blun- dy & Holland (1990), respectively. Average pres- sures from Schmidt (1992) and Anderson & Smith (1995) are estimated at 2.01 kbar and 2.08 kbar, respectively. These amphiboles show high varia- tions in calculated pressures within both barom- eters used. Standard deviations are 0.83 kbar and 0.97 kbar for Schmidt (1992) and Anderson & Smith (1995), respectively. Consequently, this is also ref lected in the pressure-corrected temper- atures calculated using Holland & Blundy (1994) and Blundy & Holland (1990). Type II amphibole grains show average tem- peratures of 622 °C, 682 °C, and 617 °C, which were determined based on calibrations of Otten (1984), Holland & Blundy (1994), and Blundy & Holland (1990), respectively. Determined average pressures are calculated to be 2.59 kbar and 2.79 kbar with standard deviations of 0.77 kbar and 0.81 kbar using barometers of Schmidt (1992) and Anderson & Smith (1995), respectively. Thermobarometers applied to representative amphibole grains are shown in Figure 10. The Type I amphibole core is represented by grain Amp23 (sample C3-1, analysis no. 12); the Type I amphibole rim, by grain Amp12 (sample C7-3, analysis no. 4); and the Type II amphibole replac- ing clinopyroxene, by grain Amp11 (sample C7-3, analysis no. 3). Crystallization conditions of the Type I amphibole cores are clearly distinguishable from those of the Type I amphibole rims and Type II amphibole grains. On the other hand, pressures and temperatures of the latter two groups are very similar and fall close to the estimated errors of pressure determination, making them indistin- guishable based on calculations alone. Fig. 10. Positions of thermo- barometers for representative clinopyroxene grain Cpx9 (sample C4-1, analysis no. 5), Type I amphibole core – Amp23 (sample C3-1, analy- sis no. 12), Type I amphibole rim – Amp12 (sample C7-3, analysis no. 4), and Type II amphibole replacing clinopy- roxene – Amp11 (sample C7- 3, analysis no. 3). The applied geothermobarometers are list- ed in Table 2, along with their corresponding abbreviations. 283Petrography and geothermobarometry of quartz diorite from Pohorje Mountains, Slovenia Biotite thermometry The analysed biotite grains yielded average temperatures of 669 °C and 687 °C according to the thermometers of Luhr et al. (1984) and Henry et al. (2005), respectively. The calculated temper- atures are shown in Table 4. The measured biotite grains were petrographically associated with Type I amphibole cores. They were in contact with am- phiboles or completely enclosed within Type I am- phibole in the core regions (Fig. 5a, c). Discussion Quartz diorite body is part of the larger PIC; therefore, we should consider its crystallization in the light of the PIC formation. Poli et al. (2020) explain its formation as a series of chemically di- verse melt pulses intruding different crust levels, leading to a variety of observed lithologies. Quartz diorite is considered the first to form from basal- tic melts by cumulus processes. Modelling of the cumulus process of quartz diorite has shown that the most important cumulus mineral was clino- pyroxene, whereas amphiboles plus plagioclases were subordinate (Poli et al., 2020). Our ther- mobarometric calculations show that the clino- pyroxene formed first, at the highest pressures and temperatures ranging from 840–900 °C and 6.70–7.70 kbar. This is consistent with modelled cumulus process as well as with petrographic ob- servations, which indicate that amphiboles crys- tallized later, replacing the early-formed pyroxene and sometimes forming uralitic texture. The first amphiboles to crystallize were Type I amphibole cores. They crystallized at 670–730 °C and 6.45–6.50 kbar. These conditions are consist- ent with calculations of amphiboles crystallization in the less evolved GDT. Poli et al. (2020) deter- mined average temperatures of 666 °C and pres- sures of 6.08 kbar. Similar averages of 695 °C and 6.91 kbar were obtained by Sotelšek (2019). These similarities in pressures and temperatures of am- phiboles from quartz diorite and the less evolved GDT suggest their coeval formation. Temperatures derived from biotite grains and Type I amphibole cores are consistent, confirming the accuracy of the calculations and supporting the interpretation that these amphiboles crystallized contemporane- ously with the less evolved GDT. Type I amphibole rims were formed at lower P–T conditions near 585–640 °C and ~2.00 kbar. Slightly higher conditions of 617–682 °C and 2.59–2.79 kbar were calculated from Type II am- phibole grains. The distinctly different chemical composition of the Type I amphibole rims and the replacement and assimilation of pyroxene by Type II amphibole grains compared to Type I amphibole cores clearly point to their later formation. These results can be related to the emplacement of the shallower parts of the GDT pluton (more evolved granodiorite sensu Poli et al., 2020). Sotelšek (2019) reports pressures from the shallower NW parts of the pluton in the range of 2–3 kbar and temperatures of 635–699 °C, which is compara- ble to the Type I amphibole rims and Type II am- phibole growth conditions. Therefore, amphiboles from these two groups are assumed to have formed contemporaneously with the emplacement of more evolved GDT. Conclusions Based on the presented data, we can relate all observations and calculations to the evolution of the whole PIC. Quartz diorite body formed in several stages recorded in the pressures and tem- peratures of formation of clinopyroxene, amphi- boles, and biotite. Pyroxene grains were the first to form by cumulus processes at 840–905 °C and 6.70–7.70 kbar, followed by Type I amphi- bole cores at 675–730°C and 6.45–6.50 kbar, which corresponds to the formation conditions of the less evolved GDT. 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