7) 58–71www.elsevier.com/locate/lithos

Lithos 95 (200

Formation of magmatic titanite and titanite–ilmenite phase relationsduring granite alteration in the Tribeč Mountains, Western

Carpathians, Slovakia

Igor Broska a,⁎, Daniel Harlov b, Peter Tropper c, Pavol Siman d

a Geological Institute, Slovak Academy of Science, Dúbravská cesta 9, P.O.Box 106, 840 05 Bratislava, Slovak Republicb GeoForschungsZentrum Potsdam, Telegrafenberg 144 73 Potsdam, Germany

c Faculty of Geo-and Atmospheric Sciences, Institute of Mineralogy and Petrography, University of Innsbruck,Innrain 52, A-6020 Innsbruck, Austria

d Geological Survey SR, Mlynská dolina 1, 817 04 Bratislava, Slovak Republic

Received 9 November 2005; accepted 18 July 2006Available online 26 September 2006

Abstract

In this study, formation of titanite, in Carboniferous I-type granites/granitoids from the Tribeč Mountains (Slovakia), and itssubsequent alteration products are described. Titanite occurs in early magmatic differentiates of I-type granites/granitoids. Calculationof model mineral equilibria in the system K2O–CaO–FeO–Al2O3–TiO2–SiO2–H2O–O2 (KCFATSHO) indicates that titanite formsin granites/granitoids as a consequence of a reaction between titanomagnetite, biotite, and anorthite in a fluid-rich environment underrelatively oxidizing conditions, during the later stages of magma crystallisation. Evidence for this reaction can be found in lowtemperature inclusions of Ti-rich magnetite and biotite inclusions in the titanite, as well as in the formation of titanite not onlyinterstitially, but also locally in quartz. The titanite alteration process has lead to the complete replacement of titanite by ilmenite,quartz, REE-bearing epidote, and allanite while preserving the characteristic euhedral, diamond shape of the former titanite.Completely altered titanite grains become optically opaque due to the presence of ilmenite. The formation of REE-bearing epidote andallanite is probably due to the release of REE from the titanite during alteration. This can be explained by model hydration reactionssuch as titanite+anorthite+annite+H2O=ilmenite+clinozoisite+muscovite+quartz. Calculation of mineral equilibria involvingmagmatic precursor minerals, such as plagioclase and biotite, indicate that the formation of ilmenite from titanite requires an influx ofH2O and/or an increase in fO2. Titanite with the highest degree of ilmenite replacement occurs in a strongly mylonitized granite, inwhich the rock-forming minerals have been replaced by sericite, epidote, and chlorite. This breakdown of titanite to ilmenite is acommon phenomenon in some granites from the southwest area of the Tribeč Mountains, indicating widespread late-stage fluidactivity, associated with high fO2 during the subsolidus cooling.© 2006 Elsevier B.V. All rights reserved.

Keywords: Titanite; Ilmenite; Western Carpathian Mountains; Granitoid; Oxygen fugacity; Water fugacity

⁎ Corresponding author.E-mail address: igor.broska@savba.sk (I. Broska).

0024-4937/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.lithos.2006.07.012

1. Introduction

Titanite, CaTiSiO4(O,OH,F), occurs in rocks from awide range of geological environments. These includemainly intermediate, calc-alkalic plutonic rocks or

59I. Broska et al. / Lithos 95 (2007) 58–71

granites with I-type characteristic (e.g. Lee and Silver,1964; Lee et al., 1969; Sawka et al., 1984; Helmy et al.,2004) nepheline syenites, pegmatites, or alpine-typeveins (c.f. Deer et al., 1982); as well as a wide variety ofmetamorphic rocks, most commonly calc-silicates(Gieré and Williams, 1992). When the assemblagetitanite+magnetite+quartz occurs with orthopyroxeneand/or amphibole, relatively high oxygen fugacities areimplied (Wones, 1989). The conditions under whichtitanite crystallises and is stable as well as the importanceof titanite-bearing equilibria have recently been dis-cussed in series of studies (Xirouchakis and Lindsley,1998; Frost et al., 2000; Kunz et al., 2000; Xirouchakiset al., 2001a,b).

The primary structural unit of titanite is representedby chains of corner-sharing TiO6 octahedra and SiO4

tetrahedra, which result in large, irregular, seven-coor-dinated polyhedra enclosing Ca (Deer et al., 1982).Detailed structural refinement of natural titanite indicatesthat Al, Fe2+, and Fe3+ favour domain formation in theoctahedral chains (Zabavnikova, 1957; Ribbe, 1982;Holényi andAnnerstein, 1987; Gieré, 1992), whereas theREE substitute for Ca (Deer et al., 1982). In nature, (Al,Fe3+ +F,OH)⇔ (Ti+O) is the most common substitu-tion for Ti in titanite (Enami et al., 1993). Enami et al.(1993) have also shown that the specific substitution (Al,Fe3+ +OH)⇔ (Ti+O) commonly occurs in titanite fromlow temperature environments, whereas the substitution(Al, Fe3++F)⇔ (Ti+O) predominantly occurs in tita-nite from high temperature rocks. While the naturallyoccurring end-member vuagnatite, CaAlSiO4OH, is che-mically equivalent to the hypothetical Al–OH end-mem-ber of Al-rich titanite, its crystal structure is differentfrom that of titanite. As a consequence, vuagnatite doesnot represent the Al–OH component in titanite solidsolutions (McNear et al., 1976). The Al–F end-memberof titanite, CaAlFSiO4, has a significantly smaller unitcell volume than CaTiSiO5. As a consequence, titanitesolid solutions with high Al–F contents tend to occur inhigh-pressure eclogite facies rocks (Franz and Spear,1985; Enami et al., 1993; Carswell et al., 1996) as well asin high-pressure experiments (Troitzsch and Ellis, 1999,2002; Tropper et al., 2002). These experimentalinvestigations have also revealed that the Al–F compo-nent in the titanite solid solution is not merely a functionof pressure, but also a function of temperature and, mostimportantly, of bulk composition in terms of Al and Ti(Tropper et al., 2002).

Titanite reaction rims on ilmenite have been describedby Harlov et al. (2006) in samples from four metapelitic-and amphibolite-facies terranes. The titanite rims, andhence the stability of titanite (CaTiSiO4O) and Al–OH

titanite, i.e. the hypothetical end member CaAlSiO4OH,are discussed in terms of fH2O–and fO2–involving equi-libria among clinopyroxene, amphibole, biotite, ilmenite,magnetite, and quartz in the systems CaO–FeO/Fe2O3–TiO2–SiO2–H2O–O2 (CFTSH) and CaO–FeO/Fe2O3–Al2O3–SiO2–H2O–O2 (CFASH).

The opposite process, i.e. titanite replacement by aTiO2 phase during later-stage hydrothermal activity, hasalso been observed. For example, pseudomorphs ofanatase after titanite have been described in an allanite-bearing pegmatite near the crest of the Blue RidgeMountains in Roanoke County, Virginia, U.S.A. (Mitch-ell, 1964). These pseudomorphs vary in size up to 4 cm intheir longest dimension, and have the typical wedge-shape of titanite. In general, translucent, dark-colouredtitanite from a wide variety of geological environmentshas been found to be partly replaced by very fine-grainedaggregates of REE-rich minerals such as allanite,monazite, and bastnäsite, in addition to rutile, quartz,calcite, fluorapatite, and chlorite (Pan et al., 1993). Thisalteration typically forms along fractures and boundariesin the titanite during hydrothermal alteration.

The goal of this study is to describe, on the basis oftextural relationships among the mineral phases, themagmatic formation of titanite during the later stages ofI-type granite crystallization and then interpret the sub-sequent subsolidus hydrothermal alteration of thesetitanite grains to pseudomorphs after titanite that containilmenite, quartz, REE-epidote, and allanite.

2. Geological setting

The Tribeč Mountains in Slovakia are part of theWest-Carpathian core mountains. They occur within theTatric unit, which formed during the Palaeozoic and theMesozoic up to the Eo-Alpine orogeny (Plašienka,1997). The Tribeč Mountains are represented by aPalaeozoic crystalline basement (Middle Variscan Unitaccording to Bezák et al., 1997), with a Mesozoic coversequence coupled with a horst structure bounded byNeogene faults (Bezák, 2004). Two granite/granitoidsuites have been distinguished within the granite massifof the TribečMountains (Fig. 1). These include allanite-magnetite-bearing granites/granitoids (granites/grani-toids with I-type affinity) and monazite-ilmenite-bearinggranites/granitoids with S-type characteristics (Petríkand Broska, 1994; Petrík and Kohút, 1997; Kohút et al.,1999). The I-type granite/granitoid suites are thepredominant unit in this mountain chain and titanite isthe dominant accessory mineral. Specifically, they arecharacterized by the presence of plagioclase with An30cores and biotite with Fe / (Fe+Mg) range from 0.43 to

Fig. 1. Geological sketch map of the Tribeč Mountains showing sample locations.

60 I. Broska et al. / Lithos 95 (2007) 58–71

0.51, and TiO2 contents of approximately 2–3 wt.%.Such TiO2 contents are lower than that for biotites fromS-type granites in the same mountain range whichgenerally have TiO2 contents above 4 wt.% (Petrík andBroska, 1994). A subset of these I-type granites/granitoids have been altered under low-temperaturemetamorphic conditions. This has led to the formation ofsecondary mineral assemblages. U/Pb dating of zircongives an intrusion age of 306±10 Ma (Broska et al.,1990).

3. Analytical technique

Polished thin sections of the samples were firststudied by polarized optical microscope. Back scatteredelectron (BSE) imaging was performed on a CAMECASX 100 at the Geological Survey of the Slovak Republicin Bratislava. Operating conditions for electron micro-

probe (EMP) analysis were 15 kV accelerating voltageand 20 nA beam current. Counting times ranged from 10to 40 s for each element. Standards included BaF2 (F),wollastonite (Ca, Si), TiO2 (Ti), Al2O3 (Al), hematite(Fe), apatite (P), MgO (Mg), synthetic REE phosphates(REE+Y), HfO2 (Hf), zircon (Zr), rodonite (Mn), UO2

(U), NaCl (Cl), FeS2 (S), SrTiO3 (Sr), PbS (Pb), andalbite (Na). Detection limits for these elements are asfollows (in wt.%): F: 0.20–0.28; Cl: 0.01; P: 0.02; Th, Y,and Zr: 0.06; REE 0.05–0.1; and other elements: 0.01–0.02.

Fluorapatite was analyzed on a CAMECASX50 at theMuseum of Natural History in London using the sameEMP analytical procedure as described by Williams(1996). Operating conditions were 15 kV, 25 nA beamcurrent with a beam diameter of 1–5 μm, depending onthe apatite grain size. Care was taken in the determinationof F and a PC1 (multi-layer crystal) was used to eliminate

61I. Broska et al. / Lithos 95 (2007) 58–71

the potential interference from the P 3rd-order line.Standards were the same as above.

4. Mineral distribution and chemistry

4.1. Petrography and mineralogy of the investigatedsamples

The samples in this study were collected from I-typegranites/granitoids in the Tribeč mountains which arelocally enriched in titanite (Petrík and Broska, 1994).These include samples T-88, T-70, T-22, and T-14 (Fig. 1),which, in addition to titanite, contain abundant accessoryapatite, allanite, magnetite, epidote, and zircon.

Sample T-88 is an amphibole-biotite tonalite (quartz22 vol.%, plagioclase 57 vol.%, K-feldspar 5 vol.%, biotite13 vol.%, hornblende 0.1 vol.%) from the Zlatno villagearea, 1700 m south-west of Javorov Hill, which belongs tothe lesser evolved granitoid rocks from the TribečMountains. It contains more then 1.5 vol.% titanite andmagnetite. Sample T-70 is a biotite-bearing tonalite (quartz25 vol.%, plagioclase 56 vol.%, K-feldspar 6 vol.%, biotite11 vol.%) from an abandoned quarry near the town ofNitra. It contains more than 1 vol.% titanite in addition tomagnetite. Sample T-22 is an amphibolite-biotite tonalite(quartz 34 vol.%, plagioclase 48 vol.%,K-feldspar 6 vol.%,biotite 10 vol.%), which contains around 1.9 vol.% titanite.It is from an abandoned quarry near the Jelenec–Zlatnoroad. Sample T-14 was taken from a strongly altered(mylonitized) granite located 2 km east of sample T-22 and300 m N from the old quarry next to the Jelenec dam.Plagioclase and biotite in both T-22 and T-14 have beennearly completely altered by the processes of “reactionsoftening”. This means sericitization, saussuritization, andalbitization due to an excessive amount of fluid infiltrationunder low-grade metamorphic conditions. Nomuscovite ispresent in any of the samples, except as low-grade sericite.Samples T-22 and T-14 are notable with regard to theirvariable degrees of superimposed low-grade metamor-phism. Here quartz is characterized by low-temperaturecataclastic flow and crystal-plasticity on the grain bound-ary, or has only undulose extinction. Biotite and plagioclasehave been totally destroyed by penetrating corrosive fluids.Such paragenesis is typical for greenschist-facies meta-morphic conditions. In both samples T-22 and T-14, thebiotites have been chloritised probably at temperatures ofaround 340 °C.

4.2. Titanite and its primary and secondary inclusions

Both magmatic and secondary titanite occur in samplesT-22 and T-70 and, to a relatively lesser extent secondary

titanite, in sample T-88. Primary titanite forms largeeuhedral, wedge-shaped crystals, which locally reach upto 1 mm in diameter (Figs. 2 and 3; Table 1). These occuras discrete grains in the matrix and also occur asintragranular grains, often in close association withmagnetite (Fig. 2A). Occasionally, sectoral zonal titaniteis found, which is indicative of a magmatic origin(Fig. 2B). Primary titanite contains relatively largenumbers of Ti-enriched magnetite (Fig. 2C and D) aswell as occasional biotite (Fig. 2C and E) and fluorapatiteinclusions (Fig. 2A and E). Titanite is found locally asinclusions in late magmatic quartz indicating that itformed during the later stages ofmagmatic crystallization.

Alteration of primary titanite to ilmenite-rich, wedge-shapedpseudomorphs is very characteristic of sample T-22(Fig. 3A, B, C and D). Secondary titanite probably reflectscrystallization during discrete retrogressive events promo-ted by moderate heating or enhanced fluid activity (Corfuand Stone, 1998) and is primarily due to the breakdown ofbiotite (TiO2≈2 wt.%) since there is no primary ilmenitein the rock. Secondary titanite occurs as fine-grainedaggregates (≈50 μm in size) replacing magmatic biotiteand appears to be coeval with chlorite formation (Fig. 3E).It also occurs as veins of tiny aggregates in the biotite(Fig. 3F). Formation of secondary titanite can be sche-matically described by a reaction such as:

Anorthite þ Ti� bearing Annite

¼ Titanite þ Epidote þ Chloriteþ Quartz ð1ÞIn terms of its chemical composition, primary mag-

matic titanite (analyses 101–109, Table 1) differs slightlyfrom secondary titanite (analyses 110–111, Table 1) due,in part, to higher REE contents in the magmatic titanite. Interms of Al and Fe, both titanite types have similaramounts, except for one altered titanite (T-22, anal. 110),in which the Al content is relatively higher. Since Al andFe substitute for Ti on the octahedral site, they show aninverse correlation with Ti. This is in accordance withsubstitutions such as (Al, Fe3++OH, F)⇔ (Ti+O) asshown inFig. 4.Mössbauer spectroscopy indicates that theFe3+ contents are high in the unaltered titanites rangingfrom 60% in sample T-70 to 85% in sample T-88 (Broskaet al., 2004a).

A number of mineral phases occur as inclusions intitanite and genetically, these can be discriminated intominerals from primary and secondary mineral assem-blages. Primarymineral inclusions, representedmainly byzircon, fluorapatite, biotite, and titanomagnetite, havebeen found in titanite from the unaltered granite, i.e.sample T-88. Secondary mineral inclusions includenewly-formed ilmenite, REE-bearing epidote, allaniteand chlorite.

Fig. 2. BSE images of titanite from unaltered tonalites in the TribečMountains. These images include a titanite, magnetite and fluorapatite associationin sample T-70 (A) and sectoral zonality of primary titanite in sample T-88 (B). In sample T-88, a number of inclusions of titanomagnetite and biotitein titanite are present (C). Also shown is a close-up of an exsolved titanomagnetite with ilmenite lamellae (D) and a biotite inclusion (E). Afluorapatite-titanite association is shown in (F).

62 I. Broska et al. / Lithos 95 (2007) 58–71

Fig. 3. BSE images of altered titanites grains from an amphibole-biotite tonalite (sample T-22). These show altered titanite with a inclusion ofbiotite (A and B) as well as secondary REE-rich epidote phases (position 401, 402) (C). Fig. 3D shows a porous titanite with secondary ilmeniteor a strongly altered titanite grain (sample T-14). Breakdown of biotite leads also to the formation of new titanite (E) as well as titanite veins inbiotite (F ).

63I. Broska et al. / Lithos 95 (2007) 58–71

Table 1Representative titanite analyses (in wt.%)

Sample T-70 T-70 T-88 T-88 T-88 T-22 T-22 T-22 T-22 T-22 T-22

Point 101 102 103 104 105 106 107 108 109 110 111

P2O5 0.10 0.09 0.13 0.11 0.09 0.06 0.15 0.01 0.02 0.02 0.07SiO2 29.52 29.97 29.57 28.74 29.09 30.51 29.94 30.96 30.78 30.47 29.95TiO2 36.33 35.66 35.53 34.66 35.26 37.62 36.52 37.59 36.49 34.94 36.04ZrO2 b.d. 0.08 b.d. 0.09 b.d. 0.14 b.d. b.d. b.d. b.d. b.d.HfO2 b.d. 0.25 b.d. 0.45 0.56 b.d. b.d. b.d. 0.23 b.d. b.d.ThO2 b.d. b.d. 0.05 0.04 0.04 b.d. 0.07 0.05 b.d. b.d. b.d.Al2O3 1.05 1.30 1.10 1.14 1.21 1.21 1.10 1.58 1.83 2.31 1.84Y2O3 0.48 0.28 0.49 0.56 0.25 0.09 0.36 b.d. 0.16 b.d. b.d.La2O3 0.18 0.14 0.25 0.31 0.22 b.d. 0.48 b.d. b.d. b.d. b.d.Ce2O3 0.36 0.23 0.36 0.76 0.37 b.d. 0.60 b.d. b.d. b.d. b.d.Pr2O3 0.12 0.24 0.07 0.25 b.d. b.d. 0.18 b.d. b.d. b.d. b.d.Nd2O3 0.86 0.49 0.78 1.39 0.75 0.08 0.84 b.d. b.d. b.d. b.d.Sm2O3 0.11 0.08 0.21 0.24 b.d. b.d. 0.17 0.06 b.d. b.d. 0.11Eu2O3 0.14 b.d. b.d. b.d. 0.13 b.d. b.d. b.d. b.d. b.d. b.d.Gd2O3 0.19 0.19 0.25 0.27 0.09 b.d. 0.36 0.12 0.09 0.12 b.d.Tb2O3 b.d. b.d. 0.08 b.d. b.d. b.d. 0.10 0.11 b.d. 0.09 b.d.Dy2O3 0.07 b.d. 0.23 0.26 0.12 b.d. b.d. 0.11 b.d. b.d. 0.15Ho2O3 0.09 0.06 0.13 b.d. 0.07 0.19 0.07 b.d. b.d. 0.18 0.27Er2O3 0.29 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.08 b.d.Yb2O3 0.18 0.19 0.05 b.d. b.d. b.d. 0.14 0.06 b.d. 0.09 b.d.Lu2O3 b.d. b.d. 0.10 0.12 b.d. 0.06 b.d. 0.33 b.d. b.d. b.d.CaO 27.52 28.32 27.65 27.03 28.57 29.61 27.75 29.87 29.01 29.24 29.87MnO 0.17 0.17 0.14 0.20 0.20 0.03 0.11 0.06 0.13 0.05 b.d.FeOtot 1.36 1.65 1.56 1.52 1.65 0.59 1.45 0.75 0.62 1.58 1.03F b.d. 0.20 1.39 0.21 b.d. 1.28 b.d. b.d. 0.34 0.59 0.37Cl 0.02 b.d. 0.02 b.d. b.d. 0.01 0.02 0.01 0.02 0.02 b.d.Total 99.11 99.59 100.13 98.37 98.66 101.48 100.42 101.71 99.72 99.78 99.70O_F b.d. −0.086 −0.586 −0.088 b.d. −0.538 b.d. b.d. −0.144 −0.248 −0.248O_Cl −0.004 b.d. −0.005 b.d. b.d. −0.003 −0.004 −0.002 −0.004 −0.005 b.d.Total 99.11 99.51 99.54 98.28 98.66 100.94 100.41 101.71 99.57 99.53 99.45Formulae calculated by the method of sum valencies

Position XTh 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Y 0.008 0.005 0.008 0.010 0.004 0.002 0.006 0.000 0.003 0.001 0.001La 0.002 0.002 0.003 0.004 0.003 0.000 0.006 0.000 0.000 0.000 0.000Ce 0.004 0.003 0.004 0.009 0.004 0.000 0.007 0.000 0.000 0.000 0.000Pr 0.002 0.003 0.001 0.003 0.000 0.000 0.002 0.000 0.000 0.000 0.000Nd 0.010 0.006 0.009 0.017 0.009 0.001 0.010 0.000 0.001 0.000 0.000Gd 0.002 0.002 0.003 0.003 0.001 0.000 0.004 0.001 0.001 0.001 0.000Tb 0.000 0.000 0.001 0.001 0.000 0.000 0.001 0.001 0.000 0.001 0.000Dy 0.001 0.000 0.002 0.003 0.001 0.000 0.000 0.001 0.000 0.000 0.002Ho 0.001 0.001 0.001 0.000 0.001 0.002 0.001 0.000 0.000 0.002 0.003Er 0.003 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.000Yb 0.002 0.002 0.001 0.000 0.000 0.000 0.001 0.001 0.000 0.001 0.000Lu 0.000 0.000 0.001 0.001 0.000 0.001 0.000 0.003 0.000 0.000 0.000U 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Ca 0.982 0.992 0.942 0.976 1.014 0.983 0.979 1.014 0.998 0.997 1.025Mn 0.005 0.005 0.004 0.006 0.006 0.001 0.003 0.002 0.003 0.001 0.000Fe2+ 0.017 0.020 0.006 0.006 0.006 0.000 0.000 0.000 0.000 0.000 0.000Sr 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Sm 0.001 0.000 0.001 0.001 0.000 0.000 0.001 0.000 0.000 0.000 0.001Eu 0.002 0.000 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.000 0.002Pb 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Na 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Total 1.062 1.065 1.023 1.077 1.091 1.005 1.062 1.045 1.024 1.047 1.062

64 I. Broska et al. / Lithos 95 (2007) 58–71

Table 1 (continued )

Sample T-70 T-70 T-88 T-88 T-88 T-22 T-22 T-22 T-22 T-22 T-22

Point 101 102 103 104 105 106 107 108 109 110 111

Position YTi 0.910 0.877 0.850 0.878 0.878 0.877 0.904 0.896 0.881 0.836 0.868Zr 0.000 0.001 0.000 0.002 0.000 0.002 0.000 0.000 0.000 0.000 0.000Hf 0.000 0.002 0.000 0.004 0.005 0.000 0.000 0.000 0.002 0.000 0.001Al 0.041 0.050 0.041 0.045 0.047 0.044 0.043 0.059 0.069 0.086 0.069Fe3+ 0.024 0.028 0.040 0.041 0.044 0.017 0.044 0.022 0.019 0.047 0.031Mg 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Total 0.951 0.931 0.891 0.929 0.931 0.923 0.947 0.955 0.952 0.923 0.939

Position ZSi 0.983 0.980 0.941 0.968 0.963 0.945 0.985 0.981 0.988 0.970 0.959P 0.003 0.003 0.003 0.003 0.002 0.001 0.004 0.000 0.000 0.000 0.002S 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Total 0.986 0.983 0.944 0.972 0.966 0.947 0.990 0.981 0.988 0.970 0.961

Position WF 0.000 0.021 0.140 0.022 0.012 0.125 0.000 0.018 0.035 0.059 0.038Cl 0.001 0.000 0.001 0.000 0.000 0.001 0.001 0.001 0.001 0.001 0.000O 0.999 0.979 0.859 0.978 0.988 0.874 0.999 0.982 0.964 0.940 0.962

Note: analyse numbers correspond to Figs. 2 and 3; b.d. = below detection limit.

65I. Broska et al. / Lithos 95 (2007) 58–71

4.2.1. BiotiteBiotite inclusions in titanite most likely originated as

an earlier magmatic phase and titanite is later (Figs. 2Cand 3A,B). Microprobe analysis of biotite inclusions intitanite from sample T-88 show a higher MgO content(approximately 13 wt.%) in comparison to the MgO

Fig. 4. Ti vs. Al+Fe3+ in titanite from this study. The black circlesindicate primary titanite and the open circles indicate secondarytitanite. The stippled line shows the (Al+Fe3++F, OH)⇔ (Ti+O)substitution.

content frombiotite in thematrixwhich is around 11wt.%.The Fe/ (Fe+ Mg) ratio for the biotite inclusions is below0.45, which is slightly lower than the Fe/ (Fe+Mg) ratiofor the interstitial matrix biotite, i.e. Fe / (Fe+Mg), i.e.approximately 0.48. In sample T-22, the Fe/ (Fe+Mg)ratio ranges from 0.44 to 0.50 (Table 2). The higher Mgfraction in the biotite inclusions, compared to grains inthe matrix, is most likely due to its earlier crystallizationand later armouring by titanite. This would suggest thatthe biotite inclusions did not experience the later re-equilibration, which did affect the interstitial biotitegrains. Therefore, the biotite inclusions are interpreted tobe relics of an earlier growth stage, which again impliesa late-stage magmatic origin for the titanite.

4.2.2. Fe–Ti oxides

4.2.2.1. Titanomagnetite. Magnetite and ilmeniteoccur together as composite inclusions in the titanite(Fig. 2C and D Table 3). This suggests that the ilmeniteoriginally comprised an ulvöspinel component in theoriginal titanomagnetite grain, which has subsequentlyunmixed via the oxidation of the ulvöspinel (Budding-ton and Lindsley, 1964) or:

6 UlvPspinel ¼ 6 Ilmenite þ 2Magnetite þ O2 ð2Þ

Titanomagnetite (magnetite-I) also occurs as relic mi-neral inclusions in the titanite indicating the magmatic

Table 2Representative microprobe analyses of biotite (in wt.%)

Sample T-88 T-88 T-88 T-88 T-22 T-22 T-22 T-22

Position In ttn In ttn In matrix In matrix In ttn In matrix In ttn In matrix

Point 301 302 303 304 305 306 307 308

SiO2 38.20 37.45 37.78 37.95 38.70 37.18 38.14 37.88TiO2 1.74 1.69 2.23 2.37 1.34 2.04 1.38 1.47Al2O3 15.41 15.60 15.77 15.83 15.33 16.09 15.99 16.50Cr2O3 0.00 0.03 0.05 0.01 0.00 0.00 0.03 0.01MgO 12.93 12.89 11.27 11.38 12.86 10.99 12.54 11.02CaO 0.11 0.10 0.12 0.07 0.29 0.19 0.35 0.18MnO 0.38 0.38 0.38 0.44 0.28 0.26 0.30 0.30FeOtot 17.52 17.81 18.55 17.97 18.15 19.44 17.60 18.91NiO 0.01 0.04 0.00 0.03 0.00 0.00 0.01 0.00Na2O 0.01 0.03 0.05 0.05 0.04 0.03 0.03 0.03K2O 9.64 9.83 9.61 9.55 9.55 9.49 9.57 9.78F 0.42 0.35 0.35 0.37 0.27 0.19 0.17 0.19Cl 0.06 0.04 0.05 0.05 0.12 0.11 0.18 0.14Total 96.43 96.25 96.20 96.08 96.94 96.01 96.28 96.41O_F −0.18 −0.15 −0.15 −0.15 −0.11 −0.08 −0.07 −0.08O_Cl −0.01 −0.01 −0.01 −0.01 −0.03 −0.02 −0.04 −0.03Total 96.24 96.10 96.04 95.91 96.80 95.91 96.16 96.30Formulae calculated on the basis of 22 oxygen atomsSi 5.727 5.648 5.703 5.718 5.771 5.642 5.717 5.705Ti 0.196 0.192 0.253 0.268 0.150 0.233 0.155 0.166Al4 2.273 2.352 2.297 2.282 2.229 2.358 2.283 2.295Al6 0.450 0.420 0.509 0.530 0.466 0.519 0.541 0.635Cr 0.000 0.003 0.006 0.001 0.000 0.000 0.004 0.001Mg 2.890 2.899 2.537 2.557 2.860 2.486 2.802 2.475Ca 0.018 0.017 0.019 0.011 0.047 0.031 0.056 0.029Mn 0.040 0.040 0.040 0.046 0.029 0.027 0.031 0.031Fe 2.196 2.246 2.342 2.264 2.264 2.467 2.206 2.382Ni 0.001 0.005 0.000 0.004 0.000 0.000 0.001 0.001Na 0.003 0.010 0.014 0.016 0.012 0.009 0.007 0.010K 1.844 1.890 1.850 1.836 1.817 1.837 1.830 1.879Fe / (Fe+Mg) 0.43 0.44 0.48 0.47 0.44 0.50 0.44 0.49

Note: analyse numbers correspond to Figs. 2 and 3.

66 I. Broska et al. / Lithos 95 (2007) 58–71

titanite probably grew in equilibrium or at the expense ofthe titanomagnetite. Magnetite in the matrix (magnetite-II)shows a low Ti content in comparison to those included intitanite.

4.2.2.2. Ilmenite. Ilmenite generally forms continuousrims around the titanite grains as well as fills cracks andpatches in the titanite grains (Fig. 3A, B and C). Locally,ilmenite pseudomorphs after titanite occur in what mightbe termed black pseudomorph “envelope” grains(Fig. 3D). Ilmenite grains, which form pseudomorphsafter titanite, are rich in Mn (up to 0.147 a.p.f.u, Table 3).The calculated hematite component is low (Xhmb0.033).

4.2.3. FluorapatiteFluorapatite texturally occurs in two generations. The

older generation is commonly found as inclusions inbiotite. However, the texturally younger generation forms

discrete, hexahedral crystals both inside and on the grainrim of the primary titanite (Fig. 2A and F). This stronglysuggests contemporaneous formation of fluorapatite withtitanite during the later stages of granite crystallization(Corfu and Stone, 1998).

The fluorapatite inclusions are slightly enriched inS and Cl relative to fluorapatite from other granitic types(Table 4). The REE contents are low and do not exceed0.016 a.p.f.u. The low Mn and Fe and relatively higherS and Cl contents are typical of fluorapatite compo-sitions in granites with I-type affinity (Broska et al.,2004b).

4.2.4. Allanite — REE-bearing epidoteSome titanite grains contain irregularly distributed

REE-rich epidote and small allanite inclusions (Fig. 3C;Table 5). Allanite inclusions in titanite most likelyoriginated from the leaching of REE from the magmatic

Table 3Microprobe analyses of primary Ti-magnetites and its exsolved ilmenite lamellae (No. 201–205) and secondary ilmenites as the breakdown productof titanite (No. 206–211) (in wt.%)

Sample T-88 T-88 T-88 T-88 T-88 T-22 T-22 T-22 T-22 T-22 T-14

min ilm ilm mag mag mag ilm ilm ilm ilm ilm ilm

Point 201 202 203 204 205 206 207 208 209 210 211

SiO2 0.52 0.63 0.16 0.15 0.35 0.23 0.16 0.22 0.22 0.27 0.33TiO2 50.16 50.62 15.79 16.83 5.57 52.29 52.72 52.49 52.36 52.58 51.85Al2O3 0.20 0.32 0.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Fe2O3 3.21 2.69 36.29 33.75 58.00 0.48 0.17 0.41 0.12 0.06 0.15FeO 40.47 40.39 44.02 44.43 36.40 41.39 40.58 41.14 40.86 40.00 43.74MnO 4.33 4.50 1.24 1.18 0.24 5.29 6.30 5.47 5.24 6.91 3.24MgO 0.49 0.68 0.00 0.09 0.00 0.00 0.10 0.00 0.00 0.00 0.00CaO 0.00 0.09 0.06 0.13 0.28 0.43 0.36 0.61 0.92 0.47 0.00K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Cr2O3 0.00 0.13 0.35 0.28 0.10 0.00 0.09 0.00 0.10 0.11 0.00Total 99.38 100.05 98.01 96.84 100.94 100.11 100.48 100.34 99.82 100.41 99.30Si 0.013 0.016 0.006 0.006 0.013 0.006 0.004 0.006 0.006 0.007 0.008Ti 0.953 0.953 0.459 0.494 0.159 0.990 0.994 0.991 0.992 0.992 0.990Al 0.006 0.009 0.005 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Fe3+ 0.061 0.051 1.055 0.992 1.653 0.009 0.003 0.008 0.002 0.001 0.003Fe2+ 0.855 0.845 1.422 1.450 1.153 0.871 0.850 0.863 0.861 0.839 0.929Mn 0.093 0.095 0.041 0.039 0.008 0.113 0.134 0.116 0.112 0.147 0.070Mg 0.018 0.025 0.000 0.005 0.000 0.000 0.004 0.000 0.000 0.000 0.000Ca 0.000 0.002 0.002 0.005 0.011 0.012 0.010 0.016 0.025 0.013 0.000K 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000Cr 0.000 0.003 0.011 0.009 0.003 0.000 0.002 0.000 0.002 0.002 0.000Xilm 0.967 0.973 0.995 0.998 0.996 0.999 0.999 0.999Xhem 0.033 0.027 0.005 0.002 0.004 0.001 0.001 0.001Xusp 0.461 0.493 0.159Xmt 0.539 0.507 0.841

Note: analyse numbers correspond to Figs. 2 and 3.Ferrous and ferric ration calculated according to Droop, 1987.

67I. Broska et al. / Lithos 95 (2007) 58–71

titanite similar to what was observed in the study ofPan et al. (1993). The REE-bearing epidote surroundingthe titanite appears to be a reaction product betweentitanite and the surrounding mineral assemblage, i.e.plagioclase, K-feldspar, and quartz, during late stagesecondary alteration or:

Titanite þ Plagioclase þ K�feldspar þ H2O

¼ REE�bearing Epidote

þ Ilmenite þMuscovite ð3Þ

Some titanite grains contain irregularly distributed,small allanite and REE-bearing epidote grains (Table 5).The REE-bearing epidote contains more than 85% Fe3+,which was estimated on the basis of a diagram of Al vs.REE+actinides (Petrík et al., 1995). The source for therelatively high Fe3+ content in both the REE-bearingepidote and allanite most likely came from the Fe3+

component present in the host titanite.

5. Discussion

5.1. Origin of magmatic titanite

Titanite most likely originated in the KCFATSHO(K2O–CaO–FeO–Al2O3–TiO2–SiO2–O2) system froma model reaction involving biotite, amphibole, K-feldspar, plagioclase, and magnetite or:

7 Actinolite þ 2 K � feldspar þ 3 Titanomagnetite

þ 3 H2O ¼ 3 Titanite þ 2 Annite þ Quartz ð4Þ

where the stoichiometric coefficients for reaction (4) arecalculated using the program REACTION (Spear, 1990,written comm.).

Matrix biotite, in titanite-bearing I-type granitic rocksfrom the Tribeč Mountains, contains significantly lessTiO2 (1–2.5 wt.%; Table 2) than typical biotite (4 wt.%of TiO2) from monazite bearing, or S-type, graniticrocks (Petrík and Broska, 1994). This is because the first

Table 5Microprobe analyses of REE-rich-allanite-epidote solid solution

Sample T-22 T-22

Mineral Aln REE ep

Point 401 402

SiO2 33.22 37.58TiO2 1.08 0.28Al2O3 18.31 22.19FeO 13.54 11.82CaO 17.40 23.73La2O3 3.61 0.00Ce2O3 8.53 1.86Pr2O3 0.83 0.76Nd2O3 3.66 1.31Sm2O3 0.45 0.00Y2O3 0.17 0.47UO2 0.00 0.00Total 100.80 100.00Si (T) 2.969 3.078

68 I. Broska et al. / Lithos 95 (2007) 58–71

biotite equilibrates with titanomagnetite, which hadalready consumed the majority of the Ti from the bulkrock. Ti-enriched magnetite or magnetite-ilmenite pairsare common inclusions in titanite, especially in sampleT-88. Locally, numerous, low Ti magnetite grains arefound only in the vicinity of contemporaneous titanite.This would suggest that both, biotite and titanomagnetite,served as source of Ti for titanite and that the titanite mostlikely originated from a reaction involving biotite, titano-magnetite, and probably an anorthite component in theplagioclase, during deanorthization. Breakdown of rela-tively Mg-enriched biotite was observed in the unalteredgranitic rock sample T-88 (Fig. 2C) as well as in thealtered rock sample T-22 (Fig. 3A and B). Breakdown ofTi-enrichedmagnetite is common in sample T-88 (Fig. 2Cand D). Titanite formation stimulated both high f H2O andhigh fO2, although the more important of these is the

Table 4Microprobe analyses of apatite (in wt.%)

T-88 T-88 T-88 T-22 T-22 T-22

SO3 0.17 0.17 0.12 n.d. n.d. n.d.P2O5 41.20 41.22 41.19 40.80 40.11 40.47SiO2 0.28 0.50 0.30 0.20 0.17 0.31CaO 56.16 56.06 55.79 54.66 55.06 54.37La2O3 0.10 0.13 0.11 0.02 0.20 0.15Ce2O3 0.20 0.29 0.26 0.19 0.15 0.26Nd2O3 0.03 0.10 0.04 0.01 0.02 0.00Al2O3 0.00 0.00 0.00 0.00 0.00 0.00FeO 0.07 0.16 0.08 0.06 0.09 0.28MnO 0.08 0.11 0.08 0.10 0.10 0.09MgO 0.00 0.03 0.00 0.02 0.00 0.01SrO 0.11 0.07 0.09 0.07 0.06 0.10Na2O 0.01 0.02 0.03 0.09 0.07 0.01F 2.95 2.88 2.46 2.83 2.84 2.75Cl 0.18 0.19 0.05 0.06 0.07 0.05OH 0.29 0.32 0.51 0.33 0.32 0.36Total 101.82 102.25 101.10 99.42 99.24 99.20O_F,Cl 1.28 1.26 1.05 1.20 1.21 1.17Total 100.54 100.99 100.06 98.22 98.03 98.04Formulae calculated to 13 oxygen atomsS 0.014 0.013 0.010 n.d. n.d. n.d.P 2.955 2.944 2.977 2.991 2.959 2.979Si 0.024 0.042 0.026 0.017 0.015 0.027Ca 5.097 5.067 5.104 5.071 5.140 5.065La 0.003 0.004 0.003 0.001 0.006 0.005Ce 0.006 0.009 0.008 0.006 0.005 0.008Nd 0.001 0.003 0.001 0.000 0.001 0.000Al 0.000 0.000 0.000 0.000 0.000 0.000Fe 0.005 0.011 0.006 0.004 0.006 0.021Mn 0.006 0.008 0.006 0.007 0.008 0.006Mg 0.000 0.004 0.000 0.002 0.000 0.002Sr 0.005 0.003 0.004 0.003 0.003 0.005Na 0.002 0.002 0.005 0.015 0.012 0.002XApFAp 0.79 0.77 0.66 0.77 0.78 0.76XApClAp 0.03 0.03 0.01 0.01 0.01 0.01XApHAp 0.18 0.20 0.33 0.22 0.21 0.24

Al M(2) 1.000 1.000M(1)+M(3)Ti 0.073 0.017Al 0.929 1.142Fe2+ 1.012 0.810Total 2.013 1.969Ca A(1) 1.000 1.000A(2)Ca 0.666 1.082La 0.119 0.000Ce 0.279 0.056Pr 0.027 0.023Nd 0.117 0.038Sm 0.014 0.000Y 0.008 0.020U 0.000 0.000A(2) 1.230 1.219Total 8.212 8.266

Note: analyses number correspond to Fig. 3, formulae calculated onthe basis of 12.5 oxygen atoms.

increase in fO2, which occurred during the later stages offormation calc-alkaline granite formation (Fig. 5).

Utilizing the REACTION program (Spear, 1990,written comm.), coupled with Schreinemakers projectionin the KCFATSHO system, it is possible to calculate afurther set of titanite-forming reactions, involving phasessuch as biotite, muscovite, K-feldspar, plagioclase, andmagnetite. This leads to the following model reactions:

3Anorthite þ 3K�feldspar þ 3Titanomagnetite

þ 3H2O ¼ 3 Titanite þ 3Muscovite

þ 2Magnetite þ 3 Quartz; ð5Þ

10 Anorthite þ 6 K�feldspar þ 10 Titanomagnetite

þ 6 H2O ¼ 10 Titanite þ 15 Annite

þ 10Muscovite þ 10 Quartz; ð6Þ

Fig. 5. Schematic Schreinemakers diagram, illustrating the formation of titanite in granites involving magmatic minerals such as biotite, K-feldspar,plagioclase, and magnetite in the system KCFATSHO (K2O–CaO–FeO–Al2O3–TiO2–SiO2–O2). The grey-shaded area indicates the range of titanitestability in terms of fO2 and f H2O.Abbreviations.Ann: annite, An: anorthite,Mt:magnetite, TiMt: titanomagnetite, Ilm: ilmenite, ttn: titanite,Mu:muscovite,Qtz: quartz.

69I. Broska et al. / Lithos 95 (2007) 58–71

and

5 Anorthite þ 5 Annite þ 5 Titanomagnetite þ 5O2

¼ 5 Titanite þ 5Muscovite

þ 3Magnetite þ 5 Quartz ð7Þ

Here, muscovite also takes form of sericite in pla-gioclase. Reactions (5)–(7) constrain the stability oftitanite in these rocks in terms of f H2O and fO2, similarto what was discussed in the study of Harlov et al.(2006). Fig. 5 shows that ilmenite formation is facilitatedby high f H2O as well as high fO2. These reactionsindicate that the breakdown of Ca-amphibole (oranorthite)+ titanomagnetite resulted in a high Ti and Caactivity environment which allowed for the subsequentformation of titanite. This is the reason why titanite is atypical accessory mineral in I-type granites/granitoids(cf. Thieblemont et al., 1988; Force, 1991).

That titanomagnetite could have been served as asource of Ti during the formation of titanite is shown byreactions (5) and (7). This is supported by the relativelyhigh amount of Ti-enriched magnetite in these rocks asarmoured inclusions in the titanite itself. The new mag-netite most likely grew, along with titanite, from thedecomposition of biotite, titanomagnetite, and anorthite.

Application of the titanomagnetite-ilmenite thermometer/oxygen barometer of Andersen and Lindsley (1988) andGhiorso and Sack (1991) yields temperatures of 550–600 °C and a log fO2 of approximately −13, which agreeswell with the log fO2 estimated using the titanite oxygenbarometer of Wones (1989). At 550–660 °C, log fO2=− 13 falls about half way between the fayalite–magnetite–quartz (FMQ) and hematite–magnetite (HM) buffers.

5.2. Alteration of magmatic titanite

Partial replacement of titanite by ilmenite is seen insamples T-22 and T-14, which have experienced somealteration (Fig. 3)). This process is most likelyassociated with the sericitization of plagioclase andchloritization of biotite in the matrix, which took placeunder reducing conditions, since formation of ilmenitewould involve Fe2+ as opposed to Fe3+. It is alsoprobable that the porosity observed in the altered titaniteoccurred during ilmenite formation, as a product of theassociated volume change coupled with a dissolution–reprecipitation processes (cf. Putnis, 2002).

The process of titanite breakdown to ilmenite can ideallybe described by model reactions involving magmaticphases such as biotite, plagioclase, and magnetite in the

70 I. Broska et al. / Lithos 95 (2007) 58–71

system KCFATSHO (K2O–CaO–FeO–Al2O3–TiO2–SiO2–O2:

3 Titanite þ 13 Anorthite þ Annite þ 4 H2O

¼ 3 Ilmenite þ 8 Clinozoisite

þMuscovite þ 5Quartz ð8Þ

6 Titanite þ 18 Anorthite þ 2Magnetite þ 6 H2O

¼ 6 Ilmenite þ 12 Clinozoisite

þ 6 Quartz þ O2ð9Þ

These reactions show that ilmenite formation is alwaysassociated with the hydration of the primary assemblage.Reaction (9) indicates that ilmenite is more stable thantitanite under reducing conditions. Reaction (8) alsoallows for the formation of sericite in plagioclase.Sericitization of plagioclase, as well as the breakdownof magmatic biotite, was observed in both, the unalteredgranitic rock sample (T-88) as well as in the altered rocksamples (T-22 and T-14). One titanite analysis from analtered sample (T-22) is enriched in the Al+Fe3+

substitution (Table 1), indicates that the (Al, Fe3+)+(F,OH) component can also increase during the alteration oftitanite according to the model reaction:

3 Titanite þ 5 Anorthite þ Anniteþ 4 H2O

¼ 8 Al–OH Titaniteþ 3 Ilmenite

þMuscovite ð10ÞExperimental and thermodynamic calibration of

titanite-involving reactions, such as (4)–(10), couldpotentially be used as a tool for the estimation of the P–T–fO2–f H2O conditions present during post-magmaticalteration of the titanite-bearing granitic and granitoidhost rocks. In the case of the titanite-bearing granites andgranitoids from the Tribeč Mountains, P–T conditionswere probably low to medium grade as estimated indi-rectly from surrounding crystalline basement rocks(Krist et al., 1992; Zatko and Broska, 1996). The pre-sence of a high a(H2O) corrosive fluid under reducingconditions appears to have played a significant roleduring subsequent fluid/rock overprinting. In the case ofthe Tribeč Mountains, this alteration process probablytook place contemporaneously during shear zone defor-mation and subsequent rapid uplift.

Acknowledgements

The research has been supported by Grant VEGASAV #4097 to I. Broska. Constructive manuscript re-views by D. Xirouchakis and H.J. Förster are gratefullyappreciated.

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