Rutile and Its Applications in Earth Sciences

Earth-Science Reviews 102 (2010) 1–28

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Rutile and its applications in earth sciences

Guido Meinhold

CASP, University of Cambridge, West Building, 181a Huntingdon Road, Cambridge CB3 0DH, UK article info abstract

Article history: Rutile is the most common naturally occurring titanium dioxide polymorph and is widely distributed as an Received 5 August 2009 accessory mineral in metamorphic rocks ranging from greenschist to eclogite and granulite facies but is also Accepted 7 June 2010 present in igneous rocks, mantle xenoliths, lunar rocks and meteorites. It is one of the most stable heavy Available online 12 June 2010 minerals in the sedimentary cycle, widespread both in ancient and modern clastic sediments. Rutile has a wide range of applications in earth sciences. It is a major host mineral for Nb, Ta and other high Keywords: field strength elements, which are widely used as a monitor of geochemical processes in the Earth's crust and rutile mineral geochemistry mantle. Great interest has focused recently on rutile geochemistry because rutile varies not only by bulk geothermometry composition reflected, for instance, in its Cr and Nb contents but also by the temperature of crystallisation, oxygen isotopes expressed in the Zr content incorporated into the rutile lattice during crystallisation. Rutile geochemistry and geochronology Zr-in-rutile thermometry yield diagnostic data on the lithology and metamorphic facies of sediment source thermochronology areas even in highly modified sandstones that may have lost significant amounts of provenance information. – Lu Hf isotopes Rutile may therefore serve as a key mineral in sediment provenance analysis in the future, similar to zircon, which has been widely applied in recent decades. Importantly, rutile from high-grade metamorphic rocks can contain sufficienturaniumtoallowU–Pb geochronology and (U–Th)/He thermochronology. Furthermore, in situ Lu–Hf isotope analysis of rutile permits insights into the evolution of the Earth's crust and mantle. Besides that, rutile is also of great economic importance because it is one of the favoured natural minerals used in the manufacture of white titanium dioxide pigment, which is a major constituent in various products of our daily life. Heavy mineral sands containing a significant percentage of rutile are therefore the focus of exploration worldwide. This paper aims to provide an overview of the applications of rutile in earth sciences, based on a review of data published in recent years. After giving a summary of various rutile-bearing lithologies, the focus lies on rutile geochemistry, Zr-in-rutile thermometry, O isotope analysis, U–Pb geochronology, (U–Th)/He thermochronology and Lu–Hf isotope analysis. A final outline of the economic importance of rutile highlights the demand for further rutile-related research in earth sciences. © 2010 Elsevier B.V. All rights reserved.

Contents

1. Introduction ...... 2 2. Physical properties and geochemical composition ...... 3 2.1. General description ...... 3 2.2. Crystal structure...... 4 2.3. Crystal chemistry ...... 5 3. Occurrences ...... 6 3.1. Rutile in metamorphic rocks ...... 6 3.2. Rutile in igneous rocks and mineralisation ...... 8 3.3. Rutile in sedimentary rocks ...... 9 3.4. Rutile in extraterrestrial rocks ...... 9 4. Applications of rutile in earth sciences ...... 10 4.1. Rutile geochemistry ...... 10 4.1.1. Introduction ...... 10 4.1.2. Fe content ...... 10 4.1.3. Nb and Ta contents ...... 10

E-mail address: [email protected].

4.1.4. Cr and Nb contents ...... 11 4.1.5. Other trace elements ...... 11 4.1.6. Examples ...... 12 4.2. Zr-in-rutile thermometry ...... 13 4.2.1. Introduction ...... 13 4.2.2. Examples ...... 14 4.2.3. Zr diffusion ...... 14 4.3. Oxygen isotopes ...... 15 4.3.1. Introduction ...... 15 4.3.2. Examples ...... 16 4.4. U–Pb geochronology ...... 16 4.4.1. Introduction ...... 16 4.4.2. Examples ...... 17 4.4.3. Pb diffusion ...... 19 4.5. (U–Th)/He thermochronology ...... 19 4.5.1. Introduction ...... 19 4.5.2. Examples ...... 19 4.6. Lu–Hf isotopes ...... 20 4.6.1. Introduction ...... 20 4.6.2. Examples ...... 21 5. Economic importance of rutile...... 21 5.1. Introduction ...... 21 5.2. Economic importance ...... 22 6. Summary ...... 23 Acknowledgements ...... 23 References ...... 23

1. Introduction al., 2006; Zack and Luvizotto, 2006; Baldwin and Brown, 2008; Luvizotto and Zack, 2009). Moreover, rutile geochemistry combined

With an estimated TiO2 concentration of about 0.7 wt.% (Rudnick with Zr-in-rutile thermometry can help to constrain the sediment and Fountain, 1995), titanium is the ninth most abundant element of the provenance and has therefore already been applied successfully to Earth's continental crust. The most important titanium minerals are sedimentary strata from the Precambrian to the Holocene worldwide rutile (TiO2), ilmenite (FeTiO3) and titanite (CaTiSiO5)(Figs. 1 and 2). (e.g. Zack et al., 2004b; Stendal et al., 2006; Triebold et al., 2007; Rutile is an accessory mineral in a variety of metamorphic and igneous Meinhold et al., 2008; Morton and Chenery, 2009). rocks and occurs as a detrital mineral in clastic sediments. Although the Rocks exposed on the Earth's surface are prone to weathering and main formula of rutile is TiO2, there are commonly several possible erosion. These processes have continuously modified the Earth's substitutions for titanium, for example, Al, V, Cr, Fe, Zr, Nb, Sn, Sb, Hf, Ta, surface for probably more than 3.9 billion years producing clastic WandU(e.g.Graham and Morris, 1973; Hassan, 1994; Fett, 1995; sediments. Some of the key pieces of evidence for that may record Murad et al., 1995; Smith and Perseil, 1997; Rice et al., 1998; Zack et al., detrital zircons as old as 4.4 Ga from metaquartzites and metaconglo- 2002; Bromiley and Hilairet, 2005; Scott, 2005; Carruzzo et al., 2006). merates of the Yilgarn Craton, Western Australia (Mojzsis et al., 2001; Variations in the geochemical composition are host rock specificand Wilde et al., 2001). Clastic sediments are composed of various minerals allow the rutile source to be traced and the chemical and physical (e.g. quartz, feldspar and mica) and lithic fragments and additionally properties during rutile formation to be characterised. contain a minor amount of heavy minerals. The sediment composition Great interest has focused on rutile geochemistry, because rutile is is primarily affected by the mineralogy of the primary source rock and a major host mineral for high field strength elements (HFSE), amongst by a complex set of parameters such as weathering, transport, others Nb and Ta, which are widely used as geochemical fingerprints deposition and diagenesis that modify the sediment during the of geological processes such as magma evolution and subduction- sedimentary cycle (e.g. Morton, 1985; Morton and Hallsworth, 1999). zone metamorphism (e.g. Foley et al., 2000; Rudnick et al., 2000). For Besides whole-rock petrography and heavy-mineral analysis, many years, the significance of Nb and Ta concentrations and Nb/Ta geochemical studies of whole rock and specific detrital minerals are values of crustal and mantle rocks and the Earth's hidden suprachon- powerful tools in provenance characterisation. Understanding clastic dritic Nb/Ta reservoir have been the subject of a lively debate (e.g. sediment provenance is important for exploration of mineral Green, 1995; Foley et al., 2000; Rudnick et al., 2000; Kalfoun et al., resources, basin analysis and palaeotectonic reconstructions. The 2002; Zack et al., 2002; Xiao et al., 2006; Miller et al., 2007; Aulbach et most common heavy minerals such as zircon, tourmaline, garnet and al., 2008; Baier et al., 2008; Bromiley and Redfern, 2008; Schmidt et chrome spinel have long been used as provenance indicators by virtue al., 2009). of their geochemical and isotope signatures (e.g. Morton, 1991; von Besides that, the Cr and Nb contents of rutile allow discrimination Eynatten and Gaupp, 1999; Morton et al., 2004, 2005; Mange and between various rutile source lithologies such as metapelitic rocks Morton, 2007). The exception is rutile, which received only minor (e.g. mica-schists, paragneisses and felsic granulites) and metamafic attention until 2002 (Götze, 1996; Preston et al., 1998, 2002). rocks (e.g. eclogites and mafic granulites) (Zack et al., 2004b; Triebold However, rutile geochemistry, geothermometry and geochronology et al., 2007; Meinhold et al., 2008). Furthermore, the incorporation of yield diagnostic data on source-rock lithology and metamorphic facies Zr into the rutile crystal lattice has a strong dependence on even in highly modified sandstones that may have lost significant temperature and pressure, which has allowed the development of amounts of provenance information. Rutile may therefore serve as a Zr-in-rutile geothermometers (Zack et al., 2004a; Watson et al., 2006; key mineral in sediment provenance analysis in the future, similar to Tomkins et al., 2007). Several studies have already shown that Zr-in- zircon, which has been widely applied in recent decades. rutile thermometry is an attractive method to calculate temperatures Studying the geochemical and physical parameters of rutile is not of high-grade and ultrahigh-grade metamorphic rocks (e.g. Spear et only of scientific value. Rutile is an economically important mineral G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 3

Fig. 2. Theoretical TiO2 content in various Fe–Ti oxide phases (modiﬁed from Reyneke and Wallmach, 2007). Titanite, a calcium titanium silicate, is shown for comparison.

Both methods are evaluated in unravelling specific source characteristics and in use as a chemostratigraphic indicator. Furthermore, oxygen isotope analysis using the quartz–rutile mineral pair is discussed. In the past, powerful new analytical methods such as in situ U–Pb and Hf isotope analyses have been developed, which significantly contribute to unravelling the geological history of natural rutile and its host lithologies and are therefore addressed here too. Finally, Section 5 summarises the economic importance of rutile and shows the need for further rutile-related scientific research.

Fig. 1. Transmitted light photomicrographs showing rutile crystals (a) in eclogite from the Cabo Ortegal complex, NW Spain (Harker Collection no. 146227) and (b) in mafic 2. Physical properties and geochemical composition granulite from the Saxonian Granulite Massif, Germany (Harker Collection no. 26002). © 2009. Sedgwick Museum of Earth Sciences, University of Cambridge. The 2.1. General description photomicrographs were taken by the author and are reproduced with permission. Mineral abbreviations (Kretz, 1983) are as follows: Cpx — clinopyroxene, Grt — garnet, Rt — rutile, and Zo — zoisite. Abraham Gottlob Werner created the name rutile (Ludwig, 1803), which he assigned to a mineral originally known as “red schorl”. The first description of “red schorl” is commonly attributed to Romé de because of its use in the manufacture of white titanium dioxide l'Isle (1783); however, von Born (1772), as pointed out by Papp pigment (Stanaway, 1994; Korneliussen et al., 2000), which is a (2007), already mentioned “red schorl” a few years earlier. Klaproth component in products of our daily life such as paint, paper, plastics, (1795) used “red schorl” (rutile) for the description of the element toothpaste and sunscreen cream (Pearson, 1999; Carp et al., 2004; titanium, which he named after the Titans of Greek mythology. Note Gambogi, 2008). Mineral sands containing large percentages of rutile that William Gregor originally discovered titanium (which he named are therefore a focus of exploration worldwide (e.g. Goldsmith and menackanite) in ilmenite in 1791 (Trengove, 1972). Force, 1978; Force, 1991; Pirkle et al., 2007; Schlüter, 2008). Although it has long been thought that Horcajuelo (also called Recently, the search for secondary standards of natural rutile to Cajuelo) in the province of Burgos in Spain is the type locality of rutile, assess measurement methods and demonstrate the quality of a thorough study by Papp (2007) has recently revealed that the type acquired geochemical data (Luvizotto et al., 2009b) has also been a locality of rutile is Revúca in Slovakia. focus of scientific study. Hence, the scope of this paper is to provide an The name “rutile” is derived from the Latin rutilus because of the overview of the applications of rutile in earth sciences, introduced deep red colour observed in some specimens in transmitted light. with an outline of the physical properties and geochemical compo- Rutile can be translucent or opaque. Yellowish and brownish colours sition of rutile and a brief overview of various source lithologies for are also very common. A rarity is natural rutile with blue colour, rutile. The latter part is relative brief because Force (1991) already which has only been described so far as needle-like inclusions in gave a comprehensive overview of specific rutile sources, except for garnet from ultrahigh-pressure metasedimentary rocks of the Greek extraterrestrial material. Rhodope Massif (Mposkos and Kostopoulos, 2001). In reflected light The current paper has the following structure: Section 1 states the rutile with bluish colour has been reported from several meteorites objectives of this work; Section 2 presents a review of the physical (El Goresy, 1971). The blue colour of meteoritic rutile may be due to a properties and geochemical composition of natural rutile and other stoichiometric deficiency of oxygen in the rutile structure (El Goresy,

TiO2 polymorphs; Section 3 provides an overview of possible source 1971). Experiments on synthetic rutile have shown that blue colours lithologies including metamorphic rocks, igneous rocks, mineralisa- occur in rutile samples grown or annealed under reducing conditions tion, sedimentary rocks and extraterrestrial rocks; Section 4 discusses (Bromiley and Hilairet, 2005). Khomenko et al. (1998) demonstrated the applications of rutile geochemistry and Zr-in-rutile thermometry. that the colour of blue rutile is mainly due to intervalence charge 4 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

Fig. 4. Structure of rutile (after Baur, 2007) approximately parallel [100], rotated by 4° around [001] and 8° around [010]. (a) Perspective view; one unit cell. (b) Perspective polyhedral view; three unit cells in [001] direction, corner sharing between two octahedral rutile type chains. Fig. 3. Ternary system FeO–Fe2O3–TiO2 showing the major high-temperature solid- solution series magnetite–ulvöspinel, haematite–ilmenite, pseudobrookite–ferropseudobrookite (modiﬁed from Buddington and Lindsley, 1964). Phases were plotted on mole percentage basis. Rutile crystallises in the tetragonal space group P42/mnm and is the most common phase, with unit cell parameters a=4.594 Å and c=2.959 Å for pure rutile (Baur, 1956)(Table 1). Natural rutile, 3+ 4+ transfer between Ti and Ti ions on adjacent interstitial and however, commonly contains various trace elements such as Nb, V octahedral sites (see Bromiley and Hilairet, 2005). and Fe, as outlined in Section 2.3, and hence has distinctly higher unit −3 −3 Rutile has a density of 4.23 g cm , but can range up to 5.50 g cm cell parameters (e.g. Černý et al., 1999). The structure of pure rutile is (Deer et al., 1992), and thus belongs to the heavy mineral suite, which shown schematically in Fig. 4. In the unit cell, each Ti4+ ion is −3 are minerals with density N2.8 g cm .Rutileiscommonlydiamagnetic surrounded by six oxygens at the corners of a slightly distorted, (non-magnetic), and therefore, it can easily be separated from the regular octahedron while each oxygen surrounded by three Ti4+ ions paramagnetic (weakly magnetic) and ferromagnetic (strongly magnet- is lying in a plane at the corners of an approximately equilateral ic) heavy mineral fraction using the Frantz isodynamic separator (Buist, triangle (Deer et al., 1992; Baur, 2007). Baur (2007) gives a more 1963a). However, rutile can also contain a high proportion of Fe making detailed crystallographic description. it magnetic, and hence it could remain in the magnetic heavy mineral Rutile is a high-pressure and high-temperature polymorph and is fraction (Buist, 1963a; Hassan, 1994). Bramdeo and Dunlevey (2000) isostructural with stishovite, a high-pressure silica polymorph (Fig. 5). mentioned anomalous behaviour of detrital rutile (due to substitution of Stishovite is a major phase in subducting oceanic crust under lower 4+ cations other than Ti in the rutile crystal lattice; Fig. 8)during mantle conditions (Ono et al., 2001) and has also been described from industrial magnetic and electrostatic mineral separation, which can impact-related rocks (Chao et al., 1962) and meteorites (Sharp et al., cause rutile loss. Recent studies show that Co-implanted rutile can 1999). The behaviour of rutile at high and ultrahigh pressures become ferromagnetic (Akdogan et al., 2006). The melting point of pure therefore offers an analogy to explore post-stishovite phase transitions rutile is around 1825–1830 °C (MacChesney and Muan, 1959; Deer (El Goresy et al., 2001; Bromiley et al., 2004). The low-temperature et al., 1992). Note that synthetic rutile can be produced by heating a polymorphs of titanium dioxide are anatase (tetragonal) and brookite solution of TiCl4 to 950 °C or by heating anatase to above 730 °C (Deer (orthorhombic). Under relatively low temperatures and pressures, et al., 1992). rutile is metastable with respect to anatase when the TiO2 crystal size is less than ∼14 nm, because the surface energy of rutile is then much 2.2. Crystal structure higher than that of anatase (see Smith et al., 2009 for discussion). Besides rutile, anatase and brookite, there are at least three

In nature, titanium dioxide mainly occurs in three structural additional TiO2 polymorphs (Table 1). The TiO2(B) polymorph has a states: rutile, anatase and brookite (Fig. 2). Together they form the structure closely related to that of VO2(B) (Marchand et al., 1980), the TiO2 end-member of the ternary system FeO–Fe2O3–TiO2 (Fig. 3). TiO2(II) polymorph has an α-PbO2-type structure (Simons and

Table 1

Physical parameters of selected TiO2 polymorphs.

Rutile Anatase Brookite TiO2(B) TiO2(II) TiO2(H) Density (g cm− 3) 4.23–5.5 3.82–3.97 4.08–4.18 3.64 4.33 3.46 Crystal system Tetragonal Tetragonal Orthorhombic Monoclinic Orthorhombic Tetragonal

Space group P42/mnm I41/amd Pbca C2/m Pbcn I4/m Unit cell parameters (Å) a=4.594 a=3.785 a=9.184 a=12.16 a=4.59 a=10.18 c=2.959 c=9.514 b=5.447 b=3.74 b=5.44 c=2.97 c=5.145 c=6.51 c=4.94 β=107.29°

Comment VO2(B)-related structure α-PbO2-type structure Hollandite-type structure Reference (1) (2) (3) (4) (5) (6)

References: (1) Cromer and Herrington (1955), Baur (1956), Deer et al. (1992); (2) Cromer and Herrington (1955), Deer et al. (1992); Howard et al. (1991); (3) Baur (1961), Deer et al. (1992); (4) Marchand et al. (1980); (5) Simons and Dachille (1967), Hwang et al. (2000); (6) Latroche et al. (1989). G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 5

1965) and reﬂected light microscopy (Mader, 1980) have to be used. The most reliable technique to identify mineral polymorphs is laser micro-Raman spectroscopy. A compilation of Raman bands for the

three major structural TiO2 polymorphs is shown in Fig. 6. Rutile can be identiﬁed by bands at wavenumbers 143, 247, 447 and 612 cm− 1 (Porto et al., 1967; Tompsett et al., 1995) and anatase by bands at wavenumbers 144, 197, 400, 516 and 640 cm− 1 (Ohsaka et al., 1978). Brookite is characterised by several bands. Strong bands are at wavenumbers 153, 247, 322 and 636 cm− 1 (Tompsett et al., 1995).

2.3. Crystal chemistry

Presently, analysis of rutile can be routinely performed by sophisticated techniques such as electron microprobe (EMP), proton microprobe (PIXE) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) so that differences in geochemical composition can easily be identified (Fig. 7). The disadvantage of the LA-ICP- MS technique is that it makes a crater often several tens of micrometres in diameter whereas the first two techniques are nondestructive to the sample, but they have higher detection limits (especially EMP) for the concentration of certain elements compared with LA-ICP-MS facilities. For very tiny rutile crystals analysed in thin sections, it is recommended that the Si content is measured in order to identify beam interferences with adjacent silicate minerals (Carruzzo et al., 2006; Baldwin and Brown, 2008). Smith and Perseil (1997) considered Si substitution in rutile as “highly contentious at non-ultrahigh pressure” and thus if Si is detected in rutile of non-ultrahigh- pressure rocks it is likely to be due to analytical error, microinclusions, or introduction into defective parts of the crystal structure (Smith and Perseil, 1997). Moreover, very fine zircon lamellae can occur in rutile (Schmitz and Bowring, 2003; Downes et al., 2007), which may cause

Fig. 5. Pressure–temperature diagram (after Okamoto and Maruyama, 2004; Baldwin et al., 2004). Phase boundaries for rutile and TiO2(II) are based on phase equilibrium experiments, nominally dry synthesis experiments and reference data (after Withers et al., 2003). A range of geotherms is also shown. Abbreviations: GS, greenschist facies; AM, amphibolite facies; GR, granulite facies; BS, blueschist facies; EC, epidote facies.

Dachille, 1967) and the highly metastable TiO2(H) polymorph has a hollandite-type structure (Latroche et al., 1989). For several decades, the last two were only known from synthetic polymorphs. However, Hwang et al. (2000) described an epitaxial (about 8 nm thick) slab of the TiO2(II) polymorph between twinned rutile bicrystals as inclusion in garnet of diamondiferous quartzofeldspathic rocks from the

Saxonian Erzgebirge, Germany, which was the ﬁrst natural TiO2(II) polymorph found on Earth. This occurrence was explained by Hwang et al. (2000) to have formed during ultrahigh-pressure prograde metamorphism close to the rutile–α-PbO2 phase boundary in the diamond stability ﬁeld at depths of at least 130 km. The rocks containing this TiO2(II) polymorph may have equilibrated at pressures in excess of 70 kbar (Withers et al., 2003)(Fig. 5). Another natural TiO2(II) polymorph was reported in omphacite from a coesite- bearing eclogite in the Dabie Mountains, China (Wu et al., 2005). Wu et al. (2005) suggested subduction of continental material to depths of over 200 km. El Goresy et al. (2001) discovered a natural shock- induced TiO2(II) polymorph from shocked garnet–cordierite–silli- manite gneiss clasts of the Ries crater, Germany. Its petrographic setting is entirely different from that of the epitaxial slab in the Saxonian diamondiferous gneisses (see description in El Goresy et al.,

2001 for further details). Another natural shock-induced TiO2(II) polymorph has been identiﬁed in breccias from the Chesapeake Bay impact structure in Virginia, U.S.A. (Jackson et al., 2006).

Because the mineral polymorphs of TiO2 cannot be distinguished by their geochemical composition other identification methods such Fig. 6. Raman spectra of the TiO2 polymorphs rutile, anatase and brookite. as X-ray diffraction (Spurr and Myers, 1957; Raman and Jackson, Wavenumbers of main Raman bands are indicated (see text for explanation). 6 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 elevated Zr contents if such zircon lamellae-rich rutiles are analysed. Thus, rutile measurements with Si contents N300 ppm showing abnormally high Zr contents should be excluded from the data set (see Zack et al., 2004a; Luvizotto and Zack, 2009 for further discussion). Rutiles from diamondiferous kyanite-bearing eclogites can contain elevated Al contents, which can be explained by several tiny rods of corundum (Sobolev and Yefimova, 2000). Ilmenite and magnetite may also occur as tiny lamellae in rutile. In general, if such mineral rods are smaller than the electron beam size a mixture of them and rutile is analysed. Literature data show a wide range of certain trace elements, in particular Al and Fe, in rutile from crustal and mantle eclogites, which most likely reflects the presence of corundum and ilmenite lamellae (Sobolev and Yefimova, 2000). Most naturally occurring rutile corresponds to the general formula 4+ TiO2, with titanium occurring as Ti . Note that titanium also exists in different states of oxidation: besides Ti4+, there are also Ti3+,Ti2+ and Ti0 (MacChesney and Muan, 1959). In rutile, there are commonly several Fig. 8. Ionic charge versus ionic radius (Shannon, 1976) for elements that substitute Ti 6+ 6+ possible substitutions for titanium such as hexavalent (W and U ), in natural rutile (see text for explanation and references). Note that the ionic radius of pentavalent (Nb5+,Sb5+ and Ta5+), tetravalent (Zr4+,Mo4+,Sn4+,Hf4+ Ta5+ is about 0.015 Å smaller than that of Nb5+ (Tiepolo et al., 2000). and U4+), trivalent (Al3+,Sc3+,V3+,Cr3+,Fe3+ and Y3+) and divalent (Fe2+, and to a lesser degree Mg2+,Mn2+ and Zn2+) cations (Graham analysis may not be representative for the bulk composition of a rutile and Morris, 1973; Brenan et al., 1994; Hassan, 1994; Fett, 1995; Murad et grain. That is particularly critical for calculating the crystallisation al., 1995; Smith and Perseil, 1997; Rice et al., 1998; Zack et al., 2002; temperatures using Zr-in-rutile thermometry and for in situ isotope Bromiley and Hilairet, 2005; Scott, 2005; Carruzzo et al., 2006). For analysis. instance, Fe3+ and Nb5+ incorporation (Fe3++Nb5+↔2Ti4+) main- Rutile is the dominant carrier of HFSE (e.g. Foley et al., 2000; Kalfoun taining charge neutrality can compensate for substitution of tetravalent et al., 2002; Zack et al., 2002). For example, in eclogites 1 modal-% of Ti4+ ions. Several further examples can be found in the literature (e.g. rutile can carry more than 90% of the whole-rock content for Ti, Nb, Sb, Urban et al., 1992; Michailidis, 1997; Smith and Perseil, 1997; Rice et al., Ta and W and considerable amounts (5–45% of the whole-rock content) 1998; Scott and Radford, 2007). Substitution of Ti4+ in the rutile crystal of V, Cr, Mo and Sn (Rudnick et al., 2000; Zack et al., 2002). Because rutile lattice is based on the ionic radius and ionic charge of the substituted dominates the budget of Nb and Ta, Nb+Ta concentrations and Nb/Ta cation (Fig. 8). Cathodoluminescence (CL) and backscattered electron values of rutile should be identical to that of the host rock (Rudnick et al., (BSE) images of polished rutile grains can reveal complex oscillatory 2000; Zack et al., 2002; Carruzzo et al., 2006). Schmidt et al. (2009) zonation patterns or patchy zoned crystals (e.g. Michailidis, 1997; recently made a critical note on this subject, based on Nb/Ta zoning in Carruzzo et al., 2006; Birch et al., 2007), which indicate variations in the eclogitic rutile. In general, the rutile structure can accommodate up to geochemical composition in the rutile crystal lattice. Thus, a single-spot 37 wt.% Nb2O2 in solid solution (Roth and Coughanour, 1955; Tien et al., 1969). Villaseca et al. (2007) suggested that around 10–35% of the whole-rock Zr content of peraluminous granulites could be contained in rutile. The needle-like blue rutile inclusions in garnet from ultrahigh- pressure metasedimentary rocks of the Greek Rhodope Massif contain a

small but signiﬁcant amount of SiO2 (Mposkos and Kostopoulos, 2001) that indicates high-temperature/high-pressure (HT/HP) conditions and represents stishovite component in rutile (H.-J. Massonne, in Mposkos and Kostopoulos, 2001). Rutile can also contain considerable amounts (tens to thousands of

ppm) of H2O, structurally bounded as hydroxyl (OH), which has been reported from both synthetic rutile (Bromiley et al., 2004; Bromiley and Hilairet, 2005) and natural rutile (Rossman and Smyth, 1990; Hammer and Beran, 1991; Vlassopoulos et al., 1993; Zhang et al., 2001). Vlassopoulos et al. (1993) pointed out that rutile is one of the most “hydrous” nominally anhydrous minerals (NAMs: Bell and Rossman, 1992) so far identiﬁed. Experimental investigations have shown that OH solubility in NAMs increases with pressure (e.g. Lu and Keppler, 1997; Bromiley et al., 2004; Mierdel and Keppler, 2004; Rauch and Keppler, 2004). Zhang et al. (2001) presented values of

about 4300 to 9600 ppm H2O in rutile from eclogites of the Dabie Mountains, China. Therefore, besides pyroxene and garnet, rutile is also an important NAM to recycle water into the mantle (Zhang et al., 2001; Zheng et al., 2003; Bromiley et al., 2004).

Fig. 7. Comparison of Nb concentrations in rutiles analysed by EMP and LA-ICP-MS. Data 3. Occurrences were taken from Zack et al. (2002) and Xiao et al. (2006). Dark grey diamonds are rutiles from eclogites, grey squares represent rutiles from quartz veins, and the white 3.1. Rutile in metamorphic rocks circles represent rutiles from garnet–mica schists. Solid line represents a 1:1 correlation; dotted lines are the upper and lower range of 20% and 30% deviations Rutile is mainly formed during medium- to high-grade metamor- from the 1:1 line respectively. Note that EMP gives a slightly lower value compared to LA-ICP-MS for most of the analysed rutiles, also recognised by Xiao et al. (2006). Future phic processes (e.g. Goldsmith and Force, 1978; Force, 1980, 1991) studies may help clarifying if this is an analytical artefact. (Fig. 9), but it can also form in low-grade metamorphic rocks (e.g. G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 7

sample of the Rocciavre Massif, Western Alps. Smythe et al. (2008) noted that ilmenite lamellae are abundantly present in mantle- derived rutile. Eclogite is the major rock type under high-grade metamorphic rocks containing large percentages of rutile (Korneliussen and Foslie, 1985; Liou et al., 1998; Korneliussen et al., 2000; Zack et al., 2002; Chen et al., 2005; Huang et al., 2006; Zhang et al., 2006). Korneliussen and Foslie (1985) estimated that about 90% of the titanium in eclogites of the Sunnfjord region of the Western Gneiss Region (WGR), Norway, is hosted in rutile. Eclogite from the Western Ligurian Alps contains up to 4 vol.% of rutile (Liou et al., 1998). Eclogite is a plagioclase-free metamorphic rock composed of ≥75 vol.% of garnet and Na-rich clinopyroxene (omphacite) and mainly forms by subduction of gabbroic or basaltic rocks to great depths where rutile crystallises from Fe–Ti oxides and Ti-bearing silicates during metamorphic recrystallisation (Krogh, 1980, 1982; Korneliussen and Foslie, 1985; Liou et al., 1998; Korneliussen et al., 2000; Miller et al., 2007; Figs. 5 and 10). Eclogite has a density of up to 3.6 g cm− 3 (Hills and Haggerty, 1989; Rudnick and Fountain, 1995), higher than any other crustal rock (Hacker, 1996), even peridotite, which it exceeds by 0.2–0.4 g cm− 3 (Rudnick and Fountain, 1995). Experimental data suggest that rutile is the main Ti carrier in eclogite below 150 kbar under sub-solidus conditions, even in relatively Ti-poor systems (Okamoto and Maruyama, 2004). However, under ultrahigh-pressure metamorphic conditions close to the coesite–stishovite phase bound-

ary it is more likely to be the TiO2(II) polymorph instead of rutile (Withers et al., 2003; Fig. 5). In general, the stability of rutile in subducted lithosphere is a complex function of whole-rock composition, temperature and pressure (e.g. Zhang et al., 2003; Klemme et al., 2005; Bromiley and Redfern, 2008; Fig. 10). Fig. 9. Illustrations showing the main stages of rutile crystallisation from ilmenite and Since rutile is a major accessory mineral in eclogite and plays a biotite during prograde metamorphism. (a) Rutile crystallisation from ilmenite in low- major role in the Earth's HFSE budget (in particular Nb and Ta) (see ﬁ to medium-grade metasedimentary rocks of the Erzgebirge (modi ed from Luvizotto et Section 2.3), in the last decade, eclogite has received much attention al., 2009a). (b) Rutile crystallisation from biotite in granulite facies paragneisses of the Ivrea–Verbano Zone (modiﬁed from Luvizotto and Zack, 2009). Mineral abbreviations regarding its whole-rock and mineral geochemical composition (e.g. (Kretz, 1983) are as follows: Bt = Biotite, Chl = Chlorite, Ilm = Ilmenite, Rt = Rutile. Rudnick et al., 2000; Zack et al., 2002; Xiao et al., 2006; Miller et al., 2007; Schmidt et al., 2009). In addition, the processes returning

Banfield and Veblen, 1991; Luvizotto et al., 2009a). Rutile in low- to medium-grade metamorphic rocks typically occurs as small (∼20– 100 μm), scattered grains, generally needle-like crystals, or polycrystalline aggregates. Banfield and Veblen (1991) recognised that within each sample analysed, the rutile crystals are uniform in size, but they are smaller in samples from the chlorite and chloritoid zones than in samples from the garnet and staurolite zones. The needle-like, euhedral morphology of the crystals show that rutile grew during metamorphism, rather than being detrital in origin (Banfield and Veblen, 1991). Luvizotto et al. (2009a) recently described prograde rutile crystallisation in low- to medium-grade metasedimentary rocks from the Saxonian Erzgebirge, Germany. The rutiles form polycrystalline aggregates made of fine-grained intergrowths of rutile and chlorite that replaces ilmenite (Fig. 9). Luvizotto et al. (2009a) suggested that rutile has been derived from ilmenite breakdown due to following simplified reaction:

Ilmenite þ Silicates þ H2O→Rutile þ Chlorite

Rutile in high-grade and ultrahigh-grade metamorphic rocks (e.g. eclogites, granulites) forms mainly single crystals in the matrix but also occurs as inclusion in other minerals such as garnet, pyroxene, amphibole and zircon (Fig. 1). These rutile grains can show euhedral Fig. 10. Experimentally determined formation of rutile, titanite and ilmenite for a mid- to subhedral forms with oval shapes or irregular shapes, with grain ocean ridge basalt–H2O system (after Liou et al., 1998). The P–T field phase boundaries sizes from a few μm up to a few mm (Hills and Haggerty, 1989; Brenan were not reversed and hence should be considered as synthesis boundaries, although et al., 1994; Zack et al., 2002; Huang et al., 2006; Xiao et al., 2006; they are topologically consistent with natural occurrences of Ti-phases. Liou et al. (1998) furthermore pointed out that these Ti-rich phases are not related to one another Janoušek et al., 2007; Chen and Li, 2008). Brenan et al. (1994) by simple polymorphic transition, and thus two or even three of them may coexist – described large (1 5 mm in size), euhedral single crystals of rutile under certain physicochemical conditions, but this was not investigated that contain fine exsolution lamellae of ilmenite from an eclogite vein experimentally. 8 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 extremely dense eclogite from great depths back to the Earth's surface Choukroun et al., 2005; Downes et al., 2007; Smythe et al., 2008) and (e.g. Guillot et al., 2000; Neufeld et al., 2008), supplemented by metallic ore deposits (e.g. Bayley, 1923; Force, 1980; Czamanske et al., geochronological studies (e.g. Baldwin et al., 2004; Glodny et al., 1981; Force, 1991; Rice et al., 1998; Clark and Williams-Jones, 2004; 2005; Kylander-Clark et al., 2008), have been much discussed. Scott, 2005; von Quadt et al., 2005; Scott and Radford, 2007). The Unfortunately, the original mineral assemblage of lower crustal occurrence of large rutile crystals (up to 4 cm in size and larger) is rocks such as eclogite and eclogite facies rocks are subject to limited to some granitic pegmatites and vein mineralisation (Watson, retrogression during their ascent from great depths to the Earth's 1922; Deer et al., 1992; Černý et al., 1999, 2007) and are described surface. For example, in eclogites and eclogite facies rocks from the from syn-metamorphic quartz veins of eclogite facies (Franz et al., Western Ligurian Alps, rutile was subsequently replaced by ilmenite 2001; Gao et al., 2007). and titanite along margins and cracks (Liou et al., 1998). Xiao et al. In alpine fissures, rutile can occur as reddish needles in transparent (2006) described thin titanite (10–20 μm) replacement surrounding quartz crystals. They are then called rutilated quartz or “fléches rutile and a thin ilmenite (a few μm) rim at the rutile margin from an d'amour” (“arrows of love”) and are classified as gemstones, with eclogite and nearby quartz vein, respectively, of the Dabie–Sulu known localities in Brazil, Switzerland and U.S.A. (Pough, 1998). ultrahigh-pressure terrane in east-central China. Note that, under Blue quartz is another type of rutilated quartz (e.g. Wise, 1981). conditions of rapid exhumation (as fast as subduction; Rubatto and The “blue” colour of quartz is derived from Rayleigh scattering of light Hermann, 2001; Baldwin et al., 2004) the original mineral assemblage by abundant inclusions of nanometre-scale acicular rutile, but other is largely preserved and allows insights into the pressure, temperature minerals may also occur as inclusions, for instance, ilmenite (e.g. and geochemical conditions present at great depths. Rutile in eclogitic Wise, 1981; Zolensky et al., 1988). In many cases, acicular rutile in (E-type) diamonds and diamondiferous eclogites (Prinz et al., 1975; quartz has been formed by exsolution of Ti from the quartz crystal Mvuemba Ntanda et al., 1982; Sobolev et al., 1997; Sobolev and lattice (Cherniak et al., 2007a). Rutilated blue quartz has been Yefimova, 2000) are accessible at the Earth's surface due to fast ascent described, for example, from granites, granodiorites, rhyolites, from the Earth's mantle as xenoliths in kimberlite pipes. The extensive charnockites and gneisses (Wise, 1981; Zolensky et al., 1988, and studies of the composition of eclogite in recent years have sig- references therein), and is restricted in occurrence mainly to the nificantly contributed to the increase of geochemical data for natural Precambrian, in particularly to middle to late Proterozoic rocks rutile, and thus they have opened new ways for rutile characterisation (Zolensky et al., 1988) of the Grenville province. Note that blue quartz such as rutile geochemistry and Zr-in-rutile thermometry, as outlined incorporated into detritus eroded from these rocks has proven to be a in Section 4. reliable provenance indicator with stratigraphic significance both in Rutile also occurs in the form of oriented, needle-like rods, known the Scottish Highlands, in western Ireland and in the eastern parts of as sagenitic texture. Shau et al. (1991) described these from matrix North America (Phillips, 1973; Fitches et al., 1990; Kline, 1991; Dewey biotite of an orthogneiss of the Tananao metamorphic complex, NE and Mange, 1999; Maria Mange, pers. comm., 2010). Taiwan. Van Roermund et al. (2000) described oriented, needle-like Rutile in granitic rocks can have several origins; it can be a primary rutile rods of 2–15 μm in diameter and up to 200–300 μm in length igneous, peritectic, xenocrystic, or secondary phase (Carruzzo et al., from protogranular and porphyroclastic garnet from garnet peridotite 2006; Clarke and Carruzzo, 2007). Secondary rutile can form because of the WGR. Attoh and Nude (2008) recently described spindle shaped of hydrothermal alteration (chloritisation) of Ti-rich biotite (Carruzzo rutile rods of b3 μm in diameter, b50 μm long and arranged in a et al., 2006), by oxidation of ilmenite (Sakoma and Martin, 2002)orby rectilinear pattern in garnet megacrystals from mafic granulites of the exsolution from Ti-bearing phases such as clinopyroxene and garnet Pan-African Dahomeyide suture zone, SE Ghana. Oriented, needle-like (Zhang et al., 2003). rutile rods in garnet are commonly taken as an indicator for UHP Primary igneous rutile can have significant concentrations of HFSE metamorphism (Ye et al., 2000; Mposkos and Kostopoulos, 2001; (e.g. Nb and Ta). Niobian rutile (also known as ilmenorutile) is a Hwang et al., 2007; Attoh and Nude, 2008). They show crystallo- variety of rutile with an atomic ratio of Nb/TaN1, while tantalian rutile graphically controlled growth of the exsolution rods and suggest (also known as strüvertite) has an atomic ratio of Nb/Tab1(Černý et transformation in the garnet crystal structure involving substitution al., 1964). Both are accessory minerals in peraluminous to peralkaline of Ti4+ in the precursor garnet structure (Zhang et al., 2003). Hwang granites and substantial components of hydrothermal assemblages et al. (2007) investigated the origin of oriented, needle-like rutile rods associated with alkaline intrusive rocks (Černý et al., 1964, 1999; in garnet from eclogitic rocks of Sulu, from diamondiferous quartzo- Černý and Chapman, 2001). In both rutile varieties, Fe3+ is always feldspathic rocks of the Saxonian Erzgebirge and from felsic granulite present to accommodate the overcharged (Ti4+,Nb5+ and Ta5+) of Bohemia. Their results argue against a simple solid-state precip- cation population (Smith and Perseil, 1997). itation scenario. The authors favour a mechanism where oriented According to Bailey (1961) and Marvin (1971), in alkaline rocks, rutile needles form by cleaving and healing of garnet with rutile carbonatites and carbonate veins in particular, rutile tends to be deposition because of the natural analogue of oriented titanite enriched in Nb and poor in Ta. However, primary rutiles from needles in biotite. Nonetheless, their study clearly shows the need carbonatites can be free of Nb, and have ubiquitous V and elevated Fe for further investigation of the origin of oriented rutile needles in contents (Ripp et al., 2006). Chrome-rich rutile in carbonatites is garnet of high-grade and ultrahigh-grade metamorphic rocks (see commonly related to mantle-derived xenoliths (Ripp et al., 2006). Griffin, 2008). Anderson (1960) mentioned niobian rutile from the carbonate-rich metamorphic zone of the Idaho batholith. Tollo and Haggerty (1987) 3.2. Rutile in igneous rocks and mineralisation described niobian rutile from nodules of the Orapa kimberlite, Botswana. Kimberlitic rutile in general has higher Nb/Ta ratios Additional sources of rutile can be quartz veins (e.g. Watson, 1922; compared with rutile from granites and granitic pegmatites (Tollo and Deer et al., 1992), granites (e.g. Force, 1980; Scott, 1988; Force, 1991; Haggerty, 1987). Metasomatised mantle peridotite and continental Michailidis, 1997; von Quadt et al., 2005), pegmatites (e.g. Force, lithospheric mantle have Nb/Ta ratios N17.5, chondritic to suprachon- 1980; Černý et al., 1989; Force, 1991; Deer et al., 1992; Okrusch et al., dritic (Kalfoun et al., 2002). Unmetasomatised peridotites commonly 2003), carbonatites (e.g. Bailey, 1961; Ripp et al., 2006; Doroshkevich have Nb/Ta ratios b17.5, subchondritic (Kalfoun et al., 2002). et al., 2007), kimberlites and xenoliths of metasomatised peridotite Michailidis (1997) studied niobian rutile (some with substantial (e.g. McGetchin and Silver, 1970; Dawson and Smith, 1977; Jones tungsten content) from the Fanos aplitic granite, northern Greece. Černý et al., 1982; Kramers et al., 1983; Tollo and Haggerty, 1987; Schulze, et al. (1999) described niobian rutile from the McGuire pegmatite, 1990; Rudnick et al., 2000; Grégoire et al., 2002; Kalfoun et al., 2002; Colorado, and its breakdown into secondary minerals such as G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 9 pseudobrookite, ferropseudobrookite, titanian ferrocolumbite and (Reyneke and Wallmach, 2007). Authigenic rutile can often be identified ilmenite. Further examples of exsolution and breakdown of niobian by its polysynthetic twin lamellae (Mader, 1980). rutile are found in the literature (Uher et al., 1998; Černý and Chapman, Rutile has been recognised as an important component of heavy 2001; Černý et al., 2007). Carruzzo et al. (2006) described several rutile mineral suites since the very early days of sedimentary petrography types from peraluminous granite of the late Devonian South Mountain (e.g. Boswell, 1933, and references therein). Hubert (1962) intro- Batholith, Nova Scotia. The size of the primary igneous rutile duced the zircon–tourmaline–rutile (ZTR) index as a quantitative grains ranges from 0.04 to 0.28 mm (with minor larger grains), indicator of the mineralogical maturity of the heavy mineral suite in with rare euhedral to commonly anhedral shapes. Carruzzo et al. sandstones. Buist (1963a,b) determined the rutile concentration of (2006) recognised that these grains have increasing concentrations of heavy mineral separations of beach sands from southern Australia Fe+Mn, Zr, Nb, Sn, Ta and W with increasing chemical differentiation of using a Frantz isodynamic separator and Geiger counter X-ray the South Mountain Batholith and concluded that rutile is a sensitive diffractometer. Raman and Jackson (1965) used X-ray diffraction monitor of Nb–Ta–Sn–W in the batholith. Rutile with high Nb+Ta after sample treatment with hydrofluoric acid for the qualitative concentrations and low Nb/Ta values, reflecting variable partitioning of detection and quantitative estimation of rutile in small amounts in Nb and Ta into a fluid phase, is commonly associated with granitic sediment. From the 1980s, microprobe techniques were used for pegmatites and in case of the South Mountain Batholith may represent single-grain chemical analyses supplying additional information to crystallisation during H2O-oversaturated conditions (Carruzzo et al., conventional heavy mineral analysis for sediment provenance studies 2006). (e.g. Morton, 1985, 1991). This caused a resurgence of interest in

Concentrations of boron and H2O can increase in granite magmas heavy mineral analysis both in academic research and in industry. during the late stage of emplacement and can led to explosive release Rutile is chemically and physically stable and not prone to of volatiles forming tourmaline breccia dykes and pipes, some of destruction during the sedimentation cycle and can therefore provide which have rutile as the main accessory phase (e.g. Müller and Halls, important information about source area lithologies. Rutile has similar 2005). Such rutile has highly variable amounts of V, Fe, Nb, Sn and W hydraulic and diagenetic behaviour as zircon, and Morton and (Müller and Halls, 2005). Putnis (1978) and Putnis and Wilson (1978) Hallsworth (1994) therefore introduced the rutile–zircon index noted that rutile formed at low temperatures (less than 450 °C, (RuZi) for provenance characterisation, deﬁned as: hydrothermal) contains notable Fe concentrations. Such rutile is susceptible to exsolution of a Fe-bearing phase such as hematite Rutile (Putnis, 1978; Putnis and Wilson, 1978). RuZi = × 100 Rutile + Zircon

3.3. Rutile in sedimentary rocks with rutile and zircon given as counts per sample. This index is based The largest sedimentary sources of rutile are ﬁne-grained clastic on the premise that ratios of minerals with similar hydraulic and sediment and heavy mineral sands (placer deposits). For example, diagenetic behaviour most likely reﬂect provenance characteristics

Valentine and Commeau (1990) studied the TiO2 whole-rock content (Morton and Hallsworth, 1994). Use of the rutile–zircon index as a of Pleistocene and Holocene sediments from surficial and several core guide to provenance is especially important in clastic sediments that samples of the Gulf of Maine where rutile is the main titanium source have undergone advanced burial diagenesis and hence may have lost present in the silt and clay fraction. Based on their data, the authors significant amounts of provenance information (Morton and Halls- estimated the amount of TiO2 to exceed 647 million metric tons (t) and worth, 1994, 1999). Sands with high RuZi indicate that rutile-bearing could show that the Gulf of Maine hosts a large titanium resource. lithologies (metapelitic and/or metamafic rocks) are abundant in the Placer deposits commonly contain high percentages of zircon, rutile source region, whereas low RuZi indicates a prevalence of rutile-poor and ilmenite that are concentrated to economic grade (e.g. Force, lithologies (such as igneous rocks). Since rutile and zircon are both 1991; Roy, 1999; Dill, 2007a). Examples are marine placer deposits in stable minerals (Pettijohn, 1941; Hubert, 1962; Morton and Halls- southeastern Australia (e.g. Roy, 1999) and along the NW coast of worth, 1994, 1999), RuZi values can also reflect inheritance from pre- South Africa (e.g. Dill, 2007a; see Section 5). In continental placer existing clastic sediment. To date, the method has successfully been deposits, titanium minerals occur mainly in rutile–ilmenite aggregates applied in several conventional heavy mineral studies (e.g. Whitham called “nigrine” (Clark, 1993; Dill, 2007a; Dill et al., 2007). Nigrine is a et al., 2004; Morton et al., 2005; Morton and Chenery, 2009). variety of rutile with high iron concentration (Clark, 1993). Sophisticated methods for rutile provenance characterisation are dis-

Pseudorutile (Fe2Ti3O9; Temple, 1966; Teufer and Temple, 1966)is cussed in Section 4. 2+ formed by Fe removal during oxidation of ilmenite (FeTiO3)(Teufer and Temple, 1966; Grey and Reid, 1975; Mücke and Chaudhuri, 1991; 3.4. Rutile in extraterrestrial rocks Grey et al., 1994). Its status as a distinct mineral phase is still a subject of lively debate (Dill, 2007a, and references therein). Removal of Fe3+ from Rutile has also been described from extraterrestrial material such pseudorutile due to leaching and hydrolisation results in leucoxene as lunar rocks and meteorites. Extraterrestrial rutile can have several (Mücke and Chaudhuri, 1991). The latter term, introduced by Gümbel origins, such as reduction from ilmenite, exsolution from chromite (1874), had long been applied to alteration products with high Ti and primary crystallisation as a minor accessory mineral (Buseck and concentration. In present usage, leucoxene refers to a mineral Keil, 1966; Harper, 1996). Rutiles from lunar rocks were described, for concentrate with about 65–90 wt.% TiO2 (Fig. 2) and is a mixture of example, in Apollo 11, 12, 14 and 17 samples (Keil et al., 1970; Wood pseudorutile and rutile (Grey et al., 1994; Reyneke and Wallmach, 2007). et al., 1970; Marvin, 1971; Hlava et al., 1972; Hill et al., 2006). They In conclusion, pseudorutile and leucoxene indicate more oxidising occur within ilmenite as thin exsolution lamellae of less than 2 μm supergene or hypogene conditions in the provenance area (Dill, 2007a). (Keil et al., 1970) and 2–5 μm(Wood et al., 1970) in size. They also In sedimentary rocks rutile, anatase and brookite can form dia- occur as small anhedral grains less than 20 μm in diameter adjacent to genetically from Ti-rich pore-solutions, which may derive from or enclosed by ilmenite (Keil et al., 1970; Marvin, 1971; Hlava et al., alteration of ilmenite, titanite and biotite (Mader, 1980; Morad, 1986; 1972). Marvin (1971) identiﬁed a niobium-enriched mineral from

Valentine and Commeau, 1990). Paine et al. (2005) ascribed alteration lunar rocks and soils, which was a niobian rutile (6.4% Nb2O5)ina of ilmenite to pseudorutile and anatase in Pliocene placer deposits microbreccia fragment of an Apollo 12 sample. That rutile was also of southeastern Australia to postdepositional weathering. The TiO2 enriched in Ta, La and Ce. Hlava et al. (1972) found niobian rutile (7.1% polymorphs are commonly alteration endmembers of Fe–Ti oxides Nb2O5) in a lithic fragment of KREEP composition (K — potassium, 10 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

REE — rare earth elements and P — phosphorus) with basaltic texture 2002) were published. This was probably because of the lack of major- in an Apollo 14 sample. element composition, in conjunction with a scarcity of rutile One of the pioneers studying meteoritic rutile was Paul Ramdohr geochemical data from potential source lithologies. For example, who identiﬁed rutile in the Mt. Browne chondrite and in several Götze (1996) suggested that rutile with elevated concentrations of Sn mesosiderites (Ramdohr, 1963, 1965). El Goresy (1965) mentioned a and W implies ore-bearing source rocks. Preston et al. (1998, 2002) euhedral rutile crystal enclosed in troilite of the Odessa iron meteorite demonstrated that detrital rutile in Triassic continental red-beds in and accessory rutile in the Dalgaranga iron meteorite. Buseck and Keil the Beryl Field, North Sea, comprises almost pure TiO2, with only a (1966) described rutile associated primarily with ilmenite and small proportion containing appreciable Nb2O5 or FeO. chromite from several meteorites (Allegan, Bondoc, Esterville, Farm- More recently, however, rutile has attracted a lot of interest as new ington and Vaca Muerta) (see Kimura et al., 1991). Rutile is most studies have demonstrated the high potential of the trace-element abundant in the Farmington L-group chondrite where it occurs in ﬁne signature of rutile, including Zr-in-rutile thermometry, for character- lamellae in polycrystalline ilmenite (Buseck and Keil, 1966). Referring ising sediment source areas and hence for quantitative provenance to Ramdohr (1963, 1965), Buseck and Keil (1966) suggested that this analysis, as will be shown in the following sections. rutile was derived from ilmenite breakdown due to the following reaction: 4.1.2. Fe content

2FeTiO3→2TiO2 þ 2Fe þ O2 The Fe content has been suggested to be an indicator of metamorphic origin since metamorphic rutile contains mostly N1000 ppm Fe Experimental studies revealed that ilmenite could not coexist with (Zack et al., 2004a). However, lamellae-rich regions in rutile can show rutile and remain stable at high temperatures as they react to form considerable Fe enrichment (Banfield and Veblen, 1991; Liou et al., 1998; Sobolev and Yefimova, 2000). Therefore, careful examination of FeTi2O5 (Fig. 3), a mineral in the pseudobrookite solid solution series (MacChesney and Muan, 1959; Buseck and Keil, 1966). During cooling rutile at the microscale is necessary to ensure that measurements pseudobrookite decomposes to rutile+ilmenite at and below 1140± yielding elevated Fe contents were carried out in a homogeneous part 10 °C (Lindsley, 1965), indicating that the mineral assemblage ob- of the grain, as discussed in Section 2.3. fi served in the Farmington meteorite formed below that temperature Ban eld and Veblen (1991) recognised that the Fe content in rutile (Buseck and Keil, 1966). generally increases with metamorphic grade, although they cautioned In the Vaca Muerta mesosiderite the rutile occurs together with that this observation needs further research to determine whether the ilmenite and chromite, both in thin bands within ilmenite (Kimura et correlation is independent of whole-rock composition and other aspects al., 1991) and in fine lamellae in chromite, as well as in individual of metamorphic history. They suggested the potential of such a grains of up to 65 μm in diameter (Buseck and Keil, 1966). Nazarov et correlation might be applicable as a thermometer in rocks that have al. (2002) reported rutile from the Dhofar 303 lunar highland experienced temperatures less than 500 °C. However, rutile formed at meteorite. El Goresy (1971) described Nb-rich rutile from the Toluca low temperatures (less than 450 °C, hydrothermal) also contains high N iron meteorite in both silicate-bearing and silicate-free sulphide concentration ( 0.5 wt.%) of Fe (Putnis, 1978; Putnis and Wilson, 1978; inclusions. Later, Harper (1996) also analysed niobian rutiles from this Müller and Halls, 2005), which suggests that the Fe content cannot be meteorite and discovered formerly live 92Nb, which forms in super- used to identify metamorphic rutile in heavy mineral separates. novae by p-processes (Harper, 1996) and decays by electron capture Dawson and Smith (1977) assumed that their mica–amphibole– 92 – – to Zr with a half-life of about 36 Ma (Nethaway et al., 1978). rutile ilmenite diopside (MARID) group of xenoliths resulted from Extraterrestrial rutile may therefore bring quantitative data for the crystallisation of an oxidised magma in the uppermost mantle, and initial abundance of short-lived, now extinct, radionuclides (e.g. 92Nb) that all the Fe in rutile from these rocks is trivalent. Sobolev and in the solar system's parental molecular cloud, which has been the Yefimova (2000) noted that the Fe content in rutile from crustal and subject of recent discussion (Schönbächler et al., 2002, 2005; Wadhwa mantle eclogites and diamond inclusions depends on whole-rock et al., 2007, and references therein). The most interesting application composition, oxygen fugacity (fO2) and pressure and temperature of short-lived radionuclides is their potential usage as fine-scale conditions. Hence, it is worthwhile to calculate the ferric Fe content of chronometers to study processes in the early solar system (Harper, rutile by either partitioning the measured total iron content into Fe2O3 1996; Wadhwa et al., 2007). and FeO using the stoichiometric method of Droop (1987) or by using +3 Mössbauer spectroscopy. The Fe content is controlled by fO2 (e.g. Buddington and Lindsley, 1964), and thus, presence of Fe+3 indicates 4. Applications of rutile in earth sciences high fO2 during crystal growth. For example, many ultrahigh temperature (UHT) terrains contain oxidised (high fO ) mineral 4.1. Rutile geochemistry 2 assemblages (Harley, 2008, and references therein). Zhao et al. (1999) used fO as barometer for rutile–ilmenite assemblages in mantle 4.1.1. Introduction 2 xenoliths from kimberlites. Rutile is a major host mineral for Nb, Ta and other HFSE, which are widely used as geochemical fingerprints of geological processes such as magma evolution and subduction-zone metamorphism (e.g. Foley 4.1.3. Nb and Ta contents et al., 2000; Rudnick et al., 2000). Although Nb/Ta values of crustal and Nb and Ta have the same oxidation state and nearly identical ionic mantle rocks have been studied for a long time, processes that lead to radii (Shannon, 1976; Tiepolo et al., 2000; Fig. 8) and thus should the fractionation of Nb and Ta and to the formation of the Earth's remain tightly coupled during chemical processes within the crust– hidden suprachondritic Nb/Ta reservoir are still the subject of a lively mantle system. This should lead to relatively constant Nb/Ta ratios of debate, as outlined in Section 4.1.3. minerals and rocks, close to the chondritic value of about 17.65 Besides its application in igneous and metamorphic petrology, (McDonough and Sun, 1995). However, continental crust, island arc rutile geochemistry can also be applied in sedimentary provenance volcanic rocks and many oceanic basalts are characterised by studies. Banfield and Veblen (1991) were one of the first who subchondritic Nb/Ta values (e.g. Green, 1995; Rudnick and Fountain, suggested that rutile geochemistry may be useful in determining the 1995; Rudnick et al., 2000; Foley et al., 2002; Schmidt et al., 2009). A provenance of rutile. Nevertheless, until 2002, only a few papers geochemically complementary reservoir is therefore required to related to the mineral geochemistry of rutile and its application to accommodate the mass imbalance in Nb and Ta between continental sedimentary provenance studies (Götze, 1996; Preston et al., 1998, crust and depleted mantle (McDonough, 1991; Rudnick et al., 2000). G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 11

The processes leading to major fractionation of Nb and Ta, and thus to subchondritic Nb/Ta values, have been the subject of prolonged debate because they are important for understanding the formation of the continental crust (e.g. Foley et al., 2002; Xiao et al., 2006). As outlined in Section 3.1, rutile is a major accessory mineral in eclogite, which mainly forms by subduction of gabbroic or basaltic rocks to great depths. During metamorphic recrystallisation, rutile crystallises from Fe–Ti oxides and Ti-bearing silicates. It dominates the budget of Nb and Ta in eclogite, and thus Nb/Ta of whole-rock eclogite reflects this ratio in rutile (Rudnick et al., 2000; Zack et al., 2002). Experimental studies by Brenan et al. (1994) have shown that a small amount of rutile (∼0.2 wt.%) is enough to prevent HFSE enrichment in the mantle wedge by fluids generated during subduction zone metamorphism. Thus, rutile has long been regarded as a major factor controlling the slab-to-mantle flux of HFSE (e.g. Brenan et al., 1994; Green, 1995). Subchondritic Nb/Ta of the continental crust and island arc volcanic rocks has been ascribed to melting of subducted slabs in the presence of rutile (e.g. Rudnick et al., 2000). Rudnick et al. (2000) suggested that refractory eclogite produced by slab melting is the “missing reservoir” to accommodate the mass imbalance in Nb/Ta between continental crust and depleted mantle. This reservoir possibly exists in the Earth's deep mantle (Rudnick et al., 2000). Alternatively, it may be in the Earth's core (Wade and Wood, 2001). Experimental studies on the partitioning of Nb and Ta between rutile and melts have shown that rutile favors Ta over Nb (e.g. Foley et al., 2000, 2002; Klemme et al., 2005). Consequently, partial melting of subducted rutile-bearing eclogite with chondritic Nb/Ta results in melts with suprachondritic Nb/Ta and a residue depleted in Nb that cannot be the “missing reservoir” with suprachondritic Nb/Ta (e.g. Foley et al., 2002; Klemme et al., 2005). Xiao et al. (2006) studied Nb and Ta in eclogites from the Dubi–Sulu UHP metamorphic belt in east-central China and suggested the following model: During the early stage of subduction, hotter regions of the subducting slab will experience significant dehydration in the presence of amphibole and absence of rutile (b15 kbar; Fig. 10), which leads to suprachondritic Nb/Ta in the residual amphibole eclogites with complementary subchondritic Nb/Ta in the released fluids. A large proportion of these fluids (containing Nb, Ta, Ti, etc.) can be retained in cold regions inside the subducting slab, forming hydrated cold eclogites with subchondritic Nb/Ta. Subduction continues and the slab, consisting of these hydrated cold eclogites, reaches greater depths where rutile finally appears (N15 kbar; Fig. 10) and controls the Nb and Ta budget. Thus, melting of these hydrated cold eclogites will form magmas with negative Nb and Ta anomalies and subchondritic Fig. 11. Nb versus Cr discrimination diagrams for rutile from different metamorphic Nb/Ta values. Because early-dehydrated slab with suprachondritic Nb/ lithologies. (a) According to Zack et al. (2004b). Note that rutile from felsic granulite Ta rations cannot be melted, refractory residual eclogites have highly facies rocks can have exceptionally high Nb contents up to 28,000 ppm and more. variable Nb/Ta from subchondritic to suprachondritic (Xiao et al., (b) According to Triebold et al. (2007). Positive log(Cr/Nb) values mostly indicate a 2006). Nonetheless, Xiao et al. (2006) suggested that they form the metamafic source for rutile while negative values suggest derivation from metapelitic geochemically complementary reservoir to the continental crust since rocks. (c) According to Meinhold et al. (2008). Note that Zack et al. (2002, 2004b) introduced the terms “metamafic” and “metapelitic” to discriminate the rutile source, their overall average Nb/Ta is suprachondritic. although, for simplification, it seems more appropriate to use the terms “mafic” and “felsic” respectively. 4.1.4. Cr and Nb contents Zack et al. (2002, 2004b) suggested that Cr and Nb abundances in rutile (Fig. 11a) can effectively distinguish between metamafic and paragneisses, felsic granulites). Rutiles with CrNNb and those with metapelitic source lithologies. For simplification, Triebold et al. (2007) CrbNb, the latter however accompanied by Nbb800 ppm, are introduced log(Cr/Nb) values to discriminate between metamafic and interpreted to be derived from metamafic rocks (e.g. eclogites and metapelitic source lithologies (“1:1” line; Fig. 11b). This method is mafic granulites). Rutiles from amphibolites plot in both fields applicable except for low Cr and low Nb contents. Based on literature because the protoliths of amphibolites are of either sedimentary or data of Nb/TiO2 ratios of whole rock for pelites, Zack et al. (2002, mafic igneous origin. 2004b) calculated that rutile in metapelites contains 900–2700 ppm Nb. Combined with reference data, Meinhold et al. (2008) proposed 4.1.5. Other trace elements that the lower limit of Nb in metapelitic rutiles should be set at Smythe et al. (2008) noted that Mg and Al contents distinguish 800 ppm and that the discriminant boundaries between metamafic rutile derived from crustal and mantle sources (Fig. 12), and Al, Cr and and metapelitic source lithologies should therefore be modified as Nb contents further allow distinction between various mantle- shown in Fig. 11c. Rutiles with CrbNb accompanied by NbN800 ppm derived rocks such as eclogite, metasomatic rutile-dominated nodules are interpreted to be derived from metapelitic rocks (e.g. mica-schists, and mica–amphibole–rutile–ilmenite–diopside (MARID: Dawson and 12 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

Table 2 List of natural rocks containing rutile with economically important elements (compiled from Williams and Cesbron, 1977; Scott, 1988; Urban et al., 1992; Clark and Williams- Jones, 2004; Scott, 2005). For example, elevated concentrations of W and Sb in rutile strongly suggest a source from a mesothermal gold deposit (see Fig. 13). The V content in rutile can be used as a guide to mineralisation even in highly weathered rocks (Scott, 2005). Geochemical data of rutile from ancient and modern clastic sedimentary rocks can therefore provide useful ﬁngerprints to identify the type of mineralisation.

Type of deposit Characteristic elements in rutile

Volcanogenic massive sulphide Cu–Zn deposits Sn (W and/or Cu) Mesothermal and related gold deposits Sb, W and/or V Magmatic–hydrothermal Pd–Ni–Cu deposits Ni, Cu Granite-related Sn deposits Sn, W Granite–pegmatite Sn–W deposits Sn, W, Nb, Ta Porphyry and skarn Cu and Cu–Au deposits Cu, W (and sometimes V)

hidden suprachondritic Nb/Ta reservoir. Here, the reader is referred to Fig. 12. Discrimination between rutile derived from crustal and mantle sources, a selection of recent literature for further information (e.g. Xiao et al., according to Al and Mg contents in rutile (after Smythe et al., 2008). 2006; Aulbach et al., 2008; Baier et al., 2008; Bromiley and Redfern, 2008; Schmidt et al., 2009). Smith, 1977) xenoliths. Magnesium is one of the least compatible Since the work of Zack et al. (2004b), rutile geochemical elements in rutile (see Fig. 8). Therefore, Mg-rich rutile is most likely constraints on sediment provenance have been included in several to be found under HP and UHP conditions and hence in mantle rocks. publications related to sedimentary strata from the Neoproterozoic to Moreover, rutile from mantle rocks (e.g. diamondiferous eclogite) can the Holocene worldwide. contain an elevated Al content, which can be explained by a number of Stendal et al. (2006) used rutile geochemistry to establish that the tiny rods of corundum (Sobolev and Yefimova, 2000). These rods are rutiles in young alluvial and eluvial heavy mineral deposits of the smaller than the electron beam size a mixture of them and rutile is Yaoundé region in southern Cameroon were derived from the analysed. adjacent Neoproterozoic micaschists of the Yaoundé Group. Besides the major discriminants, Cr and Nb, there are also other Triebold et al. (2007) analysed detrital rutile from Early Palaeozoic trace elements that can characterise the source of rutile. For example, metasedimentary rocks and Holocene river sediments of the Erzge- when elements such as V, Ni, Cu, Sn, Sb and W are detected in high birge, Germany. They demonstrated that rutile compositions in river concentration in rutile, they can be considered to be anomalous and sediments mirror those of the surrounding country rocks. This led suggest a source from metallic ore deposits (e.g. Urban et al., 1992; them to conclude that rutile is an accurate tracer of source rock Clark and Williams-Jones, 2004; Scott, 2005)(Fig. 13). For instance, characterisation in sedimentary provenance studies. rutile from mesothermal gold mineralisation commonly contains Uher et al. (2007) analysed niobium–tantalum mineral assem- between 0.12 and 5.9 wt.% WO3. Table 2 shows a compilation of blages (including Nb–Ta-rich rutile) from alluvial placer deposits in various rutile-bearing deposits and the characteristic trace elements southwest Slovakia, which were most likely sourced from granitic incorporated into the rutile crystal lattice. pegmatites of the Bratislava Granitic Massif. Meinhold et al. (2008) investigated detrital rutile from Carbonif- 4.1.6. Examples erous to Early Triassic sandstones of Chios Island, Greece. They As outlined in Section 4.1.3, Nb and Ta concentrations in rutile recognised a change in source rock lithology from the Carboniferous allow tracing the formation and evolution of the continental crust. with dominantly metamafic rutile to the Early Triassic with more Hence, a large number of publications exists discussing Nb and Ta metapelitic rutile. Zr-in-rutile thermometry has confirmed this values and Nb/Ta ratios of crustal and mantle rocks and the Earth's change in the sediment source, which was explained by plate-tectonic reorganisation during the subduction of Palaeotethys at the southern margin of Laurussia in the Late Palaeozoic (Meinhold et al., 2008). Morton and Chenery (2009) studied the rutile source of Jurassic to Palaeocene sandstones in hydrocarbon exploration wells of the Norwegian Sea. Their rutile data confirm the presence of five distinct sand types sourced from different parts of the Norwegian and Greenland landmasses to the east and west of the basin, established by previous studies, concentrating on provenance-sensitive heavy mineral ratios, garnet geochemistry, tourmaline geochemistry and detrital zircon geochronology (Morton and Chenery, 2009). Moreover, these authors demonstrated the importance of rutile geochemistry as a provenance tracer, since the method yields diagnostic data on source rock lithology and metamorphic facies even in highly modified sandstones that may have lost significant amounts of provenance information. This is because of the ultrastable nature of rutile under both diagenetic and surficial weathering conditions (Pettijohn, 1941; Hubert, 1962; Morton and Hallsworth, 1999, 2007). Although the successful application of rutile geochemistry to single-mineral provenance studies has been shown above, there are at least two publications that clearly demonstrate that the discrimina- Fig. 13. Summary of Ti, Fe, Cr, V and W contents of rutile from variably metamorphosed tion diagrams based on Cr and Nb may not be strictly valid. Bakun- mesothermal gold deposits (after Clark and Williams-Jones, 2004). Czubarow et al. (2005) pointed out that the Cr–Nb discrimination G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 13 diagram of Zack et al. (2002, 2004b) is not applicable for rutile from Ferry and Watson (2007) suggested that the Zr content of rutile the Sudetes Fe–Ti-rich eclogites, which plot in the metapelite field. depends on the activity of SiO2 as well as temperature, which had Rutiles from eclogite of the ultrahigh-pressure metamorphic area at been confirmed by experimental data. This observation let them to the Saidenbach reservoir of the Erzgebirge in Germany (Massonne, conclude that the Zr-in-rutile thermometer may now be applied to

2001) also plot in the field of metapelitic source lithologies (Triebold rocks without quartz, if the activity of SiO2 is estimated. The et al., 2007; their fig. 5). Based on whole-rock geochemical data, maximum introduced uncertainty by unconstrained activity of SiO2 Massonne and Czambor (2007) suggested that the protoliths of the was given with about 60–70 °C at 750 °C (Ferry and Watson, 2007). Saidenbach eclogites were basaltic to trachyandesitic in composition The new calibration of the Zr-in-rutile thermometer is remarkably and formed in a within-plate geotectonic setting with a relatively low similar to that described by Watson et al. (2006). Ferry and Watson degree of melting. The Saidenbach eclogites have high Nb/Ti ratios. (2007) gave examples showing that the Zr contents of rutile that Rutile dominates the Nb and Ti budget in eclogites, and rutiles in the record 1100, 750 and 500 °C using the thermometer of Watson et al. Saidenbach eclogites inevitably have high Nb concentrations, and (2006) record 1093, 750 and 502 °C with the revised calibration for an thus, they plot in the field for metapelitic rutile. Despite these activity of SiO2 =1. Ferry and Watson (2007) also gave a preliminary shortcomings, the Cr–Nb discrimination diagram, as it stands now, is evaluation of the dependence of Zr-in-rutile thermometers on useful and should be applied in sediment provenance analysis until pressure. more rutile data of various source rock lithologies are available to Tomkins et al. (2007) discussed the pressure dependence, already place better constraints on its discrimination boundaries. emphasised by Watson et al. (2006), and presented three new Zr-in- rutile thermometers based on experimental data (Fig. 14). They 4.2. Zr-in-rutile thermometry clearly demonstrate that pressure, especially ultrahigh pressure (see also discussion in Chen and Li, 2008), does have an effect on the 4.2.1. Introduction uptake of Zr in rutile. The new thermometer equations by Tomkins et The partitioning of zirconium (Zr) into rutile coexisting with al. (2007) are, in the α-quartz field zircon or other Zr-rich phases has a strong dependence on B 83:9+0:410 × P temperature (T)(Zack et al., 2004a; Watson et al., 2006; Tomkins et TðÞC = −273 fi : − al., 2007). Zack et al. (2004a) were the rst presenting an empirically 0 1428 R ×ln Zrppm calibrated Zr-in-rutile thermometer (Fig. 14), expressing temperature as: in the β-quartz field B TðÞC = 127:8× ln Zr −10 B 85:7+0:473 × P ppm TðÞC = −273 : − 0 1453 R ×ln Zrppm with an error of ±50 °C. The calibration is based on analyses of rutile grains from 31 metamorphic rocks with rutile–quartz–zircon assem- and in the coesite field blages spanning a temperature range from 430 to 1100 °C. Watson et al. (2006) presented a revised Zr-in-rutile thermometer : : ðÞB 88 1+0206 × P − based on experimental data (at ∼10 kbar) and constrained by natural T C = 273 0:1412−R ×ln Zr rutiles from metamorphic rocks (Fig. 14), expressing temperature as: ppm

− with P in kbar, and R is the gas constant, 0.0083144 kJ K 1. An obvious ðÞB 4470 − T C = : − Zrppm 273 7 36 log10 input parameter in their equation is the pressure. Hence, this thermometer is suitable for rutiles of known source, meaning of with an error of ±20 °C. The two thermometers intersect at a tem- known pressure during rutile crystallisation. For detrital rutile, perature of about 540 °C but diverge significantly both at lower and however, the pressure under which the source rock had formed is higher temperatures (Fig. 14). Watson et al. (2006) considered this commonly unknown. To avoid speculation about the input parameter behaviour to indicate possible pressure dependence and emphasised ‘pressure’, the equation of Watson et al. (2006) should be used for the need for further investigation. detrital rutile or for rutile of unknown origin in general. Although it was originally thought that the Zr-in-rutile thermometer is only valid for metapelitic rutile (Zack et al., 2004a), recent studies have demonstrated that it is also valid for rutile from metamafic lithologies (e.g. Zack and Luvizotto, 2006; Triebold et al., 2007) and for detrital metamafic rutile (e.g. Meinhold et al., 2008; Morton and Chenery, 2009). Chen and Li (2008) have shown that the Zr-in-rutile thermometers by Watson et al. (2006) and Tomkins et al. (2007) yield similar shapes of the frequency histograms of temperatures (Fig. 15). However, the Zr-in- rutile thermometer of Watson et al. (2006) gives about 70 °C lower temperatures compared with the Zr-in-rutile thermometer of Tomkins et al. (2007) for eclogitic rutile from the central Dabie UHP metamorphic zone. The thermometer of Zack et al. (2004a) shows a wider spread in the frequency histograms of temperatures. The differences in shape and range of the frequency histograms of temperatures reflect the different approaches of the various Zr-in-rutile thermometers to calculate the temperature. Hereby, the pressure dependence of Zr incorporation into the rutile crystal lattice is an important factor to be considered, which is well illustrated in Fig. 14. The thermometers of Zack et al. (2004a) and Fig. 14. Comparison of Zr-in-rutile thermometers of Zack et al. (2004a), Watson et al. (2006) and Tomkins et al. (2007). For the latter thermometer, only calculations at 10, Watson et al. (2006) intersect at a temperature of about 540 °C 30 and 60 kbar are shown. but diverge significantly both at lower and higher temperatures. The 14 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

thermometer of Tomkins et al. (2007) with overestimation of the maximum temperature point for the Zack et al. (2004a) empirical calibration. In general, overestimation of temperature with Zr-in-rutile thermometry is only possible where mineral assemblages in equilibrium with rutile are quartz-free while underestimation can occur by absence of zircon and/or in partly reset mineral assemblages (Zack et al., 2004a; Baldwin and Brown, 2008; Harley, 2008; Luvizotto and Zack, 2009). Although Tomkins et al. (2007) noted that “Zr-in-rutile thermometry is not going to be a magic bullet in thermometry”, clearly it is an attractive method to calculate temperatures of high- grade and ultrahigh-grade metamorphic rocks (Spear et al., 2006; Zack and Luvizotto, 2006; Miller et al., 2007; Baldwin and Brown, 2008; Harley, 2008; Luvizotto and Zack, 2009). In the case of detrital rutile, Zr-in-rutile thermometry is an important technique in sediment provenance analysis especially in highly modiﬁed sandstones that may have lost signiﬁcant amounts of provenance information (Morton and Chenery, 2009).

4.2.2. Examples The reliability of the new Zr-in-rutile thermometers of Zack et al. (2004a) was demonstrated, for example, for eclogites and granulites from the Sudetes of SW Poland (Bakun-Czubarow et al., 2005)andfora wide variety of eclogites from Germany, Greece, Italy, Norway, Switzerland and Turkey (Zack and Luvizotto, 2006). Spear et al. (2006) showed the successful application of the Watson et al. (2006) calibration on blueschist facies rocks from Sifnos Island, Greece and Vaggelli et al. (2007) on high-pressure rocks from the Western Alps, Italy. Zack et al. (2004b) ﬁrst applied the combined use of detrital rutile geochemistry and Zr-in-rutile thermometry for quantitative sediment provenance analysis. Subsequent studies by Triebold et al. (2007) and von Eynatten et al. (2005) have demonstrated that the trace element composition of detrital rutile is unrelated to the grain size of the host sediment. They furthermore revealed that high-grade metamorphic rutile might preserve its geochemical signature to much lower temperatures, suggesting that rutile may survive metamorphic conditions on a retrograde path below 550 °C. Stendal et al. (2006) have also shown that relic rutile can retain its original composition during low- to medium-grade metamorphism, indicating that it can survive temperatures as high as 620 °C. Thus, the generally accepted views of rutile breakdown during low-grade metamorphism at greenschist facies and formation during medium-grade metamorphic conditions (Force, 1980; Zack et al., 2004b) may not be strictly valid. Luvizotto et al. (2009a) who recognised prograde rutile growth from ilmenite in low- to medium-

Fig. 15. Frequency histograms (bin width=25 °C) showing calculated formation grade metasedimentary rocks of the Erzgebirge, Germany, as outlined in temperatures for eclogitic rutile from the central Dabie UHP metamorphic zone with Section 3.1, have recently addressed this subject. data from Chen and Li (2008). Abbreviations TZ, TW and TT correspond to the Zr-in-rutile Meinhold et al. (2008) compared results obtained by using the Zr- thermometers of Zack et al. (2004a), Watson et al. (2006) and Tomkins et al. (2007) in-rutile thermometers of Zack et al. (2004a) and Watson et al. (2006) respectively. T was calculated from Eq. (3) in Zack et al. (2004a); T was calculated at Z T on detrital rutile from Carboniferous to Early Triassic sandstones of 28 kbar. Besides histograms, some statistical parameters are also given. n — number of data used, Min — minimun value, Max — maximum value, Med — Median, Avg — average Chios Island, Greece. They demonstrated the discrepancy between (arithmetic mean), Std — Standard deviation (1σ), Sk — Skewness, Ku — Kurtosis. both thermometers, with the Zr-in-rutile thermometer of Zack et al. (2004a) giving a wider spread in the frequency histograms of temperatures compared with the thermometer of Watson et al. thermometer of Watson et al. (2006) gives nearly identical results to the (2006), which was also pointed out by Chen and Li (2008), as discussed thermometer of Tomkins et al. (2007) using the α-quartz equation at in Section 4.2.1. 10 kbar, which is the pressure at that the Zr-in-rutile thermometer of Morton and Chenery (2009) successfully used Zr-in-rutile ther- Watson et al. (2006) was experimentally calibrated. In the temperature mometry to characterise the rutile source of Jurassic to Palaeocene range between 750 °C and 1150 °C the thermometer of Zack et al. sandstones in hydrocarbon exploration wells of the Norwegian Sea, (2004a) yields comparable results to the Tomkins et al. (2007) coesite- accompanied with application of rutile geochemistry, as outlined in ﬁeld equation at 30 kbar. Nonetheless, the thermometer of Zack et al. Section 4.1.6. (2004a) shows a wider spread in the frequency histograms of Note that for provenance identiﬁcation of detrital rutile the temperatures (Chen and Li, 2008; Meinhold et al., 2008) which supports possibility of polyphase recycling has to be kept in mind. the use of the Zr-in-rutile thermometer of Watson et al. (2006) for sediment provenance studies of detrital rutile. Baldwin and Brown 4.2.3. Zr diffusion (2008) explain the trend that the Zr-in-rutile thermometer of Zack et al. Cherniak et al. (2007b) studied the Zr diffusion in natural and (2004a) always gives a higher temperature than, for instance, the synthetic rutile and provided evidence that Zr concentrations in rutile G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 15

juvenile mantle-derived magmas, which contrast with those from “contaminants” that experienced low temperature and surﬁcial process such as hydrothermal alteration and sedimentary recycling and hence have elevated δ18Ovalues(e.g.Mojzsis et al., 2001; Wilde et al., 2001; Valley, 2003; Valley et al., 2005). The isotopes used are 18Oand16O, which are incorporated into the lattice during crystallisation. In current studies, oxygen isotope analyses on minerals are commonly performed by secondary ion mass spectrometry (SIMS) (e.g. Valley, 2003)and various laser techniques (e.g. Li et al., 2003; Valley, 2003; Zhang et al., 2006). The O isotope composition of a mineral is reported in delta notation (δ18O) relative to VSMOW (Vienna Standard Mean Ocean Water), which has an 18O/16O value of (2005.2±0.45)×10−6 (Gon- onﬁantini, 1978). The corresponding equation is as follows: 23 18 = 16 6 O O 7 δ18O = 4sample −15 ×103 18 = 16 O O VSMOW

with δ18O values in per mil (‰). Experimental studies by Moore et al. (1998) on synthetic and Fig. 16. Zr centre-retention criteria for rutile of different radii cooling at a linear rate natural rutile have shown that the closure temperatures for O from a range of maximum temperatures (after Cherniak et al., 2007b). The critical diffusion in rutile are high (Fig. 17), with about 650 °C for a crystal cooling rate depends on the maximum temperature, grain radius and diffusion μ −1 parameters. When cooling rates are slower than this critical value, the peak- with a 100- m radius and a cooling rate of 10 °C Ma . That means a temperature Zr signature in the centre of a rutile grain is not preserved over the rutile crystal with a 100-μm radius loses its initial core composition cooling path. For illustration purposes, the field of ultrahigh-temperature (UHT) only after heating at 600 °C for just over 10 Ma. Moore et al. (1998) metamorphism (Harley, 1998) is marked in grey. finally concluded that rutile retains its O isotope composition during a wide range of thermal events. Various minerals effectively fractionate the O isotopes. As for all can be affected by later thermal disturbance, although, based on stable isotopes, this fractionation process is a strong function of observations made by Watson et al. (2006), this is not likely to be as temperature and is time-independent. For example, quartz, calcite and rapid as Sasaki et al. (1985) suggested. Cherniak et al. (2007b) pointed albite more strongly partition 18O while diopside, hornblende, zircon, out that Zr diffusion in rutile is significantly slower than diffusion of almandine and rutile more strongly partition 16O(Matthews et al., divalent and trivalent cation substitutions and seems little affected by 1979; Chacko et al., 1996; Moore et al., 1998, and references therein). variations in trace element composition. The authors, however, made Fig. 18 demonstrates the O isotope fractionation in a coesite-bearing a cautionary remark that under a broad range of geological conditions, eclogite of the Dabie Mountains, with δ18O values of about +1.1‰ for the Zr-in-rutile thermometry is less resistant to resetting than Ti-in- quartz, −2.3‰ for garnet and −6.1‰ for rutile (Li et al., 2003). A zircon and Zr-in-titanite thermometry. They demonstrated that Zr compilation of literature data reveals that eclogitic rutile shows δ18O diffusion in rutile depends on the grain size and the cooling rate values from −8.9 to +7.1‰, with values from 3.6 to 8.0‰ for oxygen (Fig. 16). For example, a rutile grain formed under ultrahigh- isotope fractionation between quartz and rutile (Fig. 19). Fig. 20 temperature (UHT) metamorphic conditions at about 945 °C with a compares the quartz–rutile geothermometers of Agrinier (1991), grain radius of 500 μm will preserve its Zr signature in the centre of Zheng (1991) and Chacko et al. (1996). Quartz–rutile geothermometry − the grain when the cooling rate exceeds 100 °C Ma 1. Hence, rutile is a reliable method because both minerals are relatively resistant to formed under UHT conditions will retain its Zr signature only under post-formation oxygen exchange (Agrinier, 1991; Chacko et al., 1996). certain circumstances such as rapid cooling (Cherniak et al., 2007b; Fig. 16). Therefore, UHT source lithologies may be underestimated in sedimentary provenance studies with Zr-in-rutile thermometry. Chen and Li (2008) analysed eclogitic rutile from the Dabie–Sulu UHP metamorphic zone in east-central China and suggested that retrogression (with fluid presence) can release Zr from the rutile crystal lattice. This consequently causes lower calculated temperatures and does not provide the peak metamorphic temperature. Luvizotto and Zack (2009) observed large spreads in Zr concentrations for rutile grains from granulite facies metapelitic rocks of the Ivrea–Verbano Zone, Southern Alps, which they explained by Zr mobilisation due to slow cooling rates and/or fluid presence. All these points have to be kept in mind when using Zr-in-rutile thermometry.

4.3. Oxygen isotopes

4.3.1. Introduction The oxygen (O) isotope composition of minerals can yield information regarding the extent and nature of ﬂuid–mineral interactions and the temperature at the time of crystallisation or alteration (e.g. Matthews et al., 1979; Agrinier, 1991; Zheng, 1991; Chacko et al., 1996; Moore et al., 1998; Zheng et al., 1999, 2003). Many studies have shown that O isotopes Fig. 17. Dependence of the closure temperature for O isotope exchange in rutile from are a good ﬁngerprint to identify the derivation of certain minerals from crystal size and cooling rate (after Moore et al., 1998). 16 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

Fig. 18. Oxygen isotope composition of garnet, quartz and rutile from a coesite-bearing – eclogite of the Dabie Mountains. Data were taken from Li et al. (2003). Fig. 20. Comparison of the quartz rutile oxygen isotope geothermometers of Agrinier (1991), Zheng (1991) and Chacko et al. (1996).

Quartz–rutile geothermometry yields reliable temperatures for blueschist and eclogite facies rocks but may not work for granulite facies not lead to large errors in the calculated isotope temperatures rocks due to extensive re-equilibration (Chacko et al., 1996). (Matthews et al., 1979). Hence, Addy and Garlick (1974) and Matthews et al. (1979) carried out experimental studies of O isotope 4.3.2. Examples fractionation between rutile and water and tested their quartz–rutile Vogel and Garlick (1970) analysed the O isotope composition of geothermometers on a number of eclogites. Desmons and O'Neil various minerals, amongst others rutile and quartz, from eclogites in (1978) reported O isotope data of various minerals from eclogites of Europe, Venezuela and California, and they pointed out that O isotope the Western Alps, Italy, and calculated for these eclogites an average fractionations between quartz and rutile are relatively large. Thus, the formation temperature of 540 °C, using quartz–rutile and quartz– quartz–rutile pair is particularly suitable for geothermometry because phengite geothermometry. Studies by Agrinier et al. (1985) have analytical errors involved in the determination of δ18O values would shown that in eclogites of the WGR, Norway, the O isotope fractionation between rutile and quartz is small (Δ18O∼4.3–5.0‰), with quartz–rutile geothermometry yielding formation temperatures of about 680 to 715 °C. Zheng et al. (1999) analysed the O isotope composition of various minerals (i.a. rutile and quartz) from HP and UHP eclogites of the Dabie Mountains and calculated formation temperatures using amongst others quartz–rutile geothermometry. Quartz–rutile pairs from some of the eclogites yielded isotope temperatures lower than the temperatures of eclogite facies metamorphism, suggesting O isotope exchange due to retrograde ﬂuid– rock interaction (Zheng et al., 1999). Li et al. (2003) used O isotope analysis of rutile to test the validity of rutile U–Pb isochron dating on coesite-bearing eclogite from the Dabie Mountains. They determined almost identical δ18O values for different rutile grains from the same specimen (Fig. 18), which suggests attainment of O isotope homog- enisation in rutile during eclogite facies metamorphism and preser- vation during amphibolite facies retrograde metamorphism (Li et al., 2003). Gao et al. (2006) also studied the O isotope composition of mineral pairs in eclogite from the Dabie Mountains, with the quartz– rutile pair yielding an isotope temperature of 530 °C. Chen and Li (2008) emphasised the potential of quartz–rutile geothermometry to place constraints on rutile U–Pb cooling ages since O diffusion in rutile is similar to that of Pb under hydrous conditions (Moore et al., 1998; Cherniak, 2000).

4.4. U–Pb geochronology

4.4.1. Introduction Rutile typically contains between 3 and 130 ppm of uranium

δ18 – (Mezger et al., 1989)(Table 3; Fig. 21), but higher concentrations also Fig. 19. Cross plot showing O values of rutile and quartz rutile fractionation values – – in various eclogites (n=38). The frequency histogram (bin width=0.5‰) shows the occur, making Pb Pb and U Pb dating possible (e.g. Mezger et al., distribution of quartz–rutile fractionation values. Data were taken from Vogel and 1989, 1991; Möller et al., 2000; Vry and Baker, 2006). Radiometric Garlick (1970), Desmons and O'Neil (1978), Matthews et al. (1979), Agrinier et al. dating of rutile is based on the occurrences of unstable (radioactive) (1985), Zheng et al. (1999), Li et al. (2003) and Gao et al. (2006). The terms ‘hot’ and uranium isotopes 238U and 235U incorporated into the rutile crystal ‘cold’ refer to the temperature conditions during eclogite facies metamorphism, based structure, which decay over several stages (decay chain) into stable on quartz–rutile geothermometry. Note that a number of samples from the ‘cold’ 206 207 eclogite suite experienced retrograde isotope exchange subsequent to the eclogite daughter lead isotopes Pb and Pb, respectively (Jaffey et al., facies metamorphism (see Section 4.3.2). 1971; Table 4). By measuring the parent/daughter ratios and known G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 17

Table 3 Table 4 U values (in ppm) for rutile from different source lithologies compiled from literature. Half-life and decay constant values of parent–daughter pairs of uranium and thorium Note that the lowermost concentrations for U (minimum values) are deﬁned by the (data from Jaffey et al., 1971; Stacey and Kramers, 1975). detection limit of the technique applied for analysis. Felsic granulite comprises here granulite and granulite facies gneiss. Quartz vein data are mainly from eclogite facies Isotope decay Half-life value Decay constant quartz veins (n=75), supplemented by low-temperature (hydrothermal) quartz vein t1/2 λ mineralisation (n=9) and a single granitic pegmatite vein sample (n=1). (yr) (yr− 1)

Felsic granulite Eclogite Quartz vein Metasediment 238U→ 206Pb+84He+6β− 4.4683×109 1.55125×10− 10 235U→ 207Pb+7 4He+4β− 0.70381×109 9.8485×10− 10 n 185 91 85 40 232Th→ 208Pb+6 4He+4β− 14.01×109 0.49475×10− 10 Min 0.01 0.01 0.15 0.70 Max 390 170 176 143 Med 19 1 7 10 Avg 24 5 9 21 Measurements to determine the required parent/daughter ratios are Std 33 22 19 27 performed by conventional isotope dilution-thermal ionisation mass Ref (1) (2) (3) (4) spectrometry (ID-TIMS), secondary ion mass spectrometry (SIMS), of — — — Abbreviations: n number of data, Min minimum value, Max maximum value, which the sensitive high-resolution ion microprobe (SHRIMP) is an Med — Median, Avg — average (arithmetic mean), Std — Standard deviation (1σ). Ref — References: (1) Mezger et al. (1989, 1991), Romer and Rötzler (2001), Luvizotto and example, and laser ablation inductively coupled plasma mass spec- Zack (2009); (2) Zack et al. (2002), Li et al. (2003), Schärer and Labrousse (2003), Xiao trometry (LA-ICP-MS). Rutile has some advantages compared with et al. (2006), Gao et al. (2007), Miller et al. (2007), Kylander-Clark et al. (2008); (3) zircon for U–Pb dating. Firstly, rutile from granulite facies rocks contains Richards et al. (1988), Uher et al. (1998), Franz et al. (2001), Xiao et al. (2006), Gao et al. almost no Th, allowing common lead correction via 208Pb (Allen and (2007), Kylander-Clark et al. (2008); (4) Mezger et al. (1989, 1991), Corfu et al. (1994), Campbell, 2007; Zack et al., 2008; see also Ireland and Williams, 2003). Möller et al. (1995, 2000), Bibikova et al. (2001), Zack et al. (2002), Luvizotto et al. (2009a). Secondly, the isotope composition of Pb in rutile is usually highly radiogenic, and U–Pb ages are mostly concordant (Mezger et al., 1989, 1991; Mukasa et al., 1998; Möller et al., 2000; Bibikova et al., 2001). decay constants, it is possible to calculate the age when rutile cooled Thirdly, rutile appears to be resistant to subsequent resetting of Pb below its “blocking” or closure temperature. The latter is around values (Vry and Baker, 2006). 600 °C for rutile grains larger than about 0.2 mm in diameter Rutile has also some disadvantages compared with zircon for U–Pb (Cherniak, 2000; Vry and Baker, 2006), which is much higher than dating. Rutile usually has lower U contents compared with zircon. previously thought (370–500 °C: Mezger et al., 1989). The mathe- Furthermore, there is a lack of large, isotopically homogeneous and matical expression to determine the age of a rutile sample, as applied commonly available natural rutile standards to assess measurement to any closed system, is given as: methods and demonstrate the quality of acquired geochemical data, although this may change in the future (Luvizotto et al., 2009b). 1 D Eclogitic rutile commonly has low U contents (Table 3; Fig. 21), t = ln 1 + λ P which in turn leads to low radiogenic Pb contents, and can contain a relatively large proportion of common (nonradiogenic) Pb (Cherniak, where t is the elapsed time, λ the decay constant of the parent isotope, 2000; Franz et al., 2001; Schärer and Labrousse, 2003). Therefore, ln the natural logarithm, D the number of atoms of the daughter common Pb correction is important in age calculation, based on the isotope in the sample, and P the number of atoms of the parent isotope isotope composition of rutile in a single analysis (Cherniak, 2000; Li et in the sample. al., 2003). Correction for common Pb for the U–Pb data can be made using the measured 238U/206Pb and 207Pb/206Pb ratios following Tera- Wasserburg (1972) as outlined, for example, in Williams (1998). Further possibilities are the use of a Pb growth model (Stacey and Kramers, 1975) and a numerical solution if measurement of 204Pb is not possible (Andersen, 2002). Common Pb correction is also possible by using Pb ratios obtained from leached K-feldspars or the host whole-rock sample (e.g. Mezger et al., 1989). The latter method is only applicable for rutile of known igneous or metamorphic host rocks and not for detrital rutile. The problem of common Pb correction can be avoided if there is the chance to construct an isochron (e.g. Schandl et al., 1990; Li et al., 2003; Stendal et al., 2006). This, however, requires analyses of a sufﬁcient number of coexisting minerals with large U/Pb fractionation (e.g. Mukasa et al., 1998; Li et al., 2003; Schärer and Labrousse, 2003). Fig. 22 schematically illustrates the interpretation of U/Pb ratios of rutile in the conventional (Wetherill) concordia plot and in a U–Pb isochron diagram.

4.4.2. Examples Radiometric dating of rutile has been successfully carried out for more than two decades (e.g. Corfu and Andrews, 1986; Schärer et al., 1986; Richards et al., 1988). For example, Mezger et al. (1989) applied the rutile geochronometer to reconstruct the pressure–temperature evolution of Archaean and Proterozoic high-grade polymetamorphic Fig. 21. Box and whisker plots showing U values for rutile from different source terrains in North America. They recognised that within a single hand- lithologies. The box represents the middle 50%; the bar inside the box represents the specimen larger rutile grains give older ages than do smaller ones and median. ‘Outliers’ are represented by black rectangles. n — number of data used. See explained this observation with volume diffusion directly related to Table 3 for references. Although included in the calculation, note that for illustration purpose the high U value of 390 ppm of a single granulite facies rutile grain is not the dimensions of the rutile crystal. Mezger et al. (1989) furthermore − 1 shown here. deﬁned that at a cooling rate of about 0.5–1°CMa the closure 18 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

Wong et al. (1991) used the ID-TIMS method to carry out U–Pb isotope dating on rutile from Archaean greenstones and gold mineralisation in the Val d'Or region of Quebec. They determined a U–Pb age of 2684±7 Ma, which overlaps within the analytical error with previous 40Ar/39Ar ages on hornblende (2693±17 Ma and 2672±23 Ma) and thus shows the successful application of U–Pb rutile dating. Hydrother- mal rutile from the alteration zone around a quartz vein gave a Pb–Pb isochron age of about 2600 Ma that was interpreted as the time of rutile growth during vein emplacement and constrains the age of gold mineralisation. Bibikova et al. (2001) dated rutile from various rocks of the Archaean domain of the Belomorian Belt and its junction zone with the Karelian Protocraton of the Baltic Shield. The analysed rutiles gave concordant U–Pb ages between 1740 and 1810 Ma and are about 50– 100 Ma younger than the coexisting titanite, with smaller age difference in the junction zone and larger age difference in the main body of the Belomorian Belt. The difference in U–Pb ages may reflect different cooling histories of both units (see Bibikova et al., 2001 for discussion). Hirdes and Davis (2002) carried out a multigrain ID-TIMS analysis of rutile from garnet-hornblende gneiss of southeastern Ghana. The 206Pb/238U age of 576±2 Ma corrected for common Pb is concordant and was interpreted by them as a younger limit on metamorphism when the cooling isograd passed through the closure temperature of rutile. Li et al. (2003) reported the first high-precision U–Pb age for metamorphic rutile of about 218 Ma (ID-TIMS) from coesite-bearing eclogite of the Dabie Mountains using conventional U–Pb dating and the isochron dating method (see also Chen et al., 2006). They analysed two colour types of rutile, light red and reddish brown, which showed no systematic difference in the concentrations of U and Pb or of Pb isotope ratios. In addition, they showed that omphacite in eclogite has a low U/Pb ratio and thus suggested that the Pb composition of omphacite can be used for common Pb correction in U–Pb dating of rutile from eclogites. Flowers et al. (2005) obtained 206Pb/238U ages of rutile (and titanite and apatite) from a Mesozoic magmatic arc in New Zealand to constrain the timing and duration of exhumation. Franz and Romer (2007) dated Fig. 22. (a) Conventional concordia plot after Wetherill (1956) illustrating the U–Pb syn-eclogite facies rutile from the Strona–Ceneri Zone of the Southern systematic of rutile for various stages of Pb loss. Assuming a simple two-stage history, Alps using the ID-TIMS method to constrain the tectonometamorphic fi the upper concordia intercept of a best- t line gives the crystallisation age of the rutile evolution at the northern margin of Gondwana during Early Palaeozoic while the lower intercept gives the age of isotopic disturbance. Discordance is – commonly caused by Pb loss due to radiation damage of the crystal structure. Schmitz time. Further U Pb ages of rutile (and titanite) were obtained from and Bowring (2003) and Kramers et al. (2009) discuss causes of Pb loss in detail. eclogites of the WGR to assess the style and timing of exhumation and (b) Schematic 238U/204Pb–206Pb/204Pb isochron diagram for a suite of co-genetic rutile cooling of that UHP terrane (Kylander-Clark et al., 2008). There seem to grains. For example, this method has successfully been applied by Li et al. (2003).Ina be fundamental differences in the mechanisms controlling the evolution 206 204 238 204 closed system, the Pb/ Pb ratios (y-axis) plotted against the U/ Pb ratios (x- of large UHP terranes (Dabie–Sulu, WGR) that undergo protracted axis) should ideally define a straight line, termed an ‘isochron’. This, however, is normally not the case because of analytical uncertainties. Hence, the analytical errors subduction and exhumation, and smaller UHP terranes (e.g. Dora Maira must be considered when the best-fit line through the analytical data points is in the Western Alps) that undergo rapid subduction and exhumation determined by least-squares regression techniques (York, 1967, 1969). The intercept (Kylander-Clark et al., 2008, and references therein). 206 204 with the y-axis gives the initial Pb/ Pb ratio of the system (t=0). The slope of the Besides isotopic dating of rutile from metamorphic rocks, a best-fit line (regression line) yields the age of the co-genetic rutile grains. Note that the interpretation of a Pb–Pb isochron diagram is more complex (e.g. Patterson, 1956). number of studies have also been already shown the power of radiometric rutile dating in sedimentary successions from the Palaeoproterozoic to the Holocene worldwide. temperature for U–Pb diffusion in rutile is about 420 °C for grains with SHRIMP U–Pb work by Sircombe (1995, 1997) on rutile from a radius of 90–210 μm and about 380 °C for grains with a radius of 70– mineral sands in eastern Australia has shown a predominance of Late 90 μm. The significance of these conclusions has been debated, as Proterozoic/Early Cambrian grains that are exotic to the local con- discussed later in this section. tinental hinterland (Williams, 1998). Romer and Rötzler (2001) analysed rutile grains from granulite Harrison et al. (2007) used a SIMS multi-collector facility to facies rocks of the Saxonian Granulite Massif. The grains had low determine 207Pb/206Pb ages of detrital rutile from the famous Jack radiogenic Pb contents and yielded a broad range in apparent 206Pb/ Hills quartzite of Western Australia. They recognised a distinct age 238U ages, which was interpreted by the authors as being due to initial peak at 2.5 Ga, which corresponds to regional metamorphism and isotope heterogeneity. Franz et al. (2001) and Chen et al. (2005) had a local granite emplacement in the Archaean Narryer Gneiss Complex. similar problem with eclogitic rutile from Dabie and Sulu respectively. Stendal et al. (2006) carried out lead isotope analyses using a step Heterogeneity of the initial Pb isotopic composition in combination leaching process on rutile grains from alluvial heavy mineral deposits with the inability to make a sufficiently good common Pb correction and from a Neoproterozoic garnet–kyanite micaschist of the Yaoundé for each individual rutile U–Pb analysis will lead to ambiguous results. Group, southern Cameroon. The 207Pb/204Pb and 206Pb/204Pb data for G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 19 most rutiles from heavy mineral concentrates yielded scattered plots by hydrothermal fluids and natural leaching by groundwater, “after on the Pb–Pb isochron diagram, with no possibility to define a clear which it would become both incompatible in the lattice and highly age. However, those from the micaschist defined an age of about mobile in solution” (Kramers et al., 2009). Although data are still 950 Ma, which suggests that rutile in the Yaoundé Group formed pending, it is likely that in rutile radiogenic Pb is also tetravalent. In during early Pan-African metamorphism or was inherited as detrital conclusion, fluids are more likely to affect rutile in slowly cooled than in rutile from an early Pan-African source (Stendal et al., 2006). rapidly cooled terrains. The change from tetravalent to divalent Pb Birch et al. (2007) used LA-ICP-MS to date detrital rutile from the causes loss of radiogenic Pb and thus of “age” (Kramers et al., 2009). This Late Cretaceous–Tertiary gold-bearing White Hills Gravel placer may explain why rutile from slowly cooled terrains often has younger deposits of the Victorian uplands in Australia. The analysed rutiles U–Pb ages compared with coexisting titanite and hornblende Ar–Ar show up to 5.5 wt.% Nb2O5 and 2.9 wt.% WO3 and together with their ages. The disagreement between the experimental Pb diffusion data and weighted mean 206Pb/238U age of 393±10 Ma (2σ) suggest an origin the field-based observations may be because the experiments do not associated with granite intrusion in the St Arnaud district (Birch et al., fully reflect the conditions for slowly cooled terrains and hence a change 2007). of the valence state of radiogenic Pb does not occur in the experiments. Allen and Campbell (2007) analysed rutiles from a sand sample of the lower Mississippi River in the U.S.A. using LA-ICP-MS. They 4.5. (U–Th)/He thermochronology identified a major Appalachian source and noted that some trace elements (i.e. Cr, V and Zr) show strong correlation with age. The 4.5.1. Introduction latter effect is probably caused by diffusion of cation substitutions for The application of (U–Th)/He thermochronology to rutile is still in Ti4+ in the crystal lattice of rutile under slow cooling conditions (see its preliminary stages. In general, thermochronology is a temperature- Cherniak et al., 2007b). sensitive radiometric dating technique, which constrains low-tem- Taylor (2008) used an excimer laser system coupled to a perature, upper crustal processes such as timing and duration of quadrupole ICP-MS to date rutile from the North Kimberley kimberlite mineralisation, rate of exhumation and erosion of igneous and province of northwestern Australia and from a present-day stream metamorphic rocks (Farley, 2002; McInnes et al., 2005; Reiners and catchment within the Georgina Basin, Northern Territory, Australia. Brandon, 2006, and references therein). The method is based on the He identified potential source areas and discussed the application of measurement of radiogenic 4He produced from 238U, 235U and 232Th rutile dating to diamond exploration. decay (Farley, 2002; Reiners and Brandon, 2006; Table 4). The daughter helium is retained in the rutile crystal lattice until the grain 4.4.3. Pb diffusion is heated above the closure temperature where the lattice becomes The closure temperature for U in rutile is strongly dependent on weak for helium loss. Preliminary (U–Th)/He thermochronology on grain size (Mezger et al., 1991; Cherniak, 2000; see equation below). rutile by Crowhurst et al. (2002) has suggested a closure temperature Thus, if rutile grains of different sizes are dated, as is commonly the of N180–200 °C, which is about 100 °C higher than the closure case in sedimentary provenance studies, different rutile ages may not temperature for apatite (75–100 °C; Farley, 2002) but in the range of necessarily represent different igneous or metamorphic events, but the closure temperature for zircon (171–196 °C; Reiners et al., 2004). may reflect the cooling history of each individual rutile grain. Initial step-heating He diffusion experiments by Stockli et al. (2005, However, the differences between closure temperatures for rutile 2007) and Wolfe et al. (2007) suggest a closure temperature of about grains of different sizes are only of minor significance (few tens of 220–235 °C. As already documented in the previous section, the degrees for cooling rates between 1 and 10 °C Ma− 1 and grain sizes closure temperature is dependent on a series of parameters such as up to a few millimetres) (Cherniak, 2000). The corresponding grain size, shape and cooling rate. In the case of rapid cooling of the mathematical expression to determine the closure temperature (Tc) sample, the (U–Th)/He age reflects cooling of the sample through its of rutile, as applied to any other mineral, is given as: closure temperature and can often be related to a particular geological event (Dodson, 1973; McInnes et al., 2005). Slow cooling over a longer E = R T = time interval, however, will give an age that is not necessarily related c 2 = 2 = Þ ln A × R × Tc × D0 a E × Cr to any specific geological event (McInnes et al., 2005). Further details about the dependence of closure temperature from cooling rate can be where R is the gas constant, E the activation energy, A the geometric found, for instance, in Reiners and Brandon (2006). factor, D the factor for diffusion of the relevant species, a the effective diffusion radius and Cr the cooling rate (Dodson, 1973). Cherniak (2000) 4.5.2. Examples gave examples of closure temperature values of 567 °C for 70 μm-size Only a few applications of (U–Th)/He thermochronology to rutile grains and 617 °C for 200 μm-size grains, for a cooling rate of 1 °C Ma−1 have been published. Crowhurst et al. (2002) analysed rutile from a with grains of spherical geometry. Moreover, it is likely that under some metamorphic rock in South Australia and determined an average (U– conditions of slow cooling, rutile will record significantly younger U–Pb Th)/He age of 472±20 Ma that they interpreted as later stage cooling ages compared to coexisting zircon (Cherniak, 2000). Li et al. (2003) related to the Delamerian Orogeny. McInnes et al. (2005) presented pointed out that a number of field-based studies on rutile of slowly preliminary rutile and zircon age data of a porphyry copper deposit cooled terrains have demonstrated younger U–Pb ages compared with from Iran, which yielded identical ages within error supporting the coexisting titanite and hornblende Ar–Ar ages (Mezger et al., 1989; predicted similarity in rutile and zircon He closure temperatures. Bibikova et al., 2001; Hirdes and Davis, 2002; Schmitz and Bowring, Stockli et al. (2007) analysed rutile from mantle and lower crustal 2003). Although the causes of the disagreement between the experi- xenoliths from Cenozoic volcanic rocks in the western U.S.A. and mental Pb diffusion data and the field-based observations remained demonstrated that the determined (U–Th)/He ages are in excellent unclear, Li et al. (2003) expressed their preference for the field-based agreement with both 40Ar/39Ar and zircon (U–Th)/He data. To quantify rutile closure temperature estimates by Mezger et al. (1989). the position of the rutile He partial retention zone (e.g. Reiners and Kramers et al. (2009) recently discussed the valence state of Pb in Brandon, 2006) and to constrain the thermal history of Variscan zircon and suggested that radiogenic Pb is tetravalent, being similar in basement rocks, Wolfe et al. (2007) determined rutile (U–Th)/He ages ionic charge and effective ionic radius to U and Th, and hence has an of amphibolites from the borehole of German Continental Deep extremely low diffusivity. In general, the loss of radiogenic Pb causes Drilling Project, which is, at 9101 m and a cost of about US$350 million, younger U–Pb ages. However, “radiogenic Pb cannot be lost from zircon the deepest and most expensive borehole for research in Germany crystals except by being reduced to the divalent state” that can be caused (Emmermann and Lauterjung, 1997). Dunkl and von Eynatten (2009) 20 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28

Fig. 23. Schematic diagram for thermal history of speciﬁc minerals in an idealised rock during uplift. The temperature represents the closure temperature for each radiometric system of the individual mineral. The closure temperatures were taken from Cherniak (2000), Möller et al. (2000) and Crowhurst et al. (2002).

– Fig. 24. Box and whisker plots showing Hf values for rutile from different source used anchizonal hydrothermal grown rutile crystals from the sub- lithologies. The box represents the middle 50%; the bar inside the box represents the greenschist facies metamorphosed Mesozoic sandstones of Oman for median. ‘Outliers’ are represented by black rectangles. n — number of data used. See (U–Th)/He thermochronology, which allowed them to determine fluid Table 5 for references. and thermal events after Late Cretaceous ophiolite emplacement. Although the results outlined above are preliminary studies only, it unstable (radioactive) 176Lu isotope incorporated into the crystal seems obvious that (U–Th)/He thermochronology on rutile can place lattice, which undergoes spontaneous β-decay to the stable daughter − − important constraints on the igneous and metamorphic evolution of a 176Hf isotope, with a decay constant of 1.93×10 11 year 1 (Sguigna region. Moreover, as already applied for zircon (McInnes et al., 2005, et al., 1982). The decay constant of 176Lu, however, has currently been and references therein), combined U–Pb dating and (U–Th)/He under review, which led to proposals of revised decay constants, i.e. − − − − thermochronology on rutile grains can provide information on their 1.865×10 11 year 1 (Scherer et al., 2001), 1.983×10 11 year 1 − − age of formation and cooling history (Fig. 23). Note at the time of (Bizzarro et al., 2003) and 1.945×10 11 year 1 (Luo and Kong, writing this paper no study had been published about (U–Th)/He 2006). Owing to the large half-life of 176Lu of about 35–40 billion thermochronology on detrital rutile. Nonetheless, this might change years, the Lu–Hf system is suitable for tracing the history of the solar in the future since (U–Th)/He thermochronology seems useful in system and the evolution of the Earth's crust–mantle system (Patchett sediment provenance analysis to reconstruct both the age of potential et al., 1981; Patchett, 1983; Salters and Zindler, 1995; Blichert-Toft source lithologies and the timing of tectonic uplift in the source area. and Albarède, 1997; Amelin et al., 1999; Griffin et al., 2000; Choukroun et al., 2005; Amelin, 2006; Aulbach et al., 2008). 4.6. Lu–Hf isotopes The Lu–Hf isotope system is generally less disturbed by alteration processes than other isotope systems such as Rb–Sr, Sm–Nd and U–Pb 4.6.1. Introduction (see discussions in Patchett, 1983; Griffin et al., 2000; Kinny and Maas, Rutile typically has Hf concentrations between b5 and 120 ppm, 2003). Experimental studies have shown that Hf diffusion is but also higher amounts occur (Table 5; Fig. 24), and low Lu/Hf ratios, significantly slower than diffusion of divalent and trivalent cation so that correction for in situ radiogenic growth is negligible. Hafnium substitutions; for example, it is about an order of magnitude slower isotope studies of single minerals are based on the occurrences of the than Pb diffusion (Cherniak et al., 2007b). However, Luvizotto and Zack (2009) have recently shown for granulite facies metapelitic rocks – Table 5 from the Ivrea Verbano Zone that Hf incorporation in rutile is tem- Hf values (in ppm) for rutile from different source lithologies compiled from literature. perature dependent. Note that the lowermost concentrations for Hf (minimum values) are defined by the The Lu–Hf isotope system has been widely applied in earth sciences detection limit of the technique applied for analysis. Felsic granulite comprises here over the last decades. Its application is based on the fact that Lu and Hf granulite facies gneiss. Quartz vein data are mainly from eclogite facies quartz veins fi (n=74), supplemented by a single low-temperature (hydrothermal) quartz vein partition differently into speci c minerals such as garnet, zircon and sample (n=1). rutile, and Lu/Hf ratios are thereby strongly fractionated during partial melting, metamorphism and metasomatism (Salters and Zindler, 1995; Felsic granulite Eclogite Quartz vein Metasediment Amelin et al., 1999; Griffin et al., 2000; Kinny and Maas, 2003). n 173 368 75 19 Therefore, the Hf isotope composition of the Earth's crust–mantle Min 0.05 1.65 1.34 1.08 system varies widely between the depleted mantle (Lu/HfNchondritic), Max 194 189 86 21 b Med 68 12 9 4 the enriched crust (Lu/Hf chondritic) and any remaining unfractio- Avg 76 12 10 6 nated source (Lu/Hf=chondritic), as shown in Fig. 25. Different Lu/Hf Std 43 11 9 5 ratios reflect the long-term evolution of these reservoirs (Patchett et al., Ref (1) (2) (3) (4) 1981; Choukroun et al., 2005). Hafnium preferentially enters the melt Abbreviations: n — number of data, Min — minimum value, Max — maximum value, phase, which leaves a residuum with relatively higher Lu/Hf ratios for Med — Median, Avg — average (arithmetic mean), Std — Standard deviation (1σ). Ref — the subcontinental lithospheric mantle. However, metasomatism by References: (1) Luvizotto and Zack (2009); (2) Zack et al. (2002), Xiao et al. (2006), Gao melts derived from the asthenospheric mantle can introduce Hf, which et al. (2007), Miller et al. (2007), Schmidt et al. (2009); (3) Zack et al. (2002), Xiao et al. (2006), Gao et al. (2007), John et al. (2008); (4) Zack et al. (2002), Luvizotto et al. produces lithospheric mantle with relatively low Lu/Hf ratios (Chouk- (2009a). ukroun et al., 2005). The deviations of the Hf isotope composition of a G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 21

4.6.2. Examples The use of in situ Lu–Hf isotope analysis has rapidly increased in recent years because of an increase in sophisticated laser ablation multi-collector ICP-MS facilities, which allow precise isotope analysis of samples with Hf quantities as low as 25 ng (Blichert-Toft and Albarède, 1997; Amelin et al., 1999). Choukroun et al. (2005) analysed the Hf isotope composition of rutile from MARID xenoliths of the Kimberley area, South Africa. The 176Hf/177Hf ratios are highly variable

(0.2811–0.2858, εHf =−55 to +110), with much of this range found in single samples and even within single grains. They noted that such a wide range of Hf isotope composition within single samples and within single rutile grains could not be generated by radioactive decay of 176Lu in the rutile within the age of the Earth. Choukroun et al. (2005) therefore interpreted the ranges in Hf isotope composition as reﬂecting primary interaction of an asthenospheric-derived melt with ancient depleted harzburgitic mantle, which was later overprinted by metasomatism. The authors explained low 176Hf/177Hf ratios still preserved in some MARID rutile grains by mixing between an asthenospheric-derived melt and the ancient subcontinental lithospheric mantle. Aulbach et al. (2008) analysed 176Hf/177Hf of rutile in eclogite xenoliths from kimberlites of the Lac de Gras area, northern Canada. They received similar, highly variable 176Hf/177Hf ratios (0.28156–

0.28568, εHf = −43 to +103), with negligible intergrowth of radiogenic Hf in rutile since emplacement of the kimberlite, as shown by low 176Lu/177Hf ratio of 0.000039±0.000077 (1σ). They recognised a correlation between Nb/Ta and minimum 176Hf/177Hf of eclogitic rutiles, and interpreted the low 176Hf/177Hf and suprachondritic Nb/Ta values as acquired during interaction with a component derived from ancient metasomatised subcontinental lithospheric mantle. By contrast, they interpreted rutile with high 176Hf/177Hf and subchondritic Nb/Ta values as having preserved its primary HFSE concentrations and isotope characteristics. Their study clearly shows that Lu–Hf isotope analysis combined with trace element geochemical data of rutile is particularly helpful for a better understanding of the evolution of the Earth's crust and mantle. New studies are under way – – Fig. 25. (a) Schematic illustration of Lu Hf isotope evolution in the Earth's crust mantle to improve Lu–Hf isotope analysis on rutile (Ewing et al., 2009). system (modified from Patchett et al., 1981; Kinny and Maas, 2003). Partial melting in At the time of writing this paper, no study had been published the Earth's mantle at time t1 results in divergent Hf isotope evolution paths for the newly generated crust (low Lu/Hf) and the residual mantle (high Lu/Hf). This is because about Lu–Hf isotope analysis of detrital rutile. However, this might Hf enters the melt phase and Lu is preferentially retained in the mantle, which becomes change in the future since the Lu–Hf isotope composition of rutile more radiogenic with time. Hence, any rutile formed within the crust has extremely represents an estimate of the protolith composition at the time of low Lu/Hf, which over time diverges in composition from the remainder of the host crystallisation and therefore is helpful in tracing potential source rock. At time t2, a variety of possible sources may contribute to newly formed crust. 176 177 (b) Schematic illustration showing εHf as function of crystallisation age. The Hf/ Hf rocks in sediment provenance studies. ratio and the εHf value of a sample (calculated for the age of the sample) can be used to produce a growth line that indicates the depleted mantle curve. The intersection yields 5. Economic importance of rutile a depleted mantle (TDM) model age. This model age could reflect the time (t1) at which the source of the magma from which a mineral (e.g. rutile) crystallised was extracted from the depleted mantle reservoir. Alternatively, the model age may reflect a mixing 5.1. Introduction age of more ancient (e.g. with TDM model age of t1) with more juvenile (with a TDM model age of t3) crust. Although the primary purpose of this paper is to provide information on various applications of rutile in earth sciences, an outline of the economic importance of rutile is essential because the sample from that of the chondritic uniform reservoir (CHUR) are com- academic issues mentioned above have also important commercial monly expressed in epsilon units (εHf) as given by following equation implications. (Patchett et al., 1981): One of the major subjects for earth scientists is the exploration and evaluation of mineral raw materials, including hydrocarbons, gold, 2 3 diamonds, chromium, iron, nickel and platinum group metals but also 176 = 177 6 Hf Hf 7 titanium minerals. The world total rutile reserves are estimated to ε = 4sample −15 ×104 Hf 176 = 177 be 45 million t and those of ilmenite are about 680 million t, with Hf Hf chondrite ilmenite supplying about 92% of the world's demand for titanium Samples with higher than chondritic 176Hf/177Hf at time t have minerals (Gambogi, 2009). Titanium minerals are commercially 176 177 positive εHf values; those with lower than chondritic Hf/ Hf have important because they are processed to titanium metal, which is negative εHf values, and hence chondrites per definition have εHf =0. used, for instance, in the aerospace industry because of its low weight, The 176Hf/177Hf ratios are used to determine Hf model ages, which are high strength and resistance to heat and corrosion. Rutile is one of the a measure of the average time since the source of the magma from favoured minerals for the production of titanium dioxide white which a mineral (e.g. rutile) crystallised was extracted from the pigment, dominantly through the chloride manufacturing process depleted mantle reservoir (Fig. 25b). (Stanaway, 1994; Korneliussen et al., 2000). The main applications of 22 G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 titanium dioxide white pigment are in the manufacture of paint (51% 2000), with Sierra Leone being an exception. Thus, an alternative of total production), paper (19%) and plastics (17%) (Pearson, 1999; source for high-grade TiO2 ores (such as eclogite) has to be found. Carp et al., 2004; Gambogi, 2008). Other uses include ceramics, coated The eclogites of the Western Gneiss Region, Norway, contain fabrics and textiles, floor coverings, printing ink, roofing granules, several million tons of rutile, and are therefore a large rutile resource food colouring (E171), tablet coating, toothpaste and as a UV absorber (Korneliussen and Foslie, 1985; Korneliussen et al., 2000). The in sunscreen cream with high sun protection factors (Carp et al., 2004; eclogites occur as pods and lenses within amphibolite to granulite Gambogi, 2008, and references therein). Thus, titanium dioxide facies metamorphosed Proterozoic/sub-Caledonian gneisses and have (rutile) is always present in our daily life. Moreover, since Fujishima rutile concentrations in the range of 1 to 4 wt.%, although higher and Honda (1972) successfully showed the application of TiO2 as a concentrations occur locally (Korneliussen, 1980; Korneliussen and photoanode to decompose water by visible light, anatase has received Foslie, 1985). Ilmenite is important in the economic evaluation of much attention in photocatalysis (Carp et al., 2004). This use has also rutile-rich eclogite deposits, for two main reasons (Korneliussen and been extended to rutile (e.g. Lu et al., 2004; Chuan et al., 2008), Foslie, 1985). First, intergrowths of less-valuable ilmenite will lower although its reaction rate is a fifth of anatase (Chuan et al., 2008). In the purity, and accordingly the values of the rutile concentrate that can contrast to rutile containing, for example, V and Fe, pure rutile shows be produced. Second, an increase in the ilmenite concentration in no photoactivity (Lu et al., 2004). Chuan et al. (2008) used natural V- eclogite will lead to a correspondingly smaller amount of Ti available to bearing rutile from a rutile mine in the Shaanxi Province, China, to form rutile (Korneliussen and Foslie, 1985). Moreover, the grain size of decompose methylene blue and suggested the application of rutile for the rutile and the CaO content in the concentrates (should be less than large-scale photocatalytic decomposition of organic pollutants in 0.2%) are of considerable importance in the economic evaluation of quiet and still waters. rutile-rich eclogite deposits (Korneliussen et al., 2000). Further examples of rutile-bearing eclogite of economic importance are 5.2. Economic importance known from the Piampaludo deposit, Italy (Force, 1991; Liou et al., 1998), the Shubino deposit, Russia (Force, 1991) and from the Dabie– Most of the natural rutile used in industry comes from heavy mineral Sulu deposits, China (Chen et al., 2005; Huang et al., 2006; Zhang et al., sands (placer deposits) enriched in ilmenite and rutile (e.g. Force, 1991; 2006). For instance, in the Sulu UHP metamorphic terrane the rutile Roy, 1999; Pirkle et al., 2007). The world's largest sedimentary deposits modal content in eclogite is 2–5 vol.% and can be as high as 8–10 vol.% of rutile and the largest rutile mine are both in Sierra Leone. Before its (Chen et al., 2005). closure in 1995, the rutile operation in Sierra Leone supplied 137,000 t Minor economically important sources of natural rutile are ore (Mobbs, 1996), which was about two-thirds of the world's rutile output deposits (Czamanske et al., 1981; Clark and Williams-Jones, 2004), in 1994. Although rutile is commercially important, rutile mining causes amphibolitic rocks (Korneliussen et al., 2000: 40), granitic pegmatites drastic changes to the environment (Akiwumi and Butler, 2008). The and rare-earth element mineralisation (Scott, 1988; Černý et al., 1999; Sierra Rutile Mine reopened in 2006, and Sierra Leone may become one Černý and Chapman, 2001). Clark and Williams-Jones (2004) of the world's leading rutile producers in the future. In 2006, 70,360 t of discussed anomalous compositions of rutile at certain deposits for rutile (worth US$28.5 million) was exported (Bermúdez-Lugo, 2008). their potential as indicators of metallic mineralisation (see Scott, Other African rutile placer deposits occur in Cameroon (exploited 1988, 2005; Scott and Radford, 2007). Thus, detrital rutile can be used between 1935 and 1955 near Yaoundé), Gambia (mined in the 1950s), as pathfinder mineral in stream sediments to guide the exploration Guinea (deposits not yet exploited), Kenya (to commence in the near geologists to metallic mineralisation. Table 2 shows a compilation of future), Malawi (exploration has been conducted in recent years) and various rutile-bearing deposits and the characteristic trace elements South Africa (Stendal et al., 2006; Dill, 2007b; Schlüter, 2008). Rutile incorporated into the rutile crystal lattice. Moreover, besides pyrope placer deposits are also mined in Australia, India, Ceylon and U.S.A. garnet, chrome diopside and chrome spinel, rutile can also be used as (Goldsmith and Force, 1978; Force, 1991; Roy, 1999; Force, 2000; Pirkle a kimberlite indicator mineral (Smythe et al., 2008) and therefore et al., 2007). plays an important role in diamond exploration. Fig. 26 shows the world largest producers of natural rutile and the trend of growth between 2006 and 2008. For example, in 2008, the world production of natural rutile was about 608,000 t, with Australia Table 6 (309,000 t), South Africa (121,000 t) and Sierra Leone (95,000 t) Key elements in natural rutile useful for a wide range of applications in earth sciences being the three largest producers (Gambogi, 2009). However, rutile (see text for explanation). placer deposits are limited in volume and are rapidly being depleted, Key elements Applications Comment and therefore, the current producers may not be able to fulfil the Cr and Nb Source rock These elements allow discrimination world's need in the future (Korneliussen, 1980; Korneliussen et al., characterisation between rutile derived from metamafic lithologies (high Cr, low Nb) or metapelitic lithologies (low Cr, high Nb). V, Ni, Cu, Nb, Sn, Source rock Rutile containing these elements is useful as Sb, Ta and W characterisation pathfinder mineral in stream sediments to identify and trace the type of metallic mineralisation. Zr Zr-in-rutile Zr in rutile can yield the temperature of thermometry rutile crystallisation. O O isotopy O isotope data can yield information about the temperature of rutile crystallisation and the extent and nature of fluid–mineral interactions. U and Pb U–Pb U/Pb and Pb/Pb isotope ratios can yield the geochronology age of rutile crystallisation. U, Th and He (U–Th)/He (U–Th)/He isotope ratios are used to thermochronology calculate an age related to the time the rutile cooled through about 200 °C. Lu and Hf Lu–Hf isotopy The Hf isotope composition of rutile allows identifying the magmatic source by Fig. 26. World production of natural rutile by country between 2006 and 2008, reference to an Earth model. according to data in Gambogi (2008, 2009). G. Meinhold / Earth-Science Reviews 102 (2010) 1–28 23

6. Summary Aulbach, S., O'Reilly, S.Y., Griffin, W.L., Pearson, N.J., 2008. Subcontinental lithospheric mantle origin of high niobium/tantalum ratios in eclogites. Nature Geoscience 1, 468–472. Rutile is widely distributed as an accessory mineral in igneous, Baier, J., Audétat, A., Keppler, H., 2008. The origin of the negative niobium tantalum metamorphic and sedimentary rocks. Its geochemical composition anomaly in subduction zone magmas. Earth and Planetary Science Letters 267, 290–300. allows tracing the formation and evolution of the Earth's continental Bailey, D.K., 1961. Intrusive limestones in the Keshya and Mkwisi valleys, Northern crust because rutile is a major host mineral for Nb, Ta and other HFSE, Rhodesia. Quarterly Journal of the Geological Society 117, 419–442. which are widely used as a monitor of geochemical processes in the Bakun-Czubarow, N., Kusy, D., Fiala, J., 2005. Trace element abundances in rutile from – ł crust and mantle such as magma evolution and subduction-zone eclogite granulite rock series of the Z ote mountains in the Sudetes. Mineralogical Society of Poland, Special Papers 26, 132–136. metamorphism. Processes influencing the Nb/Ta ratio of minerals (e.g. Baldwin, J.A., Brown, M., 2008. Age and duration of ultrahigh-temperature metamor- rutile) and rocks are continuously topics of scientific debate. In recent phism in the Anapolis–Itaucu Complex, Southern Brasilia Belt, central Brazil — – years, many data have been generated which significantly increased constraints from U Pb geochronology, mineral rare earth element chemistry and trace-element thermometry. Journal of Metamorphic Geology 26, 213–233. our knowledge about rutile and its host lithologies. Table 6 gives a Baldwin, S.L., Monteleone, B.D., Webb, L.E., Fitzgerald, P.G., Grove, M., Hill, J., 2004. summary of key elements in natural rutile that are useful for a wide Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea. range of applications in earth sciences. For example, elements such as Nature 431, 263–267. Banfield, J.F., Veblen, D.R., 1991. The structure and origin of Fe-bearing platelets in Cr, Nb, Sb and W are used to trace the provenance of rutile. A number of metamorphic rutile. American Mineralogist 76, 113–127. publications have already shown that rutile geochemistry, Zr-in-rutile Baur, W.H., 1956. Über die Verfeinerung der Kristallstrukturbestimmung einiger thermometry and isotope studies of rutile are useful methods in both Vertreter des Rutiletyps: TiO2, SnO2, GeO2 und MgF2. Acta Crystallographica 9, 515–520. hard and soft rock geology. Rutile is also of economic importance Baur, W.H., 1961. Atomabstände und Bindungswinkel im Brookit, TiO2. Acta Crystal- because of its use in the manufacture of white titanium dioxide lographica 14, 214–216. pigment, which is a major constituent in various products of our daily Baur, W.H., 2007. The rutile type and its derivatives. Crystallography Reviews 13, fi 65–113. life. Heavy mineral sands containing a signi cant percentage of rutile Bayley, W.S., 1923. The occurrence of rutile in the titaniferous magnetites of western are therefore the focus of exploration worldwide. Because these North Carolina and eastern Tennessee. Economic Geology 18, 382–392. mineral sands are limited in volume and are rapidly being depleted, an Bell, D., Rossman, G., 1992. Water in Earth's mantle: the role of nominally anhydrous – alternative source for high-grade TiO ores has to be found. This clearly minerals. Science 255, 1391 1397. 2 Bermúdez-Lugo, O., 2008. The mineral industries of Liberia and Sierra Leone. 2006 shows the growing demand for further rutile-related research in earth Minerals Yearbook. U.S. Geological Survey. sciences. I hope that this review will serve as a good source of reference Bibikova, E., Skiold, T., Bogdanova, S., Gorbatschev, R., Slabunov, A., 2001. Titanite–rutile for earth scientists both in academic research and in industry. thermochronometry across the boundary between the Archaean Craton in Karelia and the Belomorian Mobile Belt, eastern Baltic Shield. Precambrian Research 105, 315–330. Acknowledgements Birch, W.D., Barron, L.M., Magee, C., Sutherland, F.L., 2007. Gold- and diamond-bearing White Hills Gravel, St Arnaud district, Victoria: age and provenance based on U–Pb dating of zircon and rutile. Australian Journal of Earth Sciences 54, 609–628. I would like to thank all the scientists who have been interested in Bizzarro, M., Baker, J.A., Haack, H., Ulfbeck, D., Rosing, M., 2003. 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