Detrital Rutile Grains Research Articles

LA-ICP-MS U–Pb dating and trace element analyses of detrital rutile from the Elbtal Group (Saxony, Germany): provenance constraints of the Saxonian Cretaceous Basin

AbstractThe steep sandstone cliffs of the Upper Cretaceous Elbtal Group exposed in the Eastern Erzgebirge and the Zittau Sandstone Mountains are impressive remnants of the Saxo-Bohemian Cretaceous Basin. Despite the excellent exposure, little is known about the provenance. Herein, we present LA-ICP-MS U–Pb and trace element data of detrital rutile grains separated from five different formations of the Elbtal Group to characterise and differentiate potential source regions. The Cenomanian samples of the Eastern Erzgebirge (Niederschöna and Oberhäslich formations, lower Elbtal Group) yield an U–Pb rutile age cluster at 320–330 Ma. The source rock lithology is predominantly of metapelitic origin. The Zr-in-rutile temperatures indicate amphibolite- to lower granulite-facies metamorphic conditions. Thus, the Variscan basement exposed in the Erzgebirge is assumed as proto source. The Middle Turonian to Early Coniacian samples from the Zittau Sandstone Mountains (Oybin, Lückendorf and Waltersdorf formations; upper Elbtal Group) yield similar U–Pb rutile ages with a cluster at 320–330 Ma. The source rock lithology is likewise predominantly classified as metapelitic and the Zr-in-rutile temperatures cluster in upper amphibolite- to granulite-facies metamorphic conditions. Exposures with high-grade metamorphic Variscan basement are assumed as likely proto sources for these sedimentary rocks. Sedimentary structures indicate a northerly source and thus contrast with direct input from the Variscan basement located to the south and east. Thus, the most likely sedimentary model is reworking of sediments that were eroded from the Variscan basement prior to the Turonian and deposited within a basin at the northern margin of the Bohemian Massif. Graphical abstract

Provenance of Detrital Rutiles from the Triassic–Jurassic Sandstones in Franz Josef Land (Barents Sea Region, Russian High Arctic): U-Pb Ages and Trace Element Geochemistry

Provenance study plays an important role in paleogeographic and tectonic reconstructions. Detrital zircons are commonly used to identify sediment provenance; however, a wide range of detrital zircon ages in clastic rock often represent a fingerprint of reworked older terrigenous successions rather than ages of magmatism and metamorphism in the provenance area. This study focuses on the provenance of detrital rutile grains in the Triassic–Jurassic sandstones from Franz Josef Land and shows the importance of multiproxy approaches for provenance studies. Trace element data demonstrate that most rutile grains were sourced from metapelitic rocks, with a subordinate population having a metamafic origin. The Zr-in-rutile thermometer and U-Pb geochronology suggest that detrital rutile grains were predominantly derived from rocks that underwent amphibolite facies metamorphism during the Paleozoic era, with a predominance of the Carboniferous–Permian ages. Therefore, we suggest that the provenance area for the studied sandstones on Franz Josef Land has a similar geological history to the Taimyr region and Severnaya Zemlya archipelago. We propose that this crustal domain extends across the Kara Sea and forms the basement to the north and east of FJL, representing a proximal provenance for the studied Mesozoic terrigenous rocks. This domain experienced both Middle–Late Ordovician and Carboniferous–Permian metamorphism. The comparison of U-Pb dating and the geochemistry of rutile, U-Th/He, and U-Pb dating of zircons showed that detrital rutiles are the powerful toll in provenance restoration and can give additional constrains when a provenance area locates within collisional-convergent settings.

Detrital rutile tracks the first appearance of subduction zone low T/P paired metamorphism in the Palaeoproterozoic

Earth is unique in the Solar System as the only planet characterised by an active plate tectonic regime. However, there is still no consensus on whether this was fully operational in the Archaean or if it did not develop until the Proterozoic. The metamorphic record offers valuable insight into this debate, since paired, high and low T/P metamorphic conditions are a hallmark of modern plate tectonics. However, much of the metamorphic rock record has either been eroded or overprinted by subsequent tectonothermal events. To address this issue, we examine the detrital rock record and evaluate the potential of rutile, a mineral that forms during subduction and deep-crustal metamorphic processes, as a proxy to track the existence of low T/P and paired metamorphism. At temperatures of 550°C, rutile is mostly stable at pressures higher than ca. 13 kbar. We use this relationship and the Zr-in-rutile thermometer to determine peak metamorphic temperatures of detrital rutile grains to track the temporal distribution of low T/P metamorphism. We have compiled a dataset of detrital metamorphic rutile from Archaean to Permian age to trace the occurrence of low and high T/P metamorphism through time. The earliest evidence of low T/P from detrital rutile is at about 2.1 Ga. This agrees with the earliest evidence of eclogite facies conditions from the rock record and it also implies that these conditions must have been more prevalent than the present rock record seems to indicate. Together, our study confirms that subduction zone low T/P metamorphism has been fully operating since at least the late Palaeoproterozoic.

Rutile Mineral Chemistry and Zr-in-Rutile Thermometry in Provenance Study of Albian (Uppermost Lower Cretaceous) Terrigenous Quartz Sands and Sandstones in Southern Extra-Carpathian Poland

The geochemistry of detrital rutile grains, which are extremely resistant to weathering, was used in a provenance study of the transgressive Albian quartz sands in the southern part of extra-Carpathian Poland. Rutile grains were sampled from eight outcrops and four boreholes located on the Miechów, Szydłowiec, and Puławy Segments. The crystallization temperatures of the rutile grains, calculated using a Zr-in-rutile geothermometer, allowed for the division of the study area into three parts: western, central, and eastern. The western group of samples, located in the Miechów Segment, is characterized by a polymodal distribution of rutile crystallization temperatures (700–800 °C; 550–600 °C, and c. 900 °C) with a significant predominance of high-temperature forms, and with a clear prevalence of metapelitic over metamafic rutile. The eastern group of samples, corresponding to the Lublin Area, is monomodal and their crystallization temperatures peak at 550–600 °C. The contents of metapelitic to metamafic rutile in the study area are comparable. The central group of rutile samples with bimodal distribution (550–600 °C and 850–950 °C) most likely represents a mixing zone, with a visible influence from the western and, to a lesser extent, the eastern group. The most probable source area for the western and the central groups seems to be granulite and high-temperature eclogite facies rocks from the Bohemian Massif. The most probable source area for the eastern group of rutiles seems to be amphibolites and low temperature eclogite facies rocks, probably derived from the southern part of the Baltic Shield.

Provenance of detrital rutiles from the Jurassic sandstones in the Central Sakarya Zone, NW Turkey: U-Pb ages and trace element geochemistry

This provenance study focuses on detrital rutile grains from Jurassic sandstones of the Bayırköy Formation in the central Sakarya Zone. Cr and Nb concentrations of detrital rutile grains in the Jurassic sandstones vary from 18 to 6855 μg/g and 70–13440 μg/g, respectively. Source area discrimination based on the Cr-Nb concentrations shows that 79 % of the detrital rutile grains originated from metapelitic and 21 % from metamafic rocks. The calculated rutile formation temperatures vary from 471 to 798 ℃ with an average temperature of 635 ℃ at P=10 kbar. Zr-in-rutile thermometer gives overlapping temperatures for all detrital rutile grains from both the metapelitic and metamafic sources. This demonstrates that most of the detrital rutiles sourced from metapelitic and metamafic rocks underwent similar metamorphic conditions and have similar metamorphic history. The U-Pb rutile dating yielded ages for the detrital rutiles in the time range of 346 to 319 Ma, which gives the age of metamorphism for the potential source rocks. Trace element compositions, Zr-in-rutile thermometer and U-Pb rutile geochronology show that detrital rutile grains were predominantly derived from early Carboniferous rocks that underwent metamorphism in amphibolite-facies conditions. Amphibolite-facies rocks of the Sarıcakaya Massif in the central Sakarya Zone seem to be the primary source lithologies for the detrital rutiles in the Jurassic Bayırköy Formation as it comprises previously-mentioned source lithologies and has a close geographic position to the area studied. Carboniferous Variscan metamorphism was followed by emplacement of numerous post-collisional granitoids in the central Sakarya Zone.

Unraveling the origin of the Parnaíba Basin: Testing the rift to sag hypothesis using a multi-proxy provenance analysis

Syneclises are long-lived sedimentary basins characterized by complex subsidence and erosion histories. The premise that these geotectonic units evolve from initial rifting processes following thermal (or flexural) subsidence is widespread in the geologic sciences and, to this day, remains a controversial issue. Seeking to test this hypothesis, we proceeded a novel multi-proxy provenance study aiming to identify differences (and/or similarities) in the sedimentary signal and source areas of the Jaibaras (rift) and Parnaíba (sag) basins. We conducted a detailed analysis of trace elements geochemistry of detrital rutile grains, macroscopic gravel composition and paleocurrents from the sedimentary deposits of the Aprazível Formation (Ediacaran - Cambrian, top of Jaibaras Basin) and the Ipu Formation (Ordovician, basal unit of Parnaíba Basin). Our data reveal that important changes in source areas occurred between the end of the rifting and the beginning of the sag phase, reinforcing the hypothesis that the evolution of the Jaibaras and Parnaíba basins were not genetically related. Our results demonstrate that conglomerates of the rift sequence are predominantly composed of volcanic, sedimentary, and metamorphic angular to sub-angular clasts, pointing to diverse, nearby source areas. Contrastingly, conglomerates of the initial sag sequence have greater sedimentary maturity, with dominant rounded vein quartz clasts and other minor source contributions, which suggest distant source areas, showing a consistent paleocurrent direction towards NW. Indeed, the detrital rutile trace elements geochemistry demonstrates that the source areas of these two units were distinct, revealing an important decrease in the input of granulite facies and metamafic grains in the sag basin comparing with the rift succession. In conclusion, as well as paleomagnetic and geochronological studies, the provenance methods using a multi-proxy approach proved to be an effective and powerful technique for distinguishing modifications in the sedimentary signal between rift-to-sag sequences.

Rutile as a pathfinder for metals exploration

The use of detrital rutile as an indicator of mineralisation is contingent on the identification of trace element signatures that uniquely distinguish rutile grains derived from mineralisation from those sourced from barren rocks. In order to discriminate rutile sources, principal component analysis was applied to a total of 3149 LA-ICP-MS analyses of rutile from ore environments (Au, Au-Cu, pegmatites, carbonatites, lamprophyres, VHMS) and barren igneous and metamorphic rocks. Hierarchical clustering of the results of principal component analysis (PCA) determined Sb and Cr exhibit the most chemical variation in ore-derived rutile. Rutile sourced from Au deposits and enriched in Sb, can be distinguished from rutile from pegmatites, which are enriched in Nb, Ta and Sn. Discriminating rutile from barren rocks can be done primarily using W and Fe contents, which can also provide insight on source rocks based on metamorphic grade and degree of crustal input.Clustering all rutile chemistries based on PCA of 12 elements, identified nine chemically distinct groups from ore mineralisation, and barren igneous and metamorphic rocks, primarily using variation in W and Cr contents. Two groups are solely derived of rutile from Au ores (high versus low Sb rutile). Of the remaining seven groups, one group is comprised mainly of rutile from pegmatites (high Nb, Ta, Sn), four groups are comprised solely of rutile from barren rocks and two groups are a mix of ore and non-ore rutile. Rutile from Au ore, similar to the giant Kalgoorlie and Big Bell Au deposits, is distinctive compared to rutile from all other rocks and can be distinguished from other ores and barren environments using multi-element clustering of PCA analysis. Thus rutile chemistry of detrital rutile grains is a valuable tool in Au exploration.

Interpretation and significance of combined trace element and U–Pb isotopic data of detrital rutile: a case study from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany

The U–Pb age and trace element composition of detrital rutile provide information about the metamorphic history of the source region that cannot be constrained by traditional U–Pb dating of detrital zircon. Previous provenance investigations focussed on only one of these methods. Based on a large LA-ICP-MS trace element and U–Pb isotopic dataset of detrital rutile and U–Pb isotopic data of detrital zircon from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany, this paper discusses the application and significance of combining these methods in provenance investigations. U–Pb age spectra from the detrital zircons analysed show multiple age components (multimodal age spectra) in all samples. This is in contrast with the detrital rutile data, as only one sample yielded a multimodal U–Pb age distribution. Multimodal age spectra of detrital rutile are most likely preserved in sediments from (large) catchment areas with complex geological histories. They may also be related to specific sedimentation events, such as glacial washout during the retreat of large ice shields (e.g. the Hirnantian glaciation of Gondwana). Unimodal age spectra are however not restricted to small catchment areas, if the provenance region is characterized by a pervasive thermal overprint such as the Pan-African orogeny throughout Gondwana. Unimodal age distributions may further consist of overlapping age cluster detectable by different trace element composition of the detrital rutile grains. The combined U–Pb age and trace element data from detrital rutile grains demonstrate that rutile sourced from metapelitic rocks yield reliable and precise U–Pb ages. In contrast, detrital rutile classified to be of metamafic origin generally has too low uranium concentrations to be dated reliably by LA-ICP-MS. Detrital rutile records low- to medium-grade metamorphic events in the source region and therefore has the potential to better constrain the maximum depositional age of sedimentary rocks in comparison to U–Pb dating of detrital zircon.

Rutile alteration and authigenic growth in metasandstones of the Moeda Formation, Minas Gerais, Brazil – A result of Transamazonian fluid–rock interaction

Microstructures, trace elements and U–Pb ages of rutile grains are reported from two metasandstone samples of the Moeda Formation, which is the basal unit of the Minas Supergroup in the Quadrilátero Ferrífero, Minas Gerais, Brazil. The Moeda metasandstones, deposited between 2.68 and 2.65 Ga, are intercalated with Witwatersrand-like, pyritiferous and auriferous metaconglomerate layers. Rutile from both samples shows unusually high contents of Th (1–142 ppm) and rare-earth elements (ΣREE = 1–132 ppm), with chondrite-normalized middle REE humps, and reveals post-depositional U–Pb ages of ≤2.25 Ga; only three grains yielded significantly older ages of up to 2.72 Ga, pointing to a detrital origin. The combined data set suggests that rutile formation and alteration at 2.25 Ga was caused by distinct fluid-mediated processes, which erased nearly all provenance information. Detrital, rounded rutile grains in sample A were altered by a coupled dissolution–reprecipitation process (type 1), resulting in highly porous grains. These show variable contents of rutile-compatible and -incompatible trace elements: Th (1–48 ppm), Zr (25–796 ppm), U (12–167 ppm), Pb (9–52 ppm), Cr (900–12,878 ppm), W (143–3939 ppm), Nb (1148–6168 ppm), Sb (6–63 ppm), as well as variable ratios of Zr/Hf, Y/Ho and Th/U. Rutile grains in sample B are mostly authigenic (type 2), and formed after dissolution of pre-existing detrital rutile grains and subsequent transport and homogenization of trace elements. This interpretation is supported by the anhedral shape of some grains and the finding of numerous, randomly oriented muscovite laths. The authigenic population has significantly lower, and less variable contents of trace elements compared to type-1 rutile: Th (0.5–16 ppm), Zr (21–67 ppm), U (5.8–24 ppm), Pb (6-18 ppm), Cr (1379–3153 ppm), W (9.4–70 ppm), Nb (921–3058 ppm), Sb (3.3–10 ppm), and distinctively lower ratios of Zr/Hf (7.9) and Th/U (0.2), but variable Y/Ho ratios. Significant contents of Th and REE are explained by co-precipitation with TiO2 aggregates prior to structural ripening. The close association of rutile with muscovite, the rutile MREEN humps and the results of Zr-in-rutile thermometry suggest that rutile formation and alteration in the investigated sandstones was mediated by K(Na)–Si–P-bearing aqueous fluids at temperatures of about 490 °C. The rutile MREEN humps are interpreted to result from the tetrad effect during leaching of spatially associated detrital zircon grains. Uranium–Pb ages of ≤2.25 Ga indicate that the fluid overprint started at the onset of the Transamazonian orogeny, perhaps related to the opening of the Sabará foreland basin.

Provenance of a large Lower Cretaceous turbidite submarine fan complex on the active Laurasian margin: Central Pontides, northern Turkey

The Pontides formed the southern active margin of Laurasia during the Mesozoic. They became separated from mainland Laurasia during the Late Cretaceous, with the opening of the Black Sea as an oceanic back-arc basin. During the Early Cretaceous, a large submarine turbidite fan complex developed in the Central Pontides. The turbidites cover an area of 400km by 90km with a thickness of more than 2km. We have investigated the provenance of these turbidites—the Çağlayan Formation—using paleocurrent measurements, U-Pb detrital zircon ages, REE abundances of dated zircons and geochemistry of detrital rutile grains. 1924 paleocurrent measurements from 96 outcrop stations indicate flow direction from northwest to southeast in the eastern part of the Çağlayan Basin and from north-northeast to west-southwest in the western part. 1194 detrital zircon ages from 13 Lower Cretaceous sandstone samples show different patterns in the eastern, central and western parts of the basin. The majority of the U-Pb detrital zircon ages in the eastern part of the basin are Archean and Paleoproterozoic (61% of all zircon ages, 337 grains); rocks of these ages are absent in the Pontides and present in the Ukrainian Shield, which indicates a source north of the Black Sea. In the western part of the basin the majority of the zircons are Carboniferous and Neoproterozoic (68%, 246 grains) implying more local sources within the Pontides. The detrital zircons from the central part show an age spectrum as mixture of zircons from western and eastern parts. Significantly, Jurassic and Early Cretaceous zircons make up less than 2% of the total zircon population, which implies lack of a coeval magmatic arc in the region. This is compatible with the absence of the Lower Cretaceous granites in the Pontides. Thus, although the Çağlayan Basin occupied a fore-arc position above the subduction zone, the arc was missing, probably due to flat subduction, and the basin was largely fed from the Ukrainian Shield in the north. This also indicates that the Black Sea opened after the Early Cretaceous following the deposition of the Çağlayan Formation.

RELEASE OF TRACE ELEMENTS THROUGH THE SUB-GREENSCHIST FACIES BREAKDOWN OF DETRITAL RUTILE TO METAMORPHIC TITANITE IN THE OTAGO SCHIST, NEW ZEALAND

Detrital rutile is observed in trace amounts in the sub-greenschist facies, graywacke, and argillite lithologies of the Torlesse Terrane-derived Otago Schist, New Zealand. Trace element analyses reveal that mean compositions of detrital rutile grains are characterized by high concentrations (500–3600 ppm) of V, Cr, Fe, Zr, Nb, and W, moderate amounts (100–500 ppm) of Sn and Ta, and minor amounts (50–100 ppm) of Mn and Hf. Recrystallization of detrital rutile to metamorphic titanite is first observed in the prehnite-pumpellyite facies rocks, with recrystallization largely complete by upper chlorite greenschist facies. Dissolution, material transport, and precipitation reactions were crucial in the progression of this recrystallization reaction, with pore spaces generated allowing the transportation of Ca, Si, and O to the titanite-rutile interface. Redistribution of trace elements during the mineral transition of detrital rutile to metamorphic titanite was assessed using mass-balance techniques. These calculations indicate that V, Cr, Zr, Nb, Ta, and W were released during the prograde mineral reaction. The liberation of this suite of trace elements potentially provides a source for the W and Cr enrichment observed in the orogenic deposits of the Otago Schist.

Detrital rutile geochemistry and thermometry from the Dabie orogen: Implications for source–sediment links in a UHPM terrane

This study explores the potential of detrital rutile geochemistry and thermometry as a provenance tracer in rocks from the Central Dabie ultrahigh-pressure metamorphic (UHPM) zone in east-central China that formed during Triassic continental collision. Trace element data of 176 detrital rutile grains selected from local river sediments and 91 rutile grains from distinct bedrocks in the Shuanghe and Bixiling areas, obtained by both electron microprobe (EMP) and in situ LA-ICP-MS analyses, suggest that geochemical compositions and thermometry of detrital rutiles are comparable to those from their potential source rocks. After certification of the Cr–Nb discrimination method for the Central Dabie UHPM zone, we show that 29% of the detrital rutiles in the Shuanghe area were derived from metamafic sources whereas in the Bixiling area that it is up to 76%. Furthermore, the proportion of distinct types of detrital rutiles combined with modal abundances of rutile in metapelites and metamafic bedrocks can be used to estimate the proportion of different source lithologies. Based on this method the proportion of mafic source rocks was estimated to ∼10% at Shuanghe and >60% at Bixiling, respectively, which is consistent with the proportions of eclogite (the major rutile-bearing metamafic rock) distribution in the field. Therefore, the investigation of detrital rutiles is a potential way to evaluate the proportion of metamafic rocks and even to prospect for metamafic bodies in UHPM terranes. Zr-in-rutile temperatures were calculated at different pressures and compared with temperatures derived from rock-in rutiles and garnet-clinopyroxene Fe–Mg thermometers. Temperatures calculated for detrital rutiles range from 606°C to 707°C and 566°C to 752°C in Shuanghe and Bixiling, respectively, at P=3GPa with an average temperatures of ca. 630°C for both areas. These temperature averages and ranges are similar to those calculated for rutiles from surrounding source rocks. Combined with comparable Zr distribution characteristics between detrital and source rock rutiles, demonstrating a close source–sediment link for rutiles from clastic and rock in UHPM terranes. Thus rutiles can be accurate tracers of source rock lithologies in sedimentary provenance studies even at a small regional scale. In Bixiling, Nb/Ta ratios of metamafic and metapelitic detrital rutiles fall between 11.0 to 27.3 and 7.7 to 20.5, respectively. In contrast, in Shuanghe, these ratios are highly variable, ranging from 10.9 to 71.0 and 7.6 to 87.1, respectively. When ignoring four outlier compositions with extremely high Nb/Ta in Shuanghe, a distinct clustering of Nb/Ta ratios in rutiles is shown: metapelitic detrital rutiles have Nb/Ta of 7–40 vs. metamafic detrital rutiles with Nb/Ta=11–25. The Nb/Ta characteristics in detrital rutiles from both areas may reflect the degree of fluid–rock interaction during metamorphism and/or different source lithologies. Therefore, the trace element compositions in detrital rutiles can accurately trace the lithology, proportion and fluid–rock interaction of different source rocks.

Towards identifying the origin of metamorphic components in Austrian loess: insights from detrital rutile chemistry, thermometry and U–Pb geochronology

Trace element (Cr, Nb, Zr) geochemistry and U–Pb geochronology of detrital rutile grains provide constraints on the nature of potential metamorphic sources of loess in Austria. Cr and Nb compositions reveal rutile sources with a predominance of metapelitic lithologies for all three loess samples. By contrast, Zr-in-rutile geothermometry indicates that formation temperatures for loess rutiles around Krems (at the Bohemian Massif = BM) proved to be ca 100–125 °C higher (Tmedian = 717 and 737 °C for two samples from Stratzing and Krems) than those at Wels (close to the Eastern Alps = EA; Tmedian = 612 °C), implying that rutiles in loess at Wels were derived from Alpine lower amphibolite-grade rocks, while those in loess around Krems from rocks formed under upper amphibolite to granulite-grade conditions. Metamorphic temperatures recorded in rutiles from loess at the BM closely match the ‘two-reaction’ thermobarometry estimates of the last high-T overprint (7–11 kbar and 700–800 °C) of rocks making up the Varied series and Gföhl units around Krems. This event dated at 340 to 350 Ma is believed to be captured by the detrital rutile U–Pb data as well (e.g. 349 ± 21 and 352 ± 32 Ma). All these data demonstrate the significance of proximal BM sources (Varied series and Gföhl unit drained by the Danube) in loess formation around Krems. Fluvial transport is believed to have played a substantial role in entraining and accumulating rutiles for subsequent aeolian deflation for loess near Wels. While the ultimate sources of these grains are likely to be in the Eastern Alps, the recycling of these rutiles from the flysch zone of the EA cannot be ruled out.Despite the uncertainties of Cr–Nb-based source discriminations in some cases and the potential decoupling of Zr- and U–Pb systematics recognized in rutiles, this study demonstrates that rutiles may provide unique details on the nature and metamorphic history of their parent rocks, if used with caution and by knowing its limitations under certain conditions. It is anticipated that, beyond zircon, rutile geochemistry will become a powerful provenance tracer in loess studies too. This seems to be particularly important to gain a better understanding on the erosion and rutile fertility of different metamorphic terrains and their contributions to loess material, issues that have not been adequately addressed thus far.

U–Pb SHRIMP ages of detrital granulite-facies rutiles: further constraints on provenance of Jurassic sandstones on the Norwegian margin

AbstractElectron microprobe analyses of 128 detrital rutile grains from two Jurassic sandstone samples (Hettangian and Bajocian–Bathonian in age) from hydrocarbon exploration wells on the Norwegian margin confirm that more than 85 % of the rutiles were derived from metapelitic rocks. Zr-in-rutile geothermometry confirms that about 83 % of the rutile was formed under high-grade metamorphism (>750 °C). Sixty-two rutile grains, including 60 of the identified high-temperature rutile population, were also analysed for U–Pb geochronology using SHRIMP. The 206Pb–238U rutile ages range from approximately 485–292 Ma, with a major cluster between 450 and 380 Ma. These data suggest that the detrital rutile was predominantly derived from a felsic source that experienced granulite-facies metamorphism about 450–380 Ma ago. This conclusion is consistent with derivation from high-grade Caledonian metasedimentary rocks, probably the Krummedal sequence in central East Greenland, as previously suggested by an earlier provenance study using conventional heavy mineral analysis, garnet geochemistry and detrital zircon age dating. The present study underscores the importance of rutile geochemistry and geochronology in quantitative single-mineral provenance analysis of clastic sedimentary rocks.

Rutile occurrence and trace element behavior in medium-grade metasedimentary rocks: example from the Erzgebirge, Germany

Metamorphic textures in medium-grade (~500–550°C) metasedimentary rocks from the Erzgebirge give evidence of prograde rutile crystallization from ilmenite. Newly-crystallized grains occur as rutile-rich polycrystalline aggregates that pseudomorph the shape of the ilmenites. In-situ trace element data (EMP and SIMS) show that rutiles from the higher-grade samples record large scatter in Nb content and have Nb/Ti ratios higher than coexisting ilmenite. This behavior can be predicted using prograde rutile crystallization from ilmenite and indicates that rutiles are reequilibrating their chemistry with remaining ilmenites. On the contrary, rutiles from the lowest grade samples (~480°C) have Nb/Ti ratios that are similar to the ones in ilmenite. Hence, rutiles from these samples did not equilibrate their chemistry with remaining ilmenites. Our data suggest that temperature may be one of the main factors determining whether or not the elements are able to diffuse between the phases and, therefore, reequilibrate. Newly-crystallized rutiles yield temperatures (from ~500 to 630°C, Zr-in-rutile thermometry) that are in agreement with the metamorphic conditions previously determined for the studied rocks. In quartzites from the medium-grade domain (~530°C), inherited detrital rutile grains are detected. They are identified by their distinct chemical composition (high Zr and Nb contents) and textures (single grains surrounded by fine grained ilmenites). Preliminary calculation, based on grain size distribution of rutile in medium-grade metapelites and quartzites that occur in the studied area, show that rutiles derived from quartzites can be anticipated to dominate the detrital rutile population, even if quartzites are a minor component of the exposure.

Trace element abundances in rutiles from eclogites and associated garnet mica schists

We present electron microprobe and laser ablation microprobe (LAM) data for a range of high field strength (Zr, Nb, Mo, Sn, Sb, Hf, Ta, W) and other trace elements (Al, Si, Ca, V, Cr, Mn, Fe, Pb, Th, U) in rutile from eclogites and garnet mica schists from Trescolmen, Central Alps. Most analysed rutiles are homogeneous (at least for Nb, Cr, W, Zr, V and Fe), both on a single grain scale and between grains from a single thin section. Concentrations of V, Zr, Nb, Sb and W determined by both electron and laser ablation microprobe techniques yield similar results and confirm the reliability of the analytical methods within estimated precision. Measurements of trace element contents of coexisting phases in eclogites and their modal abundances show that rutile is the dominant carrier (>90% of whole rock content) for Ti, Nb, Sb, Ta and W as well as an important carrier (5–45% of the whole rock content) for V, Cr, Mo and Sn. The crystallographic implications are that, for relatively rigid crystal sites such as in rutile, trace elements with a similar ionic radius are preferred over trace elements with the same charge but deviating size. Our results demonstrate the utility of rutile chemistry in the following applications: (1) By using a combination of the measured TiO 2 content of the whole rock and the trace element concentration of rutile, precise whole rock data on elements that are either difficult to analyze by conventional techniques such as XRF or solution ICP-MS (Nb, Sb, Ta, W) or may be susceptible to late stage alteration (Sb) can be estimated. (2) Trace element contents of detrital rutile grains are a potentially powerful tool for sedimentary provenance studies since they reflect key element ratios (e.g., Nb/TiO 2 and Cr/TiO 2) of their source rocks. In addition, measurements of trace elements in detrital rutiles might help distinguish possible source rocks, e.g., high-grade metamorphic rocks such as eclogites and high-pressure granulites from hydrothermal ore deposits and kimberlites. In view of the dominance of rutile in the Sb budget of subducting oceanic crust, and the enrichment of Sb in the slab component of subduction zones, additional experimental studies on Sb-partitioning between rutile and fluid are needed in order to understand the behaviour of Sb in subduction zones.