Sedimentary Provenance Studies Research Articles

U‐Pb Detrital Zircon Analysis – Results of an Inter‐laboratory Comparison

Inter‐laboratory comparison of laser ablation ICP‐MS and SIMS U‐Pb dating of synthetic detrital zircon samples provides an insight into the state‐of‐the art of sedimentary provenance studies. Here, we report results obtained from ten laboratories that routinely perform this type of work. The achieved level of bias was mostly within ± 2% relative to the ID‐TIMS U‐Pb ages of zircons in the detrital sample, and the variation is likely to be attributed to variable Pb/U elemental fractionation due to zircon matrix differences between the samples and the reference materials used for standardisation. It has been determined that ~ 5% age difference between adjacent age peaks is currently at the limit of what can be routinely resolved by the in situ dating of detrital zircon samples. Precision of individual zircon age determination mostly reflects the data reduction and procedures of measurement uncertainty propagation, and it is largely independent of the instrumentation, analytical technique and reference samples used for standardisation. All laboratories showed a bias towards selection of larger zircon grains for analysis. The experiment confirms the previously published estimates of the minimum number of grains that have to be analysed in order to detect minor zircon age populations in detrital samples.

An 800 million-year detrital zircon record of continental amalgamation: Tarim basin, NW China

Sedimentary provenance studies based on detrital zircon ages have proved to be a powerful tool for elucidating detailed patterns of erosion and sediment dispersal on and adjacent to the continents. This approach is commonly used to examine processes that occur over discrete intervals of geologic time, but it can also be used to address fundamental questions concerning the longer-term evolution of the continental crust. Central Asia, for example, consists of a Palaeozoic accretionary collage that contrasts with the cratonal cores of continents such as North America, which were fully consolidated during the Proterozoic. Detrital zircon provenance may thus provide important insights on the comparative evolution of these distinctly different styles of continental growth. The Tarim sedimentary basin is interpreted to be underlain by a micro-continental block that accreted to central Asia during the late Palaeozoic. Detrital zircon in pre-Permian strata of the northern Tarim basin includes Precambrian grains derived from Tarim basement, and Palaeozoic grains related to active tectonism along its margins. During this phase of tectonic amalgamation, overall sediment maturity increased up-section, consistent with similar observations from other cratons. However, in Tarim these trends reverse dramatically in Mesozoic and Cenozoic strata deposited after amalgamation of Tarim with central Asia. Palaeozoic zircon grains derived from the Tian Shan become dominant, Precambrian grains drop to trace abundances, and sandstone composition shift abruptly to immature litharenite. Moreover, a progressively increasing temporal gap occurs between zircon age and depositional age, reflecting the near absence of post-amalgamation magmatic or high-grade metamorphic rocks within the Tian Shan. Collectively, these observations support a model of Tarim and other central Asian basins as islands of long-lived tectonic stability, within an orogenic collage that has remained mobile for >250 million years.

U[sbnd]Pb LA-(MC)-ICP-MS dating of rutile: New reference materials and applications to sedimentary provenance

In response to the general lack of sufficiently abundant and high quality rutile UPb reference materials for in situ geochronology, we have characterised two new potential rutile ~1.8Ga reference materials (Sugluk-4 and PCA-S207) from granulite facies belts of the Canadian Shield, namely the northern Cape Smith Belt of Quebec and the Snowbird Tectonic Zone (Sasatchewan). Characterisation includes ID-TIMS and LA-ICP-MS UPb dating, imaging, and trace element analysis. We compare these materials with existing rutiles used already (R19 and R10; Luvizotto et al., 2009; Zack et al., 2011) and show that the measured UPb compositions (i.e. including any common Pb) of our rutiles are considerably more homogeneous. This makes possible a UPb normalisation procedure (not reliant upon a common Pb correction) that results in a significant decrease in the uncertainty contribution from the common Pb correction and better reproducibility of reference materials and unknowns for provenance analysis and other applications. The reproducibility is 2–4% (2RSD) for 206Pb/238U and 207Pb/206Pb, only slightly greater than long-term data for zircon reference materials. We show in a rutile provenance study from young orogens (Bhutan Himalaya and Canadian Cordillera) that the sensitivity of our analytical set-up allows dating of ~90% of rutiles in a sediment using a 50μm laser ablation spotsize within samples containing rutile as young as 10–20Ma, and obviates the requirement for U concentration pre-screening, thus reducing or eliminating rutile selection bias. Unsuccessful analyses are due to poor quality rutiles with predominant common Pb, 207Pb signal below detection, or U content below ~1–2ppm. We have used the ‘207Pb-method’ (using the Tera-Wasserburg diagram) to correct for substantial common Pb in very young and/or very low-U rutiles, rather than developing an on-line correction. Since rutile ages reflect mainly the time of cooling, rutile is a sensitive recorder of metamorphic thermochronological information and therefore is an excellent complement to detrital zircon U207Pb data. The contrast between zircon and rutile signatures in Himalayan samples with rutile as young as 10Ma is shown to be very dramatic (most zircons from the same sample are >480Ma, with only a few grains or metamorphic rims reflecting Miocene metamorphism); as such rutile provides complementary information about the thermal events within the source regions of the grains. Rutile UPb dating is an underexploited provenance method with wide applicability to sedimentary provenance studies.

On the visualisation of detrital age distributions

Since the development of SIMS and LA-ICP-MS technologies in the 1980s and 1990s, single grain U–Pb dating of detrital zircon has quickly become the most popular technique for sedimentary provenance studies. Currently by far the most widespread method for visualising detrital age distributions is the so-called Probability Density Plot (PDP), which is calculated by summing a number of Gaussian distributions whose means and standard deviations correspond to the individual ages and their respective analytical uncertainties. Unfortunately, the PDP lacks a firm theoretical basis and can produce counter-intuitive results when data quantity (number of analyses) and/or quality (precision) is high. As a more robust alternative to the PDP, this paper proposes a standard statistical technique called Kernel Density Estimation (KDE), which also involves summing a set of Gaussian distributions, but does not explicitly take into account the analytical uncertainties. The Java-based DensityPlotter program (http://densityplotter.london-geochron.com) was developed with the aim to facilitate the adoption of KDE plots in the context of detrital geochronology.

Reorganization of a deeply incised drainage: role of deformation, sedimentation and groundwater flow

ABSTRACTDeeply incised drainage networks are thought to be robust and not easily modified, and are commonly used as passive markers of horizontal strain. Yet, reorganizations (rearrangements) appear in the geologic record. We provide field evidence of the reorganization of a Miocene drainage network in response to strike–slip and vertical displacements in Guatemala. The drainage was deeply incised into a 50‐km‐wide orogen located along the North America–Caribbean plate boundary. It rearranged twice, first during the Late Miocene in response to transpressional uplift along the Polochic fault, and again in the Quaternary in response to transtensional uplift along secondary faults. The pattern of reorganization resembles that produced by the tectonic defeat of rivers that cross growing tectonic structures. Compilation of remote sensing data, field mapping, sediment provenance study, grain‐size analysis and Ar40/Ar39 dating from paleovalleys and their fill reveals that the classic mechanisms of river diversion, such as river avulsion over bedrock, or capture driven by surface runoff, are not sufficient to produce the observed diversions. The sites of diversion coincide spatially with limestone belts and reactivated fault zones, suggesting that solution‐triggered or deformation‐triggered permeability have helped breaching of interfluves. The diversions are also related temporally and spatially to the accumulation of sediment fills in the valleys, upstream of the rising structures. We infer that the breaching of the interfluves was achieved by headward erosion along tributaries fed by groundwater flow tracking from the valleys soon to be captured. Fault zones and limestone belts provided the pathways, and the aquifers occupying the valley fills provided the head pressure that enhanced groundwater circulation. The defeat of rivers crossing the rising structures results essentially from the tectonically enhanced activation of groundwater flow between catchments.

Canonical correlation analysis as a tool in the provenance study of overbank sediments from the small mountainous watersheds

Canonical correlation analysis (CCA) is used in this study in order to trace the lineage of overbank sediment from the initial erosion of the parent rocks down to deposition of detrital material in alluvium of the small mountainous watersheds of the Žumberak area, Croatia. It helps to elucidate relations between the hierarchically structured systems (rocks, minerals, elements) represented by the ensembles of lithological, mineralogical and geochemical variables. Taking their place in the vertical order of hierarchical complexity, geochemistry and mineralogy of the recent material are considered dependent variable regarding the related watershed lithology, with geochemical variables (major and trace elements) last in the chain. Three canonical models are built and cross-compared in order to unravel the between-level relationships and infer the basic patterns of mineral and geochemical flux from the source rocks to basin. From these, the two hierarchical (provenance) chains epitomized in recombination of the first two canonical functions have been derived highlighting complementary provenances, weathering styles, and dispersion avenues in alluvial sedimentation of the study area. The first clearly separates carbonate from siliciclastic sedimentary source while the second illuminates the origin of phyllosilicate and ferric oxyhydroxide phases with associated suite of elements in absence of clear carbonate signal.

U–Pb and Th–Pb dating of apatite by LA-ICPMS

Apatite is a common U- and Th-bearing accessory mineral in igneous and metamorphic rocks, and a minor but widespread detrital component in clastic sedimentary rocks. U–Pb and Th–Pb dating of apatite has potential application in sedimentary provenance studies, as it likely represents first cycle detritus compared to the polycyclic behavior of zircon. However, low U, Th and radiogenic Pb concentrations, elevated common Pb and the lack of a U–Th–Pb apatite standard remain significant challenges in dating apatite by LA-ICPMS, and consequently in developing the chronometer as a provenance tool. This study has determined U–Pb and Th–Pb ages for seven well known apatite occurrences (Durango, Emerald Lake, Kovdor, Mineville, Mud Tank, Otter Lake and Slyudyanka) by LA-ICPMS. Analytical procedures involved rastering a 10 μm spot over a 40 × 40 μm square to a depth of 10 μm using a Geolas 193 nm ArF excimer laser coupled to a Thermo ElementXR single-collector ICPMS. These raster conditions minimized laser-induced inter-element fractionation, which was corrected for using the back-calculated intercept of the time-resolved signal. A Tl–U–Bi–Np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias. External standards (Plešovice and 91500 zircon, NIST SRM 610 and 612 silicate glasses and STDP5 phosphate glass) along with Kovdor apatite were analyzed to monitor U–Pb, Th–Pb, U–Th and Pb–Pb ratios Common Pb correction employed the 207Pb method, and also a 208Pb correction method for samples with low Th/U. The 207Pb and 208Pb corrections employed either the initial Pb isotopic composition or the Stacey and Kramers model and propagated conservative uncertainties in the initial Pb isotopic composition. Common Pb correction using the Stacey and Kramers (1975) model employed an initial Pb isotopic composition calculated from either the estimated U–Pb age of the sample or an iterative approach. The age difference between these two methods is typically less than 2%, suggesting that the iterative approach works well for samples where there are no constraints on the initial Pb composition, such as a detrital sample. No 204Pb correction was undertaken because of low 204Pb counts on single collector instruments and 204Pb interference by 204Hg in the argon gas supply. Age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common Pb-corrected ages, a Tera–Wasserburg Concordia intercept age and a Tera–Wasserburg Concordia intercept age anchored through common Pb. The samples in general yield ages consistent (at the 2σ level) with independent estimates of the U–Pb apatite age, which demonstrates the suitability of the analytical protocol employed. Weighted mean age uncertainties are as low as 1–2% for U- and/or Th-rich Palaeozoic–Neoproterozoic samples; the uncertainty on the youngest sample, the Cenozoic (31.44 Ma) Durango apatite, ranges from 3.7–7.6% according to the common Pb correction method employed. The accurate and relatively precise common Pb-corrected ages demonstrate the U–Pb and Th–Pb apatite chronometers are suitable as sedimentary provenance tools. The Kovdor carbonatite apatite is recommended as a potential U–Pb and Th–Pb apatite standard as it yields precise and reproducible 207Pb-corrected, 232Th– 208Pb, and common Pb-anchored Tera–Wasserburg Concordia intercept ages.

Diatom (< 63 µm) distribution offshore of eastern New Zealand: Surface sediment record and temperature transfer function

Diatom microfossils preserved in 38 core top samples from offshore of eastern New Zealand are examined to develop the first offshore modern analogue dataset for diatoms in New Zealand waters. The sample set consists of seven, approximately E–W trending depth transects with samples from the continental shelf, slope and abyssal plain between latitudes 33° and 54°S. The identification of terrestrial and coastal species in open marine core top samples indicates that offshore transport of diatom microfossils occurs to an extent that could be useful for sediment provenance studies or at least to enable improved identification of transported versus in-situ deposition on the continental shelf. Cluster analysis and ordination indicate that the Chatham Rise and/or the overlying Subtropical Front are the most significant bathymetric/oceanographic features in the dataset as this location shows up as a major barrier or transition zone in terms of diatom distribution. The strongest environmental control on diatom distribution is the north–south sea surface temperature gradient. A statistically strong relationship ( r 2 = 0.81; RMSEP = 1.57) exists between diatom abundance and sea surface temperature making diatoms ideal for quantitative reconstruction of past sea surface temperatures in future paleoclimate studies.

Detrital zircon ages: Improving interpretation via Nd and Hf isotopic data

The bulk of sedimentary provenance studies use similarities in the detrital zircon age patterns or “barcodes” in sedimentary systems and potential source regions to make interpretations about palaeogeographic settings. While this “age-only” approach is generally considered to be effective, it is limiting because the timing of zircon growth events may not be unique to specific terrains and important rock forming events may be associated with little zircon growth. To a significant extent these limitations can be overcome by employing additional isotopic data sets such as Sm–Nd and Lu–Hf that provide information on the crustal evolution of the source region, and allow comparisons with sedimentary packages. As an example, the age spectra of detrital zircons in Palaeoproterozoic metasedimentary rocks in the eastern Gawler Craton in southern Australia are virtually identical to the dominant zircon growth timelines in adjacent older domains of the Gawler Craton, presenting a prima facie case that it was the source region. However, whole rock Nd isotopic data indicate that the pre-existing proto Gawler Craton was isotopically too crustally evolved ( ε Nd (1850 Ma ) − 10) to have supplied the bulk of the sediment to the relatively more juvenile metasedimentary units ( ε Nd (1850 Ma) − 1 to − 5). In addition, zircon Hf isotopic compositions from ca 2000 Ma detrital zircons in the metasedimentary rocks ( ε Hf (2000 Ma) + 2 to + 5) are significantly more juvenile than 2000 Ma rocks in the adjacent Gawler Craton ( ε Hf (2000 Ma) − 2 to − 5). The combination of bulk rock Nd and Hf zircon data suggest that the Gawler Craton is not a viable source region for the metasedimentary packages, despite the striking similarity between detrital zircon ages and zircon crystallisation events within the craton.

Pebble population dating as an additional tool for provenance studies - examples from the Eastern Alps

Abstract Detrital fission-track (FT) dating can be successfully used in provenance studies of siliciclastic sediments to define the characteristic cooling ages of the source regions during erosion and sedimentation. In order to obtain more specific information about potential source regions we have developed the pebble population dating (PPD) method in which pebbles of specific lithotype are merged and dated. Dating of both zircon and apatite crystals from such pebble populations yields age distributions, which reflect the cooling ages of the given lithotype in the source area at the time of sedimentation. By this technique it is possible to define ‘FT litho-terrains’ in the source regions and thus outline palaeogeological maps. Two examples are presented from the Eastern Alps. (i) Comparison of FT ages from a sandstone sample and a gneiss PPD sample from an Oligocene conglomerate of the Molasse Basin shows that the youngest age cluster is present only in the sand fraction and derived from the Oligocene volcanic activity along the Periadriatic zone. The lack of the youngest ages in the gneiss pebble assemblage excludes the Oligocene exhumation of the crystalline basement from mid-crustal level. (ii) Pebble assemblages of red Bunter sandstone, gneiss and quartzite were collected from an Upper Miocene conglomerate of the Molasse Foreland Basin and merged as PPD samples. Apatite and zircon FT grain age distributions of these PPD samples, representing the largest ancient East Alpine catchment, allow generating a new combination of palaeogeological and palaeo-FT-age maps of the Eastern Alps for the Late Miocene.

Focused erosion in the Alps constrained by fission-track ages on detrital apatites

Abstract Fission-track dating on detrital apatites from modern sands of the Po Delta is used for a provenance study of sediments in the Po River basin. Analysed samples show a fission-track grain-age distribution characterized by two prominent peaks at 7.7 Ma and 17 Ma. The youngest peak accounts for 46% of the total population of dated grains. This young component in the grain-age distribution is consistent with bedrock cooling ages observed in the Western Alps between the External Massifs and the Houiller unit, as well as in the Lepontine dome of the Central Alps and in the Miocene foredeep units of the Apennines, that overall represent only 12% of the orogenic source area. Results suggest that most of the sediment load in the last 10 2 –10 5 years was supplied by focused erosion of relatively small areas that experienced short-term erosion rates one order of magnitude higher than in the rest of the belt.

Provenance of Cretaceous and Paleocene sandstones in the West Greenland basins based on detrital zircon dating

The extensive and very deep ?Jurassic/Cretaceous–Palaeogene sedimentary basins offshore West Greenland have a significant petroleum exploration potential. This is particularly true for the offshore region west of Disko and Nuussuaq where a live petroleum system has been documented for many years. At present, stratigraphic knowledge in this area is almost nonexistent and analogue studies from onshore areas and offshore exploration wells to the south are therefore crucial to understanding the distribution and quality of possible reservoir rocks in the Disko–Nuussuaq offshore area. One of the main risk parameters in petroleum exploration in this region is the presence of an adequate reservoir rock. Tectonostratigraphic considerations suggest that several sand-prone stratigraphic levels are probably present, but their provenance and reservoir quality are at present poorly known both onshore and offshore. A sediment provenance study including zircon provenance U-Pb dating and wholerock geochemical analysis was therefore initiated by the Geological Survey of Denmark and Greenland (GEUS) in preparation for the Disko West Licensing Round 2006 (Scherstén et al. 2007). The main aims of this study were to: 1. Characterise the source areas and dispersal patterns for the various sandstone units of Cretaceous–Paleocene age in the Nuussuaq Basin and compare these with sandstone units in selected West Greenland offshore exploration wells (Figs 1, 2), employing advanced zircon provenance U-Pb dating using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS; cf. Frei et al. 2006). 2. Detect possible changes in sediment source with time, e.g. local versus regional sources. Zircon as a provenance tool is receiving increasing attention and has proven to be a powerful indicator of clastic sediment sources, a tracer of the Earth’s oldest materials, and a tracer of continental crust-forming processes (Froude et al. 1983; Williams &amp; Claesson 1987; Dodson et al. 1988; Fedo et al. 2003; Hawkesworth &amp; Kemp 2006). Zircon is common in continental rocks and it is assumed that its distribution in sediments will normally represent the source rocks. Although there are several complications, the sediment zircon U-Pb age frequency should in general terms mirror the relative proportions of different source materials. This assumption is particularly important if exotic components can be identified, as their frequency will provide an estimate of the exotic influx: it may also be essential in tracing sediment paths that affect the detrital compositions and subsequent diagenetic history of possible hydrocarbon reservoir rocks.

Sedimentary patterns in the late Quaternary Southern Ocean

The spatial and temporal distribution of biogenic and lithogenic sediments in the late Quaternary Southern Ocean reflects the zonal character of the Antarctic Circumpolar Current and is basically controlled by glacial dynamics in Antarctica, sea-ice distribution, temperature gradients, wind patterns, and thermohaline ocean circulation. Carbonate patterns in most places reveal a decline in biogenic carbonate preservation during glacial periods, mainly attributed to a reduced influx of North Atlantic Deep Water and increased ocean stratification, which modified deep-water chemistry towards more corrosivity. An important lithological feature of the Southern Ocean is the Circumpolar Opal Belt, which today is situated between the Polar Front and the seasonal sea-ice limit to the south. During the glacial periods the opal belt shifted to the north in response to a wider sea-ice extension that reduced light availability and diatom productivity to the south. Biosiliceous productivity to the north likely was fueled by detrital iron supplied by aeolian dust input and/or hemipelagic processes. Lithogenic fluxes generally increased during the glacial periods. Provenance studies on the origin and dispersal of detrital materials suggest combined effects of low sea-level stands, increased glaciogenic input, and enhanced current transport to have caused elevated detrital fluxes. The relative and absolute contribution of aeolian dust is difficult to decipher and awaits further clarification by integrated provenance studies of both marine sediments and more reference materials from the potential terrestrial source areas. Ice-rafted debris (IRD) represents a minor fraction of lithogenic sediments, but can be used to infer both Antarctic ice-sheet dynamics and the fate of both sea-ice and iceberg survival in the distal Southern Ocean. Future work should be concentrated on a better identification of IRD origin in terms of volcaniclastic influences, the distinction of east and west Antarctic sediment sources, and sea-ice versus iceberg transportation.

Sediment provenance in the River Eden catchment, Scotland, using chemical characterization of Fe–Ti oxide minerals and magnetic measurements

Synopsis Sediment provenance in the River Eden catchment, Scotland, has been studied using chemical characterization of Fe–Ti oxide minerals and magnetic measurements. Results show that magnetic parameters lead to a better characterization and differentiation of rock sources and sediments than the chemical compositions of Fe–Ti oxide grains, thereby establishing a basis for provenance modelling. However, the chemical characterization of titanomagnetite grains allows a more accurate interpretation of the magnetic measurements. Discriminant function analysis of magnetic parameters yields an environmentally sensible, qualitative provenance model; but the intra-source magnetic variability and the similarity of the sources in terms of magnetic concentration, composition and grain size prevent successful quantitative provenance modelling. Tributary inputs are recognized downstream along the main channel of the River Eden, despite the tendency for the sediment characteristics to be homogenized during transport. This study highlights the potential for using a combination of Fe–Ti oxides chemical compositions together with magnetic parameters in sedimentary provenance studies.

Use of mineral magnetic concentration data as a particle size proxy: A case study using marine, estuarine and fluvial sediments in the Carmarthen Bay area, South Wales, U.K.

Compositional (non-magnetic) data can correlate strongly with particle size, which deems it appropriate as a particle size proxy and, therefore, a reliable means of normalising analytical data for particle size effects. Previous studies suggest magnetic concentration parameters represent an alternative means of normalising for these effects and, given the speed, low-cost and sensitivity of the measurements may, therefore, offer some advantages over other compositional signals. In this work, contemporary sediments from a range of depositional environments have been analysed with regard to their mineral magnetic concentration and textural characteristics, to observe if the strength and nature of the relationship identified in previous studies is universal. Our data shows magnetic parameters ( χ LF, χ ARM and SIRM) possess contrasting relationships with standard textural parameters for sediment samples collected from marine (Carmarthen Bay), estuarine (Gwendraeth Estuary) and fluvial (Rivers Gwendraeth Fach and Gwendraeth Fawr) settings. Magnetic concentrations of sediments from both the marine and estuarine environments are highly influenced by the magnetic contribution of finer particle sizes; Gwendraeth Fawr River sediments are influenced by the magnetic contribution of coarser particle sizes, while sediments from the Gwendraeth Fach River are not influenced significantly by any variations in textural properties. These results indicate mineral magnetic measurements have considerable potential as a particle size proxy for particular sedimentary environments, which in certain instances could be useful for geochemical, sediment transport, and sediment provenance studies. However, the data also highlight the importance of fully determining the nature of the relationship between sediment particle size and magnetic properties before applying mineral magnetic data as a particle size proxy.

Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer

Rutile is an important carrier of high field strength elements (HFSE; Zr, Nb, Mo, Sn, Sb, Hf, Ta, W). Its Zr content is buffered in systems with quartz and zircon as coexisting phases. The effects of temperature (T) and pressure (P) on the Zr content in rutile have been empirically calibrated in this study by analysing rutile–quartz–zircon assemblages of 31 metamorphic rocks spanning a T range from 430 to 1,100°C. Electron microprobe measurements show that Zr concentrations in rutile vary from 30 to 8,400 ppm across this temperature interval, correlating closely with metamorphic grade. The following thermometer has been formulated based on the maximum Zr contents of rutile included in garnet and pyroxene: $$ T{\text{(in}}\;^ \circ {\text{C) = 127}}{\text{.8}}\, \times {\text{ln (Zr}}\,{\text{in}}\,{\text{ppm)}}\, - {\text{10}} $$ No pressure dependence was observed. An uncertainty in absolute T of ±50°C is inherited from T estimates of the natural samples used. A close approach to equilibrium of Zr distribution between zircon and rutile is suggested based on the high degree of reproducability of Zr contents in rutiles from different rock types from the same locality. At a given locality, the calculated range in T is mostly ±10°C, indicating the geological and analytical precision of the rutile thermometer. Possible applications of this new geothermometer are discussed covering the fields of ultrahigh temperature (UHT) granulites, sedimentary provenance studies and metamorphic field gradients.

Quantitative provenance analysis of sediments: review and outlook

Provenance analysis of sediments is aimed at reconstructing the parent-rock assemblages of sediments and the climatic-physiographic conditions under which sediments formed. Inferring sediment provenance from the final product, a basin fill, is anything but straightforward because the detrital spectrum evolves as the sediment is transported along the pathway from source to basin. Successful provenance analysis requires that the nature and extent of compositional and textural modifications to the detrital spectrum be recognised, if not quantified. The history of quantification in sediment-provenance studies is summarised and illustrated by tracking two fundamental ideas: the concept of the sediment-petrological province or petrofacies, and the relation between sandstone composition and (plate) tectonic environment. Progress in sedimentary provenance analysis has been closely linked with advancements in measurement technology. A brief survey of modern data-acquisition tools illustrates the possibilities and limitations of modern provenance research. An operational definition of Quantitative Provenance Analysis (QPA) is presented in which the central role of mass balance is acknowledged. Extension of this definition to include quantitative predictions obtained by forward modelling (computer simulation) of sediment production, as well as methodological improvements in data acquisition and processing is needed to cover likely future developments in QPA. The contributions to the special issue "Quantitative Provenance Analysis of Sediments" illustrate the intrinsic multidisciplinarity and rapid expansion of QPA.

When did the ultrahigh-pressure rocks reach the surface? A 207Pb/ 206Pb zircon, 40Ar/ 39Ar white mica, Si-in-white mica, single-grain provenance study of Dabie Shan synorogenic foreland sediments

A single-grain study of synorogenic, Triassic–Jurassic quartz arenites of the eastern and southern forelands of the ultrahigh-pressure (UHP) Hong'an–Dabie orogen illustrates the utility and sensitivity of three provenance analysis techniques. 40Ar/ 39Ar detrital white mica ages indicate that the Middle Triassic stratigraphic level reached ∼400 °C at ∼125 Ma, probably heated by latest Jurassic–Early Cretaceous intrusions. Un-reheated single grains are as young as the depositional age of their sedimentary hosts and yield a Triassic–Jurassic age maximum that indicates a Hong'an–Dabie source, and some Paleozoic and Proterozoic ages that are mostly younger than 207Pb/ 206Pb detrital zircon ages. Si contents of detrital white micas from the same samples range from 3.0 to 3.6 atoms pfu, with ∼70% of the micas having <3.3 Si atoms pfu. The grains with 3.3–3.6 Si atoms pfu probably originated from Hong'an–Dabie, indicating initial exposure of high-pressure (HP) and even ultrahigh-pressure rocks during the Middle Jurassic. The single-grain evaporation 207Pb/ 206Pb ages of detrital zircons provide little indication that one of Earth's most spectacular unroofing processes was active in the adjacent orogen. Proterozoic and Silurian zircon ages abound, indicating that the detritus originated from the northern margin of the Yangtze craton and regions to the southeast, in particular the South China fold belt and the Cathaysia block, but only a few Triassic zircon ages, indicating a Hong'an–Dabie source, were measured. The Triassic signal is smallest because growth of metamorphic zircon is rare and is mostly limited to rim formation on pre-existing zircons, and because neither a magmatic arc nor syn- to post-collisional magmatism have been mapped in the Hong'an–Dabie orogen. Based on the white mica ages and the Si-in-white mica analysis, the Hong'an–Dabie orogen provided as much as 80% of the foreland detritus. The ages of the oldest micas suggest that exhumation of Hong'an–Dabie began at 240±5 Ma and thus the average exhumation rates exceeded 2 mm/year during the Middle Triassic to Middle Jurassic.

Fingerprinting of bed sediment in the Tay Estuary, Scotland: an environmental magnetism approach

Abstract. Sediment fingerprinting is commonly used for sediment provenance studies in lakes, rivers and reservoirs and on hillslopes and floodplains. This investigation explores the mixing of terrestrial and marine-derived sediment in the Tay Estuary, Scotland, using mineral magnetic attributes for fingerprinting. Samples representative of the estuary sediments and of four sources (end-members) were subjected to a suite of magnetic susceptibility and remanence measurements. Sediment samples from the beds of the Rivers Tay and Earn represented fluvial inputs while samples from the Angus and Fife coasts represented marine input. Multivariate discriminant and factor analysis showed that the sources could be separated on the basis of six magnetic parameters in a simple multivariate unmixing model to identify source contributions to estuarine bed sediments. Multi-domain magnetite signatures, characteristic of unweathered bedrock, dominate the magnetic measurements. Overall contributions of 3% from the River Earn, 17% from the River Tay, 29% from the Angus coast and 51% from the Fife coast source end-members, demonstrated the present-day regime of marine sediment derivation in the Tay Estuary. However, this conceals considerable spatial variability both along-estuary and in terms of sub-environments, with small-scale variations in sediment provenance reflecting local morphology, particularly areas of channel convergence. Keywords: bed sediment, environmental magnetism, fingerprinting, Tay Estuary, Scotland

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.