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Sedimentary phosphates, chiefly composed of apatite group minerals, contain exceptionally high concentrations (10–200 ppm) of U relative to other sedimentary precipitates, making them an attractive target for U–Pb dating. Phosphate-rich sedimentary rocks are common from the Neoproterozoic onwards and commonly occur at key points in the geological record, often coinciding with periods of significant environmental flux or facies change. There is thus a clear rationale for dating phosphatic rocks. In this study, we demonstrate how spatially-resolved U–Pb dating of sedimentary apatite by laser-ablation quadrupole inductively-coupled-plasma mass-spectrometry (LA-Q-ICPMS) can provide constraints on early phosphate diagenesis and reworking in ancient rocks. Our samples are from two locations in a well-characterized stratigraphic sequence containing phosphorites, and phosphate-rich carbonates and shales in western Ireland, which span the Mississippian–Pennsylvanian (mid-Carboniferous) boundary. Sedimentary phosphate preserves precise (

Complete subduction of an oceanic plate results in slab-window opening. A key uncertainty in this process is whether the higher heat flux and asthenospheric upwelling conventionally associated with slab-window opening generate a detectable topographic signature in the overriding plate. We focus on the Baja California Peninsula, which incorporates the western margin of the Gulf of California rift. The topography and tectonics of the rift flank along the peninsula are strongly bimodal. North of the Puertecitos accommodation zone, the primary drainage divide attains a mean elevation of ca. 1600 m above sea level (asl), above an asthenospheric slab-window opened by Pacific-Farallon spreading ridge subduction along this section of the trench at ca. 17–15 Ma. To the south, mean topography decreases abruptly to ca. 800 m asl (excluding the structurally distinct Los Cabos block at the southern tip of the peninsula), above fragments of the oceanic Farallon slab which stalled following slab tear-off at ca. 15–14 Ma. Along the peninsula, a low-relief surface established atop Miocene subduction-related volcaniclastic units has been incised by a west-draining canyon network in response to uplift. These canyons exhibit cut-and-fill relationships with widespread post-subduction lavas. Here, we utilise LANDSAT and digital elevation model (DEM) data, integrated with previously published K-Ar and 40Ar/39Ar lava crystallisation ages, to constrain the onset of rift flank uplift to ca. 9–5 Ma later than slab-window formation in the north and ca. 11–10 Ma later in the south. These greatly exceed response time estimates of ca. 2 Ma or less for uplift triggered by slab-window opening. Instead, uplift timing of the high-elevation northern region is consistent with lower-lithospheric erosion driven by rift-related convective upwelling. To the south, stalled slab fragments likely inhibited convective return flow, preventing lithospheric erosion and limiting uplift to the isostatic response to crustal unloading during rifting.

A new flexible interrogation tool for 2-dimensional LA-ICP-MS element and isotope maps is presented. Called Monocle, the tool works as an add-on in the software Iolite. Initial inspection of map data is undertaken with a size and shape adjustable loupe that is moved across the map. As the loupe is panned over the map, histograms and density/probability plots of the element concentration (or ratio, or age) contained within the area under the loupe are displayed. The data of any loupe position can be saved as a region of interest (ROI) in a table. For maps with rare earth element (REE) data a live normalised REE graph can be shown. Similarly, live graphs (e.g. Wetherill or Tera-Wasserburg concordiae) can be displayed for U/Pb data. The second step of map interpretation refines the initial data selection, for example by drawing polygons over irregular zones of similar chemistry. Where areas are separated (e.g. by cracks) several polygons can be nested into one ROI to improve counting statistics. Additional means of data pooling exist. Firstly, by growing a ROI from a seed, whereby the data distribution in the seed is used to find adjacent pixels that are within a user defined statistical boundary (e.g. 1 standard deviation). Secondly, multiple criteria can be set (e.g. element A > 0.1 ppm and element B < 40 wt%) to determine which pixels (connected or unconnected) are included in a ROI. This new approach is illustrated with several examples. A Mariana Arc oceanic Mn crust is used to show how elemental maps resolve alternating periods of precipitation from variably intense hydrothermal input and how their REE systematics reflect mixing between two distinct sources. A map of a garnet from a lherzolite illustrates that with modern LA-ICP-MS instruments it is possible to obtain reproducible REE data from strongly depleted mantle minerals (e.g. La approximate to 14 ppb) with a 20 x 20 mu m(2) beam and how mineral inclusions, metasomatism and serpentinisation can be avoided to obtain data from the most pristine parts of a grain. A map of a zoned augite crystal from Mt. Etna was used to examine the distribution of Ni and Cr, whose interrelationship in the strong oscillatory zoning can be modelled with extreme fractional crystallisation. A U/Pb map of a complex zircon was used to separate data from the complex inherited core and the much younger magmatic rim. Extraction of data from 2-dimensional maps ( < 1 mu m deep) avoids limitations of conventional LA-ICP-MS analysis that typically ablates much deeper. In combination with fast aerosol transfer systems that permit high repetition rate mapping (50-80 Hz), extraction of quantitative data with map analysis tools heralds a new era of in situ chemical and isotopic analysis.

Zircon commonly exhibits textural evidence for distinct growth events (e.g. polyphase core–rim structures) and evidence for Pb mobility not linked to discrete crystallization episodes (Pb loss, incorporation of common Pb, high-temperature Pb mobilization). Interpreting complex U–Pb zircon age data therefore requires imaging of zircon crystals and texturally-controlled sampling to constrain the fine-scale processes affecting the U–Pb zircon systematics. High-resolution U–Pb laser-ablation quadrupole inductively coupled plasma mass spectrometry (LA-Q-ICPMS) zircon age maps were undertaken on zircon sampled from syn-tectonic granitoid suites from the Peruvian Eastern Cordillera that exhibit textural evidence for clearly-defined cores and rims. The images were acquired by rastering a 7 μm spot with a 3.5 J cm−2 fluence, with scan speeds of 3 μm s−1 and a 10 Hz repetition rate (ThermoScientific iCAP-Qc setup) and scan speeds of 20 μm s−1 and a 45 Hz repetition rate (Agilent 7900 system). The mapping-experiment duration for individual zircons was as fast as 10 minutes (Agilent 7900 setup). 91500 zircon was employed as the primary reference material, and secondary-standard data (Temora, Plesovice, WRS-1348, FC-1, Fish Canyon, Tardree) typically reproduce within 1% of their published crystallization ages. Zircon rim concordia ages derived from the U–Pb age maps are consistent with independent secondary ion mass spectrometry (SIMS) and thermal ionisation mass spectrometry (TIMS) constraints. Two-dimensional kernel density estimation of the combined U–Pb data from each map define clear discordia mixing lines between the rim- and core-age components, and also show Pb loss and common Pb vectors. Potential applications of the technique include the characterisation of complex polyphase zircons and characterising the U–Pb systematics of key samples for time-intensive U–Pb TIMS dating.

Zircon U-Pb LA-ICPMS ages were obtained from three metasedimentary and two metavolcanic samples from the Monte Cavallino (South Tyrol) and the Cima Vallona (Carnic Alps) tectono-metamorphic groups from the eastern South Alpine crystalline basement in NE Italy. These analyses were performed to constrain the maximum depositional ages of the South Alpine domain, and to compare the spatial and temporal provenance variations with those of adjacent terranes. The detrital zircon dataset from the metasedimentary rocks (416 grains) yield populations with age peaks at 2.7–2.9 Ga, 1.8–2.1 Ga, 1.2–0.85 Ga, and 0.65–0.45 Ga, with maximum depositional ages ranging from the latest Neoproterozoic to the Silurian. The metavolcanic zircon dataset (209 grains) documents the presence of a two Ordovician volcanic events in the South Alpine domain. The detrital zircon dataset implies that the clastic units of the South Alpine crystalline basement were (a) deposited on the peri-Gondwanan active continental margin and (b) were originally sourced from the Proterozoic and Paleozoic units of NW Gondwana and hence should no longer be considered as exotic elements. The age spectra of the three metasedimentary units highlight differences between the Ediacaran basement gneiss, the Ordovician greywacke, and the Silurian metaconglomerate, suggesting up-section age variations due to a temporal change in provenance. Collectively, these new detrital zircon U-Pb ages imply that the clastic units within the South Alpine domain recorded sedimentation at c. 550 Ma on the peri-Gondwanan active continental margin, followed by rift-related continental and marine sedimentation in a back-arc basin setting until at least the Silurian. The South Alpine domain ultimately rifted off from Gondwana due to back-arc spreading, and subsequently underwent Variscan metamorphism during accretion onto the Laurussia margin, which started at c. 380 Ma and lasted until at least c. 320 Ma.

The El Oro Metamorphic Complex (EOMC) in SW Ecuador has been the subject of debate for several decades. While previous studies have focused on the metamorphic and deformation history of the complex to determine its geodynamic evolution, the pre-metamorphic history and its association to units in the north-central Andes remains poorly understood. Here we present a U-Pb detrital zircon provenance study to provide insights into the depositional history and the geodynamic setting of the EOMC. Our results imply that the southern portion of the EOMC (the Tahuin division) is composed of an older Palaeozoic (pre-Famatinian) sequence in the south (El Tigre unit; c. 525-510 Ma), and younger Palaeozoic (post-Famatinian) sediments in the central and northern parts of the Tahuin division (La Victoria and La Bocana units; c. 370-360 Ma). The provenance of the sedimentary sequences correlates with autochthonous post-Famatinian units (440–340 Ma) in the Eastern Cordillera of Peru and the southern Cordillera Real of Ecuador. Importantly, our data provide evidence for a genetic link between the northernmost (the Biron Complex) and the southern (La Victoria and La Bocana units) sequences of the EOMC. Post-Famatinian sediments were identified in the Biron Complex (Palenque Melange division; c. 400-390 Ma) and are derived from the same sedimentary sources as the sediments of the southern EOMC. The depositional range of post-Famatinian sediments in the EOMC is therefore constrained to c. 400-360 Ma. Furthermore, we identified a Middle to Upper Triassic sedimentary sequence in the Biron Complex (Limon Playa unit; c. 240-215 Ma) that likely developed contemporaneously with c. 240–217 Ma syn-rift continental epiclastics of the Mitu Group in Peru. Combined, these new detrital zircon data demonstrate that the existing lithostratigraphic scheme is erroneous and that three temporally distinct sequences are present in the complex, with the oldest units in the south and the youngest in the north. Separation of the southern EOMC (the Tahuin division) from the autochthonous Gondwanan margin of the north-central Andes was likely due to a change in the regional subduction direction from SE to ENE at c. 140Ma, with the southern EOMC rotating in a clockwise direction into its present-day E–W orientation. This rotation also could have been a response to the first accretion of proto-Caribbean terranes, such as the Alao–Quebradagrande terrane at c. 120 Ma, with a maximum age for rotation constrained by the earliest sediments (Early (?) to Middle Albian, c. 113-105 Ma) arriving into the Celica-Lancones Basin, which unconformably overlie the Tahuin Group in the southern EOMC.

The Karagwe-Ankole belt (KAB) is a poorly understood deformation belt in the Great Lakes area of Central Africa, with several hypotheses put forward to explain the emplacement of the various generations of granites. The youngest generation of granites (G4; 1000 Ma) are spatially associated with Sn-W-Ta ore deposits, and are considered as the parental granites. The paragenesis of these mineral resources have been extensively scrutinised, but the geodynamic context and characterisation of these parental granites has been neglected. Tectonic models for the formation of this plutonic suite range from an intra-cratonic to full-scale continent–continent collision setting. In this study, the G4 intrusive suite of the KAB granites, are characterised based on whole-rock geochemical analysis and U-Pb zircon dating. Two main populations of U-Pb zircon ages are identified in the G4 granites at 1370–1420 Ma and 950–1020 Ma. The older population is attributed to inheritance of the bimodal magmatic Kibaran event, while the younger population is ascribed to the new crystallisation. G4 granites contain xenocrystic zircon, indicating inheritance of older granites or basement rocks. G4 granites are, however, much more differentiated compared to older Kibaran granites, containing higher K and Rb and lower Ca, Sr and Ba concentrations, which implicates recycling of older crustal material. The variable geochemistry, as well as the different proportions of xenocrystic zircons in the different granite bodies, suggest melting was highly localised and derived from a highly heterogeneous source region, for which an intracontinental setting is favoured. The Th/U ratios of the parental granites are lower than 0.1, which would suggest a metamorphic origin of the granites. Together with the low luminescence signal of these zircons an anatectic origin of the melt is considered, implying that the parental granites could be considered more like migmatites rather than actual granites formed by fractionation out of large magma chambers.

The Bafq iron metallogenic belt in Central Iran hosts several large Kiruna-type iron oxide-apatite deposits (including Chadormalu, Choghart, Chahgaz, Esfordi, Lake-Siah, Gazestan, Se-Chahoun, Mishdovan, Anomaly 14 and 21A). These deposits have rare earth element (REE) potential, with the REE mainly concentrated in apatite. The Chadormalu iron-apatite deposit is hosted by igneous rocks that experienced various degrees of alteration and metamorphism. Enrichment in the LREEs relative to the HREEs ((La/Yb)N = 7.4–25.5; (La/Sm)N = 1.9–3.6, and (Ce/Yb)N = 7.4–25.5) and the gentle HREE slope ((Gd/Yb)N = 2.4 to 4.6) are significant features of the Chadormalu apatite. The similarities in REE patterns across the Bafq iron metallogenic belt (Chadormalu, Anomaly 14; Gazestan, Esfordi, and Lake-Siah deposits) suggest a cogenetic evolution for the iron-apatite ores. LA-ICPMS U-Pb dating of apatite yielded ages of 529 ± 25 Ma (Chadormalu), 543 ± 32 (Chahgaz), 517 ± 25 Ma (Mishdovan) and 533 ± 19 Ma (Anomaly 14). These ages are contemporaneous with Proto-Tethyan continental-arc magmatism from 547 Ma to 525 Ma, suggesting the synchroneous formation of the magnetite-apatite mineralization with its Late Proterozoic to Early Cambrian host rocks. Younger apatite U-Pb ages include an age of 437 ± 21 Ma from Chadormalu, an age of 457 ± 140 Ma from Anomaly 14, and an age of 215 ± 11 Ma for a sample from Anomaly 21A. The younger ages are assumed to reflect resetting of the U-Pb system due to hydrothermal events related to two regional extensional episodes, i.e. Early Silurian syenite magmatism at 440–420 Ma, and Late Triassic granite-tonalite magmatism at about 210–220 Ma.

Obtaining accurate and precise apatite fission-track (AFT) ages is dependent on producing plentiful high-quality apatite grains from a sample, ideally with high spontaneous fission-track densities (c. >105 tracks.cm-2). Many natural samples, such as bedrock samples from young orogenic belts or low-grade metamorphic samples with low U contents yield low spontaneous fission-track densities. Such apatites must be counted to avoid biasing the resultant FT age. AFT dating employing LA-Q-ICP-MS spot ablation works very well for grains with high spontaneous fission-track densities which enable potential U-zoning to be detected, while also removing the need for an irradiation step and facilitating simultaneous acquisition of U-Pb and trace element data. The LA-Q-ICP-MS spot ablation thus offers several advantages compared to the External Detector Method (EDM). However, for grains with low spontaneous fission-track densities where U zoning cannot be observed, the LA-Q-ICP-MS spot ablation approach requires the counted area to mimic exactly the site of the laser spot, with the downside that this smaller counted area limits the precision of the resultant AFT age. Here we present an alternative approach to LA-Q-ICP-MS analysis of low fission-tracks density grains by generating a U distribution (238U/43Ca) map of the entire apatite surface by LA-Q-ICP-MS elemental mapping which enables characterization of U zonation. The Monocle plugin for the Iolite LA-ICP-MS data reduction software package is used to display elemental maps and extract mean 238U/43Ca values of the same area counted for the fission tracks. A typical grain-mapping session takes < 5 hours to map 80 grains. The method was employed on the Durango and Fish Canyon Tuff apatite reference materials, and on apatite from six bedrock samples with low fission-track densities (≤ 1.105 track.cm-2). Most apatite samples investigated here were previously dated by the EDM or the LA-Q-ICP-MS ablation spot method. The AFT grain-mapping ages agree with previously published EDM or LA-Q-ICP-MS spot ablation ages at the 2σ level. For each apatite sample, we simultaneously acquired U-Pb age and trace element data (Mn, Sr, La, Ce, Sm, Eu, Gd, Lu); here again the data agree with literature constraints (when available) within uncertainties. The mapping approach is therefore a practical solution to low-temperature thermochronology studies employing apatite grains with low spontaneous fission-track densities, while also facilitating investigation of the spatial relationships between thermo- and geochronometric ages and grain chemistry.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping is a rapidly expanding field in the geosciences because of the wealth of spatial information it provides on the petrogenesis of igneous, metamorphic and sedimentary rocks and ore mineral formation. The technique has also opened many new applications in forensics, archaeology and the imaging of trace metals in biological tissues. Instrumentation advances in both LA and ICP-MS systems now permit precise isotopic analysis with laser spot sizes of

Mantle plumes have been proposed to exert a first-order control on the morphology of Earth's surface. However, there is little consensus on the lifespan of the convectively supported topography. Here, we focus on the Cenozoic uplift and exhumation history of the British Isles. While uplift in the absence of major regional tectonic activity has long been documented, the causative mechanism is highly controversial, and direct exhumation estimates are hindered by the near-complete absence of onshore post-Cretaceous sediments (outside Northern Ireland) and the truncated stratigraphic record of many offshore basins. Two main hypotheses have been developed by previous studies: epeirogenic exhumation driven by the proto-Iceland plume, or multiple phases of Cenozoic compression driven by far-field stresses. Here, we present a new thermochronological dataset comprising 43 apatite fission track (AFT) and 102 (U–Th–Sm)/He (AHe) dates from the onshore British Isles. Inverse modelling of vertical sample profiles allows us to define well-constrained regional cooling histories. Crucially, during the Paleocene, the thermal history models show that a rapid exhumation pulse (1–2.5 km) occurred, focused on the Irish Sea. Exhumation is greatest in the north of the Irish Sea region, and decreases in intensity to the south and west. The spatial pattern of Paleocene exhumation is in agreement with the extent of magmatic underplating inferred from geophysical studies, and the timing of uplift and exhumation is synchronous with emplacement of the plume-related British and Irish Paleogene Igneous Province (BIPIP). Prior to the Paleocene exhumation pulse, the Mesozoic onshore exhumation pulse is mainly linked to the uplift and erosion of the hinterland during the complex and long-lived rifting history of the neighbouring offshore basins. The extent of Neogene exhumation is difficult to constrain due to the poor sensitivity of the AHe and AFT systems at low temperatures. We conclude that the Cenozoic topographic evolution of the British Isles is the result of plume-driven uplift and exhumation, with inversion under compressive stress playing a secondary role.

Apatite, the most abundant phosphate mineral in the Earth's crust and uppermost mantle, is able to accept a wide variety of trace elements into its crystal structure. Many of these trace element substitutions are below the detection limit of Electron Microprobe Analysis, but can be determined by laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS). LA-ICPMS elemental abundance determinations typically employ sample-standard bracketing using either standard glasses or an appropriate matrix-matched reference material. In this study we have undertaken laser ablation (> 3000 analyses) and low-blank solution Q(quadrupole)-ICPMS trace-element analyses on crushed 150–300 μm aliquots of Durango and McClure Mountain apatite to assess the accuracy of apatite elemental abundance determinations when using NIST 612 standard glass as the primary LA-ICPMS trace element standard. An accuracy (relative to the solution data) and precision of

On the southeastern slope of the Baranec Mount in the Western Tatra Mountains (Slovakia) an apatite-rich pegmatite-like segregation was found in the subvertical fault zone cutting metapelitic rocks. Two zones: felsic (F) and mafic (M) were found, differing in mineral assemblages and consequently in chemistry. Fluorapatite crystals yield a LA-ICP-MS U-Pb age of 328.6 ± 2.4 Ma. A temperature decrease from 634 °C to 454 °C at a pressure around 500 to 400 MPa with oxygen fugacity increasing during crystallization are the possible conditions for formation of the pegmatite-like segregation, while secondary alterations took place in the temperature range of 340 – 320 °C. The Sr-Nd isotope composition of both apatite and whole rock point toward a crustal origin of the dike in question, suggesting partial melting of (P, F, H2O)-rich metasedimentary rocks during prolonged decompression of the Tatra Massif. The original partial melt (felsic component) was mixed with an external (F, H2O)-rich fluid, carrying Fe and Mg fluxed from more mafic metapelites and crystallizing as biotite and epidote in the mafic component of the dyke.

The clastic record is commonly interrogated by analysis of detrital heavy mineral assemblages, with the bulk of modern detrital geochronological studies employing U-Pb dating of detrital zircon. However, the bias of zircon toward felsic igneous sources, and the limited ability of the U-Pb system in zircon to record low- to medium-grade metamorphic events, means that the U-Pb detrital zircon record is largely insensitive to magma-poor orogens. In this study, U-Pb ages were obtained by laser ablation–inductively coupled plasma–mass spectrometry for apatite and rutile extracted from alluvium of the French Broad River (FBR) in the southern Appalachians (southeastern United States). In contrast to previously published FBR U-Pb zircon data sets, which yield essentially no record of the most recent Appalachian metamorphic events (ca. 320 Ma) associated with assembly of Pangea, the U-Pb detrital rutile and especially the U-Pb apatite systems together provide a complete record of complex polyphase Appalachian orogenesis. It is unexpected that the apatite and rutile U-Pb Appalachian age populations differ significantly, with probable low-temperature breakdown of rutile biasing the rutile data set toward the most recent (Alleghanian) metamorphic event. These data make the FBR one of the most intensely studied river systems globally for multiproxy single-grain U-Pb analysis, clearly demonstrate dependence of provenance information on mineral proxy choice, and emphasize the resolving power of multiproxy provenance studies.

Foreland basin sedimentary strata are key records of orogenic development, but identifying detrital thermochronometers of appropriate temperature sensitivity to detect provenance shifts can be challenging. Here, we utilize the medium-temperature apatite U-Pb system as a detrital thermochronometer. With a closure temperature range of ∼375−550 °C, it is a system sensitive to the typical peak temperatures attained by the amphibolite-eclogite cores of many magma-poor Phanerozoic orogens, while apatite itself is a common accessory mineral that is virtually ubiquitous in clastic rocks. We present apatite U-Pb data from the Oligocene−Miocene Barreme and Valensole basins of the Alpine foreland in SE France, together with data from the rutile U-Pb, apatite fission-track (AFT), and zircon U-Pb systems. At ca. 26−25 Ma, an abrupt cessation of detrital apatites yielding Alpine U-Pb ages derived from the eclogite-facies core of the Western Alps records a major westward migration of the primary drainage divide of the orogen. This shift, not visible in AFT and zircon U-Pb data, was synchronous with uplift and exhumation of the Argentera external basement massif. The drainage connection from the foreland to the eclogite-facies core of the Western Alps was restored by ca. 13 Ma and likely as early as ca. 16 Ma, and the primary drainage divide location has likely remained stable since this time. The synchronicity of late Oligocene−early Miocene uplift and initial exhumation of the external basement massifs around the western Alpine arc suggests that a major westward drainage divide migration occurred throughout the Western Alps at that time.

Constraining the abundance and distribution of halogens in geological materials has the potential to provide novel insights into a broad range of earth system processes (e.g. metasomatism, melting, volatile cycling and ore formation). In this contribution we develop analytical protocols for the in situ measurement of Cl, Br and I in widely distributed standard reference materials (apatite, scapolite, silicate glass) using readily available laser ablation ICP-MS instrumentation. Ablations were performed at a range of square spot sizes (30–80μm) using a high repetition rate (25Hz) and extended analyte dwell times (up to 250ms) to improve sensitivity and signal stability. A comparison of LA-ICP-MS results with published halogen data was used to calculate the following theoretical limits of quantification; Cl=360μg/g, Br=8μg/g,I=0.75μg/g. A detailed assessment of raw signal intensities for different matrices with known halogen contents, combined with high resolution mass scans, provides new constraints on the origin of apparent halogen signals: on mass35Cl signal excesses are likely16O18OH and/or17O18O;79Br is influenced by peak shoulder overlap from40Ar40Ar (a diargon cation, Ar2+2) and a matrix-based interference (159Tb2+) for samples with Br/Tb127I signals are similar for all but the highest I materials analysed here, suggesting the presence of ubiquitous gas-based interferences. The observation that false positive halogen signals only occur during sample ablation suggests that they are either matrix derived or related to the process of sample introduction. During ablation, matrix loading may reduce plasma energy, resulting in a greater proportion of polyatomic interferences in the system. For Cl, we provide a new time dependent excess apparent Cl spline correction defined by analysis of halogen-free olivine via a modified version of the Iolite Data Reduction Scheme ‘X_Trace_Elements_IS’. The correction improves the limit of linearity to ~100μg/g for Cl in glasses down to a 38μm spot size. We test our methodology on apatite from Permian alkaline lamprophyres in the Pyrenees (Spain) and quartz-hosted melt inclusions from rhyolitic deposits at the Taupo volcanic zone (New Zealand), obtaining results comparable to electron microprobe and SIMS data. We provide recommendations for analytical best practice and highlight the need for well characterised matrix matched SRMs spanning a broad range of concentrations to allow for the identification and removal of non-analyte related contributions to measured signals.

Detrital apatite deposited before, during and after Grampian-Taconic arc accretion in western Ireland reveals dramatic changes in source provenance and provides a detailed detrital petrochronological record of a Wilson Cycle sited on the Laurentian margin. These determinations are made possible by recent improvements in source rock type diagnosis by apatite trace element analysis. In addition, by interrogating the proportion of apatite derived from peraluminous vs metaluminous melt and felsic vs mafic melt in detritus, temporal changes can be seen in the relative proportions of these magma compositions over time. We present combined trace element and U-Pb age data for detrital apatite in clastic formations from the South Mayo Trough, a uniquely well-preserved fore-arc basin accreted to the Laurentian margin during the Grampian-Taconic orogeny (∼ 475 – 460 Ma), which records the early phase of closing of the Iapetus Ocean. Apatite deposited before collision is derived from the Laurentian margin and mafic igneous rocks of the Central Iapetus Magmatic Province associated with the Neoproterozoic break-up of Rodinia / Pannotia leading to the birth of the Iapteus Ocean. Following the onset of ocean closure in the Cambrian, igneous apatite derived from the nascent Grampian-Taconic arc is detected. Apatite derived from felsic and peraluminous melts becomes progressively more dominant over apatite from more mafic and metaluminous sources as the arc evolves from an intra-oceanic to continental arc setting after collision. The subsequent Grampian-Taconic unroofing history recorded by detrital apatite records the transition from ancient Laurentian margin- and intra-oceanic arc-derived detritus, to the exhumation of the high-grade metamorphic core of the Grampian-Taconic orogen and the exposure of post-collisional continental-arc granitoids. Our results are in broad agreement with both the Grampian fore-arc provenance record (heavy mineral analysis, detrital zircon U-Pb and white mica Ar-Ar) and the Laurentian crustal reworking record derived from the geochemistry of volcaniclastic units in the South Mayo Trough. However, we also obtain novel provenance information undetected by detrital zircon in the South Mayo Trough, such as apatite derived from the Central Iapetus Magmatic Province. Critically this information is obtained from a single mineral system, which eliminates the need to consider differing mineral stabilities during weathering, transport and diagenesis. The high preservation potential for apatite in similar tectonic environments illustrates the potential to employ detrital apatite as a record of Earth's lithological composition in deep time.

International audience; Alkali feldspar 40Ar/39Ar and apatite UPb geochronological studies have typically invoked two mechanisms to account for apparent loss of radiogenic 40Ar and 206-208Pb. Some studies have suggested that the radiogenic isotopes were lost by volume diffusion and used these dates to constrain temporal variations of rock temperatures; others have argued that the radiogenic isotopes were lost due to interaction with fluids and related these dates to chemical alteration. These two end-member interpretations have fundamentally different implications for tectonic models derived from geochronological data, and therefore it is important to reliably identify the principal mechanism for loss of radiogenic isotopes. Here, we revisit the mechanisms of 40Ar loss in the famous gem-quality alkali feldspar from the Itrongay pegmatite in Madagascar. Previous studies have suggested that volume diffusion is the dominant mechanism of 40Ar loss, providing key evidence to support the use of 40Ar/39Ar dating of alkali feldspar for thermochronology. We attempted to verify these results by obtaining time-temperature paths from petrologically characterised cogenetic feldspar and apatite from the Itrongay pegmatite and comparing them with each other. However, our results suggest that only a minor component in the variability of 40Ar/39Ar dates of Itrongay feldspar is related to the diffusive loss of 40Ar, and that this loss was not compatible with the majority of previously proposed models, which hinders quantitative interpretations. The crystal studied here grew in five episodes related to the influx initially of co-existing dense SiO2-rich solution and CO2-dominated fluid (the first and supposedly the following two episodes) and subsequently of H2O-rich fluid (supposedly the final two episodes). Much greater component in the variability of the acquired 40Ar/39Ar dates is interpreted to reflect the differences in the ages of these growth episodes, which we estimate to span from 477 Ma to 176 Ma (the first four episodes). Apatite inclusions in this crystal are interpreted to be xenocrysts derived from the country rocks of the Itrongay pegmatite. These yield older UPb dates than the estimated age of their host feldspar and have apparently experienced diffusive loss of 206,207Pb prior to entrapment. Our 40Ar/39Ar results indicate that there is a lack of unambiguous evidence for diffusive loss of 40Ar from alkali feldspar that can be readily interpreted for thermochronological purposes. However, in situ 40Ar/39Ar dating of alkali feldspar appears to be a promising tool for tracking fluid-flow events in the Earth's crust whose applicability is not restricted to sedimentary rocks. Our UPb results corroborate previous suggestions that UPb dating of apatite can be used for thermochronology.

Southeastern Bulgaria is composed of a variety of rocks from pre-Variscan (ca. 0.3 Ga) to pre-Alpine sensu lato (ca. 0.15 Ga) time. The Sakar Unit in this region comprises a series of granitoids and gneisses formed or metamorphosed during these events. It is cut by a series of post-Variscan hydrothermal veins, yet lacks pervasive Alpine deformation. It thus represents a key unit for detecting potential tectonism associated with the enigmatic Cimmerian Orogenic episode, but limited geochronology has been undertaken on this unit. Here we report age constraints on hydrothermal activity in the Sakar Pluton. The investigated veins contain mainly albite&ndash, actinolite&ndash, chlorite&ndash, apatite&ndash, titanite&ndash, quartz&ndash, tourmaline&ndash, epidote and accessory minerals. The most common accessory minerals are rutile and molybdenite. Apatite and titanite from the same vein were dated by U&ndash, Pb LA&ndash, ICP-MS geochronology. These dates are interpreted as crystallization ages and are 149 &plusmn, 7 Ma on apatite and 114 &plusmn, 1 Ma on titanite, respectively. These crystallization ages are the first to document two stages of hydrothermal activity during the late Jurassic to early Cretaceous, using U&ndash, Pb geochronology, and its association with the Cimmerian orogenesis. The Cimmerian tectono-thermal episode is well-documented further to the east in the Eastern Strandja Massif granitoids. However, these are the first documented ages from the western parts of the Strandja Massif, in the Sakar Unit. These ages also temporally overlap with previously published Ar&ndash, Ar and K&ndash, Ar cooling ages, and firmly establish that the Cimmerian orogeny in the studied area included both tectonic and hydrothermal activity. Such hydrothermal activity likely accounted for the intense albitization found in the Sakar Unit.

Interpreting the wealth of new data derived from the diverse suite of modern single-grain provenance approaches available to a sedimentologist requires a thorough understanding of the potential biases in the information recorded by each mineral-provenance system. This review focuses on the various possible mineral-specific biases in U-Pb accessory mineral provenance studies employing the minerals zircon, rutile, apatite, monazite and titanite, focussing on biases resulting from variations in source-rock mineralogy (fertility). Fertility is intimately linked to the mineral petrogenesis of crystalline basement sources, which is another key aspect of this review. This petrogenetic information, which often resides in the specialist petrology literature, has great relevance to fertility studies (particularly those measuring mineral content in modern river sediment using confluence and along-trunk sampling) as trace-element abundances and/or elemental ratios in many accessory minerals can be linked to specific lithologies. Other mineral-specific biases in single-grain provenance analysis considered include physical and chemical modifications both before and after deposition, while the diverse suite of modern single-grain analytical approaches also requires understanding of potential methodological and laboratory induced-biases. A series of multi-proxy provenance studies are presented where fertility bias apparently plays a significant role. In magma-poor metamorphic belts (e.g. segments of the Himalayas and Caledonides-Appalachians), it is shown that zircon growth is limited, and monazite, apatite or rutile associated with the youngest tectonomagmatic events are significantly more fertile. Such multi-proxy provenance studies will be greatly aided in the future by high-throughput, coupled U-Pb age – trace-element analyses integrated with automated heavy mineral determinations employing highly efficient sample preparation protocols.

Apatite's ubiquity in crystalline rocks, variable trace element contents (particularly with regard to the REE, actinides and Sr), and amenability to various dating techniques based on the decay of the radioisotopes U and Th, permit specific provenance determinations. In this study, we first present a comprehensive description of the trace element behaviour of apatite in various kinds of bedrocks (igneous rocks from felsic through to ultramafic compositions, metamorphic rocks from low to high grades and of diverse protolith composition, and authigenic apatite) in which we explain why apatite is so highly diverse in terms of its trace element composition. Next, we present a synthesis of bedrock apatite trace-element compositional data from previous work, assembling a library of apatite compositions that includes the most abundant apatite-bearing lithologies in the Earth's crust, and many other less abundant rock types. Compositional statistics, classification, and a machine learning classifier are then applied to this dataset to generate biplots that can be used to determine the broad source lithology of detrital apatite, with misclassification averaging 15%. This methodology is tested in three case studies to demonstrate its utility. In these examples, detrital apatite can be convincingly linked to different lithology types, and combined apatite trace-element and U Pb data can determine the terranes from which individual apatites were likely derived. The addition of apatite trace-element information therefore enables the determination of the source lithology, making the extraction of novel information and more specific provenance determinations possible, and opening up new avenues in source-to-sink modelling.

International audience; The LA-ICP-MS method is becoming increasingly popular for uranium determinations in fission track dating of apatite, zircon or titanite. This is because the approach has several advantages over the classical external detector method (EDM), including faster sample throughput, simultaneous acquisition of additional data (such as UPb age information and trace element abundances), while removing the need for neutron irradiation. Two different approaches are used to determine U contents in LA-ICP-MS fission track dating: an absolute dating approach, or a zeta-based determination analogous to the classical EDM. Absolute age dating by LA-ICP-MS potentially suffers from small but systematic deviations in apatite U contents, which in turn propagate through to minor systematic deviations in the accuracy of absolute fission track age determinations. A zeta-based approach typically requires time-consuming counting of large numbers of zeta-standard grains (usually Durango apatite) so as to yield a precise zeta factor for every LA-ICP-MS session containing unknowns. The modification of the zeta-based approach proposed here has two major advantages. Firstly, it employs just one large primary LA-ICP-MS session to determine a precise primary zeta factor on a large number of counted Durango primary zeta grains. During subsequent secondary LA-ICP-MS sessions with unknowns, no further fission track counting of the primary zeta standard is required. This is because we reanalyse a subset of the primary zeta grains to calculate a session-specific zeta fractionation factor, which is related to variations in the instrumental operating conditions (primarily plasma tuning) between primary and secondary LA-ICP-MS sessions. This enables us to ‘reuse’ the primary zeta factor, and thus avail of its precision derived from the large spontaneous track count. The second advantage is that reusing the primary zeta grains by applying a session-specific zeta fractionation factor allows us to verify that background and drift corrections applied during the secondary LA-ICP-MS session were fully appropriate. This method has been successfully tested by dating samples of known apatite fission track age, by comparing EDM and LA-ICP-MS data from the same sample and by participating in a round robin test between international fission track laboratories where ‘blind’ fission track dating of two unknown samples was undertaken. Our LA-ICP-MS apatite fission track dating approach is also easily modifiable for fission track dating of zircon or titanite if suitable age standards are employed.

The processes involved in the magmatic–hydrothermal transition in rare-element pegmatite crystallization are obscure, and the role of hydrothermal mechanisms in producing economic concentrations of rare elements such as tantalum remains contentious. To decipher the paragenetic information encoded in zoned minerals crystallized during the magmatic–hydrothermal transition, we applied SEM-EDS and LA-ICP-MS chemical mapping to muscovite- and columbite-group minerals (CGM) from a rare-element pegmatite of the albite-spodumene subtype from Aclare, southeast Ireland. We present a three-stage model for the magmatic–hydrothermal transition based on petrography, imaging and quantification of rare-element (Li, B, Rb, Nb, Sn, Cs, Ba, Ta, W, U) zoning, integrated with geochemical modeling and constraints from published literature. Stage I marks the end of purely magmatic crystallization from a peraluminous granitic melt. In stage II, polymerized silicic melt and depolymerized alkaline aqueous melt coexist as immiscible media, both of which influence muscovite and CGM crystallization. Stage II also marks the onset of phyllic alteration of primary mineral assemblages. Hydrothermal fluid release causes further resorption of primary minerals and eventual precipitation of fine-grained albite in stage III. Muscovite and CGM both exhibit trace-element zoning, while CGM also show major-element zoning. Petrographic relationships and geochemical markers such as Ta# (=Ta/[Ta + Nb]) of individual mineral zones reveal that both mineral species crystallized contemporaneously over all three stages. Furthermore, Rayleigh fractional crystallization of muscovite is efficient in fractionating Ta from Nb. Tantalum and Nb are additionally fractionated by halogen-rich aqueous media, which remobilize both elements, but redeposit preferentially Ta-enriched oxides. Columbite–tantalite mineralization is therefore both magmatic and hydrothermal. Albite associated with stage-III muscovite and CGM was likely precipitated from a hydrothermal fluid when pH changed due to hydrolysis of primary minerals. The complex zoning and resorption of minerals indicates that bulk analyses and conventional LA-ICP-MS spot ablation analyses of muscovite in rare element pegmatites may lead to erroneous modelling of element partitioning and fluid evolution. Combined petrographic and high-resolution geochemical analysis of two mineral species (which co-crystallize and incorporate the same elements of interest) is an effective tool to assess the complex processes of crystal–melt–fluid interaction. Our three-stage model may also be applicable to the still not well understood magmatic–hydrothermal transition from fertile granitic melts to formation of Sn-W veins and greisens or porphyry-type deposits. European Commission - European Regional Development Fund Science Foundation Ireland iCRAG industry partners 24 month embargo - AC

A geological transect across the suture separating northwestern South America from the Panama Arc helps document the provenance and thermal history of both crustal domains and the suture zone. During middle Miocene, strata were being accumulated over the suture zone between the Panama Arc and the continental margin. Integrated provenance analyses of those middle Miocene strata show the presence of mixed sources that includes material derived from the two major crustal domains: the old northwestern South American orogens and the younger Panama Arc. Coeval moderately rapid exhumation of Upper Cretaceous to Paleogene sediments forming the reference continental margin is suggested from our inverse thermal modeling. Strata within the suture zone are intruded by ~12 Ma magmatic arc-related plutons, marking the transition from a collisional orogen to a subduction-related one. Renewed late Miocene to Pliocene acceleration of the exhumation rates is the consequence of a second tectonic pulse, which is likely to be triggered by the onset of a flat-slab subduction of the Nazca plate underneath the northernmost Andes of Colombia, suggesting that late Miocene to Pliocene orogeny in the Northern Andes is controlled by at least two different tectonic mechanisms.

1. Introduction Several clay-rich horizons interbedded with Mississippian (Visean) limestones in the Namur-Dinant Basin (NDB), Belgium, are interpreted to be diagenetically altered volcanic ash layers based on their lateral continuity, clay mineralogy and heavy mineral assemblages (e.g. Thorez & Pirlet, 1979; Delcambre, 1989, 1996). Whilst several aspects of these clay horizons have been studied in detail, their original (unaltered) volcanic composition and the location(s) of the source volcanoes are not well constrained. The whole-rock geochemistry of altered volcanic rocks such as bentonites and tonsteins has been employed in several other studies to gain information about the composition of the original (unaltered) ash layers and ultimately the magma from which they were derived (e.g. Spears & Kanaris-Sotiriou, 1979; Merriman & Roberts, 1990; Huff et al., 1993; Christidis et al., 1995). The major elements, which are routinely used to classify fresh or slightly altered volcanic rocks, are of limited use when classifying extensively altered volcanic rocks because several elements, including K and Na, are known to be mobile during weathering and diagenesis (Winchester & Floyd, 1977; Floyd & Winchester, 1978; Zielinski, 1982; Christidis, 1998). Instead, the classification of altered volcanic rocks relies on trace elements including Ti, the high-field-strength elements (HFSE) Hf, Nb, Ta, Zr and the rare-earth elements, which are generally considered to be immobile during most u

The Saglek Block of coastal Labrador forms the western margin of the North Atlantic Craton, where Archean gneisses and granulites have been reworked during the Paleoproterozoic. Previous work has established that the block is a composite of Eoarchean to Mesoarchean protoliths metamorphosed to upper amphibolite and granulite facies at around 2.8–2.7 Ga. New in-situ microbeam dating of accessory minerals in granoblastic gneisses reveals a complex peak to post-peak thermal history. Zircon growth at ca. 3.7–3.6 Ga provides the age of formation of the tonalitic protoliths to the gneisses. Further zircon growth in syn-tectonic granitic gneiss and monazite growth in a variety of orthogneisses confirm peak metamorphic conditions at ca. 2.7 Ga, but also reveal high-temperature conditions at ca. 2.6 Ga and 2.5 Ga. The former is interpreted as the waning stages of the 2.7 Ga granulite event, whereas the latter is associated with a younger phase of granitic magmatism. In addition, apatite ages of ca. 2.2 Ga may represent either cooling associated with the 2.5 Ga event or a previously unrecognized greenschist-facies metamorphism event that predates the Torngat Orogeny.

The Moatize-Minjova Basin is a Karoo-aged rift basin located in the Tete Province of central Mozambique along the present-day Zambezi River valley. In this basin the Permian Moatize and Matinde formations consist of interbedded carbonaceous mudstones and sandstones with coal seams. The thermal history has been determined using rock samples from two coal exploration boreholes ( ca. 500 m depth) to constrain the burial and exhumation history of the basin. Organic maturation levels were determined using vitrinite reflectance and spore fluorescence/colour. Ages and rates of tectonic uplift and denudation have been assessed by apatite fission track analysis. The thermal history was modelled by inverse modelling of the fission track and vitrinite reflectance data. The Moatize Formation attained a coal rank of bituminous coals with low to medium volatiles (1.3–1.7% Rr ). Organic maturation levels increase in a linear fashion downhole in the two boreholes, indicating that burial was the main process controlling peak temperature maturation. Calculated palaeogeothermal gradients range from 59 °C/km to 40 °C/km. According to the models, peak burial temperatures were attained shortly (3–10 Ma) after deposition. Apatite fission track ages [146 to 84 Ma (Cretaceous)] are younger than the stratigraphic age. Thermal modelling indicates two episodes of cooling and exhumation: a first period of rapid cooling between 240 and 230 Ma (Middle – Upper Triassic boundary) implying 2500–3000 m of denudation; and a second period, also of rapid cooling, from 6 Ma (late Miocene) onwards implying 1000–1500 m of denudation. The first episode is related to the main compressional deformation event within the Cape Fold Belt in South Africa, which transferred stress northwards on pre-existing transtensional fault systems within the Karoo rift basins, causing tectonic inversion and uplift. During the Mesozoic and most of the Cenozoic the basin is characterized by very slow cooling. The second period of fast cooling and denudation during the Pliocene was likely related to the southward propagation of the East African Rift System into Mozambique.

We report experiments on optimisation of LA-ICP-MS mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals. The experimental design was refined with maps on clinopyroxene and amphibole macrocrysts (mainly antecrysts) from a porphyritic lamprophyre in NE Spain, as well as on a high precision metal wire grid. In terms of spatial resolution, we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0.4 and 0.7 mu m of material, depending on ablation parameters. Maps were produced with square laser beam spots of 12 and 24 mu m. It was found that complexities can be resolved in the sample even though they are smaller than the beam diameter (e.g., 7-10 mu m discontinuities using 12 mu m laser beam). Resolution in x and y was found to be identical, probably reflecting the fast washout of the two-volume ablation cell and the short total dwell time of the analyte menu selected. Due to the excellent stage reproducibility and the limited ablation depth, it is feasible to re-ablate the identical map area many times employing different instrument parameters or analyte menus. On the magmatic crystals, LA-ICP-MS maps define very sharp compositional zoning in trace elements, highlighting complex crystallisation histories where 'normal' magmatic fractionation is not the only process. Events of mafic recharge are easily recognised as zones enriched in compatible metals such as Cr, Ni or Sc. Further, trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data. These include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones. Therefore, LA-ICP-MS mapping opens a new window of opportunity for analysis of magmatic histories. The wide combination of instrumental parameters, such as laser beam size, scan speed and repetition rate, make it possible to carry out experiments at different levels of detail. We recommend a two-step approach to mapping. The initial step involves rapid maps to gain an overview of potential complexities in the sample; this enhances representativeness of the analysed materials, as a large number of crystals and trace elements can be tested in little time. Subsequently, detailed maps can be carried out on areas of interest. An additional functionality is to create 1D-profiles from 2D-maps. The potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond. (C) 2015 Elsevier B.V. All rights reserved.

Zinc (Zn) is a micronutrient for organisms and essential for plant growth, therefore knowledge of its elemental cycling in the surface environment is important regarding wider aspects of human nutrition and health. To explore the nature of Zn cycling, we compared its weathering behaviour in a sub-recent regolith versus an ancient laterite profile of the Deccan Traps, India - an area of known soil Zn deficiency. We demonstrate that progressive breakdown of primary minerals and the associated formation of phyllosilicates and iron oxides leads to a depletion in Zn, ultimately resulting in a loss of 80% in lateritic residues. This residue is mainly composed of resistant iron oxides and hydroxides ultimately delivering insufficient amounts of bio-available Zn. Moreover, (sub)-tropical weathering in regions experiencing extended tectonic quiescence (e.g., cratons) further enhance the development of old and deep soil profiles that become deficient in Zn. This situation is clearly revealed by the spatial correlation of the global distribution of laterites, cratons (Africa, India, South America and Australia) and known regions of Zn deficient soils that result in health problems for humans whose diet is derived from such land. We also investigate whether this elemental depletion of Zn is accompanied by isotope fractionation. In the saprolitic horizons of both weathering profiles, compositions of δ66ZnJMC-Lyon lie within the "crustal average" of +0.27±0.07‰ δ66ZnJMC-Lyon. By contrast, soil horizons enriched in secondary oxides show lighter isotope compositions. The isotopic signature of Zn (Δ66Znsample-protolith up to ~ -0.65‰) during the formation of the ferruginous-lateritic weathering profile likely resulted from a combination of biotically- and kinetically-controlled sorption reactions on Fe-oxyhydroxides. Our findings suggest that oxide rich soil types/horizons in (sub)-tropical regions likely exert a control on riverine Zn isotope compositions such that these become heavier than the crustal average. This isotopic behaviour invites a broader study of global soils to test whether light isotope composition alone could serve as an indicator for reduced bioavailability of Zn.

The crystalline basement of the Tatra Mountains in the Central Western Carpathians, forms part of the European Variscides and contains fragments of Gondwanan provenance. Metabasite rocks of MORB affinity in the Tatra Mountains are represented by two suites of amphibolites present in two metamorphic units (the Ornak and Goryczkowa Units) intercalated with metapelitic rocks. They are interpreted as relics of ocean crust, with zircon δ18OVSMOW values of 4.97–6.96‰. Zircon REE patterns suggest oxidizing to strongly oxidizing conditions in the parent mantle-derived basaltic magma. LA-MC-ICP-MS U-Pb dating of magmatic zircon cores yields a crystallization age of c. 560 Ma, with inherited components at c. 600 Ma, corresponding to the Pannotia break-up event and to the formation of the Eastern Tornquist–Paleoasian Ocean. However, the zircon rims of both suites yield evidence for two different geological histories. Zircon rims from the Ornak amphibolites record two overgrowth phases. The older rims, dated at 387 ± 8 Ma are interpreted as the result of an early stage of Variscan uplift while the younger rims dated at 342 ± 9 Ma are attributed to late Variscan collisional processes. They are characterized by high δ18OVSMOW values of 7.34–9.54‰ and are associated with migmatization related to the closure of the Rheic Ocean. Zircon rims from the Goryczkowa amphibolites yield evidence of metamorphism at 512 ± 5 Ma, subsequent Caledonian metamorphism at 447 ± 14 Ma, followed by two stages of Variscan metamorphism at 372 ± 12 Ma and 339 ± 7 Ma, the latter marking the final closure of the Rheic Ocean during late-Variscan collision. The presented data are the first direct dating of ocean crust formation in the eastern prolongation of the Tornquist Ocean, which formed a probable link to the Paleoasian Ocean.

In this article, the most recent moldavite discoveries in Poland and their host sediments are characterised and discussed. They were discovered at Lasow, located about 8 km north of Zgorzelec (Poland) and Gorlitz (Germany), about 700 m from the Polish-German border, close to the Lusatian Neisse (Nysa) River. The tektites were collected from Vistulian (Wiechselian) glacial age sand and gravel of a closed quarry pit, associated with the river terraces. In the Lasow area, the moldavite-bearing sediments are Pleistocene in age and represent Lusatian Neisse terrace deposits. They were redeposited from the upper part of the drainage basin of the Lusatian Neisse, probably washed out from the Miocene sediments that filled the Zittau Depression, the Berzdorf–Radomierzyce Depression, the Visňova Depression and the tectonically uplifted Izera Mts. and Dzialoszyn Depression. The erosion of Miocene deposit occured on a large scale in the uplifted foothills of the Upper Miocene Izera, Lusatia and Kaczawa complexes. The sediment cover was removed from the Dzialoszyn Depression. The drainage basin of the Lusatian Neisse is the area where moldavites were formed by the Nordlinger Ries impact. The source area of moldavite is the same for the Miocene deposits around Gozdnica, as well as for the Pleistocene sediments at Lasow.

Prehospital emergency care in Singapore has taken shape over almost a century. What began as a hospital-based ambulance service intended to ferry medical cases was later complemented by an ambulance service under the Singapore Fire Brigade to transport trauma cases. The two ambulance services would later combine and come under the Singapore Civil Defence Force. The development of prehospital care systems in island city-state Singapore faces unique challenges as a result of its land area and population density. This article defines aspects of prehospital trauma care in Singapore. It outlines key historical milestones and current initiatives in service, training, and research. It makes propositions for the future direction of trauma care in Singapore. The progress Singapore has made given her circumstances may serve as lessons for the future development of prehospital trauma systems in similar environments. Key words: Singapore; trauma; prehospital emergency care; emergency medical services.

Apatite is an important common U- and Th-bearing accessory mineral in igneous, metamorphic and clastic sedimentary rocks. The advent of in situ U–Th–Pb apatite geochronology by the SIMS and LA-(MC)-ICP-MS methods has demonstrated the importance of having uniform and homogeneous reference materials. Recently, it has been shown that Sr and Nd isotopic data combined with U–Pb age and trace element concentration data can provide important constraints on apatite paragenesis because this phase usually exhibits high Sr and REE concentrations but has low Rb/Sr ratios which result in negligible corrections for the ingrowth of radiogenic Sr. However, as apatite can potentially have complex internal structures resulting from multiple thermal events, such as inherited cores and metamorphic overgrowths, requires that the Sr and Nd isotopic data should be measured with high spatial resolution. However isobaric interferences hamper the precise determination of Sr or Nd isotopic compositions in LA-MC-ICP-MS analysis. In this work we undertook in situ measurements of Sr and Nd isotopic compositions of eleven apatite reference materials (AP1, AP2, Durango, MAD, Otter Lake, NW-1, Slyudyanka, UWA-1, Mud Tank, McClure Mountain and SDG) commonly used in U–Th–Pb geochronology. Our obtained Sr and Sm–Nd isotopic compositions for these apatite samples are consistent with those values obtained by solution-based methods (isotope dilution and ion chromatography) using MC-ICP-MS or TIMS, which demonstrates the reliability and robustness of our analytical protocol.

The Karoo igneous rocks (174–185 Ma) of southern Africa represent one of the largest continental flood basalt provinces on Earth. Available evidence indicates that Karoo magmas either originated in the asthenosphere and were extensively modified by interaction with the lithospheric mantle prior to emplacement in the upper crust; or were produced by partial melting of enriched mantle lithosphere. However, no direct evidence of interaction by Karoo melts (or their precursors) with lithospheric mantle rocks has yet been identified in the suites of mantle xenoliths sampled by post-Karoo kimberlites in southern Africa. Here we report U–Pb ages for lindsleyite–mathiasite (LIMA) titanate minerals (crichtonite series) from three metasomatised, phlogopite and clinopyroxene-rich peridotite xenoliths from the ∼84 Ma Bultfontein kimberlite (Kimberley, South Africa), located in the southern part of the Karoo magmatic province. The LIMA minerals appear to have formed during metasomatism of the lithospheric mantle by fluids enriched in HFSE (Ti, Zr, Hf, Nb), LILE (K, Ba, Ca, Sr) and LREE. LIMA U–Pb elemental and isotopic compositions were measured in situ by LA-ICP-MS methods, and potential matrix effects were evaluated by solution-mode analysis of mineral separates. LIMA minerals from the three samples yielded apparent U–Pb ages of 177 ± 12 Ma , 178 ± 29 Ma and 190 ± 24 Ma ( ± 2 σ ). A single zircon grain extracted from the ∼190 Ma LIMA-bearing sample produced a similar U–Pb age of 184 ± 6 Ma , within uncertainty of the LIMA ages. These data provide the first robust evidence of fluid enrichment in the lithospheric mantle beneath the Kimberley region at ∼180–190 Ma, and suggest causation of mantle metasomatism by Karoo melts or their precursor(s). The results further indicate that U–Pb dating of LIMA minerals provides a new, accurate tool for dating metasomatic events in the lithospheric mantle.

The main products of volcanic activity in the teschenite-picrite association (TPA) are shallow, sub-volcanic intrusions, which predominate over extrusive volcanic rocks. They comprise a wide range of intrusive rocks which fall into two main groups: alkaline (teschenite, picrite, syenite, lamprophyre) and subalkaline (dolerite). Previous 40Ar/39Ar and 40K/40Ar dating of these rocks in the Polish Outer Western Carpathians, performed on kaersutite, sub-silicic diopside, phlogopite/biotite as well as on whole rock samples has yielded Early Cretaceous ages. Fluorapatite crystals were dated by the U-Pb LA-ICP-MS method to obtain the age of selected magmatic rocks (teschenite, lamprophyre) from the Cieszyn igneous province. Apatite-bearing samples from Boguszowice, Puńców and Lipowa yield U-Pb ages of 103± 20 Ma, 119.6 ± 3.2 Ma and 126.5 ± 8.8 Ma, respectively. The weighted average age for all three samples is 117.8 ± 7.3 Ma (MSWD = 2.7). The considerably smaller dispersion in the apatite ages compared to the published amphibole and biotite ages is probably caused by the U-Pb system in apatite being less susceptible to the effects of hydrothermal alternation than the 40Ar/39Ar or 40K/40Ar system in amphibole and/or biotite. Available data suggest that volcanic activity in the Silesian Basin took place from 128 to 103 Ma with the the main magmatic phase constrained to 128—120 Ma., Department of Mineralogy, Geochemistry and Petrology at Faculty of Earth Sciences, Univeristy of Silesia, Katowice., Azambre B., Rossy M. & Albaréde F. 1992: Petrology of the alkaline magmatism from the Cretaceous North-Pyrenean Rift Zone (France and Spain). Eur. J. Mineral. 4, 813—834. Chamberlain K.R. & Bowring A.B. 2000: Apatite-feldspar U—Pb thermochronometer: a reliable, mid-range (~450 °C), diffusion- controlled system. Chem. Geol. 172, 173—200. 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Three new U–Pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry dates obtained from late Visean Belgian bentonites are reported and are used to estimate the periodicity of early Warnantian shallowing-upwards carbonate parasequences that are interbedded with the dated bentonites. Early Warnantian parasequences exhibit mean cycle periodicity values that are consistent with the c . 100 ka Milankovitch cycle, which is the dominant Milankovitch frequency recognized from recent Pleistocene glacial records, and thus strengthen the arguments for (1) these sedimentary cycles being of glacio-eustatic origin and (2) the initiation of the main phase of late Palaeozoic glaciation before the start of or during earliest Warnantian times. The new dates also provide additional high-precision age constraints for the improved calibration of the Mississippian time scale. Using the new dates, the stratigraphical age of the Clyde Plateau Volcanic Formation, Midland Valley of Scotland, is revised from Holkerian to early Asbian. Supplementary material: U–Pb zircon CA-ID-TIMS data tables and the method of the mean cycle periodicity calculations are available at www.geolsoc.org.uk/SUP18747.

The Caledonian orogen can be traced for severalthousand kilometres from the Arctic region south-ward on both sides of the North Atlantic Ocean(Fig. 1). The orogen formed in the Palaeozoic byconvergence and collision of Laurentia, Balticaand Avalonia. Subsequently during the Variscanorogeny, Gondwana collided with the Laurasiancontinent, forming the supercontinent Pangaea(e.g. Cocks & Torsvik 2006). In terms of scale andprocesses the Caledonian orogen is often comparedwith the Himalayan–Alpine orogenic belt thatextends from western Europe to eastern Asia (e.g.Milnes 1998; van Staal et al. 1998; Labrousseet al. 2010; Streule et al. 2010). The Himalayan–Alpine orogenic belt is currently still undergoingcontraction, which will probably result in thefuture amalgamation of Eurasia with Africa andAustralia (e.g. Hsu¨ 1994).Such convergence and collisional processesresult in the amalgamation of rock units derivedfrom very diversetectonic settings.In discussing theevolving tectonic evolution in the region betweenIndonesia and Australia, McCaffrey & Abers (1991)provide a statement that summarizes many ofthe challenges facing geologists working in theCaledonides

Precise and accurate U-Pb LA-ICPMS dating of many U-bearing accessory minerals (e.g. apatite, allanite, titanite and rutile) is often compromised by common Pb. LA-ICPMS dating of these U-bearing accessory phases typically requires a matrix-matched standard, and data reduction is often complicated by variable incorporation of common Pb not only into the unknowns but also particularly into the reference material. We present here a general approach to common Pb correction in U-Pb LA-ICP-MS dating using a modified version of the VizualAge U-Pb data reduction package for Iolite (VizualAge_UcomPbine). The key feature of the method is that it can correct for variable amounts of common Pb in any U-Pb accessory mineral standard as long as the standard is concordant in the U/Pb (and Th/Pb) systems following common Pb correction. Common Pb correction of the age standard can be undertaken using either the Pb-204, Pb-207 or Pb-208((no Th)) methods, and the approach can be applied to raw data files from all widely used modern multi-collector and single-collector ICPMS instruments. VizualAge_UcomPbine first applies a common Pb correction to the user-selected age standard integrations and then fits session-wide "model" U-Pb fractionation curves to the time-resolved U-Pb standard data. This downhole fractionation model is applied to the unknowns and sample-standard bracketing (using a user-specified interpolation method) is used to calculate final isotopic ratios and ages. Pb-204- and Pb-208((no) (Th)) corrected concordia diagrams and Pb-204-, Pb-207- and Pb-208((no Th))-corrected age channels can be calculated for user-specified initial Pb ratio(s). All other conventional common Pb correction methods (e.g. intercept or isochron methods on co-genetic analyses) can be performed offline. The approach was tested on apatite and titanite age standards (for which there are independent constraints on the U-Pb crystallization age) using a Thermo Scientific iCAP-Qc (Q-ICP-MS) coupled to a Photon Machines Analyte Excite 193 nm ArF Excimer laser. Madagascar apatite, OLT1 titanite and R10 rutile were used as primary standards and were corrected for variable common Pb using the new VizualAge_UcomPbine DRS. The secondary Durango (31.44 +/- 0.18 Ma) apatite standard yielded a U-Pb TW concordia intercept age of 31.97 +/- 0.59 Ma (MSWD = 1.09; primary standard corrected by the Pb-207-method) and a U-Pb concordia age of 31.82 +/- 0.40 Ma (MSWD = 1.4; primary standard corrected by the Pb-204-method). McClure Mountain (523.51 +/- 1.47 Ma) yielded a U-Pb TW concordia intercept age of 524.5 +/- 3.7 Ma (MSWD = 0.72) while the Fish Canyon Tuff (28.201 +/- 0.046 Ma) and Khan (522.2 +/- 2.2 Ma) titanite standards yielded U-Pb TW concordia intercept ages of 28.78 +/- 0.41 Ma (MSWD = 1.4) and 520.9 +/- 3.9 Ma (MSWD = 4.2) respectively. The suitability of the Pb-208((no Th))-correction is demonstrated by the agreement between a U-Pb TW concordia intercept age of 452.6 +/- 4.7 Ma (MSWD = 0.89) and a Pb-208((no Th))-corrected TW concordia age of 448.6 +/- 4.5 Ma (MSWD = 1.4) on a c. 450 Ma rutile which exhibits variable incorporation of common Pb. A range of LA-ICPMS U-Pb dating applications are presented and include U-Pb dating of apatite from >3.8 Ga gneisses from Akilia, SW Greenland. These apatites host C-13-depleted graphite inclusions that are interpreted as biogenic in origin and representing the oldest indications of life on Earth. The U-Pb age profiles on single apatite grains presented here are characteristic of Pb loss by volume diffusion with core-rim age differences of up to 300 Ma. These data explain the scatter and poor precision of earlier U-Pb apatite age determinations on Akilia apatite. Other LA-ICPMS dating applications include U-Pb apatite dating as a rapid method for determining the age of mafic intrusions, U-Pb titanite and apatite dating of ash fall tuffs, determining temperature-time histories using multiple U-Pb thermochronometers and improving concordance in LA-ICPMS primary zircon standard datasets by analysing young, common Pb-bearing primary zircon standards that have not accumulated significant radiation damage. (C) 2013 Elsevier B.V. All rights reserved.

We would like to thank Pereira (2015) for his interest in our work and appreciate the opportunity to clarify some aspects of the Rodrigues et al . (2015) study. Here we dispute several fundamental assertions made in the discussion of our original paper.

Apatite incorporates variable and significant amounts of halogens (mainly F and Cl) in its crystal structure, which can be used to determine the initial F and Cl concentrations of magmas. The amount of chlorine in the apatite lattice also exerts an important compositional control on the degree of fission-track annealing. Chlorine measurements in apatite have conventionally required electron probe microanalysis (EPMA). Laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) is increasingly used in apatite fission-track dating to determine U concentrations and also in simultaneous U-Pb dating and trace element measurements of apatite. Apatite Cl measurements by ICP-MS would remove the need for EPMA but the high (12.97 eV) first ionisation potential makes analysis challenging. Apatite Cl data were acquired using two analytical set-ups: a Resonetics M-50 193 nm ArF Excimer laser coupled to an Agilent 7700x quadrupole ICP-MS (using a 26 mu m spot with an 8 Hz repetition rate) and a Photon Machines Analyte Excite 193 nm ArF Excimer laser coupled to a Thermo Scientific iCAP Qc (using a 30 mu m spot with a 4 Hz repetition rate). Chlorine concentrations were determined by LA-ICP-MS (1140 analyses in total) for nineteen apatite occurrences, and there is a comprehensive EPMA Cl and F data set for 13 of the apatite samples. The apatite sample suite includes different compositions representative of the range likely to be encountered in natural apatites, along with extreme variants including two end-member chlorapatites. Between twenty-six and thirty-nine isotopes were determined in each apatite sample corresponding to a typical analytical protocol for integrated apatite fission track (U and Cl contents) and U-Pb dating, along with REE and trace element measurements. Cl-35 backgrounds (present mainly in the argon gas) were ~ 45-65 kcps in the first set-up and ~ 4 kcps in the second set-up. Cl-35 background-corrected signals ranged from ~ 0 cps in end-member fluorapatite to up to ~ 90 kcps in end-member chlorapatite. Use of a collision cell in both analytical set-ups decreased the low mass sensitivity by approximately an order of magnitude without improving the Cl-35 signal-to-background ratio. A minor Ca isotope was used as the internal standard to correct for drift in instrument sensitivity and variations in ablation volume during sessions. The Cl-35/Ca-43 values for each apatite (10-20 analyses each) when plotted against the EPMA Cl concentrations yield excellently constrained calibration relationships, demonstrating the suitability of the analytical protocol and that routine apatite Cl measurements by ICP-MS are achievable.

Para-articular osteochondromas (PAOCs) are a rare benign subtype of chondroma that occur in the soft tissues around the joints. Initially hypothesized to be derived from cartilaginous metaplasia, its aetiology and pathogenesis are still not fully understood. This tumour often causes a diagnostic and management dilemma due to similar clinical and histopathological features compared with other pathology. We report the fourth case of PAOC arising from the suprapatella region of the knee joint and review the literature to update our understanding of this tumour. From the data analysed, a distinctive pattern of tumour formation within or adjacent to a fat pad structure was evident, while trauma appears to play a role in its pathogenesis. Histologically, the tumour consists of a cartilage cap, with varying degrees of trabecular bone and endochondral ossification. Importantly, there are no features of nuclear pleomorphism or increased mitotic activity suggestive of a malignant process. All tumours were surgically removed and behaved in a benign fashion without evidence of recurrence. PAOC may often be suspected for more malignant processes; thus, recognition of this entity is important as simple excision is curative.