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We identified a ca. 180 Ma diamondiferous lamproite event in Zambia, establishing a link between ultrapotassic volcanism and the early Jurassic Karoo flood basalt province of sub-Saharan Africa. The cratonic lamproites erupted through the Permo–Triassic Luangwa Rift structure, but MgO-rich ultrapotassic magma formation was unrelated to rifting and triggered by plume–lithosphere interactions during the Karoo LIP event. Elevated Li–Zn–Ti concentrations in magmatic olivine (up to 18.5 ppm Li at 86–90 mol.% forsterite) and strong Sr–Nd–Hf–Pb isotopic enrichment of the host lamproites ( 87Sr/86Sr = 0.70701–0.70855, εNd = − 10.8 to − 10, εHf = − 20.3 to − 19.1, 206Pb/204Pb = 16.8–17.5) suggest partial melting of phlogopite-metasomatized lithospheric mantle domains, at approximately 180–200 km depth. The mantle-like δ7 Li values (+2.8 to +5.7‰) of the most pristine lamproite samples are compatible with source enrichment by asthenosphere-derived melts, without significant involvement of recycled sedimentary components. This geochemical fingerprint stands in sharp contrast to the negative δ7 Li compositions of primitive K-rich volcanic rocks from collision zone settings, where the shallow mantle sources contain recycled sediment. Isotope modelling demonstrates that the sub-Saharan lamproites originate from a MARID-style metasomatized peridotitic mantle source that underwent incompatible element enrichment at ca. 1 Ga, during tectonic activity associated with Rodinia supercontinent formation. Plume-sourced basaltic and picritic magmas of the 180 Ma Karoo LIP interacted with such K-rich hydrous lithospheric mantle domains, thereby attaining enriched incompatible element and radiogenic isotope compositions. Nd–Hf isotope mass balance suggests that up to 25% of MARID-sourced lamproite melt component contributed to some of the high-Ti flood volcanic units. Although large quantities of volatiles can be transferred from Earth’s mantle to the atmosphere via plume–lithosphere interactions, it is unlikely that outgassing of mantle-sourced sulphur can exceed the climatic impact caused by the release of much more abundant carbon from thick continental roots. Thus, the excess SO2 required to account for transient atmospheric cooling during the early Jurassic, coincident with the Karoo LIP event, must have had a thermogenic origin near the surface of Earth.

Allanite is a common accessory mineral that generally incorporates considerable amounts of Th, U and light rare Earth elements in its structure, making it a useful mineral for in situ U-Th-Pb geochronology and Sm-Nd isotope measurements. Here, we present in situ U-Th-Pb ages and Sm-Nd isotopic compositions for nine allanite samples considered as potential reference materials (CAPb, Tara, Daibosatsu, LE40010, LE2808, A007, A011, A012 and SQ-51), with ages ranging from ~ 2650 Ma to ~ 12 Ma. Our study indicates that Daibosatsu and LE40010 have relatively homogeneous 147Sm/144Nd and 143Nd/144Nd isotopic compositions (147Sm/144Nd ratio variation is less than 2%) and, thus, can serve as primary reference materials for Sm-Nd microanalysis. In contrast, CAPb, Tara, LE2808, A007, A011 and A012 all show homogeneous calculated initial 143Nd/144Nd isotopic compositions, but with variable 147Sm/144Nd compositions, and thus can be used only as secondary reference materials for Sm-Nd microanalysis. Of these materials, LE40010 allanite can serve as a suitable primary reference material for in situ U-Pb dating, CAPb allanite can serve as a suitable primary reference material for in situ Th-Pb dating, and LE2808, LE40010, A007, A011 and A012 can serve as suitable secondary reference materials for in situ U-Pb geochronology. In addition, Daibosatsu is suitable as a secondary reference material for Cenozoic Th-Pb dating to monitor data reproducibility.

Highly evolved granitic melts typically experience late-stage melt-melt and fluid-melt immiscibility as well as fluid-melt and fluid-rock interaction. These processes are particularly important in the formation of deposits of the rare metals Nb, Ta, W, and Sn. We document the relation between immiscibility and alteration processes and the partitioning behavior of rare metals for the Zhaojinggou rare-metal deposit of northern China. This deposit shows a systematic change from a magmatic to a hydrothermal system, including the reaction of the exsolved fluid with earlier crystallized granite and the formation of late-stage quartz veins. The magmatic stage (Stage I) includes biotite alkali-feldspar granite (BAG) with moderate Nb-Ta mineralization. Extreme fractional crystallization of BAG eventually resulted in melt-melt immiscibility and the separation of a hydrosaline melt. Fractional crystallization of this hydrosaline albite granite (AG) melt finally exsolved a magmatic fluid. Therefore, the magmatic-hydrothermal transition (Stage II) includes a melt-dominated Stage IIa with strong Nb-Ta-Sn mineralization in AG and a fluid-dominated Stage IIb with minor Nb-Ta-Sn mineralization in muscovite and biotite greisen. Late hydrothermal processes (Stage III) formed quartz veins with important W mineralization. There are several texturally and chemically distinct generations of cassiterite and columbite-group minerals (CGM) in BAG and AG reflecting crystallization from an evolving magma. The porous and patchy-zoned reaction rims of tantalite-(Mn) and wodginite on CGM in AG are the result of fluid-melt interaction. Texture and compositions show that wolframite in AG is hydrothermal and formed through interaction of early exsolved magmatic fluids with the host granite. CGM and cassiterite in the biotite greisen and Ta-rutile in the muscovite greisen, as well as wolframite and scheelite in quartz veins that formed when fluid-rock interaction reduced the availability of H+ or F− or the temperature of the fluid decreased. The distribution and importance of mineralization demonstrate that Nb, Ta, W, and Sn strongly partitioned into the hydrosaline melt during melt-melt immiscibility and that W partitioned into the magmatic fluid during fluid-melt immiscibility. Exsolved magmatic fluids interacted with earlier crystallized rocks mobilizing rare (Nb, Ta, and Sn) and base (Fe and Ti) metals from Li-Fe mica, providing the ore elements for subordinate Nb-Ta-Sn mineralization in AG and in biotite and muscovite greisen. Thus, magmatic processes (with later metal redistribution by magmatic fluids) dominantly control economic Nb-Ta-Sn mineralization, whereas hydrothermal processes mainly control the formation of economic W mineralization.

We present Li and B isotope data for muscovite, biotite, and feldspar + quartz separated from two-mica granite and biotite granite samples from the Huayang-Wulong granite suite (south Qinling, central China). Our data demonstrate systematic differences in the Li and B isotopic compositions among these minerals. Our results indicate that early-crystallizing minerals have lower δ7Li and δ11B values than the original melt and that residual melts and late magmatic fluids may acquire anomalously high δ7Li and δ11B values. Furthermore, our data imply that (1) late melts and magmatic fluids do not reflect the composition of their source melt, (2) minerals that crystallized over a large segment of magma evolution may be isotopically zoned, and (3) mineral-selective alteration by late magmatic fluids camouflages the source of the fluid, whose δ7Li and δ11B values reflect the isotopic compositions of the altered minerals rather than the composition of the remaining rock.

We report the laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) 176Hf/177Hf ratios for cassiterite of a known age and demonstrate that the 176Hf/177Hf ratios can be measured accurately and reproducibly with adequate precision for cassiterite with Hf contents around 100 μg g−1. Although cassiterite only has minor rare earth elements (REEs), corrections for Yb and Lu interferences are required as they may affect the determination of the 176Hf/177Hf ratios. Among the investigated samples, Rond-A has a homogeneous Hf isotopic composition. We recommend cassiterite sample Rond-A as a primary reference material for in situ Hf isotope analysis. The Kard sample has a homogeneous Hf isotopic composition and is suitable as a primary reference material once its Hf isotopic composition has been confirmed by solution-based MC-ICP-MS. Samples BB#7, 19MP, and 19GX showed minor variations in their Hf isotopic compositions and, therefore, can only be used as secondary reference materials.

Analytical methods and U-Pb cassiterite data.

The Menderes Massif in Turkey represents one of the largest metamorphic core complexes in the world. It is regarded as a section of lower continental crust exhumed along low-angle detachment faults in the Late Miocene during a period of extension that affected the entire Aegean province. Syn-extensional magmatic activity within the Menderes metamorphic core complex is predominantly felsic forming several plutons, whereas mantle-derived magmatism has not been known so far. Here, we present a detailed study of the petrology and geochemistry of previously unreported mafic to intermediate lamprophyres within the Menderes Massif and assess their role in the geodynamic evolution of the core complex. The Menderes lamprophyres are mostly kersantites, with 49–60 wt % SiO2, 3.2–8.4 wt % MgO, 100–360 ppm Cr, 32–132 ppm Ni and Mg# of 37–50. Positive Pb and negative Ti–Nb–Ta anomalies suggest a clear orogenic affinity. Isotopes of Sr and Pb are relatively radiogenic (87Sr/86Sr = 0.70609–0.71076; 206Pb/204Pb = 18.88–19.03, 207Pb/204Pb > 15.71), while Nd is unradiogenic (εNd = −1.4 to −3.2). Most phenocrysts are sharply zoned with a primitive core (Mg# 77–85, up to 0.95 wt % Cr2O3 in clinopyroxene; Mg# 72–76 in amphibole) and a more evolved rim (Mg# 68–74

Early Ordovician to late Permian orogenies at different plate-boundary zones of western Pangea affected continental crust derived from the plates of North America (Laurentia), Europe (East European Craton including Baltica plus Arctida), and Gondwana. The diachronic orogenic processes comprised stages of intraoceanic subduction, formation and accretion of island arcs, and collision of several continents. Using established plate-tectonic models proposed for different regions and time spans, we provide for the first time a generic model that explains the tectonics of the entire Gondwana-Laurussia plate-boundary zone in a consistent way. We combined the plate kinematic model of the Pannotia-Pangea supercontinent cycle with geologic constraints from the different Paleozoic orogens. In terms of oceanic lithosphere, the Iapetus Ocean is subdivided into an older segment (I) and a younger (II) segment. Early Cambrian subduction of the Iapetus I and the Tornquist oceans at active plate boundaries of the East European Craton triggered the breakup of Pannotia, formation of Iapetus II, and the separation of Gondwana from Laurentia. Prolonged subduction of Iapetus I (ca. 530 –430 Ma) culminated in the Scandian collision of the Greenland-Scandinavian Caledonides of Laurussia. Due to plate-tectonic reorganization at ca. 500 Ma, seafloor spreading of Iapetus II ceased, and the Rheic Ocean opened. This complex opening scenario included the transformation of passive continental margins into active ones and culminated in the Ordovician Taconic and Famatinian accretionary orogenies at the peri-Laurentian margin and at the South American edge of Gondwana, respectively. Rifting along the Avalonian-Cadomian belt of peri-Gondwana resulted in the separation of West Avalonian arc terranes and the East Avalonian continent. The vast African/Arabian shelf was affected by intracontinental extension and remained on the passive peri-Gondwana margin of the Rheic Ocean. The final assembly of western Pangea was characterized by the prolonged and diachronous closure of the Rheic Ocean (ca. 400–270 Ma). Continental collision started within the Variscan-Acadian segment of the Gondwana-Laurussia plate-boundary zone. Subsequent zipper-style suturing affected the Gondwanan Mauritanides and the conjugate Laurentian margin from north to south. In the Appalachians, previously accreted island-arc terranes were affected by Alleghanian thrusting. The fold-and-thrust belts of southern Laurentia, i.e., the Ouachita-Marathon-Sonora orogenic system, evolved from the transformation of a vast continental shelf area into a collision zone. From a geodynamic point of view, an intrinsic feature of the model is that initial breakup of Pannotia, as well as the assembly of western Pangea, was facilitated by subduction and seafloor spreading at the leading and the trailing edges of the North American plate and Gondwana, respectively. Slab pull as the plate-driving force is sufficient to explain the entire Pannotia–western Pangea supercontinent cycle for the proposed scenario.

We analysed gabbroic and dioritic rocks from the Atud igneous complex in the Eastern Desert of Egypt to understand better the formation of juvenile continental crust of the Arabian–Nubian Shield. Our results show that the rocks are the same age (U–Pb zircon ages of 694.5 ± 2.1 Ma for two diorites and 695.3 ± 3.4 Ma for one gabbronorite). These are partial melts of the mantle and related fractionates (eNd690 = +4.2 to +7.3, 87Sr/86Sri = 0.70246–0.70268, zircon δ18O ∼ +5‰). Trace element patterns indicate that Atud magmas formed above a subduction zone as part of a large and long-lived (c. 60 myr) convergent margin. Atud complex igneous rocks belong to a larger metagabbro–epidiorite–diorite complex that formed as a deep crustal mush into which new pulses of mafic magma were periodically emplaced, incorporated and evolved. The petrological evolution can be explained by fractional crystallization of mafic magma plus variable plagioclase accumulation in a mid- to lower crustal MASH zone. The Atud igneous complex shows that mantle partial melting and fractional crystallization and plagioclase accumulation were important for Cryogenian crust formation in this part of the Arabian–Nubian Shield. Supplementary material: Analytical methods and data, calculated equilibrium mineral temperatures, results of petrogenetic modeling, and cathodluminesence images of zircons can be found at https://doi.org/10.6084/m9.figshare.c.4958822

Archean peridotite xenoliths in the ∼2.52 Ga Zhulagou diorite (Yinshan Block, North China Craton) show chemical and Li isotopic evidence for metasomatism above an ancient subduction zone. The peridotite xenoliths are composed of olivine + orthopyroxene + amphibole + phlogopite + serpentine. The peridotite xenoliths have low whole-rock Mg# (80–81) and low Mg# (81–84) in olivine, indicating that they are cumulates that formed near the crust-mantle boundary. Petrological observations, mineral trace element data and isotopic ages show that the sequence of hydrous minerals is amphibole-serpentine-phlogopite. SIMS U–Pb dating of zircon from peridotites yielded an upper intercept age at ∼2.53 Ga, and a U–Pb lower intercept age at ∼1.8 Ga. The age of ∼2.53 Ga is interpreted to date the crystallization of zircon from the metasomatized mantle melt that formed the Zhulagou cumulate peridotite. Rb–Sr mineral isochrons date phlogopite formation at ∼1760 Ma, consistent with the lower intercept age of zircon. Pargasitic amphibole from the Zhulagou peridotites has fractionated REE, pronounced depletions of Nb, Ta, Zr and Ti, and heavy δ7Li (∼+14‰) and light δ11B (∼–11‰). Combined with slightly depleted mantle whole rock eNd (∼+1.3) and high zircon δ18O (+5.6 to +7.0‰), the amphibole composition reflects that the peridotite xenoliths formed from melts that carried the geochemical and isotopic fingerprint typical for a metasomatized mantle wedge above a subduction zone. The Zhulagou peridotite xenoliths have the highest δ7Li values (∼+12‰) recorded in Archean peridotites. Isotopically heavy Li and light B in olivine, orthopyroxene, and amphibole from the peridotite xenoliths show that Li and B may decouple during partial melting or fluid release from the subducted slab. The decoupling of Li and B may have a variety of reasons, including different host minerals for Li and B in the source and different protoliths in the subducted slab. The Li and B isotopic record on the recycling of ancient material demonstrates that modern-style subduction operated already in the late Archean.

We present an analytical protocol for in situ U–Pb isotope dating of wolframite series minerals [(Fe,Mn)WO4], the main ore mineral for tungsten, by LA-SF-ICP-MS. Precision and accuracy of the protocol was intensively assessed using our newly developed well-characterized U–Pb wolframite reference material. The tungsten oxide interference on Hg and Pb was investigated in detail. The matrix effect between ferberite and hübnerite during laser ablation was thoroughly examined for wolframite series minerals with a different Mn/(Mn + Fe) ratio. The closure temperature of wolframite, with respect to the U–Pb system, was evaluated. The application of eleven wolframite samples, with ages from ∼1780 Ma to ∼26 Ma, robustly demonstrated the feasibility of our approach. Most studied wolframite series minerals yielded U–Pb concordant or subconcordant ages. Samples with a relatively high U content and negligible common Pb content typically had a 206Pb/238U age precision of ca. 1%. The new in situ data agree well with published cassiterite or wolframite ages from the same locations. LA-SF-ICP-MS, with the advantages of high sensitivity, rapidity, and relatively low cost, as well as moderate spatial resolution (i.e., 32 or 44 μm) that is sufficiently high to avoid sulfide inclusions, is the method of choice for in situ wolframite U–Pb microanalysis.

We present a comprehensive Li and B isotope study of granites, aplites, and igneous enclaves from the multi-phase Eibenstock granite in the Western Erzgebirge-Vogtland metallogenic province of Germany. The studied samples cover the entire compositional range of the granites from moderately to highly evolved and include variably altered types as obtained by magmatic fractionation, post-magmatic high- to medium-temperature and near-surface low-temperature alteration. Fractionation and alteration processes are unequivocally documented by the chemical variability of the rocks. Despite the marked imprint of these processes on bulk-rock compositions, our granite samples show only little variation in δ7Li (−0.52 to 0.75‰) and δ11B (−17.46 to −14.78‰), with surface samples defining the lower end of the δ7Li range. The narrow range in δ7Li suggests that magmatic fractionation and high-temperature overprint have a very minor effect on δ7Li. The B budget of the samples is dominated by tourmaline, which makes δ11B values insensitive for later high- to medium-temperature overprint or surficial low-temperature alteration. Depending on whether tourmaline crystallized before or after exsolution and loss of magmatic fluids, whole-rock samples have higher or lower δ11B values. Granite enclaves have δ7Li and δ11B values ranging from −1.51 to −0.81‰ and − 14.55 to −13.89‰, respectively. Some samples have chemical and mineralogical evidence for wall-rock interaction during emplacement or later overprint by external fluids. These samples show broader ranges in δ7Li (−2.61 to 2.21‰) and δ11B (−21.58 to −9.85‰). These values show that wall-rock interaction via assimilation and external fluids may affect δ7Li and δ11B to a larger extent than intra-magmatic processes, such as fractional crystallization, fluid-mediated autometasomatic overprinting, or exsolution of fluids from the melt. The offset of δ7Li and δ11B values towards the compositions of the wall rocks reflects the contrasting composition of granite and country rock and the addition of country-rock material to the granite. The magnitude of the offset reflects both the relative contribution of wall-rock derived Li and B to the granite and the magnitude of the difference in the Li and B isotopic compositions between them.

Pegmatite fields within granite plutons are commonly considered to have formed from residual melts of their host. This is not always true as demonstrated by the Tysfjord granite gneiss and its two groups of pegmatites. The Tysfjord granite gneiss, exposed in a tectonic window of the Caledonides of northern Norway, is part of the transscandinavian igneous belt (TIB) that includes several phases of granitic magmatism. In the northern Hamarøy area (Drag-Finnøy), where most rare-element pegmatites occur, Paleoproterozoic and metamorphosed Group 1 allanite–(Ce)–fluorite metapegmatites have similar bulk rock chemical composition as the TIB granite gneiss rocks, indicating that these pegmatites are residual melts. Group 1 metapegmatites, which are up to 400 m in size, are among the largest known intra-plutonic pegmatites with Nb–Y–F (NYF) signature. The formation of these unusually large granite-hosted NYF pegmatites may have been facilitated by the overall high F content of TIB granite gneisses. Undeformed Group 2 amazonite–tourmaline pegmatites yield columbite and zircon U–Pb ages in the range 400–379 Ma. These pegmatites are interpreted to be anatectic melts that formed from the partial melting of Tysfjord granite gneiss. Group 2 pegmatites, including those from Træna Island and the Sjona tectonic window (400 and 414 Ma), formed during late Caledonian ductile shearing and incipient unroofing of the central Scandinavian Caledonides and record progressively younger ages of this event from SW to NE.

In the Gejiu Sn-Cu polymetallic district, skarns with or without mineralization developed both at the contact zones between a granitic intrusion and carbonate-rich wall rocks and within carbonate-rich wall rocks. We analyzed the chemical and Sr, Nd, Pb, Li, and B isotopic compositions of mineralogically different zones in two hand specimens, i.e., a banded carbonate and a distal skarn with distinct reaction zones, to interpret chemical and isotopic variation in terms of (i) temporal compositional changes of skarn-forming fluids and (ii) reaction-induced exchange between fluids and carbonate wall rocks. The banded carbonates have seen little fluid-mediated exchange and therefore the compositions of the various bands reflect a two-component system of carbonates and detrital silicates. The compositional range of the banded carbonates represents the compositional heterogeneity of the protoliths of the distal skarn that experienced a pronounced impact by metasomatic fluids. The studied distal skarn is characterized by the vein-like aquifer (Zone I), reaction zones (Zone II and Zone III), and the carbonate aquitard (Zone IV). As evident from the distal skarn, the chemical and isotopic compositions of skarn-forming fluids change over time due to (i) processes in the fluid sources, (ii) variable contributions of different fluid sources, and (iii) reaction-induced exchange with the rocks bordering the aquifer, leading to selective addition or removal of elements from the fluid. During early interaction between aquifer fluids and its wall-rocks, the aquitard is partially consumed and the chemical and isotopic signature of the newly-formed minerals in the reaction zone represent a mixture of material derived from either fluids or wall rock. Once formed, the reaction zones largely protected the aquitard from further interaction with fluids. The Sr-budget of zones I to IV is dominated by Sr derived from the carbonate aquitard and redistributed during the consumption of older reaction zones. The Pb, Li, and B budgets of zones I to III are dominated by materials derived from the fluids. In contrast, the Nd isotopic compositions in zones II to III fall between the values of the carbonate aquitard and the aquifer. The ore elements occur in different zones, i.e., (i) scheelite, sphalerite, pyrite, and chalcopyrite precipitate in the aquifer and (ii) Sn substitutes in calc-silicates at the reaction front between zones II and III and is present in late fractures in Zone III. Thus, ore elements may have been transported by different skarn-forming fluids. The chemical and isotopic signatures of reaction zones do neither strictly reflect the nature of the reactive fluid nor reflect simple bulk mixing between fluid and wall rock, as (i) reaction-induced volume decrease may allow later fluids to infiltrate into earlier reaction zones, (ii) the fluid may be depleted in elements that have been scavenged from the fluid before, (iii) some elements having low compatibility in minerals of the reaction zones may have strongly partitioned into the fluid and are lost from the system. Although reaction zoning provides information about the nature of the reactive fluids, the mineralogically-controlled selective behavior of trace elements, i.e., most ore elements, does not allow to use the ore element content in skarn as a vector to mineralization.

The Paleozoic plate boundary zone between Laurussia and Gondwana in western Pangea hosts major magmatic and hydrothermal Sn-W-Ta, Au, and U mineralization. Individual mineral deposits represent the results of the superposition of a series of exogenic and endogenic processes. Exogenic processes controlled (1) the enrichment of the ore elements in sedimentary protoliths via residual enrichment during intense chemical weathering and via climatically or tectonically controlled redox traps, (2) the spatial distribution of fertile protoliths, and, thus, eventually (3) the spatial distribution of mineralization. Endogenic processes resulting in metamorphism and crustal melting controlled the mobilization of Sn-W, Au, and U from these enriched protoliths and, thus, account for the age distribution of Sn-W and Au mineralization and U-fertile granites. It is the sequence of exogenic and endogenic processes that eventually results in the formation of mineralization in particular tectonic zones. Whereas the endogenic processes were controlled by orogenic processes during the assembly of western Pangea itself, the exogenic processes were linked to the formation of suitable source rocks for later mineralization. The contrasting distribution of magmatic and hydrothermal Sn-W-Ta, Au, and U mineralization on the Laurussia and Gondwana sides of the plate boundary zone reflects the contrasting distribution of fertile protoliths and the contrasting tectonic situation on these margins. The Laurussian margin was an active margin during most of the Paleozoic, and the distribution of different mineralization types reflects the distribution of terranes of contrasting provenance. The Gondwanan margin was a passive margin during most of the Paleozoic, and the similar distribution of a wide range of different metals (Sn, W, Ta, Au, and U) reflects the fact that the protoliths for the various metals were diachronously accumulated on the same shelf, before the metals were mobilized during Acadian, Variscan, and Alleghanian orogenic processes.

We present a new procedure for U-Pb dating of vesuvianite using laser ablation sector field inductively coupled plasma mass spectrometry (LA-SF-ICP-MS). Vesuvianite is a common mineral in skarn ore deposits and in metamorphic and metasomatic argillaceous carbonate rocks. The age of vesuvianite growth directly dates the formation of skarn mineralization, possibly also the metamorphism and metasomatism of argillaceous limestones. Vesuvianite U-Pb dating may provide age information for hydrothermal, metamorphic, and metasomatic processes that may be hard to get by zircon U-Pb dating. We analyzed eleven vesuvianite samples. Matrix effects were corrected by using Ti-bearing andradite (schorlomite) of known age as no well-characterized vesuvianite was available as an U-Pb reference material. The robustness of the analytical protocol was assessed by additional U-Pb dating of four vesuvianite samples by ID-TIMS. The U-Pb ages determined by ID-TIMS and LA-SF-ICP-MS agree well within uncertainties. An additional seven vesuvianite samples yielded in situ U-Pb ages that agree with previously published zircon, cassiterite, or wolframite U-Pb ages from the same area. Therefore, U-Pb dating of vesuvianite by LA-SF-ICP-MS represents a fast, relatively low-cost approach with high spatial resolution that may be particularly suited to date skarn mineralization.

Major tin (Sn) deposits within the Variscan orogen are closely related to 325–270 Ma postkinematic granites that intruded the metamorphic rocks of the former precollisional accretionary wedge of the Gondwana margin. In the Erzgebirge (Germany), some of these metasedimentary rocks have high Sn contents (locally more than 1000 ppm Sn). We report cassiterite (SnO2) U-Pb ages of 395–365 Ma and high Sn contents in prograde biotite in these metasedimentary rocks. These data demonstrate that Sn was already introduced into these rocks during accretion and prograde metamorphism. Mobilization of Sn from sedimentary source rocks during prograde fluid loss in a subduction-accretion setting represents an important process of pre-enrichment of sedimentary source rocks that upon partial melting may produce Sn-enriched melts. The large-scale metamorphic mobilization of Sn, documented here for the first time, highlights the possible importance of metamorphic Sn enrichment in accretionary complexes, thereby explaining the spatial distribution of major Sn districts within the Variscan orogen.

The Sveconorwegian orogen (1.1–0.9 Ga), covering southern Norway, is known for its large pegmatite province containing more than 5000 pegmatite bodies, divided into several pegmatite fields (Fig. 1). Most of these pegmatites have a chemical niobium-yttrium-fluorine (NYF) signature. The orogen is intruded by several, large post-orogenic A-type granites that classically were thought to be the source of the pegmatite melts. This was first challenged by Müller et al. (2015) stating that some of the pegmatites were formed by anatectic melting of their amphibolitic host-rock. In this study we use U-Pb age dating of columbite group minerals and ixiolite from seven Sveconorwegian pegmatites to shed light on their formation and temporal relationship to the spatially related granites. Furthermore, the data set is utilized for providing information on whether the pegmatite formation is related to known Sveconorwegian orogenic stages or represents their own regional melting event.

Wolframite has been proposed as a U/Pb geochronometer for direct dating of W mineralisation events, but its isotopic analysis may be hampered by highly variable and low U contents (

In the originally published version of this manuscript, the Supplementary Data was supplied with an incorrect hyperlink. The hyperlink has now been corrected to give the correct supplementary data for this article.

Subduction-related shoshonitic and calc-alkaline plutons coexisted in the Paleoproterozoic Khondalite belt (North China Craton). They intruded at 1.97–1.96 Ga and were overprinted by 1.94–1.92 Ga high-temperature metamorphism. The mafic to intermediate (SiO2 = 51.8–55.5 wt%) Wudangzhao shoshonitic metamonzodiorite has high K2O (3.0–4.9 wt%) contents. In contrast, the mafic (SiO2 = 48.5–51.7 wt%) Yebaigou metagabbro is sodium-rich (Na2O/K2O > 2). In Harker diagrams, the two intrusions show different magmatic evolution trends for selected major and trace elements, suggesting that they belong to two distinct magma series. Both intrusions are enriched in light rare earth element and depleted in high field strength elements, such as Nb, Ta, and Zr, in the trace-element diagrams normalized to the primitive mantle. The low eNd 1960 Ma values (− 3.1 to + 0.6) of whole-rock samples, the low eHf(t) values (− 2.2 to + 0.9) of magmatic zircon samples, and the relatively high δ18O values (+ 5.9 to + 6.4‰) of zircon crystals indicate that the mantle source of both intrusions had been metasomatized by fluids/melts derived from subducted continental crustal material. Partial melting of the amphibole and/or phlogopite-bearing mantle yielded the calc-alkaline melt with the chemical fingerprint characteristic for the Yebaigou metagabbro. Small-volume partial melting of a similar mantle source at greater depth produced shoshonitic melts that formed the Wudangzhao metamonzodiorites. The Wudangzhao metamonzodiorites and Yebaigou metagabbros represent part of a Paleoproterozoic continental magmatic arc on an Archean basement. This study shows that shoshonitic and calc-alkaline magmatism may exist coevally above ancient subduction zones and, thus, could provide some clues for distinguishing upper and lower plates in deeply eroded ancient collisional belts.

We present new geochemical and isotopic data for rock samples from two island arc volcanoes, Erromango and Vulcan Seamount, and from a 500 m thick stratigraphic profile of lava flows exposed on the SW flank of Vate Trough back-arc rift of the New Hebrides Island Arc (NHIA). The basalts from the SW rift flank of Vate Trough have ages of similar to 0.5 Ma but are geochemically similar to those erupting along the active back-arc rift. The weak subduction component in the back-arc basalts implies formation by decompression melting during early rifting and rifting initiation by tectonic processes rather than by lithosphere weakening by arc magma. Melting beneath Vate Trough is probably caused by chemically heterogeneous and hot mantle that flows in from the North Fiji Basin in the east. The melting zone beneath Vate Trough back-arc is separate from that of the arc front, but a weak slab component suggests fluid transport from the slab. Immobile incompatible element ratios in South NHIA lavas overlap with those of the Vate Trough depleted back-arc basalts, suggesting that enriched mantle components are depleted by back-arc melting during mantle flow. The slab component varies from hydrous melts of subducted sediments in the Central NHIA to fluids from altered basalts in the South NHIA. The volcanism of Erromango shows constant compositions for 5 million years, that is, there is no sign for variable depletion of the mantle or for a change of slab components due to collision of the D'Entrecasteaux Ridge as in lava successions further north.

The Pb isotope composition of the upper mantle beneath Central Europe is heterogeneous due to the subduction of regionally contrasting material during the Variscan and Alpine orogenies. Late Variscan to Cenozoic mantle-derived melts allow mapping this heterogeneity on a regional scale for the last ca. 340 Myr. Late Cretaceous and Cenozoic anorogenic magmatic rocks of the Bohemian Massif (lamprophyres, volcanic rocks of basanite/tephrite and trachyte/phonolite series) concentrate mostly in the Eger Rift. Cretaceous ultramafic lamprophyres yielded the most radiogenic Pb isotope signatures reflecting a maximum contribution from metasomatised lithospheric mantle, whereas Tertiary alkaline lamprophyres originated from mantle with less radiogenic 206Pb/204Pb ratios suggesting a more substantial modification of lithospheric source by interaction with asthenospheric-derived melts. Cenozoic volcanic rocks of the basanite/tephrite and trachyte/phonolite series define a linear mixing trend between these components, indicating dilution of the initial lithospheric mantle signature by upwelling asthenosphere during rifting. The Pb isotope composition of Late Cretaceous and Cenozoic magmatic rocks of the Bohemian Massif follows the same Pb growth curve as Variscan orogenic lamprophyres and lamproites that formed during the collision between Laurussia, Gondwana, and associated terranes. This implies that the crustal Pb signature in the post-Variscan mantle is repeatedly sampled by younger anorogenic melts. Most Cenozoic mantle-derived rocks of Central Europe show similar Pb isotope ranges as the Bohemian Massif. Keywords: Lead isotopes, Lamprophyres, Volcanic rocks, Mantle components, Bohemian massif, Variscan orogeny

Highlights • Geochemically diverse Late Cretaceous small-volume magmatism in the Sava-Vardar Zone. • Late Cretaceous ultrapotassic lava, equivalent of minette and kersantite. • Magma derivation from a LREE and K enriched, garnet-bearing anciently metasomatized mantle source. • Magmatism occurred either in a fore-arc setting or is associated with transtensional tectonics. Abstract Late Cretaceous global plate reorganization associated with the inception of counterclockwise rotation of Africa relative to Europe initiated in the Balkan region small-volume magmatism of diverse geochemical signature along the enigmatic Sava-Vardar Zone. We study a Late Cretaceous lamprophyric sill in Ripanj village near Belgrade to constrain this magmatic episode. The lamprophyre is characterized by high contents of Na, P, Fe and Al, and low contents of K, Ca and Mg. Its original nature (Na, K, Ca and Mg) is concealed by intense alteration (albitization of feldspar and partial chloritization of phlogopite) that erased the ultrapotassic affinity of the rocks and resulted in extremely low K/Na ratios. The recalculated chemical composition demonstrates that the rocks are ultrapotassic, with K2O and MgO >3 wt % and K2O/Na2O > 2, and belong to the durbachite-vaugnerite series, i. e., the plutonic equivalents of minettes and kersantites. Two phlogopite concentrates gave Ar–Ar ages of 86.80 ± 0.5 Ma and 86.90 ± 0.5 Ma. Our combined elemental and Sr–Nd–Pb isotope data (87Sr/86Sr 0.70667–0.70677, 143Nd/144Nd 0.512426–0.512429, 206Pb/204Pb 18.82–19.13, 207Pb/204Pb 15.67–15.68, 208Pb/204Pb 38.92–39.19) for representative lamprophyric samples suggests magma derivation from a light rare earth elements (LREE) and K enriched, metasomatized mantle source. The content of LREE of the rocks is enriched, whereas heavy rare earth elements (HREE) is depleted. Rare earth elements (REE) of the whole rock and REE of diopside all indicate that garnet was present in their source. There are two viable and mutually-excluding geodynamic scenarios for the Late Cretaceous magmatism in the Balkans: (i) If the Sava-Vardar ocean still existed in the Late Cretaceous and was subducted under the European plate with arc volcanism along the Apuseni-Banat-Timok-Panagyurishte-Srednjogorje belt, coeval magmatism in the Sava-Vardar Zone occurred in a fore-arc setting, and may be related to ridge subduction; (ii) If the Mesozoic ocean closed already during the Upper Jurassic or Lower Cretaceous, the Late Cretaceous volcanism within the Sava-Vardar Zone represents intracontinental volcanism associated with transtensional tectonics.

There are four episodes (Neoproterozoic, early Paleozoic, early and late Mesozoic) of Sn-W-Nb-Ta mineralization in South China, accounting for more than 50% W and 20% Sn reserves of the world and hosting considerable Nb and Ta resources. The genesis for such large-scale mineralization that may have seen multiple phases of recycling of ore elements is not well unterstood. The study of the earliest mineralized granites in South China, however, may be helpful to better understand the mechanism of mineralization. We present detailed mineralogical, geochemical, and isotopic data from two typical Neoproterozoic, mineralized intrusions, i.e., the Fanjingshan and Yuanbaoshan tourmaline leucogranites. There is a characteritstic mineral succession of diverse magmatic (columbite group minerals [CGMs], Nb-Ta-bearing cassiterite) and hydrothermal (wolframite, wolframoixiolite, Nb-Ta-poor cassiterite) Sn-W-Nb-Ta oxides. Hydrothermal cassiterite and W-bearing oxides (wolframite, wolframoixiolite) in the Yuanbaoshan intrusion were deposited separately by two types, i.e., Sn-rich and Nb-W-rich fluids. In-situ U-Pb dating of zircon, columbite and wolframoixiolite yields ages of 830 ± 5, 832 ± 5 and 821 ± 5 Ma, respectively. Whole-rock eNd(t) values of −2.5 to −6.4 correspond to crustal Nd model ages of 1.6–1.9 Ga. Paleoproterozoic model ages (~1.6–2.2 Ga) for most episodes of W-Nb-Ta mineralization in South China indicate that (i) Paleoproterozoic or older sediments may have been involved in the formation of W-Nb-Ta bearing granites and (ii) contributions of juvenile material was not important for these W-Nb-Ta mineralization. Neoproterozoic peraluminous granites along the Jiangnan Orogen formed in post-collision environments, but only those in the western part show Sn (-W-Nb-Ta) mineralization. The mineralized Neoproterozoic granites of the western part have experienced more extensive fractional crystallization (lower Nb/Ta, Zr/Hf ratios and more depleted in Fe, Mg, Ca, Sr, Ba, Eu, Ti) and are richer in volatiles (H2O, B) than the barren peraluminous intrusions of the eastern part. As similarly evolved Mesozoic metaluminous granites of the Nanling area have considerably more important tin mineralization than the mineralized Neoproterozoic granites, fractionation is not the only factor controlling mineralization. Instead, other factors, such as protolith and conditions of partial melting may account for the more important Mesozoic tin mineralization.

International audience; The W-Sn Maoping deposit and related W-Sn deposits from the world-class Nanling Range in Southeast Chinaformed at ca. 160 Ma and experienced several phases of metal addition and metal redistribution between 160and 130 Ma. Isotopic dating of ore mineral (wolframite) of Maoping demonstrates that W was deposited first,during a hydrothermal event at ca. 160 Ma. Successive fluid episodes, at ca. 156 Ma (Mo and Sn-rich fluid) and152 Ma (REE-rich fluid), resulted in the formation of REE- and Fe-Cu-Zn-sulfide minerals. A last fluid eventoccurring at ca. 130 Ma was responsible for the deposition of Zr-REE-Nb-Ta minerals that are attributed tomagmatic fluids derived from unexposed magmatic bodies. The three episodes of fluid circulation post-dating Wdeposition resulted in partial to complete resetting of the isotopic systems (mica, wolframite, xenotime), whichare conventionally used for dating such deposits. We show that W and Sn mineralization in the Nanling Rangeformed during a unique fluid event at ca. 160 Ma. Later fluid episodes redistributed the previously depositedmetals and sequentially introduced additional metals, including Mo-Sn, Fe-Cu-Zn, and Zr-REE-Nb-Ta. Directdating of paragenetically well-constrained minerals is therefore critical for determining the age and the durationof mineralizing processes and for characterizing the fluid evolution of magmatic-hydrothermal systems, as exemplifiedin the Nanling Range.

We study the causes of Mg-Cr-Ti-V-P-MREE enrichment in a 134 m thick mafic sill emplaced in a single magma pulse. Whole-rock chemistry indicates that TiO2 (up to 5.51 wt%) and P2O5 (up to 1.60 wt%) enrichment occurred in a closed system. Immiscibility processes during magmatic crystallization and interaction with late fluids seem to have played little or no role for the Ti-P distribution. Liquid lines of descent for anhydrous and hydrous conditions reveal that the melt did not follow a Fenner trend (anhydrous), which may lead to strong Ti or P enrichment, but a Bowen trend (hydrous), during crystallization at low fO2 (∆FMQ-2) and low water contents (0.5% H2O). The Mg-Cr-Ti-V-P-MREE-rich samples are cumulates and their composition is offset from the liquid line of descent due to postcumulus compaction and compositional convection. Theoretical formulation of compaction and compositional convection demonstrates that classical postcumulus scenarios of strong undercooling (sill

The orogenic development after the continental collision between Laurussia and Gondwana, led to two contrasting associations of mantle-derived magmatic rocks on the territory of the Bohemian Massif: (i) a 340–310 Ma lamprophyre-lamproite orogenic association; and (ii) a 300–275 Ma lamprophyre association of anorogenic affinity. Major types of potassic mantle-derived magmatic rocks recognized in the orogenic and anorogenic associations include: (i) calc-alkaline to alkaline lamprophyres; (ii) alkaline ‘orthopyroxene minettes’ and geochemically related rocks grouped here under the new term lampyrite; and (iii) peralkaline lamproites. These three types significantly differ with respect to mineral, whole-rock and Sr–Nd–Pb–Li isotope composition and spatial distribution. The calc-alkaline lamprophyres occur throughout the entire Saxo-Thuringian and Moldanubian zones, whereas the different types of malte-derived potassic rocks are spatially restricted to particular zones. Rocks of the Carboniferous lamprophyre-lamproite orogenic association are characterized by variable negative εNd(i) and variably radiogenic Sr(i), whereas the rocks of the Permian lamprophyre association of anorogenic affinity are characterized by positive εNd(i) and relatively young depleted-mantle Nd-model ages reflecting increasing input from upwelling asthenospheric mantle. The small variation in the Pb isotopic composition of post-collisional potassic mantle-derived magmatic rocks (of both the orogenic and anorogenic series) implies that the Pb budget of the mantle beneath the Bohemian Massif is dominated by the same crust-derived material, which itself may include material derived from several sources. The source rocks of ‘orthopyroxene minettes’ are characterized by isotopically light (‘eclogitic’) Li and strongly radiogenic (crustal) Sr and may have been metasomatized by high-pressure fluids along the edge of a subduction zone. In contrast, the strongly Al2O3 and CaO depleted mantle source of the lamproites is characterized by isotopically heavy Li and high SiO2 and extreme K2O contents. This mantle source may have been metasomatized predominantly by melts. The mantle source of the lamprophyres may have undergone metasomatism by both fluids and melts.

The 563.7 ± 6.1 Ma old, early-syntectonic Mon Repos complex is a predominantly metaluminous, magnesian, calc-alkalic granodioritic to granitic intrusion. Major and trace element variations imply that the rocks evolved through fractional crystallization processes involving amphibole, biotite, Fe-Ti oxides, zircon, and apatite. Rocks less evolved than granodiorite show evidence of hornblende accumulation. Initial Sr (87Sr/86Sr: 0.7090–0.7111) and Nd (eNd: −5.3 to −12.3) isotopic compositions of the granodiorites and granites are highly heterogeneous and vary with SiO2 contents indicating that assimilation of older crustal components occurred. Initial 206Pb/204Pb (16.65–17.65) and 207Pb/204Pb ratios (15.52–15.60) are similar to other mafic-intermediate complexes from the Damara belt. One monzodiorite and two quartz monzonites are K2O-, LILE-, and HFSE enriched and have similar SiO2 contents as the granodiorites. These samples are similar to post-collisional mafic magmas from elsewhere in the world. Their e Nd values (−3.8 to −4.3), 87Sr/86Sr ratios (0.7051–0.7073) and trace-element characteristics imply that their unexposed parental melts are derived from a lithospheric mantle source that was contaminated and metasomatized by crustal material during ancient subduction processes. The data are explained by assuming a “flat” subduction model where melting predominantly involves ancient continental mantle lithosphere and crust with limited, if any, melting of the underlying asthenospheric mantle. During flat subduction, a sliver consisting of buoyant oceanic lithosphere was amalgamated with the base of the ancient continental lithosphere of the overriding plate. The oceanic mantle lithosphere and the oceanic crust dehydrated (but did not melt) and these fluids lowered the solidus of the overlying continental mantle lithosphere and crust. This scenario can explain the occurrence of rare K2O- and LILE-enriched monzodiorites and quartz monzonites with crustal-like isotopic compositions observed in this study as well as some more alkaline rocks in the belt. Because the metasomatized continental lithospheric mantle has lower solidus temperatures than peridotitic mantle, it is very likely that such metasomatized rocks may melt early during flat subduction. Thus, K2O-enriched monzodiorites to monzogranites are not restricted to late stages of the evolution of an orogen but may already form at the onset of an orogeny.

The Red Indian Line (RIL) in central Newfoundland is the suture, where the main tract of the Iapetus Ocean was closed at ~452 Ma during accretion of the peri-Gondwanan Victoria arc with the composite active Laurentian margin. The protracted deformation history of this soft collision started at ~471 Ma with accretion of oceanic terranes to the active composite Laurentian margin. After Iapetus closure both colliding active margins were progressively deformed and metamorphosed during Silurian and Devonian (Salinic, Acadian and Neoacadian orogenic cycles). Peak conditions of the very low- to medium-grade, heterogeneously distributed metamorphism were determined by pseudosection techniques within the range of 2–7 kbar, 230–450 °C during increase of the metamorphic field gradient from ~12 °C/km to ~32 °C/km over time. Multiple metamorphic crystallisation stages were dated by white mica 40Ar/39Ar spot and plateau ages, additional Rb-Sr mineral isochrons involving white mica and one U/Pb age of titanite. All resulting ages between 439 ± 4 Ma and 356 ± 16 Ma postdate the closure of Iapetus. Results differ along two transects: The oldest ages of 443–421 Ma (Salinic orogenic cycle) were observed along the northern transect through the RIL zone with minimal younger overprint. Hence low temperature, intermediate to high pressure conditions (4.0–7.0 kbar, 230–340 °C) achieved during Taconic-Salinic underthrusting are well preserved. During Acadian dextral transpression the Taconic-Salinic structural wedge was tilted subvertically. In contrast, rocks along the southern transect through the RIL zone mainly show Acadian ages of 408–390 Ma with local preservation of older ages. Acadian deformation occurred under low temperature/low pressure conditions (~250–450 °C, 2.5–4.6 kbar). Also Silurian terrestrial cover rocks were buried under these conditions. Acadian-Neoacadian deformation (393–340 Ma) becomes younger towards the northwest and progressively localized in transcurrent fault zones. This final foreland deformation at shallow crustal level established the Acadian/Neoacadian orogenic front in central Newfoundland slightly northwest of the RIL.

The Hämmerlein polymetallic deposit is hosted in skarn, schists, and gneisses that reached their metamorphic peak at ~ 340 Ma during the Variscan orogeny. The deposit is spatially closely associated with one of the most voluminous granites of the Erzgebirge, the Eibenstock granite which intruded the metamorphic units at ~ 320 Ma, and locally also developed greisen mineralization. Cassiterite is the main ore mineral in the Hämmerlein skarn and in greisen mineralizations associated with the Eibenstock granite. The age of skarn formation is bracketed by multi-mineral Rb-Sr isochron ages of the gneisses (~ 340 Ma) and the end of ductile deformation (> 330 Ma). The dated calc-silicate minerals of the skarn have elevated Sn contents, which implies that some Sn was present in the system during regional metamorphism, i.e., well before the emplacement of the Eibenstock granite. Tin in the > 330 Ma old skarn silicates possibly was mobilized from the metamorphic wall rocks. Retrogression of the skarn mineral assemblage may have released some Sn that formed cassiterite in an assemblage with chlorite and fluorite. The Sr isotope signatures of fluorite indicate that this late assemblage is not related to cooling of the metamorphic rocks, but to the emplacement of the Eibenstock granite, which introduced additional Sn into the skarn. Thus, mineralization in the Hämmerlein deposit includes Sn that was introduced during two different events from different sources.

We present high-precision trace element and Sr-Nd-Pb isotope data for Pliocene flood basalts located at Sire (eastern rift wall) and Chefe Donsa (western rift wall) sections from the main Ethiopian rift (MER). These basalts are tholeiitic to mildly alkaline and were derived by moderate degrees of melting (~10–20%) of a spinel lherzolite containing minor amounts of amphibole within the lithospheric mantle. Strontium, Nd and Pb isotopic compositions ( 87 Sr/ 86 Sr: 0.7040–0.7057, 143 Nd/ 144 Nd: 0.52164–0.51287, 206 Pb/ 204 Pb: 17.75–19.20, 207 Pb/ 204 Pb: 15.53–15.64 and 208 Pb/ 204 Pb: 38.12–38.86) are between the inferred composition of the Afar mantle plume and an unspecified enriched lithospheric component, suggesting interaction of melts from asthenospheric and lithospheric mantle domains rather than melting of homogeneous mixed sources or magma mixing. It is proposed that in the Oligocene the impinging Afar plume creates zones of metasomatically enriched mantle. Later, lithospheric thinning as a result of incipient rifting leads to decompression and melting of this metasomatically enriched mantle due to its lower solidus temperature. The chemistry of the Pliocene lavas therefore reflect two associated scenarios namely (i) upwelling plume material from the advancing Afar plume may have induced metasomatism in the lithospheric mantle (ii) mobilization and melting of this enriched lithospheric mantle material resulted in melts characterized by variable mixtures of the two mantle reservoirs.

A detailed study of the Sr- and O- isotopic composition of minerals in the Upper Group 2 (UG2) unit of the eastern Bushveld Complex revealed significant variations in the pegmatoidal footwall pyroxenite and the UG2 chromitite layer itself. Initial 87Sr/86Sr ratios (Sri) of interstitial plagioclase in the footwall rocks are significantly higher than in adjacent rocks of the Critical Zone. The δ18O values of plagioclase-pyroxene and plagioclase-chromite mineral pairs in footwall pyroxenite and chromitite are consistent with oxygen isotope exchange from crystallization temperatures down to 700 °C and 800 °C, respectively, whereas in other parts of the UG2, plagioclase and pyroxene δ18O values are consistent with O isotope equilibration at liquidus crystallization temperatures of approximately 1150 °C. We propose that the higher initial 87Sr/86Sr of plagioclase in the UG2 chromitite and the footwall pyroxenite reflects infiltration of fluid derived from dehydrating country rocks beneath the Bushveld Complex. Fluids could have been introduced either late or during chromitite crystallization. The chromitite layer and its pegmatoidal footwall could have acted as barriers to entrap late stage crustal fluids. Alternatively, reaction of fluids with the chromite-bearing crystallizing mush layer would induce hydration melting of pyroxene and plagioclase supplying Cr and Al to the melt, thus invoking further chromite formation. This dissolution-reaction releases Cr from pyroxene, which along with pre-existing disseminated chromite could refine the chromitite layers. The pegmatoidal UG2 footwall constitutes the reaction front-line of this process, which recrystallized to a coarse-grained rock upon cooling. This study emphasizes the role of crustal fluids and late- and post-magmatic processes in layered intrusions taking place at subsolidus temperatures, whereby isotopic and chemical compositions may be significantly changed.

Der Zeitabschnitt Proterozoikum bis Silur umfasst aus stratigraphischer Sicht wegen des hohen Anteils allochthoner tektonostratigraphischer Einheiten das schwierigste und in der Vergangenheit umstrittenste Kapitel des Erläuterungsbands zur Stratigraphischen Tabelle von Deutschland (ESTD 2005). Mittlerweile hat insbesondere für einige der bisher als proterozoisch und frühpaläozoisch eingestuften Einheiten der Varisziden eine Neubewertung stattgefunden. Dies betrifft Einheiten aus dem Erzgebirge, dem Granulitgebirge, der Schwarzburger Antiform, Teile des südlichen und mittleren Schwarzwalds, den Bayerischen und Oberpfälzer Wald sowie den Eckergneis-Komplex im Harz. In der STD 2016 sind diese Einheiten in Form der stratigraphischen Reichweiten der Protolithalter abgebildet. Die betreffenden Daten und Zusammenhänge werden im Erläuterungsband erklärt. Mit der Stratigraphischen Tabelle Deutschland 2016 liegt somit nicht nur eine Auflage mit aktualisierten Angaben für die autochthonen Einheiten auf Grund revidierter biostratigraphischer und geochronologischer Resultate vor, erstmals werden auch die metamorphen allochthonen Komplexe, die zuvor als Glieder stratigraphischer Einheiten abgehandelt wurden, explizit benannt.

Tertiary rift-related intraplate basanites from the Batain basin of northeastern Oman have low SiO 2 ( 9.73 wt.%) and moderate to high Cr and Ni contents (Cr > 261 ppm, Ni > 181 ppm), representing near primary magmas that have undergone fractionation of mainly olivine and magnetite. Rare earth element systematics and p-T estimates suggest that the alkaline rocks are generated by different degrees of partial melting (4–13%) of a spinel-peridotite lithospheric mantle containing residual amphibole. The alkaline rocks show restricted variations of 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ranging from 0.70340 to 0.70405 and 0.51275 to 0.51284, respectively. Variations in Pb isotopes ( 206 Pb/ 204 Pb: 18.59–18.82, 207 Pb/ 204 Pb: 15.54–15.56, 208 Pb/ 204 Pb: 38.65–38.98) of the alkaline rocks fall in the range of most OIB. Trace element constraints together with Sr–Nd–Pb isotope composition indicate that assimilation through crustal material did not affect the lavas. Instead, trace element variations can be explained by melting of a lithospheric mantle source that was metasomatized by an OIB-type magma that was accumulated at the base of the lithosphere sometimes in the past. Although only an area of less than 1000 km 2 was sampled, magmatic activity lasted for about 5.5 Ma with a virtually continuous activity from 40.7 ± 0.7 to 35.3 ± 0.6 Ma. During this period magma composition was nearly constant, i.e. the degree of melting and the nature of the tapped source did not change significantly over time.

The 547 ± 7 Ma old Achas intrusion (Damara orogen, Namibia) includes magnesian, metaluminous to slightly peraluminous, calcic to calc-alkalic granodiorites and ferroan, metaluminous to slightly peraluminous, calc-alkalic to alkali-calcic leucogranites. For the granodiorites, major and trace element variations show weak if any evidence for fractional crystallization whereas some leucogranites are highly fractionated. Both, granodiorites and leucogranites are isotopically evolved (granodiorites: εNdinit: − 12.4 to − 20.5; TDM: 2.4–1.9; leucogranites: εNdinit: − 12.1 to − 20.6, TDM: 2.5–2.0), show similar Pb isotopic compositions, and may be derived from late Archean to Paleoproterozoic crustal source rocks. Comparison with melting experiments and simple partial melting modeling indicate that the granodiorites may be derived by extensive melting (> 40%) at 900–950 °C under water-undersaturated conditions (< 5 wt.% H2O) of felsic gneisses. Al-Ti and zircon saturation thermometry of the most primitive granodiorite sample yielded temperatures of ca. 930 °C and ca. 800 °C. In contrast to other lower crust-derived granodiorites and granites of the Central Damara orogen, the composition of the magma source is considered the first-order cause of the compositional diversity of the Achas granite. Second-order processes such as fractional crystallization at least for the granodiorites were minor and evidence for coupled assimilation-fractional crystallization processes is lacking. The most likely petrogenetic model involves high temperature partial melting of a Paleoproterozoic felsic source in the lower crust ca. 10–20 Ma before the first peak of regional high-temperature metamorphism. Underplating of the lower crust by magmas derived from the lithospheric mantle may have provided the heat for melting of the basement to produce anhydrous granodioritic melts.

Tourmaline and muscovite are common gangue minerals in magmatic-hydrothermal ore deposits. Tourmaline chemical and B-isotope compositions are widely used to constrain ore-forming conditions, sources and processes. Muscovite occurs in the same environments as tourmaline and is a significant boron host, but its geochemical information has not been exploited to the same extent. We report on a study of B-isotope (SIMS) and chemical (microprobe, LA-ICP-MS) variations in coexisting tourmaline and muscovite from the Panasqueira W-Sn-Cu deposit in Portugal. This is the largest W-deposit in Europe and it consists of sub-horizontal, meter-thick W-Sn-Cu-bearing quartz veins hosted by clastic metasediments above the greisen cupola of a late-Variscan peraluminous granite. Tourmaline is the main hydrothermal mineral formed during alteration of the metasediments but it is absent from the greisen. The tourmaline has intermediate schorl-dravite compositions and is chemically zoned, with increases in Fe/Mg and F from core to rim, while Ca and Al contents decrease. The B-isotope composition (δ11B) of tourmaline ranges from -7 and -11‰ in 90% of the grains, consistent with a granitic source. There is no isotopic zoning but a slight variation with distance from the ore veins. Muscovite is abundant in the greisen and it forms cm-thick vein selvages, where it is locally intergrown with tourmaline. The median δ11B values of muscovite from the greisen and selvages are the same (-17 to -18‰), whereas late muscovite has lower values (to -23‰). The B-isotopic compositions of tourmaline-mica pairs are consistent with isotopic equilibrium as the system cooled from about 500° to 300°C. Muscovite has relatively high concentrations of lithophile elements (Li, Rb, Cs, Tl, Nb, W, Sn, and Ta) compared with tourmaline, which is richer in V, Sr, Ti, and Zn. This contrast relates partly to crystal-chemical differences but also to the fact that tourmaline formed mainly by mineral replacement in the host rocks whereas muscovite formed directly from the hydrothermal fluids and thus better reflects their composition.

Magmatic-hydrothermal systems form a variety of ore deposits at different proximities to upper-crustal hydrous magma chambers, ranging from greisenization in the roof zone of the intrusion, porphyry mineralization at intermediate depths to epithermal vein deposits near the surface. The physical transport processes and chemical precipitation mechanisms vary between deposit types and are often still debated. For this study, we investigate the fluid evolution from proximal to distal settings at the Pirquitas and Chinchillas Mines in NW Argentina and the Sweet Home Mine, Colorado. New results from fluid inclusion and isotopic analyses indicate a contribution of magmatic fluids in the formation of the SnAg Pirquitas Mine, even though no direct association to a magmatic intrusion is visible. Therefore, this deposit may represent a rather distal setting. In contrast, the Ag-Pb-Zn Chinchillas Mine is hosted in volcanic extrusive units and is directly associated to an underlying dacite diatreme. In that respect, this deposit is proximal to a volcanic complex, but due to its shallow emplacement is distal to an inferred magmatic intrusion at depth. The Ag-polymetallic Sweet Home Mine (currently mined for gemmy rhodochrosite) is related to an assumed hidden Mo porphyry, but may be located more proximal to a magmatic intrusion as compared to the other deposits. Performing fluid inclusion analysis, Raman spectroscopy, noble gas isotopic compositions and LA-ICPMS measurements as well as the analysis of stable (H, O, S) and radiogenic (Pb, Sr) isotopic compositions, we aim to reconstruct the evolution and P-T-x properties of the ore-forming fluids in the respective ore deposits. As all studied deposits are characterized by a distinct sulfide mineralization stage, we also investigate whether this stage has formed by mixing of magmatic fluids with variable amounts of externally derived fluids. Furthermore, numerical modelling of the transition from a porphyry to an epithermal environment, considering country rock permeability, fluid pressure distribution, fluid temperatures, and varying locations of the magmatic plume, is used to build a quantitative model for the formation of these types of epithermal deposits.

The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO 2 ) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE 2 O 3 ). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE 2 O 3 contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes.

The Nanling region of South China hosts the largest W-Sn metallogenic province in the world, accounting for more than 54% of global tungsten resources as well as important resources of tin and rare metals. An important feature of this province, which is shared by a number of other W-Sn metallogenic provinces, is that W deposits occur separately from Sn and Sn-W deposits, with the latter concentrated in the western part of the region (especially along the deep, NE-trending Chenzhou-Linwu fault) and the W deposits to the east of them. All the deposits are associated with ilmenite series, peraluminous granites. However, the granites associated with the Sn and Sn-W deposits can be distinguished from the W granites by their higher bulk-rock εNd values and their higher zircon εHf values. Most importantly, the Sn and Sn-W granites are characterized by higher zircon saturation temperatures (800 ± 20°C) than the W granites (650°–750°C). The Sn and Sn-W granites also contain abundant mantle-derived mafic microgranular enclaves, whereas such enclaves are rare in the W granites. A model is proposed in which the protolith to the W granites released W to the melt as a result of the breakdown of muscovite. The temperature of melting, however, was too low for biotite to melt. In the west, particularly along the Chenzhou-Linwu fault (the location of the Sn and Sn-W deposits), higher temperatures enabled the breakdown of both muscovite and biotite and the consequent release of both Sn and W to form Sn and Sn-W granites. This model, which is based on differences in the protolith melting temperature and thus mobilization temperatures for Sn and W, is potentially applicable to any Sn-W metallogenic province in which the Sn and Sn-W deposits are spatially separated from the W deposits.

The Late Paleozoic Variscan Orogen of Europe and North Africa comprises reworked Neoproterozoic to Early Paleozoic crust of the northern Gondwanan shelf that collided with Laurussia. The orogen is characterized by an arcuate trend of the Rheic suture along two orthogonal orogenic arcs and an apparently arbitrary juxtaposition of contrasting paleogeographic proxies to the south of the suture. The comparison of the sedimentary provenance, paleontological, lithostratigraphic, tectonic, and magmatic record demonstrates a contiguous but bipartite, i.e. a western and an eastern, shelf to the south of the Rheic Ocean. Here we reconstruct the development and architecture of the Paleozoic shelf of northern Gondwana preceding the formation of Pangea. In the early Paleozoic both shelf segments were affected by a heterogeneous extension whereby age and composition of extension-related magmatic rocks varies systematically from Cambrian alkaline and tholeiitic rocks in the western shelf to Ordovician calc-alkaline and peraluminous rocks in the eastern shelf. The regional variation in age and composition of the magmatic rocks reflects an eastward decreasing rate of extension along northern Gondwana. The higher extension in the western shelf culminated in the formation of the Armorican Spur. The subsequent intra-Ordovician compressional event, i.e. the “Sardic phase” and the “Cenerian orogeny”, exclusively affected the eastern shelf. Early Devonian collision of the Armorican Spur with Laurussia initiated the subduction accretion stage of the Variscan orogeny resulting in the formation of the Rheno-Hercynian–Moravo-Silesian Arc. At that time, the eastern shelf remained in a passive margin setting. Triggered by Late Devonian rifting along the eastern margin of Arabia, the eastern shelf decoupled from the Gondwanan plate and was displaced eastward, parallel to the northern margin of remaining mainland Gondwana. Early Carboniferous collision of the eastern shelf with the western shelf resulted in orogen wide transpressional tectonics and the formation of the Ibero-Armorican Arc. The tectonic interplay between the two Gondwanan shelf segments is the underlying cause of the final patchwork pattern of paleogeographic markers and the arcuate shape of the Variscan orogenic belt.

International audience; Columbite-tantalite group minerals are the most common Nb-Ta minerals. Columbite-tantalite is particularly suitable for U-Pb dating due to its high U and low common Pb contents. In situ isotopic dating of columbite-tantalite by LA-ICP-MS or SIMS requires certified reference material to properly account for potential matrix effects linked to substitutions between Nb and Ta and between Mn and Fe. Our study has two objectives: i) establish a database of reference materials for in situ U-Pb isotopic dating of columbite-tantalite minerals and ii) test the capability of SIMS to in situ U-Pb date columbite-tantalite minerals of different chemical composition. Tests of in situ U-Pb dating demonstrate that SIMS can easily be used to date columbite-tantalite minerals with errors and precisions overlapping the reference ID-TIMS age. There are, however, significant matrix effects for non-matching Nb-Ta-Fe-Mn compositions of sample and reference material. Matrix effects are highly correlated with the Ta/(Ta + Nb) ratio of columbite-tantalite, due to the significant difference in the atomic mass of Nb and Ta. The Mn/(Mn + Fe) ratio does not significantly contribute to the observed matrix effect as the two elements have similar atomic masses. The linear correlation between Ta/(Nb + Ta) and ((206Pb/238U)SIMS/(206Pb/238U)ID-TIMS) obtained for columbite-tantalite minerals of known ID-TIMS age demonstrates that the SIMS matrix-effect can be properly accounted for by using the chemical composition as determined by EMPA. The ability to measure 204Pb by SIMS also allows the use of reference materials with a small common lead contribution and to calculate accurate and precise ages for columbite-tantalite minerals with contributions of common lead.

Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma.

We present a statistical approach to data mining and quantitatively evaluating detrital age spectra for sedimentary provenance analyses and palaeogeographic reconstructions. Multidimensional scaling coupled with density-based clustering allows the objective identification of provenance end-member populations and sedimentary mixing processes for a composite crust. We compiled 58 601 detrital zircon U–Pb ages from 770 Precambrian to Lower Palaeozoic shelf sedimentary rocks from 160 publications and applied statistical provenance analysis for the Peri-Gondwanan crust north of Africa and the adjacent areas. We have filtered the dataset to reduce the age spectra to the provenance signal, and compared the signal with age patterns of potential source regions. In terms of provenance, our results reveal three distinct areas, namely the Avalonian, West African and East African–Arabian zircon provinces. Except for the Rheic Ocean separating the Avalonian Zircon Province from Gondwana, the statistical analysis provides no evidence for the existence of additional oceanic lithosphere. This implies a vast and contiguous Peri-Gondwanan shelf south of the Rheic Ocean that is supplied by two contrasting super-fan systems, reflected in the zircon provinces of West Africa and East Africa–Arabia.