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Metarodingites are metasomatized mafic dykes that are embedded within serpentinized mantle rocks and commonly contain garmet. Garnet in this rock type has the potential to preserve compositional and chronological information of the entire metamorphic-metasomatic evolution, from the ocean floor to deep subduction. In this study, we investigate the chemical and chronological record of garnet from chloritized metarodingites and garnet veins, from the Zermatt-Saas unit (Unter Theodulgletscher unit and Pfulwe pass). Compositional major and trace element maps reveal that a first generation of Ti-rich garnet is consumed during chloritization, while a second generation of Ti-poor garnet grows in textural equilibrium with chlorite and titanite. In both metarodingite and garnet vein, garnet rim displays an enrichment in Cr, suggesting that late garnet records the infiltration of fluids equilibrated with serpentinites. Fluids liberated from dehydrating serpentinites infiltrate the metarodingite leading to the first garnet generation dissolution, chloritization and titanite crystallization. To validate this hypothesis, we performed LA-ICPMS U-Pb dating of garnet, titanite and zircon. U-Pb dating of garnet core and rim, returned overlapping ages between ca. 44 and 46 Ma, which coincide with previous estimation of peak metamorphic conditions. Titanite from the metarodingite samples yields an age of ca. 45 Ma, which indicates that fluid release and chloritization occurred indeed at peak conditions. Garnet veins cutting across the foliation of the metarodingite and associated titanite are instead resolvably younger and yield ages of ca. 38-39 Ma and ca. 36 Ma, respectively. Zircon in chloritized mafic dykes from Pfulwe pass consists of a Jurassic magmatic core and a metamorphic rim of ca. 47 Ma, confirming that the major fluid-release event and related metasomatism occurred between 45-47 Ma. Rutile yields a younger age of ca. 34 Ma, probably linked to re-setting during exhumation. In conclusion, we show how garnet from metarodingites preserves the metamorphic-metasomatic history and can be used to gather information on (de)hydration reactions during subduction. The consistency of our multi-mineral geochronological data further indicates that petrochronology of garnet from metarodingites is a robust way to track in time metasomatic events in the subducted oceanic lithosphere.

Garnet xenocrysts from kimberlites provide unique insights into the composition, structure and evolution of the subcontinental lithospheric mantle (SCLM). For example, different metasomatic events in the SCLM are reflected in compositional differences between garnet xenocrysts. As mantle metasomatism largely controls the physical and chemical properties of the SCLM, it exerts first order control over the genesis of kimberlitic magmas and diamond formation. However, dating mantle lithologies and processes is complicated by high ambient temperatures that allow the equilibration of most isotopic systems up to the time of kimberlite eruption. As a consequence, the temporal connection between metasomatic events in the mantle and kimberlite genesis is commonly ambiguous.In this study, we applied LA-ICPMS U-Pb dating to 43 harzburgitic, lherzolithic and megacrystic garnet xenocrysts from the ~376 Ma diamondiferous V. Grib kimberlite, Russia, in order to investigate the link between different types of mantle metasomatism and kimberlite genesis.Our results indicate that, with two possible exceptions, only harzburgitic garnet overlaps in age with the kimberlite eruption, whereas lherzolitic and megacrystic garnet crystals are ~20 to 130 million years older. Furthermore, garnet U-Pb ages and Ni-in-garnet temperatures of ~820 to 1200 °C do not correlate. This, and the high closure temperature of U-Pb in garnet (≥900 °C) suggests that the garnet U-Pb ages indeed reflect metasomatic events in the SCLM. However, the U-Pb ages could also reflect cooling ages. In this case, the metasomatic events recorded in the garnet crystals must still have occurred up to ~130 million years prior to the eruption of the V. Grib kimberlite.These findings have far-reaching implications for the genesis of (diamondiferous) kimberlites, as they clearly show that the time lag between metasomatic events in the SCLM, as recorded in kimberlitic garnet xenocrysts, and kimberlite eruption may extend to tens of millions of years.

Understanding the disruption of a tectonic nappe that experiences a subduction-related pressure temperature (P-T) loop is challenging. Thrust imbrications may disrupt single nappes during its subduction and/or exhumation which can be revealed by detailed petrological and geochronological work. Garnet commonly forms during subduction. It most likely hosts early prograde, peak high-pressure (HP) and subsequent metamorphic mineral inclusions making such assemblages a useful tool for detailed petrological and geochronological investigations. Multiple approaches were used to determine the detailed P-T loop of the Cycladic Blueschist Unit passive margin sequence (Greece) such as Zr-in-rutile thermometry coupled with quartz-in-garnet elastic barometry, average P-T and phase equilibrium thermodynamic modeling. U-Pb garnet and zircon geochronology age data were in addition determined to complement already existing age data.The results of this approach reveal that the passive margin sequence in Thera (Santorini), Ios and Naxos was subducted as a coherent continental fragment at a subduction rate of ~2.1 km/My and a heating rate of ~12 °C/My. Prograde and peak HP metamorphism occurs at c. 50 and c. 40 Ma respectively. Along Thera, Ios and Naxos, prograde and peak P-T condition increase from sub-blueschist to upper blueschist facies metamorphism. Subsequently, the sequence was disrupted by one or several thrust faults during its exhumation. The passive margin sequence of Naxos was thrust onto the Ios sequence during the Oligocene at c. 30 Ma. This imbrication is revealed by different exhumation rates of ~6 km/My for the passive margin sequence of Naxos and of ~3 km/My for the one of Ios. The passive margin sequence of Thera, Ios and the upper part of Naxos was exhumed to upper crustal levels, whereas the lower part of the Naxos passive margin sequence was exhumed to the lower crust leading to thermal relaxation of 9–96°C following tectonic accretion. This indicates that thermal relaxation following tectonic accretion in the Cyclades controlled the thermal evolution of the evolving Cycladic orogen during a tectonically quiet period before lithospheric extension.

The Saharo-Arabian desert is part of the largest near-continuous chain of drylands stretching from north-western Africa to the northern China. This harsh and often hyper-arid belt acts as a transition zone separating major biogeographic realms, including the Palearctic, Afrotropics and Indomalayan. This aridity is thought responsible for the creation of unique geographic endemism between Africa and Eurasia. However, there are no direct hydroclimate records from the Arabian hyper-arid interior before the mid-Pleistocene, leaving the terrestrial hydroclimate and the role of Arabia as a biogeographic crossroads or barrier largely unknown.We use desert speleothems preserved from the northern Arabian interior to identify past humid phases over the last 8 million years. These are particularly useful terrestrial climate archives as they act as underground rain gauges, requiring a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Our data reveal evidence of multiple ‘windows of opportunity’ of climate amelioration, allowing biogeographic exchange and dispersals to occur across the Arabian hyper-arid zone. Further, the novel analyses of the isotopic composition (d18O and d2H) of speleothem fluid inclusion waters, representing ‘fossil rainwater’, reveal the diminishing influence of tropical rain-belt precipitation in Arabia across Earth’s transition from a largely ‘ice-free’ northern hemisphere to an ‘ice-age’ world. The extent of Arabian aridity may thus be important in controlling biogeographic dispersals through the Arabian corridor, becoming increasingly less favourable through time. This is supported by fossil evidence which suggest that exchange between biogeographic regions across the Old World Savannah Biome were favoured in the Late Miocene, but became increasingly latitudinally fragmented from the Pliocene onwards. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally.

Aim: Using geochemical proxies to record changes in environmental conditions during the Ediacaran-Cambrian timeMethods: Thin section petrography combined with high-resolution analyses of trace elements and U-Pb, Sr, B and Li isotopes by LA-ICPMS (single and multi-collector)Problem: Identification of pristine early diagenetic carbonate phases and their distinction from late diagenetic and altered carbonates. In this study, we use high spatial resolution multi-element and isotope analyses to identify pristine carbonate phases in samples from recent drill cores from Namibia, drilled by International Continental Scientific Drilling Program project GRIND-ECT. GRIND-ECT aims to capture, in drill core, the Ediacaran-Cambrian transition in key successions worldwide.The method applied allows for relatively high sample throughput (>200) and precise detection of heterogeneous altered domains. Exclusion criteria are the presence or increased concentration of various trace elements (Al, Rb, LREE ...), heterogeneity of the 87Sr/86Sr isotope ratio, a lack of discernible populations in U/Pb isotope space, resulting in non-correlated scattering, and too young U-Pb dates.To date, about 10-15% of the samples analyzed yielded a U-Pb date consistent with depositional age or an early post-depositional age. Geochronologic control of ancient sedimentary sequences is critical for evaluating cause and effect and rates of change in ancient environments. However, precision of LA-ICPMS ages (ca. 1-2%, e.g., 6-11 Ma) is insufficient to resolve changes in the Ediacaran-Cambrian oceans on timescales relevant for biological and environmental change. Therefore, the ages of these pre-characterized samples need to be refined using high-precision methods (Cantine et al., EGU 2023).Analyses of Li and B isotopes are in progress on the pre-characterized, potentially pristine carbonate areas. We expect to see a change in the Li, B and Sr isotope records through Ediacaran-Cambrian time hopefully with significant anomalies. The correlation of the three isotope systems would be a confirmation for us that we are targeting pristine, early diagenetic carbonates.

Establishing geochronological controls on ancient sedimentary successions is critical for evaluating cause and effect, as well as rates of change, in ancient environments. Towards this goal, U-Pb dating of carbonate phases by in situ LA-ICP-MS offers a rapid and reasonably precise method for evaluating not only depositional ages but also the ages of post-depositional processes affecting carbonate rock. However, this technique is still in its first decade of application to carbonate rocks. Determining the best practices for applying this technique and evaluating the meaning, reliability, and robustness of the data it produces remain areas of interest. In this study, we present the first results from U-Pb dating and geochemical characterization of samples from recent drillcores from Namibia, drilled by International Continental Scientific Drilling Program project GRIND-ECT. GRIND-ECT aims to capture, in drillcore, the Ediacaran-Cambrian transition in key successions worldwide. The Namibian portion of GRIND-ECT targets the Nama Group of southern Namibia, well-known for its abundant fossils and detailed geochemical and geochronological records from outcrop, with the goal of elucidating changes in the Earth system during the diversification of early animals. With both abundant interbedded ashes amenable to U-Pb zircon dating and abundant carbonate, these drillcores offer a natural experiment for comparing results from LA-ICP-MS carbonate dating and other geochronological techniques. Our results show that a significant fraction of samples yield geologically meaningful ages when dated using LA-ICP-MS. These ages are consistent with depositional or early post-depositional ages. Microbially-influenced facies are often the most successful. Theses ages can be further refined using higher-precision techniques. Efforts to date vein calcites, which are often very low in U, have not yet yielded robust ages. Integration of Sr and trace and rare earth element data indicate the promise and the limitations of using these proxies as tests for “datability.”

One the world’s largest geothermal reservoirs, “The Geysers” in the California Coast Ranges, is underlain by a composite granitic pluton at shallow depth (~1–3 km, based on geothermal well penetration). Published U-Pb zircon geochronology indicates that this Geysers Plutonic Complex (GPC) intruded between c. 1.8 and 1.1 Ma in three major pulses: the oldest formed a cap of orthopyroxene-biotite microgranite porphyry, followed by orthopyroxene-biotite granite and hornblende-biotite-orthopyroxene granodiorite dominating at deeper levels. Lavas and minor pyroclastic deposits of the overlying Cobb Mountain Volcanic Center erupted between c. 1.2–1.0 Ma. The Geysers-Cobb Mountain plutonic-volcanic association shares common magmatic origins rooted in asthenospheric upwelling into a migrating slab window, where lower-crustal hybridization of mantle-derived magmas was followed by upper-crustal intrusion and differentiation. When and how shallow intrusions or eruptions were fed from this common source, however, remains unclear. This can be reconstructed from crystal-scale analysis of trace elements, oxygen and hafnium isotopes in zircon that can uniquely track magmatic processes in an evolving, long-lived magma system.GPC microgranite zircons display strongly negative Eu anomalies, high levels of incompatible trace elements, and near-solidus Ti-in-zircon temperatures (~670 °C for aTiO2 = 0.55 and aSiO2 = 1). This is distinct from zircons from GPC granite and granodiorite that have moderately negative Eu anomalies, inconspicuous trace element enrichments, and variable Ti-in-zircon temperatures (~850–700 °C). Unlike trace elements, O and Hf isotopes in zircon are indistinguishable between GPC microgranite porphyry and the main population of granite-granodiorite zircons (δ18O = +4.76 to +9.18; εHf = +1.4 to +10.7). There is, however, a subgroup of zircon in GPC granite and granodiorite with elevated δ18O (~8.05) and lower εHf (~4.4) indicating that some late-stage melts experienced higher degrees of assimilation compared to the other magma types. Zircons from Cobb Mountain lavas are similar to those from the GPC granite and granodiorite, but distinct from the granophyre.We set up a thermal model for zircon crystallization to satisfy the following observations: (1) evolved magma from which zircon crystallized was continuously present between c. 2.1 and 1.1 Ma, and (2) crystal recycling from the GPC microporphyry stage in subsequent intrusive or eruptive pulses was negligible. A magma reservoir at ~7 km depth which incrementally grew in three stages matches requirements imposed by zircon ages and compositions: (1) initial magma accumulation at low recharge fluxes starting at 2.1 Ma (0.1 km3/ka), (2) a brief flare-up at 1.6 Ma (4 km3/ka for 50 ka), (3) a return to low recharge fluxes (0.1 km3/ka) between 1.3 and 1.1 Ma. The total injected magma volume amounts to ~300 km3, three times the volume of the GPC as constrained by geothermal wells. According to this model, magma accumulation was long-lived, thus capable of sustaining protracted geothermal activity, but the main igneous growth occurred almost instantaneously. One implication is that accumulation of large volumes of magma can be rapid, and may require special circumstances that are only realized ephemerally despite overall long-lived magmatic activity.

The novel technique of U-Pb dating of garnet allows us to date rocks that were previously impossible to put into a temporal context, either because of the absence of traditional geochronometers such as zircon, monazite, and rutile or because of isotopic disequilibrium, e.g. Lu-Hf or Sm-Nd. The possibility to exclusively date garnet crystals can give us important information to understand the geological evolution of a particular region.In this contribution, we present data from a garnet-quartz vein from the Cabo Ortegal complex, NW Iberian Massif. In the vein, andraditic garnet is associated with chlorite and serpentine in fissures, which cut the foliation of the surrounding lithologies. Field evidence thus indicates that vein formation postdates the formation of the regional foliation (ca. 390 Ma). However, until now, it is unknown, if vein formation is related to thrusting and fluid circulation during the uplift of the area (350-330 Ma) or as the consequence of igneous intrusions (ca. 300 Ma). Vein garnet was analysed in two analytical sessions. The analyses yielded unanchored lower intercept ages of 253.5 ± 7.6 Ma (MSWD = 1.1, n = 62/64) and 252.2 ± 9.5 Ma (MSWD = 1.33, n = 40/40). Those results are much younger than the basement rocks and structures in the Cabo Ortegal complex. The obtained ages coincide with the Permo-Triassic rifting widely documented from other geological domains of the Iberian Peninsula, but has never before been recognised in the Allochthonous Complexes of NW Iberian massif. The study of these types of samples may therefore provide clues to the geological history of the Cabo Ortegal Complex, which may not be available from other techniques and lithologies.

Reduced landward moisture transport due to the cold upwelled surface waters of the Humboldt Current System (HCS) is one of the primary triggers of hyperarid conditions in the Atacama Desert. Marine sediments exposed along the coastline of northern Chile provide a unique archive of land-ocean coupling between coastal upwelling related HCS and paleoclimate in the Atacama Desert during the Neogene. Here we aim to establish a refined stratigraphic framework for the emplacement of diatom-rich deposits of the Bahía Inglesa Formation at Quebrada Tiburón (27°S).The marine sediments exposed at Quebrada Tiburón lie transgressively above the pre-Cenozoic basement. A c. 9m-thick succession of laminated diatomaceous muds is intercalated with sandy deposits. Benthic foraminiferal assemblages and test morphology reveal a shift from trochospiral and planospiral (predominantly epifaunal) to serial (infaunal) morphotypes between sands and diatomaceous muds, respectively. Together with plankton assemblages dominated by diatoms and Globigerina bulloides, the diatomaceous muds reflect a highly productive coastal upwelling regime and low oxic, eutrophic conditions at the seafloor. However, occasional layers of bioturbation within the diatomaceous succession also imply phases of relaxed upwelling conditions. The new stratigraphic framework will thus allow the assessment of Neogene upwelling behavior and variability off Chile on orbital time scales.Preliminary results based on calcareous nannoplankton, diatoms and planktonic foraminifera indicate a stratigraphic range from the upper Miocene (Messinian) to the lower Pliocene for the diatomaceous muds. Evidence from the δ18O of the benthic foraminifera Uvigerina peregrina further ties the upper part of the succession to an uppermost Zanclean age < 3.9 Ma. In a next step, the stratigraphic framework will be further improved by new data from magnetostratigraphy, Sr isotopes, and tephrochronology.This study contributes to CRC 1211 “Earth-Evolution at the dry limit”, funded by the Deutsche Forschungsgemeinschaft (DFG).

The global development and modern distribution of arid zones in subtropical regions (drylands) are likely associated with the global cooling marking the dawn of the Quaternary (~2.6 Ma). This coincides with global shifts in ocean circulation patterns, the intensification of the Walker-Hadley circulation, declining atmospheric CO2, the initiation of glacial–interglacial cycles and the intensification of Northern Hemisphere glaciation, the combination of which has led to the current global distribution of non-polar deserts at ~30° latitude. Although modern drylands represent Earth’s largest terrestrial biome, covering ~46% of global land surfaces and supporting a global population of ~3 billion people, it is currently unclear how drylands will change under future climate change scenarios. Speleothems, preserved in arid-zone caves, are particularly useful terrestrial climate archives as they act as underground rain gauges, which require a minimum of ~300 mm a-1 precipitation, pedogenesis and vegetation cover to form. Moreover, they can be accurately and precisely dated and are subsequently a valuable tool in identifying past large-scale hydrological and vegetation changes in ancient drylands. Here, we present new data from speleothems during past ‘warm periods’ from the Arabian hyper-arid zone. We apply a novel technique of extracting speleothem fluid inclusions waters to reconstruct the isotopic composition (d18O and d2H) of ‘fossil rainwater’ preserved in the speleothem fabric pristinely over millions of years. Speleothem evidence suggests that during the last 7 million years, the Sahara-Arabian desert experienced numerous intermittent humid phases, typically occurring with periods of low global ice-volume and warmer global temperatures. We further explore tropical push-pull mechanisms driving heating of the deep tropics and subsequent expansion of the tropical zone and synchronicity of humid phases regionally. These results have significant implications for understanding the drivers of dryland aridity in non-polar deserts globally.

Carbonates make up about one-quarter of Earth’s sedimentary record, and contain valuable biogeochemical records used to reconstruct Earth history. In situ U-Pb dating of carbonates using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers the possibility of dating these records directly, as well as deposition, diagenesis, and deformation. To fully assess the potential of this technique, laser ablation ages must be compared with other geochronological constraints. Geochemical (e.g., stable isotopes or trace elements) and petrographic context provide further guidance in the measurement and interpretation of carbonate-derived dates. This contribution presents case studies from our ongoing work, spanning Proterozoic and Phanerozoic samples from the marine realm, including the Neoproterozoic of Oman and Svalbard and the Cambro-Ordovician of North America. We highlight measured dates and with special focus on dating deposition and early diagenesis and integrating petrographic and geochemical data. We highlight the role of microbial mats and early marine cements in creating “datable” carbonates and discuss implications for sampling.

Geochronology provides the time frame for various fields of research in the earth sciences that investigate the geological history from the mineral scale to tectonic plates. The reconstruction of pressure–temperature-time (P–T–t) paths of metamorphic rocks from collisional settings such as orogenic belts, for example, is commonly achieved by linking chronological (U–Pb) and trace element data from U-rich accessory phases such as zircon, monazite, titanite, or rutile, with thermobarometric information derived from rock-forming minerals such as garnet. The ability to extract both types of information from one mineral makes garnet arguably the most versatile and powerful petrochronometer. Garnet has an extensive P–T stability field for a wide variety of rock compositions, and changes in P–T conditions during garnet growth are recorded in compositional changes. Garnet U–Pb ages can thus be linked to compositionally distinct garnet domains, providing a direct link between P–T estimates and chronological data. Although still in its infancy, U–Pb dating of metamorphic garnet by LA–ICPMS is an evolving petrochronological tool with a vast potential and a plethora of possible applications.This contribution discusses the advantages and limitations of this method, as well as the significance and meaning of garnet ages. The benefits of the method, as compared to conventional isotope dilution techniques, are the ease of sample preparation, rapid data acquisition and processing, high spatial resolution, and relatively low costs. However, the very low (≤1-100 ng/g) and variable U content of regional metamorphic garnet and the frequently ubiquitous presence of inclusions of U-rich accessory minerals are obstacles that affect the precision and accuracy of garnet U–Pb dates, or may render a particular garnet sample undateable altogether. These various aspects of garnet U–Pb dating by LA–ICPMS will be examined by discussing metamorphic garnet from the Alps, which had previously been dated by Sm-Nd chronology (Pollington and Baxter, 2010).Pollington, A.D., Baxter, E.F., 2010. High resolution Sm–Nd garnet geochronology reveals the uneven pace of tectonometamorphic processes. Earth and Planetary Science Letters 293, 63–71. https://doi.org/10.1016/j.epsl.2010.02.019

Recent advances in analytical techniques and instrumentation allow for the analysis of increasingly smaller sample volumes and lower concentrations. This development significantly expands the possibilities of in-situ geochronology, e.g., LA-MC-ICPMS. Minerals with low U (and Pb) contents such as garnet become the target of in-situ U-Pb geochronology since ages can potentially be obtained from single (sub-)mm-sized garnet grains in thin sections. In this contribution, we explore the current limits of in-situ U-Pb geochronology: what are the minimum concentrations from which an accurate and precise U-Pb age can be obtained?For that purpose, we have analysed garnets from three different localities that were unsuccessfully analysed in the past using a single-collector sector-field Element XR instrument at FIERCE. These garnets have been re-analysed at FIERCE using a Neptune Plus MC-ICPMS coupled to a RESOLution-LR ArF Excimer laser. The analyses were performed in static mode measuring the masses 206Pb and 207Pb with Secondary Electron Multiplier (SEM) and 202Hg, 204Pb and 238U with the Multiple Ion Counters (MIC). With a spot diameter of 193 μm (round) and a fluence of 2 J/cm2 at 15 Hz, ca. 18 µm pit depth was ablated in 18s analysis time, resulting in a total of 2 µg of ablated material. This is more than 2,000 times less material compared to conventional isotope dilution analyses and 3,000 times less U than for a typical LA-ICPMS zircon analysis (20 µm spot). Although the analysed garnets typically have U contents below 10 ng/g, about 15–30 spots are commonly sufficient to define a regression line in the Tera-Wasserburg diagram, yielding a precision of typically

The northern extent of the supercontinent Gondwana in the late Neoproterozoic-Cambrian is not well defined. In most localities the continental margin is covered by thick sedimentary successions, formed following the successive rifting of Tethyan Oceans that episodically detached continental terranes from the edge of the supercontinent. East of the Mediterranean, despite the continental continuity between the Arabian-Nubian-Shield (ANS) and the Tauride block (a Cadomian terrane), the original transition between the two crustal domains is inaccessible and remains obscured. In Israel, investigations of Late Ediacaran, late-stage igneous intrusions of the ANS in the South, together with granulite xenoliths from the lower crust in the North, allow us to probe into the North-Gondwana edge in the late Neoproterozoic and envisage its transition towards the peri-Gondwana Cadomian realm, as well as the evolution of the North Gondwana crust subsequently to the Neoproterozoic. Geochronology and isotopic geochemistry of alkaline intrusions in the Amram massif (southern Israel) as well as doleritic intrusions in the late Neoproterozoic Zenifim Formation (subsurface of south-central Israel) has revealed an igneous and thermal imprint at ca. 550 Ma recorded by the reset of apatite U-Pb ages, together with additional apatite U-Pb dates taken to represent crystallization. Nd and Hf isotopes in apatite, zircon and whole rock also show the ca. 550 Ma intrusions are isotopically distinct from the ANS and resemble Cadomian magmatism in the Taurides. Granulite xenoliths from the lower crust under the lower Galilee (North Israel) contain abundant zircons of distinct U-Pb-Hf properties. These include detrital grains remnant of Neoproterozoic sediment that was subducted and relaminated to the lower crust, late Carboniferous zircons (peaking at 300 Ma) with contrasting εHf(t) signatures, some of which represent syn-Variscan magmatism, and zircons with the age of the host Pliocene basalt. We demonstrate that the Cadomian (ca. 550 Ma) igneous and thermal imprint on the North ANS may have been driven by proto-Tethys subduction that brought about sediment relamination to the North Gondwana lower crust in the latest Neoproterozoic. The late Carboniferous ages recorded in the xenoliths involve both the reworking of depleted ANS basement as well as the relaminated sediment in the means of metamorphism and minor magmatism. Carboniferous thermal disturbance was associated with the formation of continental scale basin and swell architecture across present-day N Africa, Arabia and Iran, and the development of ‘Hercynian unconformities’ in these areas, that were located at the time south of the passive(?) margin of Paleo-Tethys.

Situated between Africa and Eurasia in the eastern Mediterranean, the island of Cyprus has developed on the northern margin of the southern Neotethys by the accretion of three terrains, the Mamonia complex, the Troodos ophiolite, and the Kyrenia terrane. The Kyrenia terrane comprises a tectonic stack of Triassic to Eocene rock units interleaved with basic and acid volcanics and minor metamorphic inliers, alongside an Oligocene-Miocene flysch. Our U-Pb-Hf detrital zircon investigation in the Kyrenia Triassic to Eocene section reveals a large amount of Neoproterozoic zircons (950-600 Ma), alongside Silurian (∼430 Ma), Carboniferous (∼300 Ma), Triassic (∼240 Ma), and Upper Cretaceous (∼85 Ma) zircons. The Precambrian age profile of all three studied units resembles that of Paleozoic sandstones of the Tauride Block, as well as that of Paleozoic and Mesozoic sandstones found across North Africa. It is interpreted as reflecting the reworking of Paleozoic sandstone units from the Taurides or other peri-Gondwanan source. The presence of a substantial proportion of ~300 Ma zircons, as early as in Triassic sediments of the Kyrenia, is of significant interest because Carboniferous magmatism is confined to the Paleotethyan realm which is traced north of the Taurides. Deposition of the Kyrenia sequence closer to a Northern Tethyan province would better fit its detrital zircon signal. The detrital signal of the Kyrenia, indicative for Eurasian terranes north of the Mediterranean, also differs significantly from that of the Mamonia Complex (SW Cyprus) in which only Afro-Arabian sources are distinguished. Thus, in view of its unusual detrital zircon content, the Kyrenia sequence stands out in the Eastern Mediterranean as an exotic rock pile that cannot be straightforwardly correlated with its neighboring geologic environment.

Recent developments on analytical capabilities in the field of in-situ laser ablation mass spectrometry (LA-ICPMS) have expanded the applications of U-Pb geochronometers in low-U minerals such as carbonates (Roberts et al. 2020) or garnets (Millonig et al., 2020). The rapid development of the technique requires well-characterized, matrix-matched reference materials, which are essential for ion probes or LA-ICPMS due to potential matrix effects. However, given the unavailability of standards for some minerals, the use of non-matrix-matched standards, i.e. reference materials that are different to the sample, have been also addressed (Piccione et al., 2019).In this contribution, we explored the possibility of using carbonate reference materials for in-situ U-Pb dating of sulphates. For that purpose, we selected samples from the Messinian Salinity Crisis because their ages are well established by cyclostratigraphy and thus can be compared with ages obtained by LA-ICPMS analysis. Data was acquired using a RESOLution 193 nm ArF excimer laser coupled to a (I) sector field ICP-MS (ElementXR) or (II) multicollector ICP-MS (Neptune Plus).The majority of the samples (27 out of 32) failed due to the elevated common-Pb content and low 238U/204Pb ratios. Nevertheless, five of the samples showed greater amounts of U and U/Pb ratios of up to 600; therefore, regression lines could be drawn and ages are calculated with 5-10 % of uncertainty. These ages obtained are within error of the cyclostratigraphic ages already published (Vasiliev et al., 2017). Millonig et al., (2020) Earth Planet. Sci. Lett. 552, 116589; Piccione et al. (2019) Geosphere 15 (6), 1958– 1972; Roberts et al. (2020) Geochronology 2, 33–61; Vasiliev et al. (2017) Palaeogeogr. Palaeoclimatol. Palaeoecol. 471, 120-133.

Hydrothermal Ag-Bi-Co-Ni-As±U (five-element) veins are particularly prevalent across Central Europe, where this type of mineralization has been mined throughout the ages for its high-grade resources of Ag, Co, Ni, and U. The timing and the detailed geodynamic setting in which this style of mineralization formed remains, however, insufficiently understood due to the limited amount of geochronological data. In this contribution, we report the results of innovative LA-ICP-MS U-Pb geochronology on the carbonate gangue of Ag-Bi-Co-Ni-As±U mineralization from six districts in the Erzgebirge/Krušné Hory metallogenic province of Germany and the Czech Republic, with the goal to constrain the timing of ore formation in the context of Central Europe's geodynamic framework.In-situ U-Pb ages of twelve samples, including dolomite-ankerite, calcite, and siderite cogenetic with Co-Ni-Fe-arsenides, range from 129.4 ± 8.2 to 85.93 ± 3.4 Ma. The ages of Ag-Bi-Co-Ni-As±U and fluorite-barite-Pb-Zn veins from the same occurrence (Annaberg-Buchholz district) overlap each other, suggesting that these two styles of mineralization are genetically related and may form coevally. The compilation of geochronological data from other Ag-Bi-Co-Ni-As±U occurrences in Europe suggests that the origin of this style of mineralization in Central Europe can be related to continental rifting associated with the Mesozoic opening of the Atlantic and/or the Alpine Tethys (200-100 Ma). This provides for the first time evidence for the formation of Ag-Bi-Co-Ni-As±U vein mineralization across Central Europe in response to continental rifting.

Europe´s major Sn and W resources are hosted by magmatic-hydrothermal ore deposits of the Variscan Belt: e.g. in Cornwall, the Erzgebirge, the Iberian Massif, and the French Massif Central. In the Erzgebirge, several major skarn bodies are located in the Schwarzenberg district (12 x 15 km). Although recent geochronological data relates (skarn) ore-formation to late- and post-orogenic magmatic-hydrothermal activity, details on the nature and duration of mineralization events remain insufficiently understood.In this study we present innovative in-situ LA-ICP-MS U-Pb geochronology of garnet from several skarn prospects in the Schwarzenberg district, which is complemented with available geochronological data on intrusions and mineralization in order to constrain the timing of skarn formation within the Variscan orogenic cycle.Eighteen garnet dates range from 338.2 ± 2.5 to 294 ± 8.3 Ma. Associated errors are in the range of 2.5 to 8.4 Ma, but generally tend to be The distribution of garnet ages implies that skarn formation occurred episodically during the ~45 Ma life-time of the Variscan orogen, with the onset of magmatic-hydrothermal activity occurring significantly earlier than previously assumed – at 338 Ma, immediately after the peak of regional metamorphism. Tin and W deposits (skarn, greisen and vein-type) seem to have formed episodically over the entire 45 Ma orogenic cycle of the Erzgebirge – this is consistent with the age range of available geochronological data related to magmatic-hydrothermal ore deposits from other internal parts of the European Variscan Belt.

In marine rift basins, rift-climax deep-water clastics in the hanging wall of rift- or basin-bounding fault systems are commonly juxtaposed against crystalline basement rocks in the footwall. Displacing highly permeable, unconsolidated sediments against low-permeable rock distinguishes these faults significantly from others displacing hard rock. Due to limited surface exposure of such fault zones, studies elucidating their structure and evolution are rare. Consequently, their impact on fluid circulation and in-fault, near-fault, and hanging wall sediment diagenesis are also poorly understood. Motivated by this, we here investigate a well-exposed strand of a major basin-bounding fault system in the East Greenland rift system, namely the Dombjerg Fault which bounds the Wollaston Forland Basin, NE Greenland. Here, Upper Jurassic and Lower Cretaceous syn-rift deep-water clastics are juxtaposed against Caledonian metamorphic basement. Previously, a ~ 1 km-wide zone of increased calcite cementation of the hanging wall sediments along the Dombjerg fault core was identified (Kristensen et al., 2016). Now, based on U-Pb calcite dating, we are able to show that cementation and formation of this zone started during the rift climax in Berrisian/Valanginian times. Using clumped isotope analysis, we determined a cement formation temperature of ~ 30–70 °C. Temperatures likely do not relate to the normal geothermal gradient, but to elevated fluid temperatures of upward directed circulation along the fault. Vein formation within the cementation zone clusters between ~ 125–100 Ma in the post-rift stage, indicating that fracturing in the hanging wall is not directly related to the main phase of activity of the adjacent Dombjerg Fault. Vein formation temperatures are interpreted to reflect a shallow burial depth of the hanging wall deposits and range between ~ 30–80 °C. Further, similar minor element concentrations of veins and adjacent cements argue for diffusional mass transfer into fractures, which in turn infers a subdued fluid circulation and low permeability of the fracture network. These results imply that the cementation zone formed a near-impermeable barrier quickly after sediment deposition and maintained this state even after fracture formation. We argue, that the existence of such a cementation zone should be considered in any assessments that target basin-bounding fault systems for, e.g., hydrocarbon, groundwater, geothermal energy, and carbon storage exploration. Our study highlights that the understanding of fluid flow properties as well as fault-controlled diagenesis affecting the fault itself and/or adjacent basinal clastics is of great fundamental and economic importance.

The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts.In contrast to previously published suggestions (Romer and Kroner, 2015; Wolf et al., 2018), we can exclude a substantial role of intense sedimentary weathering as an important control factor for later Sn and W enrichment in granite related ores of the Western Erzgebirge due to the remarkable homogeneous Hf and low O isotopes in granitic zircons that are extremely distinct to all pre-Devonian basement rocks of Saxothuringia. We document a source enrichment from meta-sedimentary rocks (575 Ma) towards metamorphic rocks (340 Ma) were restites from granulite-facies melts are enriched 6–7 times in Sn compared to UCC (upper continental crust). These rocks are also enriched in K, but depleted in Na and Ca, contain abundant muscovite, and are fertile for later melting. Further enrichment of Sn and W occurred during multiple melt production of the older igneous granites (323–318 Ma) leading finally to a general enrichment of Sn (15 times compared to UCC) in the tin granites (315-314 Ma). Multiple melt production did not lead to a very strong enrichment of ore metals in the granites but is probably very important for a general enrichment of Sn and W in the thick granite-rich crust of the Erzgebirge. Efficient leaching by hydrothermal fluids led to a very strong enrichment (up to several orders) of Sn and W in the greisen ore bodies. References:Romer, R.L.; Kroner, U. Sediment and weathering control on the distribution of Paleozoic magmatic tin-tungsten mineralization. Mineral. Depos. 2015, 50, 327–338, doi:10.1007/s00126-014-0540-5.Wolf, M.; Romer, R.L.; Franz, L.; Lopez-Moro, F.J. Tin in granitic melts: The role of melting temperature and protolith composition. Lithos 2018, 310–311, 20–30.

Tracing the origin and evolution of magmas on their pathway through the lithosphere is key to understanding the magmatic processes that eventually produce eruptions. For ancient magmatic provinces, isotope-geochemical tracers are powerful tools to probe the source regions and magma-crust interaction during ascent and storage.We present new hafnium isotopic compositions of ID-TIMS dated zircons to trace the evolution of the Middle Triassic magmatic province in the Southern Alps (northern Italy) at high temporal resolution [1]. Systematic changes in hafnium isotopic composition with time reveal a coherent temporal evolution from depleted mantle signatures towards crust-dominated signatures within less than four million years. This trend can be ascribed to progressive influence of a crustal source, incorporated into the reservoir from which these zircons crystallized. Towards the end of the magmatic episode, the εHf compositions abruptly revert within one-million-years back towards more juvenile compositions mainly recorded by the mafic to intermediate intrusive pulses (e.g. Monzoni and Predazzo), the effusive climax of basaltic lavas and the post-intrusive ash beds (e.g. Punta Grohmann) in the Dolomite region. We interpret the variation of Hf-isotopic signatures over time as a protracted contamination signal induced by interaction of the mantle-derived magmas with the lower crust.The dataset obtained in this study is further implemented into a two-component mixing model employing a range of potential crust and mantle endmember Hf isotope signatures and Hf concentrations which is directly translated into crustal melt/total melt (=sum of crustal and mantle-derived melt) ratios over time. Based on these observations we explored the thermal evolution and crustal melting as a function of time, lithology, water content and magma flux for a lower crustal magmatic system by numerical modelling. Dykes and sills of basaltic composition are incrementally emplaced at the mantle-crust boundary, which leads to changes in crustal over mantle melt ratios over time. Initial intrusions of basaltic dykes into the relatively cold lower crust cause only limited crustal melting and assimilation but ensuing magma injections into progressively hotter crust results in more extensive partial melting and assimilation of crustal material. Subsequent intrusions into the magmatic lower-crustal roots cannibalize previous intrusions with progressively less isotopic contrast due to dilution with mantle-derived magmas. This is potentially accompanied by an increase in magma flux, e.g. by delamination of dense lower crustal cumulates into the subcontinental lithospheric mantle.The observed trends in hafnium isotopic composition therefore do not necessarily require tectonic re-organizations or changes in mantle sources. Instead these trends may trace variations in mantle-crust interaction during thermally induced chemical maturation of the lower crustal magmatic roots progressively replacing ancient pelitic to mafic lower crustal lithologies by juvenile cumulates. [1] Storck, J.-C., Wotzlaw, J.-F., Karakas, O., Brack, P., Gerdes, A., Ulmer, P. Hafnium isotopic record of mantle-crust interaction in an evolving continental magmatic system, Earth and Planetary Science Letters, (in press).

Phytoplankton is one of the most important producers of oxygen, and plays an important role in the export of large amounts of carbon to the deeper ocean. Since phytoplankton is also the basis of most food webs in the ocean, understanding the dynamic system of phytoplankton is a crucial part to understand past carbon- and nutrient cycles and paleoclimatic changes. The export of nutrients is also an important factor impacting cold-water coral (CWC) reefs and may play a role in controlling their distribution. Here we present laser ablation inductively coupled mass spectrometer (LA-ICP-MS) Element/Ca measurements from Acesta excavata, a file clam, often associated with cold-water coral reefs along the European continental margin. Environmental parameters were recorded with lander systems directly deployed in the CWC reefs, which allows us to compare our geochemical data to in-situ ocean data.Our results reveal, that Ba/Ca ratios show stable baseline values with intermittent sharp peaks. The location of these peaks in between major growth lines and temperature reconstructions with Mg/Sr ratios (Schleinkofer et al., submitted) show that these peaks occur during Winter and are repeatable between samples from the same location. This indicates a strong external forcing mechanism and allows cross-dating of different bivalve shells. While the occurrence of Ba/Ca peaks correlates with phytoplankton maxima, the absolute Ba/Ca ratio does not correlate with the phytoplankton abundance.Mn/Ca ratios show similar trends as Ba/Ca ratios but the peaks are phase shifted and occur slightly delayed. These peaks could be triggered by decreasing oxygen concentrations in the water caused by the decomposition of organic material.As A. excavata does not show easily distinguishable growth lines under the light microscope despite of Mutvei staining or fluorescence microscopy, we hypothesize that P/Ca ratios might be usable to locate highly phosphorylated shell areas that usually correlate with major growth lines. P/Ca ratios show no perceivable features in the vicinity of major growth lines. Instead we recognize that Ba/Ca peaks follow a minimum in P/Ca which is possibly caused by the uptake of phosphor by plankton.These results suggest that A. excavata have potential as a promising tool for high resolution paleoenvironmental reconstructions of both intermediate and overlying surface water masses.ReferencesSchleinkofer N, Raddatz J, Evans D, Gerdes A, Flögel S, Voigt S, et al. Elemental to calcium ratios in the marine bivalve Acesta excavata: an archive for high-resolution paleoceanographic reconstructions of intermediate water masses. PLoS One. Submitted

In marine rift basins, rift-climax deep-water clastics in the hanging wall of rift- or basin-bounding fault systems are commonly juxtaposed against crystalline basement rocks in the footwall. Displacing highly permeable, unconsolidated sediments against low-permeable rock distinguishes these faults significantly from others displacing hard rock. Due to limited surface exposure of such fault zones, studies elucidating their structure and evolution are rare. Consequently, their impact on fluid circulation and in-fault, near-fault, and hanging wall sediment diagenesis are also poorly understood. Motivated by this, we here investigate a well-exposed strand of a major basin-bounding fault system in the East Greenland rift system, namely the Dombjerg Fault which bounds the Wollaston Forland Basin, NE Greenland. Here, Upper Jurassic and Lower Cretaceous syn-rift deep-water clastics are juxtaposed against Caledonian metamorphic basement.Previously, a ~1 km-wide zone of increased calcite cementation of the hanging wall sediments along the Dombjerg fault core was identified (Kristensen et al., 2016). Now, based on U/Pb calcite dating, we are able to show that cementation and formation of this zone started during the rift climax in Berrisian/Valanginian times. Using clumped isotope analysis, we determined cement formation temperatures of ~30-70˚C. Temperatures likely do not relate to the normal geothermal gradient, but to elevated fluid temperatures of upward directed circulation along the fault.Vein formation within the cementation zone clusters between ~125-100 Ma in the post-rift stage, indicating that fracturing in the hanging wall is not directly related to the main phase of activity of the adjacent Dombjerg Fault. Vein formation temperatures range between ~30-80˚C, signifying a shallow burial depth of the hanging wall deposits. Further, similar minor element concentrations of veins and adjacent cements argue for diffusional mass transfer, which in turn infers a subdued fluid circulation and low permeability of the fracture network. These results imply that the chemical alteration zone formed an impermeable barrier quickly after sediment deposition and maintained this state even after fracture formation.We argue that the existence of such a cementation zone should be considered in any assessments that target basin-bounding fault systems for, e.g., hydrocarbon, groundwater, geothermal energy, and carbon storage exploration. Our study highlights that the understanding fluid flow properties as well as fault-controlled diagenesis affecting the fault itself and/or adjacent basinal clastics is of great fundamental and economic importance. References:Kristensen, T. B., Rotevatn, A., Peacock, D. C. P., Henstra, G. A., Midtkandal, I., and Grundvag, S. A. (2016). Structure and flow properties of syn-rift border faults: The interplay between fault damage and fault-related chemical alteration (Dombjerg Fault, Wollaston Forland, NE Greenland), J. Struct. Geol., 92, 99-115, doi:10.1016/j.jsg.2016.09.012.

The rise of animals occurred during an interval of Earth history that witnessed highly dynamic atmosphere-ocean redox conditions; regional, transient glaciations; extraordinarily low magnetic field intensities potentially related to inner core formation; and perturbations to the global carbon cycle of a size not seen before or since. The largest of these, the Shuram carbon isotope excursion, has been invoked as a driving mechanism for, or consequence of, various biological and geological events during the Ediacaran Period. However, there are a number of major controversies regarding the Shuram, including its timing. Without age constraints on its onset or duration, it is impossible to confidently connect the Shuram Event with any biological or geological upheavals.Here, we apply multiple methods, including Re-Os on black shales and U-Pb LA-ICP-MS dating on carbonates, to well-preserved Ediacaran stratigraphy from Oman, deriving new age controls in previously undated parts of the stratigraphy. Our new data show that paired Re-Os shale and U-Pb carbonate analyses constrain the onset and duration of the Shuram excursion in Oman. The results—which are consistent with recent age constraints on Shuram-bearing stratigraphy from Northwest Canada (Rooney et al. 2019, Goldschmidt)—demonstrate the utility of leveraging multiple geochronological techniques within a single basin to constrain deposition in deep to shallow depositional environments. The results also provide key absolute age constraints on the onset of the Shuram excursion in the stratigraphy where it was first defined, critical for testing global correlation schemes, constructing a temporal framework for the Ediacaran period, and identifying causal mechanisms during this interval of geobiological and geodynamic dynamism.

Zannone is a very important island, located in the Neogene-Quaternary extensional domain of the Tyrrhenian back-arc basin, as it is the unique spot where the Paleozoic (?) crystalline basement is hypotesized to be exposed in central Apennines. The exposure of such hypothetical basement in the Zannone Island is very problematic as it implies very large normal displacements (> 3 km) along surrounding faults. No such displacements are known along faults close to Zannone Island.In this work, we study the hypothetical Paleozoic crystalline basement exposed in the Zannone Island with the main aim of understanding its geological nature and relationships with the surrounding rocks. We use a multidisciplinary approach including 1) interpretation of seismic reflection profile; 2) field survey; 3) petro-textural observations; 4) microthermometry on fluid inclusions; 5) geochemical analyses of stable and clumped isotopes; 6) Illite crystallinity and mineralogical analyses of clays and host rocks; 7) analyses of minor gaseous species (He, Ne, and Ar concentrations and isotope ratios) in fluid inclusions; 8) U-Pb geochronology of syn-tectonic calcite, and 9) K-Ar dating of syn-kinematic clay minerals.Our results show that the hypothetical Paleozoic (?) crystalline basement exposed on the Zannone Island is, instead, represented by siliciclastic rocks of very low metamorphic grade. This is testified by the quartzarenites nature of the rocks, the presence of chloritoid and by the observed incipient foliation marked by fine-grained white micas and disposed parallel to the bedding. The contact between such siliciclastic rocks and the overlapping Triassic Dolostone is represented by a low-angle thrust cut by sets of high-angle normal faults with associated calcite mineralizations. K-Ar dating on clay minerals in fault gouge reveals that at least one event of authigenesis (i.e. fluid-assisted tectonic activity) occurred in Zannone Island

Silicic magmatism in the Central Andes forms rhyolitic to dacitic volcanic deposits that range from large-volume ignimbrites (>1000 km3) to small local dome eruptions. The mass proportion between mantle-derived magmatic contributions to crustal melting was previously estimated to range from 20 to 70 % based on Sr-O isotope data obtained on separated feldspar and quartz contained as crystal cargo. New O-Hf isotope data from in-situ ion-probe and laser ablation measurements of U-Pb-dated zircons further constrain type, proportion, and processes of crustal input into silicic magmas. Variations in time and space of these geochemical parameters are documented here using representative samples that cover the entire Central Andes over 20 Ma and 800 km distance. Systematic covariations in isotope tracers relate to increasing crustal thickening through time during Andean orogenesis. Collectively, Sr-Nd-Pb-Hf-O isotopic signatures vary in space and time and temporally reflect increasing crustal input during ignimbrite flare-ups as the crust becomes thermally matures. Spatial variations derive from different crustal domains in the Central Andes and reflect the different age and composition of crustal components.Remarkably, inherited zircon representing basement involved in crustal assimilation is exceedingly rare over the entire province. This most probably reflects high temperatures that exceed zircon saturation temperatures of crustal melts in ignimbrite-forming magmas. This observation distinguishes silicic ignimbrite-forming magmatism from typical granitoid-forming magmatism in orogenic settings where abundant older zircons inherited from the crust are commonly found.

The quality of uranium-series ages depends on the accuracy and precision at which the decay constants of 234U, 230Th and 238U are determined. Here, we present intermediate results for a revision of the decay constants of 234U and 230Th. Therefore, we examined a selection of different materials in secular equilibrium using isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). New approaches of our study in particular concern the characterization of routines for measuring all isotopes on Faraday cups, i. e. low abundance isotopes on cups with 10^13 Ohm amplifiers, and a different selection of materials in comparison to previous studies. λ_234 could be determined so far at a precision of 24 ε and agrees with the latest literature value of Cheng et al. (2013) within its error margins.