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<p>Global seawater isotope reconstructions from Precambrian marine carbonates must overcome particular difficulties on two fronts: i) accurate age constraints for global stratigraphic correlations and... more
<p>Global seawater isotope reconstructions from Precambrian marine carbonates must overcome particular difficulties on two fronts: i) accurate age constraints for global stratigraphic correlations and interpretations, and ii) the relative timing of syn- to post-depositional processes. Neoproterozoic cap dolomites have emerged as promising archives for seawater isotope reconstructions, in the context of major geochemical disturbances in the Earth system, including the evolution of complex life, significant shifts in the carbon cycle, Cryogenian glaciations, all in the tectonic framework of continental breakup. However, absolute age constraints are required to set the chronological context of such isotope reconstructions. The direct dating of carbonates by laser ablation ICP-MS U-Pb is an increasingly applied tool, which may help to overcome age uncertainties. Here, we investigate a suite of petrographic sections from the base of the Jacoca Formation cap dolomite, at the Capitão Farm section, Sergipano belt, Brazil, overlying the glacially influenced Sturtian Jacarecica Formation diamictite. The goals of our study are to: i) provide chronological constraints on the timing of the Sturtian deglaciation and ii) to reconstruct the diagenetic history of this unit after carbonate deposition. To this end, in-situ U-Pb geochronology was combined with X-ray diffraction (XRD), and selected element geochemistry data on two cogenetic dolomite phases (D1: finely crystalline dolomite and D2: coarsely rhombic dolomite texture) recognized by optical microscopy- and CL-imagery. Powder XRD patterns, Mg/(Mg+Ca) molar ratios for both D1 and D2 dolomite phases (0.43 to 0.50), as well as petrographic observations, demonstrate a dolomite-dominated mineralogy. Laser ablation U-Pb analyses of the D2 phase yield an isochron in Tera-Wasserburg space, with a lower intercept age of 670±16 Myr and an upper intercept common Pb <sup>207</sup>Pb/<sup>206</sup>Pb value of 0.8805±0.0012. This, therefore, suggests an early dolomitization stage that is consistent with an expected ca. of 660 Myr for post-Sturtian cap dolomites. In contrast, data from an area of the D1 phase defines an isochron age of 555±30 Myr and a more radiogenic common initial <sup>207</sup>Pb/<sup>206</sup>Pb value of 0.8375±0.0026, implying that the U-Pb system was reset long after carbonate dolomitization. The timing of this resetting overlaps with the known Pan-African/Brasiliano tectono-metamorphic event, which folded these geological units, and suggests a post-depositional overprint. Our preliminary data indicates that: i) a reasonable Sturtian dolomitization age is recorded in the Jacoca Formation cap dolomite and that ii) a significant later diagenetic event appears to have reset the U-Pb carbonate system during an episode of crustal deformation. Therefore, U-Pb dating of ancient post-glacial cap dolomites can provide absolute age records of syn- to late-diagenetic geological processes that operated in the aftermath of Cryogenian glaciations. Consequently, these data can help both to anchor isotope and element geochemistry data interpretations, and to highlight potential complexities associated with the subsequent geological evolution of marine carbonate archives.</p>
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Research Interests: Earth Sciences, Geology, Geochemistry, Volcano, Physical sciences, and 4 moreMagma, Zircon, Magma Chamber, and Solidus
Research Interests: Geology, Geochemistry, Petrology, Volcano, Rhyolite, and 3 moreVolcanism, Caldera, and Earth Science
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ABSTRACT Very coarse-grained amphibole xenocrysts (potassian magnesiohastingsite) hosted in an early monzonite stock at the Mt Milligan Cu-Au porphyry deposit, British Columbia, Canada contain coeval sulfide and silicate melt inclusions... more
ABSTRACT Very coarse-grained amphibole xenocrysts (potassian magnesiohastingsite) hosted in an early monzonite stock at the Mt Milligan Cu-Au porphyry deposit, British Columbia, Canada contain coeval sulfide and silicate melt inclusions of primary origin. The sulfide melt inclusions have a bulk composition comparable to Cu-rich ISS. Late growth zones in the amphibole are devoid of sulfide inclusions and contain only low salinity, chalcopyrite-bearing fluid inclusions(average 7.4 wt% NaCleq.). Thermobarometry constrains the minimum conditions of sulfide entrapment (amphibole crystallization) to ˜8 kbar and ˜700°C. LA-ICPMS analyses of 22 sulfide melt inclusions show that it was highly enriched in Au (50± 20 ppm, 1sigma), Ag (140± 70 ppm, 1sigma) and Ni (5000 ± 3000 ppm, 1sigma). Ratios of Cu/Au (7500± 2500, 1sigma) and Au/Ag (0.45± 0.24, 1sigma) are identical to metal ratios in porphyry- stage veins, demonstrating that these metals were not fractionated from one another during suspected volatile exsolution, fluid-melt partitioning, and subsequent transport and precipitation of ore metals. The extremely Au- rich composition of the sulfide melt may reflect fractional crystallization of the sulfide liquid prior to entrapment in the amphibole. Both the xenocrysts and rare, high Mg, alkali basalt xenoliths hosted in the intrusions are depleted in Cr, Co, Ni and Cu, reflecting the sequestering of the base metals into a sulfide liquid in a mid- crustal magma chamber where amphibole and Cr-spinel were cumulus phases. The results of this study show that a Cu-Au-rich sulfide melt coexisted with a amphibole-saturated alkalic basaltic liquid in mid-crustal magma chamber prior to the emplacement of the main intrusions and associated porphyry stage mineralization at Mt. Milligan. This sulfide melt appears to have destabilized with the appearance (exsolution) of a single-phase low salinity aqueous fluid. Identification and analysis of ore metals in sulfide melt inclusions in relatively common xenocryst phases may serve as a useful exploration tool for predicting the metal ratio of undiscovered Cu-Au porphyry deposits in the Canadian Cordillera.
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Abstract Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus in Russia has produced world-class exposures of Pliocene-Pleistocene age granites and ignimbrites at the Tyrnyauz and Chegem volcanic... more
Abstract Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus in Russia has produced world-class exposures of Pliocene-Pleistocene age granites and ignimbrites at the Tyrnyauz and Chegem volcanic centers just to the east of Europe's highest mountain and active volcano, Mount Elbrus. This represents one of the world's best-preserved examples of silicic magmatism in a continental collision environment. We report results of a multi-method zircon petrochronologic (U--Pb, O--Hf isotopes, trace elements) investigation of six ignimbrites, lavas, and associated granodioritic porphyries from these localities. We observe two pulses of magmatism at 2.92 and 1.98 Ma related to Chegem and Tyrnyauz, respectively. High precision CA-ID-TIMS dating of zircons from the top and bottom of the Chegem ignimbrite and its associated porphyry yield indistinguishable age spectra recording 160 kyr of magma assembly and differentiation, with 2.9181 ± 0.0014 Ma eruption age as is constrained by the youngest dated zircon population. Together with overlapping O and Hf isotopic values, this suggests that they represent a large volume of pre-eruptively homogenized magma with ~20% crystals. Zircons have isotopically diverse cores (δ18O = +3.4–6.7‰, eHf = +0.8 to +5.6) while the rims (+5.75 ± 0.20‰, eHf = 3.3 ± 0.7) are in isotopic equilibrium with associated unaltered glass and major phenocryst phases. The neighboring and younger ignimbrites and granites of the nearby Elbrus and Tyrnyauz centers have overlapping higher δ18O and lower eHf zircon values and cluster narrowly in age around 1.98 Ma, suggesting a common source for all these ignimbrites, likely in the Tyrnyauz area. Isotopic data for Chegem, Elbrus and Tyrnyauz zircons and rocks require the contribution of a high proportion (25–55%) of Paleozoic crust to magma petrogenesis. The origin of sudden spikes of voluminous silicic magmatism is further investigated using thermomechanical modeling of the collisional environment. We show that the voluminous silicic volcanism at Chegem, Tyrnyauz and Elbrus is best explained by heating of the lower crust by asthenospheric upwelling after a relict slab detached and sank into the mantle at approximately 5 Ma. This timing is coincident with both the beginning of rapid uplift of the Greater Caucasus and initiation of major volcanism. After this initial melting, continuing delamination of the lithosphere and lower crust from the subducting plate produced broad mantle melting and basaltic volcanism, potentially explaining continued regional-scale magmatism in both the Greater and Lesser Caucasus.
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The Ruwai skarn deposit is the largest polymetallic skarn deposit in Borneo and is located in the Schwaner Mountains. The skarns and massive orebodies are hosted in marble of the Jurassic Ketapang Complex, which was intruded by Cretaceous... more
The Ruwai skarn deposit is the largest polymetallic skarn deposit in Borneo and is located in the Schwaner Mountains. The skarns and massive orebodies are hosted in marble of the Jurassic Ketapang Complex, which was intruded by Cretaceous Sukadana granitoids. The prograde-stage garnet and retrograde-stage titanite yielded U-Pb ages of 97.0 ± 1.8 to 94.2 ± 10.3 Ma and 96.0 ± 2.9 to 95.0 ± 2.0 Ma, respectively. These ages are similar to Re-Os ages obtained on sulfides (96.0 ± 2.3 Ma) and magnetite (99.3 ± 3.6 Ma). The U-Pb zircon ages reveal that magmatism at Ruwai occurred in three phases, including the Early Cretaceous (ca. 145.7 and 106.7–105.7 Ma; andesite-dacite), Late Cretaceous (ca. 99.7–97.1 Ma; diorite-granodiorite), and late Miocene (ca. 10.94–9.51 Ma; diorite-dolerite). Based on geochemical and stable isotopic data (C-O-S) the Ruwai skarn ores are interpreted to have formed from oxidized fluids at ca. 160 to 670°C. The ore-forming fluids and metals were mostly magmatic in o...
Research Interests: Geology, Geochemistry, Economic Geology, Cretaceous, Magmatism, and 3 moreZircon, Skarn, and Titanite
Bor and Cukaru Peki are world-class porphyry deposits spatially and genetically associated with the Cretaceous Timok magmatic complex. This research was conducted to determine the age and geochemical affinity of the magmatic rocks that... more
Bor and Cukaru Peki are world-class porphyry deposits spatially and genetically associated with the Cretaceous Timok magmatic complex. This research was conducted to determine the age and geochemical affinity of the magmatic rocks that formed these ore deposits. Our new geochemical analyses of magmatic rocks from Bor and Cukaru Peki deposits imply they comprise adakite-like compositions that have undergone the amphibole fractionation and sulphide saturation processes. The zircon ages indicate that the Bor system was formed in the age span between 84.5?82 Ma, while the Cukaru Peki system was created in the age span between 86.5?85 Ma.
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Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution... more
Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U–Th–Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span ~ 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km3/1000 year by hot (900 °C), initially zircon-undersaturated dacite into a vertically extensive magma body since ~ 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~ 180 km3, temporally oscillating δ18O and εHf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (~ 200 km3 of melt in a vertically extensive system) and the potential...
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Research Interests: Geology, Sedimentology, Geochronology, Holocene, Volcano, and 3 moreTephra, Radiometric Dating, and Lava
Research Interests: Geology, Geochemistry, Geophysics, Paleontology, Provenance, and 5 moreGondwana, Orogeny, RIFT, American science, and Detritus
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Crustal-scale magmatic systems act as filters between the mantle and the atmosphere, and can generate large volcanic eruptions that pose significant hazards while altering Earth’s climate. Quantifying the growth rates, magma fluxes, and... more
Crustal-scale magmatic systems act as filters between the mantle and the atmosphere, and can generate large volcanic eruptions that pose significant hazards while altering Earth’s climate. Quantifying the growth rates, magma fluxes, and duration of storage at different crustal levels is crucial for understanding such systems, but these parameters are poorly constrained due to the scarcity of exposed crustal sections. Here we present the first detailed reconstruction of magma emplacement and differentiation time scales of a complete crustal-scale igneous system exposed in the southern Alps (Ivrea-Sesia region, northern Italy) to quantify the magma fluxes and duration of transcrustal magmatism. Integrated zircon U-Pb petrochronology and numerical modeling provides unprecedented evidence that the volcanic and plutonic bodies are directly related to each other both chemically and temporally, suggesting that the entire magmatic system grew rapidly from its deepest roots to the erupted pr...
Research Interests: Earth Sciences, Geology, Geochemistry, Volcano, Magmatism, and 3 moreMagma, Magma Chamber, and Caldera
Carbonate U-Pb dating of samples from rift-bounding faults of intracontinental basins in the Borborema province, northeastern Brazil, indicate recurrent tectonic activity during Pangea breakup lasting for >150 m.y. from the Late... more
Carbonate U-Pb dating of samples from rift-bounding faults of intracontinental basins in the Borborema province, northeastern Brazil, indicate recurrent tectonic activity during Pangea breakup lasting for >150 m.y. from the Late Triassic to the Paleocene, reactivating inherited strike-slip Neoproterozoic–Cambrian shear zones. Triassic ages indicate that brittle deformation started some 80 m.y. before previously known, most likely related to rifting along the incipient Central Atlantic. The subsequent Cretaceous opening of the South Atlantic caused renewed fault activity during rifting and basin development. Furthermore, recurrent Cenozoic tectonic activity along the rift-bounding faults is indicated, suggesting that structural inheritance of the Neoproterozoic–Cambrian continental-scale Borborema shear zone system has been responsible for accommodation of recurrent tectonic stress from Mesozoic rifting to the present day.
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Magma chambers feeding hazardous Plinian eruptions of Somma-Vesuvius have been present throughout most of the volcano’s lifetime.
Research Interests: Geology, Geochemistry, Science, Medicine, Volcano, and 3 moreMagma, Magma Chamber, and Large Igneous Province
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Tin-tungsten magmatic-hydrothermal deposits are sources of critical raw materials (Sn, W, Nb, Ta, Li), key to the development of technologies involved in the green transition. However, the current and projected supply of many of these... more
Tin-tungsten magmatic-hydrothermal deposits are sources of critical raw materials (Sn, W, Nb, Ta, Li), key to the development of technologies involved in the green transition. However, the current and projected supply of many of these mineral commodities is often dominated by entities whose practices or geopolitical setting may raise issues from a social, political, or environmental standpoint. To meet a steadily increasing demand, new responsible mineral extraction projects must therefore be developed. Successful exploration and economic appraisal of newly identified mineral deposits require (1) an understanding of the ore-forming processes to build an exploration model, and (2) an early estimate of the deposit size to facilitate well-targeted investments. One key parameter that helps to achieve both goals is the knowledge of absolute timing and duration of the mineralisation process.We present new analytical developments in U-Pb dating of strategic Sn-W ore minerals (cassiterite, wolframite, scheelite) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We used a suite of Sn-W mineral specimens to characterise U/Pb downhole fractionation behaviour and polyatomic interference patterns for these three matrices, allowing the optimisation of ablation and ICP-MS settings. In parallel with technical developments, we compiled a large library of potential primary and secondary cassiterite, wolframite, and scheelite reference materials (RMs) which we characterised for major and trace elements. To further our understanding of geochemistry of Sn-W phases, we also performed high-resolution compositional mapping of key trace elements (e.g. U, Pb, REE) with an ultra-fast washout laser ablation system.Promising RM candidates will be developed into primary RMs with a careful characterisation of compositional homogeneity and precise age determination by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS). Thus characterised RMs and a set of analytical best practices will be made available to laboratories wishing to test and further develop such methods. The ultimate goal of this effort is to build a set of community shared materials and techniques that will allow precise and accurate temporal characterisation of Sn-W mineralisation.
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ABSTRACT http www.rsc.org Publishing Journals JA article.asp?doi b705533a
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... Matthias I. Horvath1, Marcel Guillong2, Ines Günther-Leopold1, Andrei Izmer3, Niko Kivel1, Renato Restani1, Christian Hellwig4 and Detlef Günther5 1Laboratory for Materials Behavior, Nuclear Energy and Safety ... [39] Lamontagne, J.,... more
... Matthias I. Horvath1, Marcel Guillong2, Ines Günther-Leopold1, Andrei Izmer3, Niko Kivel1, Renato Restani1, Christian Hellwig4 and Detlef Günther5 1Laboratory for Materials Behavior, Nuclear Energy and Safety ... [39] Lamontagne, J., Noirot, J., Desgranges, L., Blay, T., Pasquet ...
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Research Interests: Geology, Geochemistry, Geochronology, Proterozoic, Volcano, and 4 moreZircon, Rhyolite, Trace element, and Canyon
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Research Interests: Geology, Geochemistry, Geophysics, Gondwana, Volcano, and 4 morePetrogenesis, Rhyolite, Volcanism, and Caldera
Metaeclogites from the Devesil Unit, East Rhodopes are studied. Well preserved eclogite paragenesis is presented by omphacite+garnet+rutile and is obliterated by still high temperature retrograde assemblage of newly formed garnet,... more
Metaeclogites from the Devesil Unit, East Rhodopes are studied. Well preserved eclogite paragenesis is presented by omphacite+garnet+rutile and is obliterated by still high temperature retrograde assemblage of newly formed garnet, diopside, amphibole, plagioclase, titanite, and quartz. The P-T conditions of the high pressure metamorphism are in the range 620–665 °C and 1.8–2.0 GPa, whereas the retrograde stage occurs at temperature 600–650 °C and pressure 0.6–0,8 GPa. Cathodoluminescence images and LA-ICP-MS dating of zircon grains point to multiple metamorphic origin of the mineral the earliest with Late Permian–Early Triassic age, followed by Early Jurassic and Early Cretaceous metamorphic events.
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The unlined Bedretto tunnel crosses large parts of the pre-Triassic basement of the Gotthard massif (Central Alps), giving the possibility to study late-Variscan plutonic rocks (Rotondo granite) and their Caledonian (poly-)metamorphic... more
The unlined Bedretto tunnel crosses large parts of the pre-Triassic basement of the Gotthard massif (Central Alps), giving the possibility to study late-Variscan plutonic rocks (Rotondo granite) and their Caledonian (poly-)metamorphic host rocks (Tremola and Prato series). The Rotondo granite consists mostly of an equigranular, fine-grained granite and to a lesser extent of a porphyritic granite. Commonly, the Rotondo granite is massive or only slightly foliated. Ductile deformation is localized along discrete shear zones composed of granitic or quartz-biotite-rich lithologies. This paper reviews the geology of the Bedretto tunnel with emphasis on the Rotondo granite and presents constraints based on kinematic, microstructural, and U–Pb geochronological evidence, which can be summarized as follows: (1) Both granitic and quartz-biotite-rich shear zones (QB-SZ) in the Rotondo granite generally dip moderately to steeply towards north and are related to top-to-south reverse shearing, in...
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Fast-scanning quadrupoles more representatively record LA-ICP-MS transient fluid inclusion signals. This allows to (1) target smaller inclusions than before; (2) accurately record polyphase inclusion signals; (3) better characterise fluid... more
Fast-scanning quadrupoles more representatively record LA-ICP-MS transient fluid inclusion signals. This allows to (1) target smaller inclusions than before; (2) accurately record polyphase inclusion signals; (3) better characterise fluid chemistry.
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Thirty-two trace elements were examined in the tree rings of downy oak to evaluate the pollution levels close to a cement plant isolated in a rural context and an industrial area where multiple sources of air pollution are or were... more
Thirty-two trace elements were examined in the tree rings of downy oak to evaluate the pollution levels close to a cement plant isolated in a rural context and an industrial area where multiple sources of air pollution are or were present. Tree cores were collected from trees growing 1 km from both the cement plant and the industrial area that are located 8 km from each other. The analysis of the trace elements was performed on annual tree rings from 1990 to 2016 using laser ablation inductively coupled plasma mass spectrometry. Trace elements Cs, Mg, Mn, S and Zn reflected the emission history of the cement plant. Their values have increased since early 2000s, when the cement plant started its activity. However, the lack of significant trends of pollutants in the tree rings from the industrial area and the possible effect of translocation and volatility of some elements left open questions. The very weak changes of the other trace elements in the period 1990–2016 suggest those elem...
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The late Eocene-to-early Oligocene Taveyannaz Formation is a turbidite series deposited in the Northern Alpine Foreland Basin (close to the Alpine orogenic front). Double dating of zircons with the fission-track and the U–Pb methods is... more
The late Eocene-to-early Oligocene Taveyannaz Formation is a turbidite series deposited in the Northern Alpine Foreland Basin (close to the Alpine orogenic front). Double dating of zircons with the fission-track and the U–Pb methods is applied on samples from the Taveyannaz Formation to reconstruct the exhumation history of the Central-Western Alps and to understand the syn-collisional magmatism along the Periadriatic lineament. Three samples from this unit show similar detrital zircon fission-track age populations that center at: 33–40 Ma (20%); 69–92 Ma (30–40%); and 138–239 Ma (40–50%). The youngest population contains both syn-volcanic and basement grains. Combined with zircon U–Pb data, it suggests that the basement rocks of Apulian-affinity nappes (Margna Sesia, Austroalpine) were the major sources of detritus, together with the Ivrea Zone and recycled Prealpine flysch, that contributed debris to the Northern Alpine Foreland Basin. Furthermore, the rocks of the Sesia–Lanzo Zon...
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To reflect magmatic conditions, volcanic rocks must retain their compositions through eruption and post-eruptive cooling. Mostly, this is the case. However, welded ignimbrites from the Yellowstone–Snake River Plain magmatic province... more
To reflect magmatic conditions, volcanic rocks must retain their compositions through eruption and post-eruptive cooling. Mostly, this is the case. However, welded ignimbrites from the Yellowstone–Snake River Plain magmatic province reveal systematic modification of the lithium (Li) inventory by post-eruptive processes. Here we show that phenocrysts from slowly cooled microcrystalline ignimbrite interiors consistently have significantly more Li than their rapidly quenched, glassy, counterparts. The strong association with host lithology and the invariance of other trace elements indicate that Li remains mobile long after eruption and readily passes into phenocrysts via diffusion as groundmass crystallisation increases the Li contents of the last remaining melts. Li isotopic measurements reveal that this diffusion during cooling combined with efficient degassing on the surface may significantly affect the Li inventory and isotopic compositions of volcanic rocks. Utilisation of Li for...