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  • 1
    Article
    Article
    Squeezing out the slab - modelling the release of Li, Be and B during progressive high-pressure metamorphism (2007)
    Associated volumes
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    In: Chemical geology, Amsterdam [u.a.] : Elsevier, 1966, 239(2007), 3/4, Seite 323-335, 0009-2541
    In: volume:239
    In: year:2007
    In: number:3/4
    In: pages:323-335
    Description / Table of Contents: A model for the release of Li, Be and B from progressively dehydrating altered oceanic crust during subduction is presented. Combining clinopyroxene/fluid partition coefficients determined experimentally in an earlier study Brenan et al. [Brenan, J.M., Ryerson, F.J., Shaw, H.F., 1998. The role of aqueous fluids in the slab-to-mantle transfer of boron, beryllium, and lithium during subduction: Experiments and models. Geochim. Cosmochim. Acta 62, 33373347] with apparent mineral/clinopyroxene partition coefficients as observed in natural high-pressure metamorphic rocks Marschall et al. [Marschall, H.R., Altherr, R., Ludwig, T., Kalt, A., Gméling, K., Kasztovszky, Zs., 2006a. Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks. Geochim. Cosmochim. Acta 70, 47504769] results in a set of mineral/fluid partition coefficients for high-pressure metamorphic minerals. Mineral modes of altered oceanic crust as a function of pressure and temperature along a given subduction path can be derived from thermodynamic calculations using the program PerpleX. Combination of these modes with mineral/fluid partition coefficients results in whole rock/fluid partition coefficients at any stage of the PT path including information on the amount of fluid released at any depth. Based on these data, the concentrations of Li, Be and B in subducting rocks and released fluids along a given PT path can be modelled. The derived information on B concentrations in rocks and fluids are combined with the temperature-dependent fractionation of B isotopes in order to model the B isotopic evolution of subducting rocks and released fluids. Model calculations are performed for two slightly different chemical compositions (hydrous MORB without K and with 0.5 wt.% K2O), in order to demonstrate the impact of phengite on the boron budget. Provided the necessary input data are available, the concept of such a model could be employed to quantify the trace element release from the slab from any lithology along any reasonable PT path.
    Type of Medium: Article
    ISSN: 0009-2541
    Language: English
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  • 2
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    Young magmatism and Si‐rich melts on Mars as documented in the enriched gabbroic shergottite NWA 6963 (2022)
    Details
    Publication Date: 2023-11-28
    Description: Enriched shergottites contain interstitial Si‐rich mesostasis; however, it is unclear whether such mesostasis is formed by impact or magmatic processes. We use laser ablation multicollector inductively coupled plasma mass spectrometry U–Pb measurements of minerals within the interstitial Si‐rich mesostasis and of merrillite within the coarse‐grained groundmass of Martian‐enriched gabbroic shergottite Northwest Africa (NWA) 6963. The date derived of tranquillityite, Cl‐apatite, baddeleyite, and feldspar from the Si‐rich mesostasis is 172.4 ± 6.1 Ma, and the derived merrillite date is 178.3 ± 10.6 Ma. We conclude, based on textural observation, that merrillite is a late magmatic phase in NWA 6963, that it was not produced by shock, and that its U–Pb‐system was not reset by shock. The indistinguishable dates of the gabbroic merrillite and the minerals within the Si‐rich mesostasis in NWA 6963 indicate that the Si‐rich mesostasis represents a late‐stage differentiated melt produced in the final phase of the magmatic history of the gabbroic rock and not a shock melt. This can likely be transferred to similar Si‐rich mesostases in other enriched shergottites and opens the possibility for investigations of Si‐rich mesostasis in enriched shergottites to access their magmatic evolution. Our results also provide a crystallization age of 174 ± 6 Ma (weighted average) for NWA 6963.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Dr. Rolf M. Schwiete Stiftung http://dx.doi.org/10.13039/501100020027
    Keywords: ddc:552 ; Mars ; shergottites ; mesostasis
    Language: English
    Type: doc-type:article
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  • 3
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    Squeezing out the slab - modelling the release of Li, Be and B during progressive high-pressure metamorphism (2007)
    Elsevier
    In:  Chemical Geology, 239 (3/4). pp. 323-335.
    Details
    Publication Date: 2019-09-23
    Description: A model for the release of Li, Be and B from progressively dehydrating altered oceanic crust during subduction is presented. Combining clinopyroxene/fluid partition coefficients determined experimentally in an earlier study Brenan et al. [Brenan, J.M., Ryerson, F.J., Shaw, H.F., 1998. The role of aqueous fluids in the slab-to-mantle transfer of boron, beryllium, and lithium during subduction: Experiments and models. Geochim. Cosmochim. Acta 62, 3337–3347] with apparent mineral/clinopyroxene partition coefficients as observed in natural high-pressure metamorphic rocks Marschall et al. [Marschall, H.R., Altherr, R., Ludwig, T., Kalt, A., Gméling, K., Kasztovszky, Zs., 2006a. Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks. Geochim. Cosmochim. Acta 70, 4750–4769] results in a set of mineral/fluid partition coefficients for high-pressure metamorphic minerals. Mineral modes of altered oceanic crust as a function of pressure and temperature along a given subduction path can be derived from thermodynamic calculations using the program PerpleX. Combination of these modes with mineral/fluid partition coefficients results in whole rock/fluid partition coefficients at any stage of the P–T path including information on the amount of fluid released at any depth. Based on these data, the concentrations of Li, Be and B in subducting rocks and released fluids along a given P–T path can be modelled. The derived information on B concentrations in rocks and fluids are combined with the temperature-dependent fractionation of B isotopes in order to model the B isotopic evolution of subducting rocks and released fluids. Model calculations are performed for two slightly different chemical compositions (hydrous MORB without K and with 0.5 wt.% K2O), in order to demonstrate the impact of phengite on the boron budget. Provided the necessary input data are available, the concept of such a model could be employed to quantify the trace element release from the slab from any lithology along any reasonable P–T path.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.chemgeo.2006.08.008
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  • 4
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    Metasomatic formation and petrology of blueschist-facies hybrid rocks from Syros (Greece): Implications for reactions at the slab–mantle interface (2009)
    Elsevier
    In:  Lithos, 107 (1-2). pp. 53-67.
    Details
    Publication Date: 2020-07-15
    Description: Chemical disparities at the interface between subducting oceanic crustal rocks and the harzburgitic mantle lead to the formation of reaction zones in the mantle above the subducting slabs composed of hybrid rocks that may carry exotic trace-element patterns and isotopic signatures. Subsequent burial of these metasomatised rocks as part of the progressively subducted slab could deliver trace elements and volatiles to the source region of arc magma. A natural laboratory to study reactions at the slab–mantle interface maybe found in exhumed high-pressure mélanges, where sedimentary, mafic and ultramafic lithologies are juxtaposed and metamorphosed at high-P/T conditions. A mélange zone of that type is found in northern Syros, where metasomatic reaction zones (“blackwalls”) formed on a metre scale at the contact of metasedimentary blueschists and serpentinite. Five different zones within such a contact display the assemblages (I) glaucophane+garnet+phengite+epidote, (II) glaucophane+epidote+chlorite, (III) chlorite+epidote+omphacite±albite (IV) chlorite±titanite±rutile±apatite and (V) serpentine+chromite. Accessory phases, such as apatite, allanite, rutile, titanite, tourmaline, zircon and monazite are abundant in zones II to IV. The observed succession of assemblages together with whole-rock major and trace-element compositions reflect the two dominant processes that are thought to have operated along the lithological contact: (A) diffusion of chemical components driven by the compositional contrast of the juxtaposed rocks, and (B) flux of hydrous fluids along the contact, which depleted (e.g., LILE, SiO2) or enriched (e.g., B, LREE) certain elements in various zones. Thermodynamic modelling is able to closely predict the succession of mineral assemblages as they are expected from diffusion of Mg and Ca across the contact zone. Employed to various P–T conditions and different juxtaposed rock types, this type of modelling could be used to access and evaluate larger portions of the subduction system. Our results support existing models that suggest that mixing and redistribution of major and trace elements in subduction zones may be related to the formation of hybrid rocks in mélange zones
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.lithos.2008.07.015
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  • 5
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    Assessment of Chalk as an Archive for the Lithium Isotope Composition of Seawater (2024)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-23
    Description: The understanding of silicate weathering and its role as a sink for atmospheric CO 2 is important to get a better insight into how the Earth shifts from warm to cool climates. The lithium isotope composition (δ 7 Li) of marine carbonates can be used as a proxy to track the past chemical weathering of silicates. A high‐resolution δ 7 Li record would be helpful to evaluate the role of silicate weathering during the late Cretaceous climate cooling. Here, we assess chalk as a potential archive for reconstructing Late Cretaceous seawater Li isotope composition by comparing Maastrichtian chalk from Northern Germany (Hemmoor, Kronsmoor) to a Quaternary coccolith ooze from the Manihiki Plateau (Pacific Ocean) as a lithological analog to modern conditions. We observe a negative offset of 3.9 ± 0.6‰ for the coccolith ooze relative to the modern seawater Li isotope composition (+31.1 ± 0.3‰; 2SE; n = 54), a value that falls in the range of published offsets for modern core‐top samples and for brachiopod calcite. Further, the negative offset between the Li isotope compositions of Manihiki coccolith ooze and modern planktonic foraminifera is 2.3 ± 0.6‰. Although chalk represents a diagenetically altered modification of pelagic nannofossil ooze, manifested by changes in the composition of trace elements, we observe a consistent offset of Li isotope data between Maastrichtian chalk and Maastrichtian planktonic foraminiferal data (−1.4 ± 0. 5‰) that lies within the uncertainty of modern values. We therefore suggest that chalk can be used as a reliable archive for δ 7 Li reconstructions. Key Points Chalk is a reliable archive for the Li isotope composition of seawater Coccolith ooze has a negative offset of 3.9 ± 0.6‰ from modern seawater for Li isotope ratios The estimated mean value for the late Maastrichtian seawater Li isotope composition is +27.5 ± 1.0‰
    Type: Article , PeerReviewed
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  • 6
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    Host-influenced geochemical signature in the parasitic foraminifera Hyrrokkin sarcophaga (2021)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-03-21
    Description: Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupledplasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol 1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 parts per thousand lower delta C-13 and 0.25 parts per thousand lower delta O-18 values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, delta O-18 or delta C-13 unless the host organism is known and its geochemical composition can be accounted for.
    Type: Article , PeerReviewed
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    Format: archive
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  • 7
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    METASOMATIC TOURMALINE IN HYBRID CONTACT-BANDS BETWEEN GNEISS AND PERIDOTITE IN THE ULTEN ZONE OF THE EASTERN ITALIAN ALPS: CHEMISTRY AND BORON ISOTOPIC COMPOSITION (2011)
    Mineralogical Association of Canada
    Details
    Publication Date: 2011-02-01
    Description: Ultramafic rocks in the Ulten Zone (UZ) high-pressure melange, in the Eastern Italian Alps, embedded in crustal gneisses, preserve a series of metasomatic hybrid bands generated by infiltration of aqueous fluids. These hybrid bands at the peridotite-gneiss contact comprise phlogopite and anthophyllite with accessory zircon, apatite and allanite. Here, we report the rare occurrence of centimeter-sized crystals of metasomatic tourmaline in two different UZ outcrops, at Mt. Hochwart and Malga Preghena. Tourmaline has a dravite-uvite-rich composition and shows optical and chemical zoning, with slightly variable Ti, Ca and Fe contents. Secondary-ion mass spectrometry (SIMS) analyses provide information on the intragrain B-isotopic zonation of the grains, which is correlated with optical and chemical zoning. The range in {delta}11B is from -7.4 to +0.3{per thousand} for the Mt. Hochwart tourmaline, generally with an isotopically lighter core and heavier rim. The {delta}11B range for Malga Preghena tourmaline is from +1.2{per thousand} in the core to -3.9{per thousand} in the rim. Variable proportions of fluids derived from both the local crustal gneisses and a subducting slab control the B-isotope composition in the metasomatic tourmaline from the UZ. Fluid mixing in hybrid crustal-ultramafic bands can be monitored by metasomatic tourmaline, which may also have a significant impact on the B isotope budget of the subducted slab and the slab-mantle interface.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 8
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    MAJOR-ELEMENT AND Li, Be COMPOSITIONAL EVOLUTION OF TOURMALINE IN AN S-TYPE GRANITE-PEGMATITE SYSTEM AND ITS COUNTRY ROCKS: AN EXAMPLE FROM IKARIA, AEGEAN SEA, GREECE (2011)
    Mineralogical Association of Canada
    Details
    Publication Date: 2011-02-01
    Description: The chemical evolution of tourmaline in a granite - pegmatite - hydrothermal system and its metamorphic country-rock on the island of Ikaria, in Greece, has been investigated to elucidate the range of compositions generated from a single intrusive system, and the relation between genetic types of tourmaline and their chemical composition. On Ikaria, an S-type granite intruded metapelites, and several aplitic and pegmatitic dykes originating from the granite cross-cut the granite as well as the country rock. Quartz-tourmaline rocks occur in both the S-type granite and in the metapelite. Tourmaline in rocks genetically related to the granite have Li concentrations between 9.3 and 473 {micro}g/g and Be concentrations between 1.5 and 41.8 {micro}g/g. Tourmaline in rocks genetically related to the metapelite have more than an order of magnitude lower concentrations (Li: 2.0-5.8 {micro}g/g, Be: 0.3-0.9 {micro}g/g). Tourmaline in these rocks is typically zoned, with abrupt changes in composition between core and rim. Generally, the cores have a high Al and low minor-element concentrations. Oscillatory-zoned tourmaline rims formed by diffusion-limited growth. Dykes in which the magma travelled far through the metapelitic country-rocks are more differentiated than others, and contain tourmaline with very low Mg/Fe in the core. The dykes interacted with the surrounding rocks in places, leading to Mg enrichment in the dykes. This interaction also introduced Mn into the dykes; spessartine-rich garnet formed with Li concentrations as high as 166 {micro}g/g. Boron-rich fluids segregating from the metapelite during an amphibolite-facies metamorphic event produced quartz-tourmaline rocks in the metapelite, which are probably unrelated to the S-type granite. The metamorphic fluids in the metapelites interacted with marble units where they were in close vicinity, leading to the formation of Ca-rich tourmaline in those quartz-tourmaline rocks. Concentrations of Li, Be and B in associated minerals decrease as follows: Li: St 〉 Bt 〉 Ms 〉 Grt 〉 Tur, Kfs 〉 Pl; Be: St 〉 Pl 〉 Ms 〉 Tur 〉 Bt 〉 Kfs 〉 Grt; B: Tur 〉〉 Ms 〉 Bt 〉 Pl 〉 Grt 〉 Kfs, St.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 9
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    TOURMALINE: AN IDEAL INDICATOR OF ITS HOST ENVIRONMENT (2011)
    Mineralogical Association of Canada
    Details
    Publication Date: 2011-02-01
    Description: Tourmaline-supergroup minerals are ubiquitous accessory minerals in rocks of the Earth's crust. They can adjust their composition to suit a wide variety of environments, and therefore display a remarkable range in stability in terms of pressure, temperature, fluid composition, and host-rock composition. Because of this compositional sensitivity, tourmaline is an excellent indicator of the environmental conditions in its host. This is further enhanced by negligible diffusion up to high temperatures and a strongly refractory character during subsequent host-rock alteration and weathering, as well as mechanical transport of grains. Whereas most prior research on tourmaline has focused on chemical and crystallographic characterizations and systematics of the tourmaline-supergroup minerals, recent studies are shifting the focus to a quantitative reconstruction of environmental conditions in the host using a combination of structural, compositional and crystallographic characteristics of the tourmaline. This thematic issue, which follows a special session at the 2009 GAC-MAC-AGU meeting in Toronto, highlights these exciting advances; here we discuss some of the obstacles that will need to be overcome to insure the practical applicability of tourmaline. The papers presented in this thematic issue of The Canadian Mineralogist show that we are standing on the brink of a major breakthrough in the use of tourmaline as a quantitative indicator of the chemical and physical properties of its host environment these properties may well make tourmaline the prime mineral for this purpose.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 10
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    TRACE-ELEMENT PARTITIONING AND BORON ISOTOPE FRACTIONATION BETWEEN WHITE MICA AND TOURMALINE (2011)
    Mineralogical Association of Canada
    Details
    Publication Date: 2011-02-01
    Description: High-grade metamorphic tourmaline and white mica from the Broken Hill area, NSW, Australia, were analyzed with laser-ablation ICP-MS and ion-probe techniques to investigate the partitioning of trace elements and fractionation of boron isotopes between these two coexisting phases. The results indicate that most trace elements show partition coefficients close to one; only elements such as Zn, Sr, the light rare-earth elements La and Ce, and Th, partition preferentially into tourmaline, whereas Rb, Ba, W, Sn, and Nb and Ta are preferentially partitioned into coexisting mica. The ion-probe measurements demonstrate that boron isotopes are strongly fractionated between mica and tourmaline, with the white mica being some 10{per thousand} lower in {delta}11B than coexisting tourmaline, which is found to be in rather good agreement with previous measurements and predictions from theory.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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