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  • FID-GEO-DE-7
  • Geoelektrik
  • Magnetismus
  • bic Book Industry Communication::H Humanities
  • English  (4)
  • French
  • Spanish
  • 2020-2023  (4)
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  • English  (4)
  • French
  • Spanish
  • German  (41)
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  • 1
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    Serpentinization-driven H2 production from continental break-up to mid-ocean ridge spreading: unexpected high rates at the West Iberia margin (2021)
    Details
    Publication Date: 2022-01-25
    Description: Molecular hydrogen (H2) released during serpentinization of mantle rocks is one of the main fuels for chemosynthetic life. Processes of H2 production at slow-spreading mid-ocean ridges (MORs) have received much attention in the past. Less well understood is serpentinization at passive continental margins where different rock types are involved (lherzolite instead of harzburgite/dunite at MORs) and the alteration temperatures tend to be lower (〈200°C vs. 〉200°C). To help closing this knowledge gap we investigated drill core samples from the West Iberia margin. Lherzolitic compositions and spinel geochemistry indicate that the exhumed peridotites resemble sub-continental lithospheric mantle. The rocks are strongly serpentinized, mainly consist of serpentine with little magnetite, and are generally brucite-free. Serpentine can be uncommonly Fe- rich, with XMg Mg/(Mg + Fe) 〈 0.8, and shows distinct compositional trends toward a cronstedtite endmember. Bulk rock and silicate fraction Fe(III)/ Fe ratios are 0.6–0.92 and 0.58–0.8, respectively; our data show that 2/3 of the ferric Fe is accounted for by Fe(III)- serpentine. Mass balance and thermodynamic calculations suggest that the sample’s initial serpentinization produced ∼120 to 〉300 mmol H2 per kg rock. The cold, late-stage weathering of the serpentinites at the seafloor caused additional H2 formation. These results suggest that the H2 generation potential evolves during the transition from continental break-up to ultraslow and, eventually, slow MOR spreading. Metamorphic phase assemblages systematically vary between these settings, which has consequences for H2 yields during serpentinization. At magma-poor rifted margins and ultraslow- spreading MORs, serpentine hosts most Fe(III). Hydrogen yields of 120 to 〉300 mmol and 50–150 mmol H2 per kg rock, respectively, may be expected at temperatures of 〈200°C. At slow-spreading MORs, in contrast, serpentinization may produce 200–350 mmol H2, most of which is related to magnetite formation at 〉200°C. Since, in comparison to slow-spreading MORs, geothermal gradients at magma-poor margins and ultraslow-spreading MORs are lower, larger volumes of low-temperature serpentinite should form in these settings. Serpentinization of lherzolitic rocks at magma-poor margins should produce particularly high amounts of H2 under conditions within the habitable zone. Magma-poor margins may hence be more relevant environments for hydrogenotrophic microbial life than previously thought.
    Description: research
    Keywords: serpentinization ; hydrogen generation ; magma-poor rifted margin ; mid-ocean ridges ; ultraslow spreading ; hydrothermal alteration ; chemosynthetic life ; seafloor weathering ; FID-GEO-DE-7
    Language: English
    Type: map
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  • 2
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    Subcritical Phase Separation and Occurrence of Deep-Seated Brines at the NW Caldera Vent Field, Brothers Volcano: Evidence from Fluid Inclusions in Hydrothermal Precipitates (2021)
    Details
    Publication Date: 2022-01-25
    Description: https://doi.org/10 .1594/PANGAEA.920208
    Description: research
    Keywords: FID-GEO-DE-7
    Language: English
    Type: map
    Format: 22
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  • 3
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    Fluid–rock interactions in the shallow Mariana forearc: carbon cycling and redox conditions (2021)
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    Publication Date: 2022-01-25
    Description: Few data exist that provide insight into pro- cesses affecting the long-term carbon cycle at shallow fore- arc depths. To better understand the mobilization of C in sediments and crust of the subducting slab, we investigated carbonate materials that originate from the subduction chan- nel at the Mariana forearc (〈 20 km) and were recovered during International Ocean Discovery Program Expedition 366. Calcium carbonates occur as vein precipitates within metavolcanic and metasedimentary clasts. The clasts repre- sent portions of the subducting lithosphere, including ocean island basalt, that were altered at lower blueschist facies conditions and were subsequently transported to the fore- arc seafloor by serpentinite mud volcanism. Euhedral arag- onite and calcite and the lack of deformation within the veins suggest carbonate formation in a stress-free environ- ment after peak metamorphism affected their hosts. Inter- growth with barite and marked negative Ce anomalies in car- bonate attest the precipitation within a generally oxic envi- ronment, that is an environment not controlled by serpen- tinization. Strontium and O isotopic compositions in car- bonate (87Sr/86Sr = 0.7052 to 0.7054, δ18OVSMOW = 20 to 24 ‰) imply precipitation from slab-derived fluids at tem- peratures between ∼ 130 and 300 ◦C. These temperature es- timates are consistent with the presence of blueschist facies phases such as lawsonite coexisting with the carbonates in some veins. Incorporated C is inorganic (δ13CVPDB = −1 ‰ to +4 ‰) and likely derived from the decarbonation of cal- careous sediment and/or oceanic crust. These findings pro- vide evidence for the mobilization of C in the downgoing slab at depths of 〈 20 km. Our study shows for the first time in detail that a portion of this C forms carbonate precipitates in the subduction channel of an active convergent margin. This process may be an important asset in understanding the deep carbon cycle since it highlights that some C is lost from the subducting lithosphere before reaching greater depths.
    Description: research
    Keywords: FID-GEO-DE-7
    Language: English
    Type: map
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  • 4
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    Past penguin colony responses to explosive volcanism on the Antarctic Peninsula (2021)
    Details
    Publication Date: 2022-01-25
    Description: Changes in penguin populations on the Antarctic Peninsula have been linked to several environmental factors, but the potentially devastating impact of volcanic activity has not been considered. Here we use detailed biogeochemical analyses to track past penguin colony change over the last 8,500 years on Ardley Island, home to one of the Antarctic Peninsula’s largest breeding populations of gentoo penguins. The first sustained penguin colony was established on Ardley Island c. 6,700 years ago, pre-dating sub-fossil evidence of Peninsula- wide occupation by c. 1,000 years. The colony experienced five population maxima during the Holocene. Overall, we find no consistent relationships with local-regional atmospheric and ocean temperatures or sea-ice conditions, although the colony population maximum, c. 4,000–3,000 years ago, corresponds with regionally elevated temperatures. Instead, at least three of the five phases of penguin colony expansion were abruptly ended by large eruptions from the Deception Island volcano, resulting in near-complete local extinction of the colony, with, on average, 400–800 years required for sustainable recovery.
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3080_ESM.xlsx
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3081_ESM.xlsx
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3082_ESM.xlsx
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3083_ESM.xlsx
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3084_ESM.xlsx
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3085_ESM.xlsx
    Description: https://static-content.springer.com/esm/art%3A10.1038%2Fncomms14914/MediaObjects/41467_2017_BFncomms14914_MOESM3086_ESM.xlsx
    Description: research
    Keywords: Biogeochemistry ; western Antarctic Peninsula ; Penguin population dynamics ; Environmental impact ; Palaeoclimate ; FID-GEO-DE-7
    Language: English
    Type: map
    Format: 16
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