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  • 1
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    What is the Origin of Widespread Cenozoic Intraplate Volcanism on the New Zealand Microcontinent?. 1st Plume Project Workshop "Plume-like instabilities in the upper mantle beneath Europe" (2006)
    In:  Ottrott, France
    Details
    Publication Date: 2006
    Keywords: TF VIII ; Task Force VIII ; Baby plumes in Central Europe
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    BIBLIOGRAPHY ILP
  • 2
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    Compositional variation and 226Ra-230Th model ages of axial lavas from the southern Mid-Atlantic Ridge, 8°48′S (2015)
    Wiley
    Details
    Publication Date: 2015-12-19
    Description: We present geological observations and geochemical data for the youngest volcanic features on the slow-spreading Mid-Atlantic Ridge at 8°48'S that shows seismic evidence for a thickened crust and excess magma formation. Young lava flows with high sonar reflectivity cover about 14 km 2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length. Three different lava units occur along an about 11 km long portion of the ridge, and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows. Basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field. Lavas from this volcanic area have 226 Ra- 230 Th disequilibria model ages of 1,000 and 4,000 years whereas the older lavas from the rift flank and the pillow mound, but also some of the lava field, are older than 8,000 years. Glasses from the northern and southern ends of the southern lava unit indicate up to 100°C cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material. The compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing. The observations on the 8°48'S lava field support the model of low frequency eruptions from single ascending magma batches that has been developed for slow-spreading ridges. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Alteration at the ultramafic-hosted Logatchev hydrothermal field: Constraints from trace element and Sr-O isotope data (2012)
    Wiley
    Details
    Publication Date: 2012-03-17
    Description: Serpentinized peridotite and gabbronorite represent the host rocks to the active, ultramafic-hosted Logatchev hydrothermal field at the Mid-Atlantic Ridge. We use trace element, δ18O and 87Sr/86Sr data from bulk rock samples and mineral separates in order to constrain the controls on the geochemical budget within the Logatchev hydrothermal system. The trace element data of serpentinized peridotite show strong compositional variations indicating a range of processes. Some peridotites experienced geochemical modifications associated with melt-rock interaction processes prior to serpentinization, which resulted in positive correlations of increasing high field strength element (HFSE) concentrations and light rare earth element (LREE) contents. Other serpentinites and lizardite mineral separates are enriched in LREE, lacking a correlation with HFSE due to interaction with high-temperature, black-smoker type fluids. The enrichment of serpentinites and lizardite separates in trace elements, as well as locally developed negative Ce-anomalies, indicate that interaction with low-T ambient seawater is another important process in the Logatchev hydrothermal system. Hence, mixing of high-T hydrothermal fluids during serpentinization and/or re-equilibration of O-isotope signatures during subsequent low-T alteration is required to explain the trace element and δ18O temperature constraints. Highly radiogenic 87Sr/86Sr signatures of serpentinite and lizardite separates provide additional evidence for interaction with seawater-derived fluids. Sparse talc alteration at the Logatchev site are most likely caused by Si-metasomatism of serpentinite associated with the emplacement of shallow gabbro intrusion(s) generating localized hydrothermal circulation. In summary the geochemistry of serpentinites from the Logatchev site document subsurface processes and the evolution of a seafloor ultramafic hydrothermal system.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records (2016)
    Wiley
    Details
    Publication Date: 2016-02-16
    Description: The rising temperature of the world's oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970-2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (〉33°C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6-year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Indian Ocean corals reveal crucial role of World War II bias for twentieth century warming estimates (2017)
    Springer Nature
    Details
    Publication Date: 2017-11-01
    Description: Indian Ocean corals reveal crucial role of World War II bias for twentieth century warming estimates Scientific Reports, Published online: 31 October 2017; doi:10.1038/s41598-017-14352-6
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 6
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    20th century δ18O seawater and salinity variations reconstructed from paired δ18O and Sr/Ca measurements of a La Reunion coral (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Sea surface salinity (SSS) is an important variable in the global ocean circulation. However, decadal to interdecadal changes in SSS are not well understood due to the lack of instrumental data. Here, we reconstruct SSS from a paired, bimonthly resolved coral δ18O and Sr/Ca record from La Reunion Island that extends from 1913‐1995. Coral Sr/Ca correlates with regional sea surface temperature (SST) back to 1966, when instrumental coverage is good, while coral δ18O does not. The slope of the monthly (annual mean) coral Sr/Ca‐SST regression is ‐0.040 mmol/mol per 1°C (‐0.068 mmol/mol per 1°C) consistent with published estimates of the Sr/Ca‐SST relationship. Coral Sr/Ca suggest a warming of 0.39°C since 1913. δ18O seawater is calculated by subtracting the temperature component from measured coral δ18O, using coral Sr/Ca as well as historical SST products. The derived δ18O seawater reconstructions are correlated (r〉0.6), and all show a significant shift in the mid‐20th century (‐0.17 to ‐0.19 permil), indicating a freshening of SSS by 0.7 psu. However, the timing of this shift depends on the temperature component and varies from 1947 (δ18O seawater calculated with historical SST) to the late 1950s (δ18O seawater calculated with coral Sr/Ca). Coral Sr/Ca shows warm temperature anomalies in the mid‐1950s, while historical SST products show warm anomalies from 1940‐45 followed by cooling in the 1950s, a pattern typical for the World War II bias. This suggests that historical SST may bias reconstructions of δ18O seawater and SSS from corals.
    Print ISSN: 0883-8305
    Electronic ISSN: 2572-4525
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Sub-arc mantle enrichment in the Sunda rear-arc inferred from HFSE systematics in high-K lavas from Java (2021)
    Kirchenbaur, M. ; Schuth, S. ; Barth, A. R. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Many terrestrial silicate reservoirs display a characteristic depletion in Nb, which has been explained in some studies by the presence of reservoirs on Earth with superchondritic Nb/Ta. As one classical example, K-rich lavas from the Sunda rear-arc, Indonesia, have been invoked to tap such a high-Nb/Ta reservoir. To elucidate the petrogenetic processes active beneath the Java rear-arc and the causes for the superchondritic Nb/Ta in some of these lavas, we studied samples from the somewhat enigmatic Javanese rear-arc volcano Muria, which allow conclusions regarding the across-arc variations in volcanic output, source mineralogy and subduction components. We additionally report some data for an along-arc sequence of lavas from the Indonesian part of the Sunda arc, extending from Krakatoa in the west to the islands of Bali and Lombok in the east. We present major and trace element concentrations, Sr–Nd–Hf–Pb isotope compositions, and high-field-strength element (HFSE: Nb, Ta, Zr, Hf, W) concentrations obtained via isotope dilution and MC-ICP-MS analyses. The geochemical data are complemented by melting models covering different source compositions with slab melts formed at variable P–T conditions. The radiogenic isotope compositions of the frontal arc lavas in combination with their trace element systematics confirm previously established regional variations of subduction components along the arc. Melting models show a clear contribution of a sediment-derived component to the HFSE budget of the frontal arc lavas, particularly affecting Zr–Hf and W. In contrast, the K-rich rear-arc lavas tap more hybrid and enriched mantle sources. The HFSE budget of the rear-arc lavas is in particular characterized by superchondritic Nb/Ta (up to 25) that are attributed to deep melting involving overprint by slab melts formed from an enriched garnet–rutile-bearing eclogitic residue. Sub-arc slab melting was potentially triggered along a slab tear beneath the Sunda arc, which is the result of the forced subduction of an oceanic basement relief ~ 8 Myr ago as confirmed by geophysical studies. The purported age of the slab tear coincides with a paucity in arc volcanism, widespread thrusting of the Javanese basement crust as well as the short-lived nature of the K-rich rear-arc volcanism at that time.
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: Gottfried Wilhelm Leibniz Universität Hannover (1038)
    Keywords: ddc:551.9 ; Rear-arc volcanism ; Superchondritic Nb/Ta ; Muria ; Sunda arc
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 8
    Electronic Resource
    Electronic Resource
    Formation and decay of a modern massive sulfide deposit in the Indian Ocean (1998)
    Springer
    Mineralium deposita 33 (1998), S. 302-309 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract In December 1993, the first massive sulfides were recovered from the Indian Ocean floor, north of the Rodrigues Triple Junction. The polymetallic deposit is situated in the fourth Central Indian Ridge segment, close to the rift axis; it is hydrothermally no longer active. The deposit appears to be typical of mid-ocean ridge massive sulfide occurrences but is in a phase of disintegration and about to be buried by sediment. The chimney structures were formed by multiple hydrothermal events and are now degraded by mass wasting showing various stages of weathering. Later-stage, low-temperature hydrothermal mineralization processes led to copper and gold enrichment. Here we report on the geological setting, mineral zonation, different sulfide types and stages of formation of the “Sonne Sulfide Field”, which is part of a larger mineralized zone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050149
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Hydrochemical evolution of Na-SO4-Cl groundwaters in a cold, semi-arid region of southern Siberia (1999)
    Springer
    Hydrogeology journal 7 (1999), S. 546-560 
    Details
    ISSN: 1435-0157
    Keywords: groundwater quality ; hydrochemical modelling ; salinisation ; Siberia ; semi-arid regions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé La région de Shira en Khakassia, dans le sud de la Sibérie, présente de nombreux phénomènes déterminant la chimie des eaux souterraines et des eaux de surface qui sont communs aux régions froides et semi-arides du monde : (1) un climat continental, (2) une localisation à l'abri des pluies, (3) un drainage de surface à faible densité, (4) la présence de lacs salés et (5) l'existence d'une minéralisation évaporitique ancienne et actuelle. Dans les zones déprimées de Shira, les eaux souterraines et lacustres les plus salées ont un faciès sulfaté (et chloruré) sodique. Les résultats de la modélisation thermodynamique laissent penser qu'elles ont évolué sous l'effet combiné de l'altération de silicates et de la dissolution de halite et de gypse, associées à la précipitation de carbonates, qui a soustrait les ions calcium et bicarbonate. Un rapport sensiblement 1:1 des ions sodium et sulfate existe même dans les eaux souterraines des aquifères ne possédant pas d'évaporites. Ceci peut indiquer la formation d'évaporites secondaires de sulfate de sodium (dans et près des lacs ou dans les profils de sols lorsque la nappe est proche de la surface), qui sont ensuite dispersées à travers la région étudiée par transport atmosphérique. Plusieurs nappes de zones urbaines sont caractérisées par de très fortes concentrations en nitrate, provenant certainement d'infiltrations d'eaux usées.
    Notes: Abstract The Shira region of Khakassia in southern Siberia exhibits many features governing the evolution of groundwater and surface-water chemistry that are common to other cold, semi-arid areas of the world: (1) a continental climate, (2) location in a rain shadow, (3) low density of surface-water drainage, (4) occurrence of saline lakes, and (5) occurrence of palaeo- and modern evaporite mineralisation. In lowland areas of Shira, the more saline groundwaters and lake waters have a sodium-sulphate (-chloride) composition. Results of thermodynamic modelling suggest that these evolve by a combination of silicate weathering and gypsum and halite dissolution, coupled with carbonate precipitation to remove calcium and bicarbonate ions. An approximately 1:1 sodium:sulphate ratio occurs even in groundwaters from non-evaporite-bearing aquifers. This may indicate the formation of secondary sodium sulphate evaporites (in or near saline lakes or in soil profiles where the water table is shallow), which are subsequently distributed throughout the study area by atmospheric transport. Several urban groundwaters are characterised by very high nitrate concentrations, conceivably derived from sewage/latrine leakage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100400050228
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  • 10
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    Detection of Gold Nanoparticles in Hydrothermal Fluids (2019)
    Society of Economic Geologists (SEG)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The transport and deposition of gold from colloidal suspensions in hydrothermal fluids has been a persistent theme in ore deposits research. Studies of active geothermal systems show that a complete model of gold transport must include both dissolved and particulate forms. However, samples of the hydrothermal fluids are commonly spiked with aqua regia after collection in order to put any solids back into solution, thus preventing a quantitative assessment of the particle load. Although attempts have been made to filter the solids, gold nanoparticles (Au NPs) will mostly pass the 0.2-〈span〉μ〈/span〉m filters that are in common use, and a simple technique for analyzing suspended particles in the liquids has been lacking. In this study, we demonstrate how time-resolved acquisition of mass 197 in a conventional inductively coupled plasma-mass spectrometer (ICP-MS) can be used to detect and measure Au NPs in the filtered liquids, with an example of well-characterized fluids from the Reykjanes geothermal field on Iceland. The technique allows for precise monitoring of the solution as it is introduced into the plasma with the capability of identifying individual particles carried in suspension. Results show that Au particles passing the 0.2-〈span〉μ〈/span〉m filters are abundant in the studied samples, and measurements of the individual particles can be used to determine their size. The experiment highlights the potential of emerging ICP-MS techniques, including very fast data acquisition and multielement analysis of single particles in time-of-flight mode, for characterization of NPs in hydrothermal fluids.〈/span〉
    Print ISSN: 0361-0128
    Electronic ISSN: 1554-0774
    Topics: Geosciences
    Published by Society of Economic Geologists (SEG)
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