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  • 1
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    Fluid escape from subduction zones controlled by channel-forming reactive porosity (2016)
    Springer Nature
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    Publication Date: 2016-12-26
    Description: Water within the oceanic lithosphere is returned to Earth's surface at subduction zones. Observations of metamorphosed veins preserved in exhumed slabs suggest that fluid can escape via channel networks. Yet, it is unclear how such channels form that allow chemically bound water to escape the subducting slab as the high pressures during subduction reduce the porosity of rocks to nearly zero. Here we use multiscale rock analysis combined with thermodynamic modelling to show that fluid flow initiation in dehydrating serpentinites is controlled by intrinsic chemical heterogeneities, localizing dehydration reactions at specific microsites. Porosity generation is directly linked to the dehydration reactions and resultant fluid pressure variations force the reactive fluid release to organize into vein networks across a wide range of spatial scales (μm to m). This fluid channelization results in large-scale fluid escape with sufficient fluxes to drain subducting plates. Moreover, our findings suggest that antigorite dehydration reactions do not cause instantaneous rock embrittlement, often presumed as the trigger of intermediate-depth subduction zone seismicity. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 2
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    Generation of intermediate-depth earthquakes by self-localizing thermal runaway (2009)
    Springer Nature
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    Publication Date: 2009-01-25
    Description: Intermediate-depth (50-300 km) earthquakes commonly occur along convergent plate margins but their causes remain unclear. In the absence of pore-fluid pressures that are sufficiently high to counter the confining pressure in such settings, brittle failure is unlikely. In such conditions, the rocks could fail by the mechanism of progressively self-localizing thermal runaway, whereby ductile deformation in shear zones leads to heating, thermal softening and weakening of rock. Here we test this hypothesis by focusing on fault veins of glassy rock (pseudotachylyte) formed by fast melting during a seismic event, as well as associated ductile shear zones that occur in a Precambrian terrane in Norway. Our field observations suggest that the pseudotachylytes as well as shear zones have a single-event deformation history, and we also document mineralogical evidence for interaction of the rocks with external fluids. Using fully coupled thermal and viscoelastic models, we demonstrate that the simultaneous occurrence of brittle and ductile deformation patterns observed in the field can be explained by self-localizing thermal runaway at differential stresses lower than those required for brittle failure. Our results suggest that by perturbing rock properties, weakening by hydration also plays a key role in shear zone formation and seismic failure; however, thermal runaway enables the rocks to fail in the absence of a free fluid phase. © 2009 Macmillan Publishers Limited.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 3
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    Volcanic arcs fed by rapid pulsed fluid flow through subducting slabs (2012)
    Springer Nature
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    Publication Date: 2012-05-27
    Description: At subduction zones, oceanic lithosphere that has interacted with sea water is returned to the mantle, heats up during descent and releases fluids by devolatilization of hydrous minerals. Models for the formation of magmas feeding volcanoes above subduction zones require largescale transport of these fluids into overlying mantle wedges 1-3. Fluid flow also seems to be linked to seismicity in subducting slabs. However, the spatial and temporal scales of this fluid flow remain largely unknown, with suggested timescales ranging from tens to tens of thousands of years 3-5. Here we use the Li-Ca-Sr isotope systems to consider fluid sources and quantitatively constrain the duration of subduction-zone fluid release at ∼ 70 km depth within subducting oceanic lithosphere, now exhumed in the Chinese Tianshan Mountains. Using lithium-diffusion modelling, we find that the wall-rock porosity adjacent to the flowpath of the fluids increased ten times above the background level. We show that fluids released by devolatilization travelled through the slab along major conduits in pulses with durations of about ∼ 200 years. Thus, although the overall slab dehydration process is continuous over millions of years and over a wide range of pressures and temperatures, we conclude that the fluids produced by dehydration in subducting slabs are mobilized in short-lived, channelized fluid-flow events. © 2012 Macmillan Publishers Limited. All rights reserved.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 4
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    Mapping movements in the deep (2009)
    Springer Nature
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    Publication Date: 2009-01-30
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
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    Modeling of craton stability using a viscoelastic rheology (2010)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 115 (B11). B11413.
    Details
    Publication Date: 2019-09-23
    Description: Archean cratons belong to the most remarkable features of our planet since they represent continental crust that has avoided reworking for several billions of years. Even more, it has become evident from both geophysical and petrological studies that cratons exhibit deep lithospheric keels which equally remained stable ever since the formation of the cratons in the Archean. Dating of inclusions in diamonds from kimberlite pipes gives Archean ages, suggesting that the Archean lithosphere must have been cold soon after its formation in the Archean (in order to allow for the existence of diamonds) and must have stayed in that state ever since. Yet, although strong evidence for the thermal stability of Archean cratonic lithosphere for billions of years is provided by diamond dating, the long-term thermal stability of cratonic keels was questioned on the basis of numerical modeling results. We devised a viscoelastic mantle convection model for exploring cratonic stability in the stagnant lid regime. Our modeling results indicate that within the limitations of the stagnant lid approach, the application of a sufficiently high temperature-dependent viscosity ratio can provide for thermal craton stability for billions of years. The comparison between simulations with viscous and viscoelastic rheology indicates no significant influence of elasticity on craton stability. Yet, a viscoelastic rheology provides a physical transition from viscously to elastically dominated regimes within the keel, thus rendering introduction of arbitrary viscosity cutoffs, as employed in viscous models, unnecessary.
    Type: Article , PeerReviewed
    Format: text
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