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  • Cambridge University Press  (1)
  • Geological Society of America (GSA)  (1)
  • Macmillan Publishers Limited
  • 1
    Publication Date: 2015-01-01
    Description: High-temperature (〉300 °C) off-axis hydrothermal systems found along the slow-spreading Mid-Atlantic Ridge are apparently consistently located at outcropping fault zones. While preferential flow of hot fluids along highly permeable, fractured rocks seems intuitive, such efficient flow inevitably leads to the entrainment of cold ambient seawater. The temperature drop this should cause is difficult to reconcile with the observed high-temperature black smoker activity and formation of associated massive sulfide ore deposits. Here we combine newly acquired seismological data from the high-temperature, off-axis Logatchev 1 hydrothermal field (LHF1) with numerical modeling of hydrothermal flow to solve this apparent contradiction. The data show intense off-axis seismicity with focal mechanisms suggesting a fault zone dipping from LHF1 toward the ridge axis. Our simulations predict high-temperature venting at LHF1 only for a limited range of fault widths and permeability contrasts, expressed as the fault’s relative transmissibility (the product of the two parameters). The relative transmissibility must be sufficient to "capture" a rising hydrothermal plume and redirect it toward LHF1 but low enough to prevent extensive mixing with ambient cold fluids. Furthermore, the temperature drop associated with any high permeability zone in heterogeneous crust may explain why a significant part of hydrothermal discharge along slow-spreading ridges occurs at low temperatures.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 2
    Publication Date: 2013-04-04
    Description: We present a theoretical and experimental study of viscous gravity currents introduced at the surface of a denser inviscid fluid layer of finite depth inside a vertical Hele-Shaw cell. Initially, the viscous fluid floats on the inviscid fluid, forming a self-similar, buoyancy-driven current resisted predominantly by the viscous stresses due to shear across the width of the cell. Once the viscous current contacts the base of the cell, the flow can be considered in two regions: a grounded region in which the current lies in full contact with the base; and a floating region. The subsequent advance of the grounding line separating these regions is shown to be controlled by the thickening of the current associated with balancing the local shear stresses. An understanding of the flow transitions is developed using asymptotic and numerical analysis of a model based on lubrication theory. © 2013 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    Macmillan Publishers Limited
    In:  EPIC3Nature Communications, Macmillan Publishers Limited, 8(15867), pp. 1-11, ISSN: 2041-1723
    Publication Date: 2017-07-26
    Description: Paleo-climate records and geodynamic modelling indicate the existence of complex interactions between glacial sea level changes, volcanic degassing and atmospheric CO2, which may have modulated the climate system’s descent into the last ice age. Between ∼85 and 70 kyr ago, during an interval of decreasing axial tilt, the orbital component in global temperature records gradually declined, while atmospheric CO2, instead of continuing its long-term correlation with Antarctic temperature, remained relatively stable. Here, based on novel global geodynamic models and the joint interpretation of paleo-proxy data as well as biogeochemical simulations, we show that a sea level fall in this interval caused enhanced pressure-release melting in the uppermost mantle, which may have induced a surge in magma and CO2 fluxes from mid-ocean ridges and oceanic hotspot volcanoes. Our results reveal a hitherto unrecognized negative feedback between glaciation and atmospheric CO2 predominantly controlled by marine volcanism on multi-millennial timescales of ∼5,000–15,000 years.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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