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  • 1
    Online Resource
    Online Resource
    Growth processes and destructive events during the evolution of volcanic islands : a case study from the Canary Islands (1999)
    Kiel
    Details Availability
    Keywords: Dissertation ; Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource ( 134Seiten = 22MB) , Ill., graph. Darst., Kt
    URL: https://oceanrep.geomar.de/id/eprint/48277/
    Language: English
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  • 2
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    Mechanism of progressive broad deformation from oceanic transform valley to off-transform faulting and rifting (2022)
    Elsevier
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zhang, F., Lin, J., Zhou, Z., Yang, H., & Morgan, J. P. Mechanism of progressive broad deformation from oceanic transform valley to off-transform faulting and rifting. Innovation, 3(1), (2022): 100193, https://doi.org/10.1016/j.xinn.2021.100193.
    Description: Oceanic transform faults (TFs) are commonly viewed as single, narrow strike-slip seismic faults that offset two mid-ocean ridge segments. However, broad zones of complex deformation are ubiquitous at TFs. Here, we propose a new conceptual model for the progressive deformation within broad zones at oceanic TFs through detailed morphological, seismic, and stress analyses. We argue that, under across-transform extension due to a change in plate motion, plate deformation occurs first along high-angle transtensional faults (TTFs) within the transform valleys. Off-transform normal faults (ONFs) form when across-transform deviatoric extensional stresses exceed the yield strength of the adjacent oceanic lithosphere. With further extension, these normal faults can develop into off-transform rift zones (ORZs), some of which can further develop into transform plate boundaries. We illustrate that such progressive complex deformation is an inherent feature of oceanic TFs. The new conceptual model provides a unifying theory to explain the observed broad deformation at global transform systems.
    Description: We benefited from discussions with Drs. Tao Zhang, Huihui Weng, Yen Joe Tan, the SCSIO Deep Ocean Geodynamics Group, the CUHK Seismology Group, and the participants of the InterRidge transform fault workshop in France, 2018. This work was supported by the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0205), NSFC grants (41976064, 41890813, 41976066, 91628301, and 91858207), CAS grants (Y4SL021001, QYZDY-SSW-DQC005, 133244KYSB20180029, 131551KYSB20200021, and ISEE2021PY03), National Key R&D Program of China grants (2018YFC0309800 and 2018YFC0310105), the Guangdong Basic and Applied Basic Research Foundation (2021A1515012227), and Hong Kong Research Grant Council grants (14304820 and 14306119).
    Keywords: Transform fault deformation ; Off-transform faulting and rifting ; Plate rotation ; Transtensional fault ; Ridge-transform interaction
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    PAPER (OA)
  • 3
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    Deformation-related volcanism in the Pacific Ocean linked to the Hawaiian–Emperor bend (2015)
    Nature Publishing Group
    In:  Nature Geoscience, 8 (5). pp. 393-397.
    Details
    Publication Date: 2019-09-23
    Description: Ocean islands, seamounts and volcanic ridges are thought to form above mantle plumes. Yet, this mechanism cannot explain many volcanic features on the Pacific Ocean floor and some might instead be caused by cracks in the oceanic crust linked to the reorganization of plate motions. A distinctive bend in the Hawaiian–Emperor volcanic chain has been linked to changes in the direction of motion of the Pacific Plate, movement of the Hawaiian plume, or a combination of both. However, these links are uncertain because there is no independent record that precisely dates tectonic events that affected the Pacific Plate. Here we analyse the geochemical characteristics of lava samples collected from the Musicians Ridges, lines of volcanic seamounts formed close to the Hawaiian–Emperor bend. We find that the geochemical signature of these lavas is unlike typical ocean island basalts and instead resembles mid-ocean ridge basalts. We infer that the seamounts are unrelated to mantle plume activity and instead formed in an extensional setting, due to deformation of the Pacific Plate. 40Ar/39Ar dating reveals that the Musicians Ridges formed during two time windows that bracket the time of formation of the Hawaiian–Emperor bend, 53–52 and 48–47 million years ago. We conclude that the Hawaiian–Emperor bend was formed by plate–mantle reorganization, potentially triggered by a series of subduction events at the Pacific Plate margins.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: archive
    DOI: 10.1038/ngeo2416
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Hybrid shallow on-axis and deep off-axis hydrothermal circulation at fast-spreading ridges (2014)
    Nature Publishing Group
    In:  Nature, 508 (7497). pp. 508-512.
    Details
    Publication Date: 2019-09-23
    Description: Hydrothermal flow at oceanic spreading centres accounts for about ten per cent of all heat flux in the oceans and controls the thermal structure of young oceanic plates. It also influences ocean and crustal chemistry, provides a basis for chemosynthetic ecosystems, and has formed massive sulphide ore deposits throughout Earth’s history. Despite this, how and under what conditions heat is extracted, in particular from the lower crust, remains largely unclear. Here we present high-resolution, whole-crust, two- and three-dimensional simulations of hydrothermal flow beneath fast-spreading ridges that predict the existence of two interacting flow components, controlled by different physical mechanisms, that merge above the melt lens to feed ridge-centred vent sites. Shallow on-axis flow structures develop owing to the thermodynamic properties of water, whereas deeper off-axis flow is strongly shaped by crustal permeability, particularly the brittle–ductile transition. About 60 per cent of the discharging fluid mass is replenished on-axis by warm (up to 300 degrees Celsius) recharge flow surrounding the hot thermal plumes, and the remaining 40 per cent or so occurs as colder and broader recharge up to several kilometres away from the axis that feeds hot (500–700 degrees Celsius) deep-rooted off-axis flow towards the ridge. Despite its lower contribution to the total mass flux, this deep off-axis flow carries about 70 per cent of the thermal energy released at the ridge axis. This combination of two flow components explains the seismically determined thermal structure of the crust and reconciles previously incompatible models favouring either shallower on-axis or deeper off-axis hydrothermal circulation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/nature13174
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The Current Energetics of Earth's Interior: A Gravitational Energy Perspective (2016)
    Frontiers
    In:  Frontiers in Earth Science, 4 (46).
    Details
    Publication Date: 2019-02-01
    Description: The Earth's mantle convects to lose heat (Holmes, 1931); doing so drives plate tectonics (Turcotte and Oxburgh, 1967). Significant gravitational energy is created by the cooling of oceanic lithosphere atop hotter, less dense mantle. When slabs subduct, this gravitational energy is mostly (~86% for whole mantle flow in a PREM-like mantle) transformed into heat by viscous dissipation. Using this perspective, we reassess the energetics of Earth's mantle. We also reconsider the terrestrial abundances of heat producing elements U, Th, and K, and argue they are lower than previously considered and that consequently the heat produced by radioactive decay within the mantle is comparable to the present-day potential gravitational energy release by subducting slabs—both are roughly ~10–12 TW. We reassess possible core heat flow into the base of the mantle, and determine that the core may be still losing a significant amount of heat from its original formation, potentially more than the radioactive heat generation within the mantle. These factors are all likely to be important for Earth's current energetics, and argue that strong plume-driven upwelling is likely to exist within the convecting mantle.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.3389/feart.2016.00046
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    How large a feedback effect does slab dewatering have on itself? (2001)
    In:  [Talk] In: AGU Fall Meeting 2001, 10.-12.12.2001, San Francisco, USA .
    Details
    Publication Date: 2019-09-23
    Description: Arc magmas are generally believed to be produced when the mantle wedge melts as a result of fluxing of a hydrous fluid from the subducting plate. Fluids liberate from the slab at different P-T conditions; key to understanding the fate of these fluids is the knowledge of the thermal structure of the downgoing plate. Earlier works have shown that this thermal structure is a function of several variables like the age of the incoming oceanic lithosphere, the convergence rate, and the dip angle. However, the impacts of chemical reactions and heat transport by fluid flow have yet to be thoroughly explored. Fluid fluxing from the slab results from metamorphic phase transitions which consume latent heat. Latent heats for the different reactions have been quantified in experimental studies. However, little is known how this cooling effect changes the timing, location, and intensity of fluid release. One way to explore this problem is to use numerical models, as previously done by Peacock et al. Here, we present results of a new self-consistent, chemo-thermo-dynamical model for mantle flow, melting, and fluid release. To solve the governing equations of the model we use a combined finite elements, finite differences, and tracer particle advection scheme. For proper internal consistency we include the cooling effects of fluid release within the temperature solution. In this study we analyze the impact of the cooling effect of metamorphic dehydration reactions on fluid release at subduction zones and water recycling into the deeper mantle. For this analysis, we divide the incoming plate into a crustal and mantle layer consisting primarily of hydrated basalts and hydrated peridotites, respectively. We then prescribe for each layer different values for the latent heats released during dewatering. In accordance to experimentally determined values, in a series of model runs, we gradually augment the chosen values for the latent heats from a minimal to a maximal cooling effect and analyze the impact of this on the timing, location, and intensity of water release. These numerical experiments provide new insight into the interactions between fluid release and latent heat consumption.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 7
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    The subduction zone water cycle revisited with novel 2D and 3D numerical models (2010)
    In:  [Talk] In: SFB 574 Subduction Workshop, 04.- 07.11. 2010, Pucón, Chile .
    Details
    Publication Date: 2019-09-23
    Description: The subduction zone water cycle, i.e. the hydration and dehydration of subducting oceanic lithosphere, is a key process in understanding arc magmatism and volatile recycling processes. Hydration of oceanic crust begins at mid-ocean ridges through hydrothermal alteration and continues more slowly as the seafloor ages. Finally, there is now robust evidence that bend-faulting at the outer rise leads to serpentinization of the cold lithospheric mantle. Dehydration occurs deeper within the subduction zone by fluid releasing metamorphic reactions. These rising fluids flux the mantle wedge where they trigger arc melting. Adiabatic mantle decompression, which requires an upward velocity component in the solid-state mantle flow, may also contribute to sub-arc melt generation. This study uses two- and three-dimensional numerical models to explore plate hydration at the outer rise and consequences of plate dehydration for mantle wedge dynamics. Hydration reactions are simulated with a 2D reaction transport model that resolves for seawater circulation as well as serpentinization. We find that bend-faults are likely to be highly serpentinized. Background serpentinization is most intense around the 270°C isotherm where the reaction rate is at its maximum. 3D mantle flow calculations are used to elucidate mantle wedge dynamics. Here we find that threedimensional diapiric upwellings, fueled by buoyant slab fluids, dominant the mantle wedge flow for a wide parameter range. These calculations clearly show that findings and intuition built upon 2D pictures will need to be revised as high resolution simulations become more feasible with the development of new codes and the availability of better hardware.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 8
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    Implications of subduction rehydration for earth's deep water cycle (2006)
    AGU (American Geophysical Union)
    In:  In: Earth's Deep Water Cycle. , ed. by Jacobsen, S. D. and Lee, S. F. M. v. d. Geophysical Monograph Series, 168 . AGU (American Geophysical Union), Washington, DC, pp. 163-276. ISBN 978-0-87590-433-7
    Details
    Publication Date: 2017-05-16
    Description: The "standard model" for the genesis of the oceans is that they are exhalations from Earth's deep interior continually rinsed through surface rocks by the global hydrologic cycle. No general consensus exists, however, on the water distribution within the deeper mantle of the Earth. Recently Dixon et a/. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. These findings are in striking agreement with the results of numerical modeling of the global water cycle that are presented here. We find that the Dixon et a/. [2002] results are consistent with a global water cycle model in which the oceans have formed by efficient outgassing of the mantle. Present-day depleted mantle will contain a small volume fraction of more primitive wet mantle in addition to drier recycling related enriched components. This scenario is consistent with the observation that hotspots with a FOZO-component in their source will make wetter basalts than hotspots whose mantle sources contain a larger fraction of EM and HIMU components.
    Type: Book chapter , PeerReviewed
    Format: text
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    DOI: 10.1029/168GM20
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    OceanRep: Book chapter
  • 9
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    How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot (2015)
    Nature Publishing Group
    In:  Nature Communications, 6 (7799).
    Details
    Publication Date: 2019-09-23
    Description: Increasingly, spatial geochemical zonation, present as geographically distinct, subparallel trends, is observed along hotspot tracks, such as Hawaii and the Galapagos. The origin of this zonation is currently unclear. Recently zonation was found along the last B70 Myr of the Tristan-Gough hotspot track. Here we present new Sr–Nd–Pb–Hf isotope data from the older parts of this hotspot track (Walvis Ridge and Rio Grande Rise) and re-evaluate published data from the Etendeka and Parana flood basalts erupted at the initiation of the hotspot track. We show that only the enriched Gough, but not the less-enriched Tristan, component is present in the earlier (70–132 Ma) history of the hotspot. Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/ncomms8799
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    A new free-surface stabilization algorithm for geodynamical modelling: Theory and numerical tests (2015)
    Elsevier
    In:  Physics of the Earth and Planetary Interiors, 246 . pp. 41-51.
    Details
    Publication Date: 2017-04-12
    Description: The surface of the solid Earth is effectively stress free in its subaerial portions, and hydrostatic beneath the oceans. Unfortunately, this type of boundary condition is difficult to treat computationally, and for computational convenience, numerical models have often used simpler approximations that do not involve a normal stress-loaded, shear-stress free top surface that is free to move. Viscous flow models with a computational free surface typically confront stability problems when the time step is bigger than the viscous relaxation time. The small time step required for stability (〈2. Kyr) makes this type of model computationally intensive, so there remains a need to develop strategies that mitigate the stability problem by making larger (at least ~10 Kyr) time steps stable and accurate. Here we present a new free-surface stabilization algorithm for finite element codes which solves the stability problem by adding to the Stokes formulation an intrinsic penalization term equivalent to a portion of the future load at the surface nodes. Our algorithm is straightforward to implement and can be used with both Eulerian or Lagrangian grids. It includes α and β parameters to respectively control both the vertical and the horizontal slope-dependent penalization terms, and uses Uzawa-like iterations to solve the resulting system at a cost comparable to a non-stress free surface formulation. Four tests were carried out in order to study the accuracy and the stability of the algorithm: (1) a decaying first-order sinusoidal topography test, (2) a decaying high-order sinusoidal topography test, (3) a Rayleigh-Taylor instability test, and (4) a steep-slope test. For these tests, we investigate which α and β parameters give the best results in terms of both accuracy and stability. We also compare the accuracy and the stability of our algorithm with a similar implicit approach recently developed by Kaus et al. (2010). We find that our algorithm is slightly more accurate and stable for steep slopes, and also conclude that, for longer time steps, the optimal α controlling factor for both approaches is ~2/3, instead of the 1/2 Crank-Nicolson parameter inferred from a linearized accuracy analysis. This more-implicit value coincides with the velocity factor for a Galerkin time discretization applied to our penalization term using linear shape functions in time.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.pepi.2015.07.003
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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