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Subduction forces and flow pattern

Conceptual illustration for the basic forces and mantle flow pattern around subduction zones.

Conceptual illustration for the basic forces and mantle flow pattern around subduction zones. The forces indicated are: F_rp: Ridge push; F_sp: Slab pull; F_nb: Negative Buoyancy of the subducting lithosphere; F_ts: Trench suction. Resisting forces: R_d (c/o) mantle drag; R_s-c: Resistance at the subduction interface; R_b: Bending resistance; R_s: Mantle resistance on the slab; R_r: Mantle resistance on the ridge.

  • Creator: Ágnes Király
  • This version: 19.04.2023
  • License: Attribution-ShareAlike 4.0 International (CC BY-NC-SA 4.0)
  • Specific citation: These graphics by Ágnes Király based on Forsyth and Uyeda (1975) are available via the open-access s-Ink.org repository.
  • Related reference: Forsyth, D., & Uyeda, S. (1975). On the relative importance of the driving forces of plate motion. Geophysical Journal International, 43(1), 163-200.
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Solid-state convection

Simulation of infinite Prandtl number, thermal convection (e.g., mantle convection).

Simulation of infinite Prandtl number, thermal convection (e.g., mantle convection). Simulations are run for variable Rayleigh numbers (Ra) and with or without internal heating (H) on a grid with 64×64 discrete nodes using an isoviscous formulation (unless marked otherwise). Equations solved are non-dimensionalised (nd) and the domain boundaries free-slip (impermeable) and insulating on both domain sides, and isothermally hot at the bottom and cold at the top. The Scientific colour map ‘vik‘ is used to represent data accurately and to all readers.

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Solid-state convection (animation)

Simulation of infinite Prandtl number, thermal convection (e.g., mantle convection).

Animated simulation of infinite Prandtl number, thermal convection (e.g., mantle convection). Simulations are run for variable Rayleigh numbers (Ra) and with or without internal heating (H) on a grid with 64×64 discrete nodes using an isoviscous formulation (unless marked otherwise). Equations solved are non-dimensionalised (nd) and the domain boundaries are free-slip (impermeable) and insulating on both domain sides, and isothermally hot at the bottom and cold at the top. The stream-function indicates the instantaneous direction of the flow at any given point in time. The Scientific colour maps ‘vik’ and ‘cork‘ are used to represent data accurately and to all readers.

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Sea-level change mechanisms (sketch)

Sketches outlining the solid-Earth induced sea-level change mechanisms over different time periods, covering elastic, viscous, and mantle convection time scales.

Sketches outlining the solid-Earth induced change of sea level over different time periods, covering elastic (instantaneous), viscous (thousand to hundred thousand years), and mantle convection (Million to Billion years) time scales. Shown are the solid Earth and oceans (filled areas) and their surfaces after an applied change to the system (lines).

On the shortest time scales, the solid Earth deforms elastically in response to an imposed load: an ice sheet uplifts the ground near areas of mass loss and depresses the ocean basins, which gain mass. The sea surface drops near the mass loss because the diminished ice sheet gravitationally attracts less seawater. Relative to the ground surface, sea-level drops near melting ice, but rises faster than average over the rest of the ocean.

Following glacial unloading, Earth deforms viscously on time scales of 1’000–100’000 years as the mantle flows back into the depressed region. This uplifts the region near the former ice sheet (locally causing relative sea-level drop) and depresses the surrounding peripheral forebulge. If the forebulge collapses beneath the sea surface, the added basin volume causes far-field (eustatic) sea-level drop.

On time scales of one Million years and longer, solid Earth processes associated with plate tectonics and mantle dynamics dominate sea-level change (Harrison, 1990; Miller et al., 2005). Shown here are the major processes that can elevate global average (eustatic) sea level (and depress it when acting oppositely). Global sea level rises when the “container” volume of the ocean basins decreases, which can have multiple reasons. Sea level also rises, if water exchange with the deep mantle becomes imbalanced.

  • Creator: Clint P. Conrad
  • This version: 27.10.2021
  • License: Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
  • Specific citation: This graphic by Clint Conrad based on Conrad (2013) is available via the open-access s-Ink repository.
  • Related reference: Conrad, C.P. (2013), The solid earth’s influence on sea level, Geological Society of America Bulletin, 125, 1027-1052, doi:10.1130/B30764.1.
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Global-scale mantle flow (sketch)

A sketch outlining the link between the viscous convection within the Earth’s mantle and tectonic surface plate motions.

A sketch outlining the link between the viscous convection within the Earth’s mantle and tectonic surface plate motions, deforming Earth’s surface across wide areas. Shown are the relative positions and motion of some of Earth’s continental (brown) and oceanic plates (blue) captured by the hypothetical cross-section through the middle of the planet. The dynamic link between surface and mantle motion is highlighted by arrows representing first-order material flow direction. This global-scale mantle flow is believed to also affect the shape, position and mobility of large low shear-velocity provinces (LLSVPs; red) at the base of the mantle (yellow) just above the Earth’s core (orange).

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3-D subduction mantle flow

3-D subduction dynamics and mantle flow model animation showing the time evolution of oceanic plate subduction and resulting mantle flow.

Animation of 3-D subduction dynamics and mantle flow showing the time evolution of oceanic plate subduction with a continental part in the middle and resulting mantle flow computed in a 3-D numerical model. Although only one specific geometry, this model is useful to visualise how slabs deform at depth, how mantle flows around their edges, and how back-arc basins form.

Description of the model evolution (see below for detailed legend) – In this model, the subducting plate is mostly oceanic, but has continental lithosphere in the middle and the overriding plate is continental (see top panels at Time 0 Myr). The oceanic slab (in blue) sinks into the mantle and, at Time 8.1 Myr, continental collision happens in the middle of the subduction zone. At this point, the trench stays quasi-stationary in the middle, but starts to retreat quickly at the sides and the slab significantly deforms at depth (from Time 9.8 Myr onward). This causes the mantle to quickly flow around the slab (see how the spheres move). The large trench retreat generates a significant amount of extension in the overriding plate that eventually causes the overriding plate to break (Time 28.4 Myr). At this point, the mantle material rises towards the surface and starts melting because of decompression in the back-arc region. Melt close to trench is due to the presence of fluids released from the slab and shows the location of the volcanic arc. As the slab keeps retreating, the opening of the back-arc basin, associated with mantle melting, continues creating a wider and wider basin that will be composed of new oceanic crust generated by mantle melting.

Legend – The 3 panels are showing different views of the same model: side/top view (top left panel), top view (top right panel), and front view (bottom panel). The slab is shown in blue, continental crust in grey. In the top view (top right panel), the subducting plate is on the left side and the overriding plate is the grey area to the left. The slab will subduct towards the right. The contour in the red-to-white colour map indicates the regions where the mantle melts and the amount of melt fraction. The spheres are tracers passively transported in the mantle and colour-coded by depth; they are useful to show how the mantle flows around the slab (toroidal flow).

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Slab-gap dynamics

Sketch of an evolution of an opening and sinking slab gap during oceanic subduction and the resulting surrounding mantle flow.

Evolution of an opening and sinking slab gap during oceanic subduction. This conclusive image is based on analog models of subduction, where the slab surface was monitored by 3-D scanning and the mantle flow was imaged using PIV technique. The opening slab gap allows mantle to flow from the sub-slab area to the mantle wedge area. However, this flow might only have an effect on the surface when the slab gap is near-surface and has a significant vertical extent.

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Earth processes

A schematic highlighting some of the most relevant Earth processes.

A schematic highlighting some of the most relevant Earth processes. Illustrated are an early Earth (without a fully developed solid inner core, left) that evolves into a dynamic, present-day-style Earth (right), which generates and erases geologic records of its transforming states and is now experiencing unprecedented environmental change. The arcuate lines surrounding globe illustrate the protective geomagnetic field that arises from the fluid dynamics within the outer core (light grey, illustrated with curled lines). The solid inner core is shown to scale as a darker grey. The mantle and crust (continental rocks are light brown, ocean floor basalts are dark brown; thicknesses greatly exaggerated, with mantle thickness to scale) is a single system driven by convection within the mantle that arises from radioactive decay of heat-producing elements and the loss of the deeply buried planet’s formational energy through cooling of the core. The lithosphere (crust and coldest mantle) is broken into separating and colliding plates whose distribution influence critical element distribution, earthquakes, volcanism, topography, critical zone, climate, water cycle, biogeochemistry, and biodiversity. The Earth is blanketed in a thin atmosphere (light blue). The profile of a landscape highlights Earth surface processes, the sedimentary record of Earth’s history, human influence, and geohazards to people. Displacement on faults may produce sudden strong earthquakes (creating significant hazards) or develop slowly with virtually imperceptible earthquakes. Landslides and coastal retreat, sea level rise, and tsunamis also present hazards to the coastal community. Uplifted hills will experience weathering (light brown) such that dense bedrock develops porosity and holds moisture and groundwater (light blue) that is exploited by vegetation. Deep groundwater aquifers (blue) are key water resources. Precipitation (blue lines) is returned to the atmosphere by evaporation and transpiration (blue dots) with excess water recharging groundwater or running off. Biologically-mediated gas exchange with the atmosphere occurs across the planet. Older sedimentary rocks (stippled brown) and young to contemporary sediments provide records of Earth’s evolving climate, biogeochemistry, and biodiversity. Humans are acting as geologic agents and affecting Earth processes in many ways, including through climate change (via urbanization, release of greenhouse gases, and vegetation change); nutrient input to terrestrial aquatic systems and the oceans (from agriculture and urban wastewater); changes in erosion and sedimentation (from land use change, dams, and other influences on river flow and sediment load); modification of the geographic distribution of biodiversity (from climate and land use change); and exacerbation of hazards (through rising sea level, more intense storms, land use change, and drought-induced wildland fires).

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Slab retreat dynamics

Three different ways to allow for fast subduction trench retreat.

Sketch of three different ways to allow for fast subduction trench retreat that are flattening of the slab from side view (top left), curvature of the slab from top view for narrow (top centre) and wide subduction zones (bottom), and partial slab damage (i.e., slab window) from side view (top right). Shown are initial (grey) and end position (black) of the plate and corresponding mantle flow (blue) that displaces mantle material from its initial region (orange) to its final region (green).

  • Creator: Fabio Crameri
  • This version: 12.09.2021
  • License: Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
  • Specific citation: This graphic by Fabio Crameri from Crameri and Tackley (2014) is available via the open-access s-Ink repository.
  • Related reference: Crameri, F., and P.J. Tackley (2014), Spontaneous development of arcuate single-sided subduction in global 3-D mantle convection models with a free surface, J. Geophys. Res. Solid Earth, 119(7), 5921-5942, doi:10.1002/2014JB010939
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