Interaction of subducted slabs with the mantle transition-zone: A regime diagram from 2-D thermo-mechanical models with a mobile trench and an overriding plate

Transition zone slab deformation influences Earth's thermal, chemical, and tectonic evolution. However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2‐D thermo‐mechanical models with a mobile trench, an overriding plate, a temperature and...

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Bibliographic Details
Published in:Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2014-05, Vol.15 (5), p.1739-1765
Main Authors: Garel, F., Goes, S., Davies, D. R., Davies, J. H., Kramer, S. C., Wilson, C. R.
Format: Article
Language:English
Subjects:
Age
Deformation
Earth Sciences
Geophysics
Mantle
Morphology
overriding plate
Plate tectonics
Rheology
Sciences of the Universe
slab morphology
slab rheology
Slabs
Strength
subduction dynamics
transition zone
trench retreat
Trenches
Viscosity
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Summary:Transition zone slab deformation influences Earth's thermal, chemical, and tectonic evolution. However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2‐D thermo‐mechanical models with a mobile trench, an overriding plate, a temperature and stress‐dependent rheology, and a 10, 30, or 100‐fold increase in lower mantle viscosity, to investigate the effect of initial subducting and overriding‐plate ages on slab‐transition zone interaction. Four subduction styles emerge: (i) a “vertical folding” mode, with a quasi‐stationary trench, near‐vertical subduction, and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/“horizontally deflected” and stagnate at the upper‐lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two‐stage mode, displaying backward‐bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subducting plate age (i.e., buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictates the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature, and slab strength, the subducting plate buoyancy, overriding plate strength, and upper‐lower mantle viscosity jump are also important controls in thermo‐mechanical subduction. For intermediate upper‐lower mantle viscosity jumps (×30), our regimes reproduce the diverse range of seismically imaged slab morphologies. Key Points Varying initial plate ages (20–100 Myr) gives four distinct subduction modes Evolving slab strength exerts key control on trench motion and slab deformation For a ×30 viscosity jump slab morphologies encompass the imaged range
ISSN:1525-2027
1525-2027
DOI:10.1002/2014GC005257