Slab width control on current global plate and trench velocities, and on Cenozoic western North America tectonics
Abstract
Subduction of tectonic plates into the Earth's mantle is accommodated by subducting plate motion and trench migration. How these two modes contribute to the subduction velocity and what controls their partitioning remain unsolved. Here we present a global compilation for 17 active subduction zones and three-dimensional numerical models of progressive free subduction showing that slab width (W) provides a first-order control on subduction partitioning, subducting plate velocity and trench velocity. In nature, subducting plate velocity increases progressively from -1 to 3 cm/yr for W = 300-600 km to 5-7 cm/yr for W = 7000 km, while the models show an increase from 2.5-3 cm/yr to 6 cm/yr. Furthermore, trench velocity decreases from 1-7 cm/yr for W = 300-600 km to -1 to 1 cm/yr for W = 7000 km in nature, whilst the models show an decrease from 6-7 cm/yr to ~1.5 cm/yr. The subduction zone data, numerical models and a scaling formulation for sinking of slabs in the upper mantle show that subducting plate velocity scales with ~Wexp(2/3), while trench velocity scales with ~1/W. Correlation coefficients for the numerical models with respect to the scaling formulation are in the range 0.95-0.99 for subducting plate velocity, trench velocity and subduction partitioning, while those for the natural data are in the range 0.70-0.72. It is thus found that slab width provides a first-order control plate velocity, trench velocity and subduction partitioning. Comparison of slab age and subduction kinematics for natural subduction zones gives significantly lower correlation coefficients (0.29-0.38), indicating that slab age provides a second-order control on trench velocity and subducting plate velocity. Our findings provide an explanation for the Cenozoic progressive decrease in subducting plate velocity and subduction partitioning of the Farallon plate, which we interpret as resulting from the progressive decrease in trench-parallel width of the Farallon slab during the Cenozoic from ~14000 km to only 1400 km at present. This decrease in slab width also explains the change from Sevier-Laramide orogenesis to Basin and Range extension in North America in the Eocene to Miocene. Shortening took place during wide-slab subduction and overriding-plate-driven trench retreat (push-back), whilst extension took place during intermediate to narrow-slab subduction and slab-driven trench retreat (pull-back).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMDI41B..02S
- Keywords:
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- 8104 TECTONOPHYSICS / Continental margins: convergent;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8170 TECTONOPHYSICS / Subduction zone processes