期刊
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
卷 17, 期 1, 页码 78-100出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015GC006125
关键词
subduction; mantle wedge; arc volcanism; small-scale convection; rheology; melting
资金
- NERC (UK) [NE/H015329/1]
- Australian Research Council Future Fellowship [FT140101262]
- Janet Watson scholarship from the Department of Earth Science and Engineering at Imperial College
- NERC [NE/K010743/1]
- National Science Foundation MARGINS program [OCE-0841079, EAR-1141976]
- Office of Science and Technology through EPSRC's High End Computing Program
- Australian Commonwealth Government
- Applied Modelling and Computation Group (AMCG) at Imperial College London
- Division Of Ocean Sciences [1358091] Funding Source: National Science Foundation
- Natural Environment Research Council [NE/I024429/1, NE/H015329/1, NE/I024488/1, NE/K010743/1] Funding Source: researchfish
- NERC [NE/I024429/1, NE/I024488/1, NE/H015329/1] Funding Source: UKRI
Arc volcanism, volatile cycling, mineralization, and continental crust formation are likely regulated by the mantle wedge's flow regime and thermal structure. Wedge flow is often assumed to follow a regular corner-flow pattern. However, studies that incorporate a hydrated rheology and thermal buoyancy predict internal small-scale-convection (SSC). Here, we systematically explore mantle-wedge dynamics in 3-D simulations. We find that longitudinal Richter-rolls of SSC (with trench-perpendicular axes) commonly occur if wedge hydration reduces viscosities to less than or similar to 1.10(19) Pa s, although transient transverse rolls (with trench-parallel axes) can dominate at viscosities of similar to 5.10(18)-1.10(19) Pa s. Rolls below the arc and back arc differ. Subarc rolls have similar trench-parallel and trench-perpendicular dimensions of 100-150 km and evolve on a 1-5 Myr time-scale. Subback-arc instabilities, on the other hand, coalesce into elongated sheets, usually with a preferential trench-perpendicular alignment, display a wavelength of 150-400 km and vary on a 5-10 Myr time scale. The modulating influence of subback-arc ridges on the subarc system increases with stronger wedge hydration, higher subduction velocity, and thicker upper plates. We find that trench-parallel averages of wedge velocities and temperature are consistent with those predicted in 2-D models. However, lithospheric thinning through SSC is somewhat enhanced in 3-D, thus expanding hydrous melting regions and shifting dehydration boundaries. Subarc Richter-rolls generate time-dependent trench-parallel temperature variations of up to similar to 150 K, which exceed the transient 50-100 K variations predicted in 2-D and may contribute to arc-volcano spacing and the variable seismic velocity structures imaged beneath some arcs.
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