Modeling The Role of Subduction in the Production and Evolution of Thermal and Chemical Heterogeneity in the Mantle
Abstract
One cornerstone of multidisciplinary chemical geodynamics is modeling. Both numerical and laboratory experiments have been employed in modeling studies of mantle dynamics. The different techniques bring different strengths to the field. There are many examples in the scientific literature where laboratory methods are used to develop empirical relationships between the response of a fluid system and simple combinations of the physical parameters that define the system. Laboratory methods are also useful in modeling fine scale thermal- chemical structures in three dimensional flow morphologies and for testing first-order features of observationally based, dynamic process models. The focus of this talk is subduction, which introduces heterogeneity deep into the mantle and acts to stir the mantle. We summarize results from laboratory experiments on the relationship between subduction and both the deep production of thermal-chemical upwellings and how mantle heterogeneity is recycled to the surface. In one set of experiments chemically laminated slabs are subducted into a deep thermal boundary layer. Different styles of buoyant upwelling evolve from the slab pile through time, which are related to the isothermal densities of the slab laminates. Observed length scales of chemical heterogeneity ranging from passive 1 km features in tendrils embedded within upwellings to active 300km wide features within plume heads have implications for melt production models. In a second set of experiments, laboratory models consider the interaction between rollback subduction and back-arc extension, three-dimensional mantle circulation and the shallow dispersion of buoyant upwellings. The models are developed to represent basic features of the Cascades subduction system. Results suggest that first order features of the Cascades system (e.g., gross spatial and temporal patterns in melt production) may be consistent with a model in which an upwelling is deformed by large scale, subduction driven shear flow in the mantle wedge. Flow induced by slab rollback efficiently draws plume material into the wedge and produces spatial offsets (~300 km) between the surfacing point of the plume head and the subsequent surface expression of the plume tail. Continued deformation of the ponded head and the tail leads to the evolution of two linear, time-progressive thermal/chemical features beneath the overriding plate which trend in opposite directions. We attempt to place basic features recorded in both laboratory models within the context of a road map for chemical geodynamics.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.U21B0405K
- Keywords:
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- 3001 Back-arc basin processes;
- 3060 Subduction zone processes (1031;
- 3613;
- 8170;
- 8413);
- 8120 Dynamics of lithosphere and mantle: general (1213);
- 8121 Dynamics: convection currents;
- and mantle plumes;
- 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism