Presenter: Chun-Jung Lin
Date: 2016/01/07
Abstract
Previous researches indicate that subducting slabs can reach the core-mantle boundary(CMB) for a wide range of assumed material properties and plate tectonic histories. The slabs that reached the CMB are likely to have a profound influence on the dynamics near the CMB. On the other hand, the plumes, which presumably emanating from a thermal boundary layer (TBL), are putatively rooted at the CMB. The interaction of slabs with ultralow velocity zones (ULVZs) and plume roots might influence their geographical location. Different type of dynamic models were developed to clarify the interaction between the subducted slab and the lower mantle: (1) 2-D large-scale models with depth-dependent material properties simulating flow through the whole mantle, to show under what conditions slabs could reach the CMB. (2) 3-D spherical models with imposed plate evolution to explore the morphology of slabs in the presence of realistic evolution of surface plates. (3) 2-D high-resolution fine-scale models were formulated to investigate the evolution of slabs near the CMB. The results of these numerical models show important consequences of deeply penetrating slabs. In areas on the CMB free of slabs, plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin. In areas beneath slabs, the basal thermal boundary layer would be thicker and plume formation infrequent. Regional spherical models with actual plate evolutionary models indicate that slabs are unlikely to be continuous from the upper mantle to the CMB, even for simple mantle structures. Furthermore, a few continuous slab-like features from the surface to the CMB may be a result of complex plate kinematics, not mantle layering.
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