Plume formation across scales: The influence of subducted slabs, chemical heterogeneities and a partially molten boundary layer
Abstract
Many observations suggest that the lowermost mantle has a heterogeneous thermal and chemical structure. Seismic models show distinct regions with sharp boundaries, such as the Large Low Shear Velocity Provinces and the Ultra-Low Velocity Zones. Some of them have been interpreted as thermo-chemical piles, plume clusters, superplumes, and partially molten regions. Additionally, geochemical data from ocean islands indicate the presence of primordial and/or recycled material at the base of the mantle, which suggests this heterogeneity is sampled when buoyant plumes rise from the core-mantle boundary and carry material towards the surface. Accordingly, plumes can provide a window to the composition of the Earth's deep interior. This makes it important to understand the processes that allow mantle plumes to inherit lower-mantle geochemical signatures and transport material from the core-mantle boundary to the surface.
Here, we consider how processes from the global to the local scale contribute to the dynamics and chemical heterogeneity of mantle plumes, using geodynamic models developed with the community code ASPECT. Our models show that the global plate motion history and the associated position of subducted slabs control the location and shape of plume generation zones, determining where plumes ascend to the Earth's surface. This behavior is independent of the presence of dense material at the base of the mantle, occurring both when plumes rise in purely thermal plume clusters and when they ascend from the edges of dense thermo-chemical piles. On a regional scale, the strength and direction of lower mantle flow induced by subducted slabs affects the entrainment of material into mantle plumes, which influences how they sample chemical reservoirs that may be present near the core-mantle boundary. If the lowermost mantle at the base of plumes is partially molten, the segregation of melt in these regions introduces additional chemical heterogeneities on the kilometer-scale that are preserved in the plume conduit. Our models show how the combined effect of mantle processes on different scales can generate the distribution and composition of hot spot volcanism we observe at the Earth's surface.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMDI33A..07D
- Keywords:
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- 1038 Mantle processes;
- GEOCHEMISTRY;
- 7270 Tomography;
- SEISMOLOGY;
- 8115 Core processes;
- TECTONOPHYSICS;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS