Plume interaction and mantle heterogeneity: A geochemical perspective
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Abstract
Mantle plumes originating from the Core-Mantle Boundary (CMB) or the Mantle Transition Zone (MTZ) play an
important role in material transfer through Earth’s interior. The hotspot-related plumes originate through
different mechanisms and have diverse processes of material transfer. Both the Morganian plumes and large low
shear wave velocity provinces (LLSVPs) are derived from the D00 layer in the CMB, whereas the Andersonian
plumes originate from the upper mantle. All plumes have a plume head at the Moho, although the LLSVPs have an
additional plume head at the MTZ. We compare the geochemical characteristics of various plumes in an attempt to
evaluate the material exchange between the plumes and mantle layers. The D00 layer, the LLSVPs and the Morganian
plumes are consisted of subducted slab and post-perovskite from the lower mantle. Bridgmanite would
crystallize during the upwelling process of the LLSVPs and the Morganian plumes in the lower mantle, and the
residual is a basalt-trachyte suite. Unlike the Morganian plumes, the crystallization in the LLSVPs is insufficient
that material accumulates beneath the MTZ to form a plume head. Typically, the secondary plumes above the
plume head occur at the edge of the LLSVPs because it is easier for bridgmanite crystal separating from the plume
head at the edge, and the residual material with low density upwells to form the secondary plumes. Meanwhile,
Na and K are enriched during the long-term crystallization process, and then the basalt-phonolite suite appears in
the LLSVPs. The geochemical characteristics of Andersonian plumes suggest that the basalt-rhyolite suite is the
major component in the upper mantle. Meanwhile the basalt-rhyolite suite also appears in the LLSVPs and the
Morganian plumes because of the assimilation and contamination in the plume head beneath the Moho.
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