Abstract
1 Between the Rodrigues Triple Junction and the Marie Celeste fracture
zone, basalts from the Central Indian Ridge ( CIR) exhibit an enrichment
in incompatible elements that increases in intensity northward. In
addition, H2O/TiO2, Al-8, and Dy/Yb ratios increase, while Na-8
remains unchanged and Fe-8 decreases. Evolution of the enriched
magma appears to be affected by elevated water contents, which lower
the mantle solidus, thereby increasing the initial depth of melting,
as well as delaying plagioclase crystallization. However, the enrichment
affecting the northern samples is not a just function of hydrous
mantle melting and crystallization. Instead of trending toward a
small melt fraction from the mantle, as predicted by hydrous melting
models, the CIR samples lie on a mixing line between N-MORB and a
source component that closely resembles present-day Reunion hot spot
lavas. Thus it appears that while hydrous melting and crystallization
affect the CIR, the enriched and wet mantle originates from the Reunion
hot spot, where it migrates eastward toward the CIR, against the
direction of motion of the lithosphere.
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