Sodium mantle rocks

What has happened to the bicarbonate and calcium delivered to the ocean by river runoff As described later, these two ions are removed from seawater by calcareous plankton because a significant fraction of their hard parts are buried in the sediment. In contrast, the only sedimentary way out of the ocean for chloride is as burial in pore waters or precipitation of evaporites. The story with sodium is more complicated— removal also occurs via hydrothermal uptake and cation exchange. Because the major ions are removed from seawater by different pathways, they experience different degrees of retention in seawater and uptake into the sediments. Another level of fractionation occurs when the oceanic crust and its overlying sediments move through the rock cycle as some of the subducted material is remelted in the mantle and some is uplifted onto the continents. 

McCandless T. E. and Gurney J. J. (1989) Sodium in garnet and potassium in clinopyroxene criteria for classifying mantle eclogites. In Kimberlites and Related Rocks, Geol. Soc. Austral. Spec. Publ. No. 14 (ed. J. Ross). Blackwell, Perth, vol. 2, pp. 827-832. 

Complex mixtures of mafic rock melt so that the lighter elements aluminum, silicon, sodium, and potassium are liberated first. These are lighter on average and more diffuse in density, so they tend to rise through the molten mantle. When they collect at the surface, light gray granite forms. 

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