Chemical stratification in the silicate earth

Abstract

A primary stratigraphic model is presented for the distribution of depleted, enriched, and primordial isotopic mantle components that have been formed by the transport of magmas at the begining of geological history. Depleted midoceanic ridge basalt source regions were established in the uppermost part of the upper mantle, while the primordial mantle was located at the middle and deepest regions of an upper mantle which was processed by anhydrous melting and crystallization. The lower mantle became heterogeneous, with enrichments at the top and depletions elsewhere. It is suggested that the present day isotopic structure of the mantle has inherited elements of this primary stratification.