Accretion, homogeneous/heterogeneous

Fig. 2.3 According to the homogeneous accretion model (a), iron-containing material (black) and silicate-containing material (colorless) condensed out at the same time, i.e., the proto-Earth consisted of a mixture of the two. The concentration of iron in the Earth s core took place later. According to the heterogeneous model (b), the iron condensed out of the primeval solar nebula first, while the silicates later formed a crust around the heavy core. From Jeanloz (1983)...

The heterogeneities of the protosolar nebula are considered as very significant by some authors I7), and as quantitatively not important by others 9). Nevertheless, it remains a fact that the model of a homogeneous accretion disc where equilibrium reaction takes place has now been replaced by a much more subtle description where a lack of homogeneity and equilibrium are facts that must be taken into account. This problem will be discussed below. 

Two recent examples of such accreted oceanic plateaus are the CCOP and the OJP. All of the lavas sampled from the OJP and most of the lavas from the CCOP are relatively homogeneous basalts with initial eNd values between +5 and +8 and broadly chondritic trace element ratios. In contrast, high-MgO lavas found in the CCOP reveal evidence of a more heterogeneous plume source region, containing both enriched (eNd <+5 (La/Nd)cn>l) and depleted (eNd < +8 (La/Nd)cn[Pg.1819]

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