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phosphorus, carbon dioxide, lead, titanium, and nickel. Iron is the most widely
distributed element and occurs intermixed in the ?-MnO2 phase; is the main constituent
in the iron oxyhydroxide phase; occurs in the detrital phase in minerals such as
pyroxene, amphibole, smectite, magnetite, and spinels; and is in the residual biogenic
phase. The strength of correlations between iron and other elements depends on the
relative abundance of iron in the various phases 68. The CFA phase only occurs in thick
crusts because the inner layers of those crusts have been phosphatised. In thin crusts or
the surface scrapes of thick crusts, calcium, phosphorus, and carbon dioxide are
associated with the ?-MnO2 and/or residual biogenic phases. CFA associated elements as
well as platinum, rhodium, and iridium generally increase with increasing crust
thickness. In contrast, cobalt and elements associated with the detrital phase usually
decrease with increasing crust thickness 69.
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