Aluminum cratonic mantle

Neither of these proposals, however, can explain the subchondritic Ca/Al of most cratonic perido-tites. If the latter are residues at higher P, more aluminum remains in the residue relative to calcium, the opposite trend of lower P residues. The anomalously low Ca/Al of cratonic perido-tites may be unique to the formation of sub-cratonic mantle, or is a secondary feature with unexplained origin. 

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