Convex tetrad effect variations in REE abundances of "North American shale composite" and "Post-Archean Australian average shale".

Abstract

REE abundances of the average shales of “North American shale composite” (NASC) and “Post-Archean Australian average shale” (PAAS) contain small but significant convex tetrad effect variations of the M-type relative to the chondritic REE. This is revealed in their REE patterns normalized by a USGS reference basalt of BCR-1. PAAS has a larger convex tetrad effect variation than NASC. The average shales are favorably used to normalize REE analyses of various geochemical samples. The tetrad effects of the average shales, however, call into question conventional interpretations of their shale-normalized REE patterns. Smooth shale-normalized REE patterns do not mean the absence of tetrad effect variations in their REE abundances relative to the chondritic REE abundances.