Figure 7. Ternary plot of the concentrations of Hf/3-Th-Ta for the low-calcic black shales (l), n = 206. The
diagram was used by Wood (1980) to determine provenance of basalts. Note that the field of the samples falls
entirely in the field identified by Wood (and Wood et al., 1979) as calc-alkaline basalts associated with destructive
plate margins.