Ti-Zr-Y diagram

Since the publication of the Ti-Zr-Y diagram we have learned a great deal about the chemistry of ocean-floor basalts and a number of types of MORE are now known. This point is made by Prestvick (1982), who showed that anomalous ocean-floor basalts from Iceland do not plot in the MORE field. More recent discrimination diagrams, however, can recognize different types of MORE (see Table 5.1). 

A number of other tectono-magmadc discrimination diagrams have been proposed based upon Ti-Zr—Y variations and these are discussed below. In addition the HPS element Nb is used, although diagrams which introduce Nb should be used with care. Nb concentrations cannot be accurately determined by XRF below about 10 ppm and precise analyses must be made by INAA. 

Pearce and Gale (1977) use a similar diagram based upon Zr/Y and Ti/Y variations to discriminate between within-plate basalts and other types of basalt, collectively termed plate margin basalts (Figure 5.6). This diagram makes use of the enrichment in Ti and Zr but not Y in within-plate basalK. 

Figure 5,6 The Zr/Y-Ti/Y discrimination diagram for basalts showing the fields of within-plate basalts and plate margin basalts (i.e. all other basalt types). Coordinates are given for the bounding line between the two fields (after Pearce and < e, 1977).

Holm P.E., 1982, Non-recognition of continental tholeiites using the Ti-Y-Zr diagram. Contn b. Mineral. Petrol.., 79, 308-310. 

Prestvick T, 1982, Basic volcanic rocks and tectonic setting. A discussion of the Zr-Ti-Y discriminadon diagram and its suitability for classificadon purposes. Lithos, 15, 241-247. Price W.J., 1972, Analytical atomic absorption spectronKtry. Heyd.en, London. 

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