Discrimination diagrams for rocks of granitic composition

24 Discrimination diagrams for clinopyroxene phenocrysts in basalts (after Leterrier et aL, 1982). Clinopyroxene coniposidons. ue (expressed in cations per six oxygens, (a) Ti vs ,VV r / - (Ca+Na) plot showing the fields of alkali basalts (A) and iholeiitic and calc-alkali basalts (T). 

These diagrams should not be used with a single clinopyroxene analysis rather, Leterrier et al. (1982) recommend that a minimum of 10 but if possible more than 20 analyses should be plotted before a meaningful result can be obtained. The method is thought to work in metabasites up to greenschist facies thereafter clinopyroxene compositions are modified by metamorphic reactions. 

Granito types classified according to tectonic setting, (after Pearce et at., 1984) 

Granites in oceanic arcs dominated by tholeiitic basalt Granites in oceanic arcs dominated by calc-alkalt basalt Granites in active continental margins 

Granites in intracontinent ring complexes Granites in attenuated continental crust Granites In oceanic islands 

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