Phenocryst-poor latite and trachyte are interpreted as the result of mineral separation, and phenocryst-rich tephrite porphyry and olivine diabase porphyry are the result of phenocryst accumulations in the magma chamber.
From oldest to youngest (Elston and Snider, 1964), they are diabase porphyry, olivine diabase porphyry, fine-grained diabase, latite or trachyte, tephrite porphyry, and rhyolite.
Rhyolite has the lowest Th/U ratio (3.1, one analysis) followed by tephrite (3.3, two analyses), latites and trachytes (3.4 to 3.7, three analyses), diabase porphyry (4.3, one analysis), olivine diabase porphyry (4.7, one analysis) and fine-grained diabase (4.2 to 4.8, three analyses).
Pyroxenes from olivine diabase porphyry plots just inside the augite field adjacent to the diopside-augite boundary (Fig.
Lanthanum to lutetium ratios range from 144, olivine diabase porphyry, to 379, tephrite porphyry.