Iron enrichment and pyroxene fractionation in tholeiites

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Abstract
Differentiation in tholeiite magma, particularly iron enrichment and silica variation, as traced in lava successions and dolerite‐granophyre suites, is discussed in the light of analytical data on phenocryst and groundmass pyroxenes and their fractionation. Broadly two trends may be distinguished: (1) an intratelluric equilibrium trend ending in a hedenbergitic pyroxene phase fayalite, such as is exhibited by the Tasmanian Red Hill dolerite‐granophyre suite, and (2) a quench trend characteristic of the subcalcic augite groundmass sequence of the volcanic suites as exemplified in the Hawaiian tholeiite series (e.g. Kilauea). This trend may in more siliceous differentiates be extended to close with assemblages carrying a ferropigeonite phase.