Abstract

Liquid-liquid unmixing and the separation of Fe- and Si-rich liquids occur during the evolution of tholeiitic basalt to rhyolite. We will report evidence from plutonic and volcanic settings to revive the initial idea by Daly to explain the dearth of intermediate magmatic compositions at the Earth’s surface. New crystallization experiments on evolved tholeiitic basalts are used to define the compositional space for the development of silicate liquid immiscibility on liquid lines of descent relevant for typical fractionated MORB , Iceland, Deccan, Mull and Snake River Plain lavas and for the Sept Iles layered intrusion where large- scale immiscibility has been recognized. Crystallization conditions favouring or inhibiting the development of immiscibility will be discussed, as well as implications for magma chamber processes and tholeiitic liquid trends.

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