Abstract
The Coral Island Xenolithic Dike (CIXD) is a composite intrusion with mafic borders and apophyses (Pulse 1) and a felsic centre with a high amount of granitic xenoliths and xenocrysts (Pulse 2). The xenoliths, most abundant in the dike core, are granitic and vary from millimetres up to 1.5 m in size. The xenolithic composite dike is low-TiO2 Gramado-type. The xenoliths are concentrated in the dacitic core, partially molten and accompanied by relict feldspar and partly resorbed quartz xenocrysts. Field, petrographic and geochemical data attest to contamination by assimilation processes in the central part. Flowage differentiation (Bagnold Effect) has concentrated the large xenoliths in the dacitic core. Evidence of xenolith partial melting comprises spherulitic K-feldspar/albite intergrowths and polycrystalline quartz aggregates. Coronas around the pyroxenes in the dacite and the absence of mesostasis in the dike magmas attest to supercooling of the system at shallow-level conditions. The ascent of the central part of the dike (dacite + xenoliths + relict xenocrysts) was only possible due to the proximity of the magma reservoir to the emplacement site and chamber recharging with hot basic magma input (Pulse 1) that prevents the system from cooling and crystallising.
Published Version
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