A flow-foliated ignimbrite related to the Åland rapakivi granite in SW Finland

Olav Eklund, Alexey Shebanov, Sören Fröjdö, Kari Yli-kyyny, Ulf B. Andersson

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    A flow-foliated felsic ignimbrite constitutes the uppermost lithological unit of the 1.58 Gyr anorogenic magmatic rocks in SW Finland. The ignimbrite is derived from an explosive eruption of hot (≅ 950 °C) phenocryst-bearing A-type (rapakivi-type granite magma.The ignimbrite is close in composition to subvolcanic rapakivi granites that occur in the margins of the kand rapakivi batholith. The subvolcanic granites crystallized under a pressure of ≅ 1 kbar and at temperatures of about 650–700 °C. However, both major and rare earth elements show that the ignimbrite- forming magma was more fractionated than the magma forming the subvolcanic varieties.Supported by evidence of mafic-felsic magma mingling, it is suggested that injection of hot mafic magma into a shallow magma chamber produced the high temperature of the ignimbrite-forming magma. This injection increased the magmatic and the volatile pressure that caused the eruption of the dry felsic magma.
    Original languageUndefined/Unknown
    Pages (from-to)548–557
    JournalTerra Nova
    Issue number6
    Publication statusPublished - 1996
    MoE publication typeA1 Journal article-refereed

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