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

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Olav Eklund , Alexey Shebanov , Soren Fröjdö , Kari Yli-kyyny and Ulf B. Andersson
Publisher: Blackwell Publishing Ltd
Publication year: 1996
Journal: Terra Nova
Volume number: 8
Issue number: 6
Start page: 548
End page: 557
ISSN: 1365-3121


Abstract

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.

Last updated on 2019-19-09 at 04:06