Open AccessPost-kinematic diorite intrusions in Archaean basement rocks around outer Fiskefjord, southern West Greenland
Author(s) -
Adam A. Garde
Publication year - 1991
Publication title -
bulletin of the geological society of denmark
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.674
H-Index - 28
eISSN - 2245-7070
pISSN - 0011-6297
DOI - 10.37570/bgsd-1991-39-07
Subject(s) - diorite , geology , geochemistry , granulite , archean , terrane , metamorphism , zircon , continental crust , mafic , anorthosite , crust , petrology , gneiss , plagioclase , facies , geomorphology , metamorphic rock , tectonics , seismology , paleontology , quartz , structural basin
About twenty small dioritic intrusions around outer Fiskefjord, southern West Greenland, which are undeformed and unmigmatised, mark the final stage in middle Archaean accretion of continental crust, deformation and high-grade metamorphism in the Akia terrane. The diorites were emplaced into hot tonalitic gneisses, some of which were thoroughly retrograded from granulite facies prior to diorite intrusion. The diorites are themselves sporadically retrograded. A conventional zircon U-Pb age of 3017 + 12/-10 Ma has been obtained from one of the diorites. The diorites have SiO2 contents between ea. 52 and 58 wt. % and up to ea. 15% MgO, and some of them border on leuconorite or anorthosite, with normative plagioclase contents up to ea. 85 wt. % . Trace element compositions are characterised by elevated amounts of Zn, Co, Ni, and especially Cr, but low contents of several LIL elements, and they were probably contaminated with sialic crust. The diorite intrusions may be related to a group of a more mafic intrusions with anomalous contents of precious metals, forming the "norite belt" some 50 km north of Fiskefjord.