SmNd age of the Fisken˦sset Anorthosite Complex, West Greenland

摘要: Abstract The Fisken˦sset Anorthosite Complex of southern West Greenland is a sheet-like layered igneous body which has been fragmented by granitoid intrusions, multiply deformed and folded, metamorphosed as high granulite facies, in some places retrogressed to lower amphibolite or greenschist facies. In localities, however, such at Majorqap qaˆva, 20 km inland from the coast, these effects are minimal. Here, metamorphic grade reached only facies with no apparent retrogression. Igneous textures structures spectacularly preserved, detailed stratigraphic sequences have established, samples primary mineralogy remains. We report Sm Nd isotopic study on this locality, attempting constrain age crystallization Complex. This complex represents useful marker unit relationships surrounding units may be compared. A five-point isochron, including data for whole-rock anorthosite, metagabbro, metaperidotite, separates calcic plagioclase mafic matrix coarse megacrystic leucogabbro, corresponds an 2.86 ± 0.05 Ga (MSWD = 2.5), initial eNd +2.9 0.4. significantly older than previous Pb whole rock ages Complex, but sufficiently close 2.8 high-grade event affected area cause partial resetting system considered. However, based integrity similar anorthositic complexes higher grade, preservation magmatic REE patterns analysed megacryst coexisting matrix, we conclude that time would imply relatively short interval, order 70 Ma, during anorthosite formation, tonalite emplacement, metamorphism took place, must accounted any tectonic model Late Archean events Greenland. case, positive value requires it was derived source long-term depletion light REE. These results add increasing indicating widespread presence depleted mantle sources Archean.