Geochemistry of the Mesoarchean Fiskenæsset Complex at Majorqap qâva, SW Greenland: Evidence for two different magma compositions
Abstract The Mesoarchean Fiskenaesset Complex was emplaced as multiple sills and dykes of magma and crystal mush into oceanic crust, forming an association of ca. 550-meter-thick layered anorthosites, leucogabbros, gabbros, hornblendites, pyroxenites, dunites, and peridotites. The complex was intruded by tonalites, trondhjemites and granodiorites (TTG), and underwent multiple phases of deformation. The Fiskenaesset Complex and bordering TTG intrusions were variably affected by granulite facies metamorphism and retrogressed under amphibolite facies conditions. This study presents new field, petrographic, and major and trace element geochemical data for the six major stratigraphic units of the Fiskenaesset Complex at Majorqap qâva, SW Greenland. In addition, new high-precision trace element data are reported for hornblendes from three stratigraphic units. The sampled major lithological units from bottom to top are: Lower Gabbro, Ultramafic, Lower Leucogabbro, Middle Gabbro, Upper Leucogabbro, and Anorthosite. Both whole-rock and hornblende trace element data are consistent with crystallization of the complex from two different parental magmas, originating from different mantle sources. Subsequent differentiation of these parental magmas in the oceanic arc crust resulted in two evolved geochemical rock suites (Suite A and Suite B), which are both characterized by depletions of HFSE (Nb, Ta, Zr and Hf) relative to Th, U, LREE and LILE (Rb, Ba), and enrichments of Sr and Pb relative to MREE; these data are consistent with a magmatic arc geodynamic setting.