Mesoarchaean Peridotite-Norite Cumulates of Sw Greenland – the Miaggoq Ultramafic Complex

Several studies focused on the ultramafic bodies of the Archaean continental crust in southern Greenland in order to gain information on early Earth petrogenetic, metamorphic and metasomatic processes. This research provides the first petrological dataset of the Miaggoq Ultramafic Complex (similar to 1 km(2)) in the Akia terrane, with a minimum age of 2997 +/- 15 Ma. It comprises ultramafic (dunite, peridotite) and mafic (orthopyroxenite, norite) rocks along with chromitites and provides a window into Mesoarchaean mantle compositions. Field observations, such as chromitite bands, mineral layering, and orthopyroxenite oikocrysts in peridotites coupled with chemical analysis displaying high abundance of chromites in the dunitic rocks and high forsterite contents (Mg# 91 to 92.5) of the olivines, all point to a layered cumulate origin for the Miaggoq body. Pseudosection calculations along with geothermometry estimations reveal peak metamorphic conditions of 850-1100 degrees C at pressures of 0.7-1.25 GPa under anhydrous conditions followed by a possible metamorphic overprint at 650-800 degrees C and 0.7 GPa with relatively dry melting (0.025-0.125 wt% H2O). MELTS fractional crystallization coupled with cumulate modelling approximated the compositional trends with conditions on similar to 3 kbar with 1 wt% H2O. This research concludes that the Miaggoq body represents a layered cumulate complex that was derived by large degrees of partial melting of the mantle with possible assimilation (synonymous with contamination) of basalts in the crust. Overall, this study provides complementary data for the Mesoarchaean cumulate bodies of the Akia Terrane and their petrological processes.