The Mesoarchaean Akia terrane, West Greenland, revisited: New insights based on spatial integration of geophysics, field observation, geochemistry and geochronology

Dating mylonitic overprinting of ancient rocks

“…Whilst high-temperature granulite-facies conditions have been established for parts of the Akia Terrane in its early history (western Fiskefjord complex and southern Alanngua complex), other regions within the terrane only reached amphibolite facies conditions 14,16,36 . A subsequent Late Mesoarchaean to Neoarchaean (2857-2700 Ma) granulite-facies metamorphic overprint (~820-850 °C at 8-10 kbar) was reached in the Alanngua complex 14 but clearly cannot have pervasively affected the area around sample 1276, as its titanite U-Pb age is not strongly affected by thermally activated diffusive radiogenic-Pb loss postmagmatic crystallization.…”

“…This Neoarchean metamorphism, which occurred alongside the Akia Terrane margin, is akin to that in adjoining terranes, indicating a shared history of thermal disturbance. Furthermore, such commonality implies these crustal elements were linked at least by this time 14,15 . Subsequent lower grade (greenschist-to amphibolite facies) c. 2630 Ma and 2540 Ma metamorphism is evidenced by metamorphic zircon overgrowths and neoblastic apatite 18 and titanite 19 , respectively.…”

“…This c. 3000 Ma Mesoarchean magmatism was coeval with high temperature, low pressure granulite-facies metamorphism 12,13 . On the northern side of the Akia Terrane 2877-2857 Ma supracrustal rocks are preserved within the Alanngua Complex 14 . These supracrustal rocks were deposited onto a Mesoarchean basement 15 , buried to >30 km depth, and partially melted, during regional high-grade metamorphism between 2857 and 2700 Ma 16 .…”

The Mesoarchean Amikoq Layered Complex of SW Greenland: Part 2. Geochemical evidence for high-Mg noritic plutonism through crustal assimilation

“…It has recently been proposed that Eoarchean mafic crust was involved in the c. 3.2 Ga diorite and 3.0 Ga tonalite Akia crust forming events on the basis of zircon Hf-isotopic evidence (Gardiner et al, 2019(Gardiner et al, , 2020. The grey tonalitic orthogneisses common to the Fiskefjord area, central Akia, are probably a second magmatic phase contemporaneous with the voluminous Taserssuaq tonalite in NE Akia (2982 ±7 Ma; Garde, 1990;Garde et al, 2000;Steenfelt et al, 2020;. This is supported by recent zircon U-Pb radiometric age determination of the tonalitic orthogneiss (2978 ±8 and 2969 ±5 Ma) that host and cut the ultramafic Seqi Complex (Szilas et al, 2018;Whyatt et al, 2020).…”