SHRIMP U-Pb zircon ages have been obtained for a sample of metasedimentary gneiss from the Smallefjord sequence in the NE Greenland Caledonides. Pre-1000 Ma zircons are interpreted as being detrital in origin; the source region contained late Archaean rocks (or younger sediments or inheritance-rich granites derived from them) and several groups of Proterozoic rocks as young as c. 1035 Ma. Zircons with 206Pb/238U ages between c. 980 Ma and 890 Ma are interpreted to have grown during a discrete high grade metamorphic event. Six analyses provided a mean 206Pb/238U age of 955 ± 13 Ma, which is interpreted as recording 'Grenvillian' metamorphism of the Smallefjord sequence. This supports regional correlation of the Smallefjord sequence with the Krummedal sequence of central E Greenland which has previously yielded evidence for tectonothermal activity at c. 1000 Ma, and provides a further indication of a northern arm of the Grenville-Sveconorwegian orogen in the North Atlantic region. Further growth of metamorphic zircon within the Smallefjord sequence occurred during the Caledonian orogeny at 445 ± 10 Ma (Upper Ordovician). This is consistent with estimates of a Middle-Upper Ordovician age for Caledonian orogenesis in central E Greenland. It contrasts with previously published SHRIMP U-Pb zircon dating of Lower Devonian (404 ±6 Ma) metamorphism within the basement gneisses of the Dove Bugt area north of the Smallefjord sequence outcrop. SHRIMP dating of zircons therefore indicates polyphase Palaeozoic metamorphism within the NE Greenland Caledonides.

First Page Preview

First page PDF preview
You do not currently have access to this article.