Provenance and Terrane Evolution of the Kalak Nappe Complex, Norwegian Caledonides:Implications for Neoproterozoic Paleogeography and Tectonics

摘要

The Kalak Nappe Complex(KNC)within the northernmost Arctic Norwegian Caledonides has traditionally been interpreted as representing the tectonically shortened margin of Baltica,consisting of a Precambrian basement and a late Precambrian to Cambrian cover deposited on the margin of the Iapetus Ocean.However,new geochronology indicates a distinctly different scenario.Detrital zircon U-Pb dating,together with the magmatic and deformation history,shows that the KNC metasediments,previously considered as a single stratigraphic sequence,belong to at least two distinct successions.Metasediments of the Svaerholt Succession,within the lower(Kolvik and Olderfjord)nappes of the KNC and affected by the late Grenvillian Rigolet deformation phase,were deposited between ca.980 and 1030 Ma,constrained by intrusive granites and the youngest detrital zircons.The Soroy Succession occurs within the Soroy-Seiland Nappe,the Havvatnet Imbricate Stack,and Veines Nappe(the upper nappes of the KNC).It was affected by the Porsanger Orogeny at or before ca.840 Ma and contains detrital zircons as young as 910 ± 15 Ma,and it was thus deposited between ca.840 and 910 Ma.The Eidvageid Paragneiss,classically interpreted as the basement to the KNC metasediments,has a similar detrital zircon population to the Soroy Succession and may be correlative to it.It cannot represent the basement to the entire KNC and was affected by metamorphic events at ca.710,670,560,and 520 Ma.The detrital zircon populations of both KNC successions are consistent with a Laurentia-Baltica affinity,with age peaks corresponding to Labradorian/Gothian,Pinwarian,and Grenville/Sveconorwegian events.The detrital age populations of the Soroy Succession bear strong similarity to those from the Moine Supergroup of Scotland,while the Svaerholt Succession is comparable with the Krummedal supracrustal sequence in Greenland.The provenance data are consistent with episodic amalgamation of two terranes,exotic to the Baltoscandian margin of Iapetus,which developed in successor basins to the Grenville Orogen along the indented Rodinia margin.