Peri-Gondwanan elements in the Caledonian Nappes of Finnmark, Northern Norway: Implications for the paleogeographic framework of the Scandinavian Caledonides

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The Kalak Nappe Complex in the northern Scandinavian Caledonides has historically been interpreted as representing the pre-Caledonian margin of Baltica consisting of a Precambrian basement and a late Precambrian to Cambrian cover, which were deformed and intruded by a Late Precambrian alkalic mafic complex during the Cambrian Finnmarkian orogeny. New evidence, however, does not fit the above interpretations very well, but instead shows that the sedimentary rocks were deposited at least in part prior to about 1000 Ma and that the complex underwent repeated tectonism and granitic magmatism prior to the emplacement of the gabbroic / alkalic complex at 570 to 560 Ma. This paper presents new U-Pb data documenting distinct episodes of orogenic activity marked by the emplacement of syn-tectonic anatectic melts and in part by anatexis at about 850 Ma and 700 to 680 Ma. Another event at 600 Ma is seen in the basal unit of the overlying Vaddas Nappe. The timing of this activity is entirely atypical for the autochthonous northern segments of the Baltic Shield, which were formed in the Archean and modified in the Palaeoproterozoic. It appears much more likely that the Kalak Nappe Complex is an exotic terrane that developed outside of Baltica, probably in the pre-Gondwanan realm or the southern Iapetus, and was then translated towards, and accreted, to Baltica during the Scandian collisional phase. In view of our present understanding the various terms previously used to designate orogenic phases (Finnmarkian, Soroyan, Porsanger) are no longer relevant or sufficient for describing the complex geological evolution of the region and we propose to terminate their use.