NJG95-3/4-09
2015
Revised structure and stratigraphy of the northwestern Repparfjord Tectonic Window, northern Norway
95
3, 4
397-422
978-82-8347-007-9

The Repparfjord Tectonic Window (RTW) consists of a ~8 km-thick low-grade, weakly deformed Early Palaeoproterozoic volcano-sedimentary succession that hosts abundant Cu mineralisations. Two major, sediment-hosted, Cu-deposits occur in the Saltvatnet Group, a Group is better characterised as containing four formations, now including also the uppermost volcaniclastic siltstones and dolostone members of the herein newly defined Gorahatjohka Formation. Field oberservations and structural analysis show that the current geometry of the Saltvatnet Group is that of a km-scale, upright, NE–SW-trending anticline, the Ulveryggen anticline, cored by the Saltvatnet Group, which thus represents the lowermost exposed rocks of the RTW. New and existing geochemical data are used to demonstrate that the two volcanic-dominated Nussir and Holmvatnet groups, which crop out on either side of the Ulveryggen anticline, have similar geochemical character and can be interpreted
as temporal and lateral correlatives. The basaltic Ulveryggen intrusions within the Saltvatnet Group are geochemically different from any other igneous rocks in the RTW, suggesting that these intruded prior to the volcanic-dominated groups in the RTW. The revised stratigraphy of the RTW is interpreted as reflecting deposition and volcanism in an evolving continental back-arc, which contrasts with the purely intraplate rift
setting inferred for most parts of the Fennoscandian Shield in the Early Palaeoproterozoic.

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