Abstract

Recent work has provided a new tectono-metamorphic framework for the Archaean evolution of the Godthåbsfjord region which can be divided into discrete tectonic units each characterized by different magmatic, structural and metamorphic histories. These tectonic units were assembled in the late Archaean, post-2750 Ma. The present structural patterns seen in the region date from the period 2750–2600 Ma and do not reflect earlier structural events, as was previously considered. Late Archaean structural evolution began with a period of interthrusting of early Archaean sialic and late Archaean oceanic crustal segments coeval with, or followed by, isoclinal nappe formation under amphibolite-facies conditions. Linear fabrics in early Archaean rocks were rotated into parallelism with those newly formed parallel to F1 hinge lines in the late Archaean rocks. A second major thrusting event emplaced granulite facies rocks structurally on top of the amphibolite facies rocks. Subsequent to this event a series of F2 upright or steeply inclined basin and dome structures formed, some of which have sheath morphology. This second folding episode acting upon the isoclinal nappes produced the regional scale interference patterns observed. The early linear fabrics were re-oriented around these second generation structures. Data are produced from selected areas to illustrate the fabric patterns and structural continuity that exists throughout the region.

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