Geological map of high-grade gneisses in the northern Vestfold Hills

The Vestfold Hills are mostly late Archaean-Palaeoproterozoic high grade gneisses that were accreted, metamorphosed and deformed during a short interval of about 50 m.y. spanning the Archaean-Proterozoic boundary. The gneisses are described relative to a simple structural framework dominated by two regional high-grade deformation episodes (D1 and D2), according to whether gneisses were affected by D1, or intruded in the D1 to pre- or syn-D2 interval.The oldest gneisses are volumetrically minor metasedimentary (Taynaya and Chelnok Paragneisses) and metabasic (Tryne Mafic Gneiss) units that were intruded by pre-D1 felsic magmas (Mossel Gneiss protolith). These units were folded and interleaved during a regional high-grade deformation event (D1-M1), and subsequently intruded by regionally extensive and compositionally diverse magmas gneisses and Crooked Lake group protolith). Pre-D1 gneisses and Crooked Lake Group intrusives were then deformed and metamorphosed in a second regional high-grade deformation event (D2-M2), closely followed by regional open warping.Subsequent geological activity in the Vestfold Hills was dominated by ocalised deformation and dyke emplacement. At least 8 major dyke suites and many localised deformation episodes have been defined based on structural, geochemical and cross-cutting criteria.