<i>In situ</i> garnet Lu–Hf geochronology and constraints on metamorphism in the northernmost Norwegian Caledonides

With notable exceptions, throughout the Norwegian Caledonides, the Scandian phase of the Caledonian Orogeny at c. 420 Ma dominates the isotopic record of many minerals. Nonetheless, important insight into the earlier arc accretion and rifting process has been gleaned across several key localities. Specifically, a detailed history of orogenic thickening during the Neoproterozoic and Cambrian, within the Kalak Nappe Complex of Arctic Norway, has been established principally via accessory mineral U–Pb geochronology. To complement this high-temperature geochronology new in situ garnet Lu–Hf geochronology and thermobarometry are presented with estimates of c . 570–585°C, 7.5–8.8 kbar at 490 ± 22 Ma and 560–570°C, 7.0–8.0 kbar at c. 460 Ma, which expand our understanding of pre-Scandian geological processes. Furthermore, an earlier event is resolved in garnet cores, hinting at a growth event at &gt;600 Ma. Combined with previously published data, these data support Neoproterozoic crustal thickening at c. 980, 840, 710, 690, 620 and 600 Ma, with later prograde events associated with Caledonian processes commencing from c. 500 Ma, probably owing to accretion of terranes onto the margin of Baltica. Peak Scandian conditions are constrained by 422 ± 14 Ma garnet growth. These tectonometamorphic events appear to correlate widely throughout the North Atlantic Region with important implications for the ultimate construction of the western seaboard of Baltica.