Metamorphic Evolution of the Lower Nappes of the Kalak Nappe Complex in Eastern Finnmark (Norway)

Garnet grains in metapelites of the lower nappes of the Kalak Nappe Complex in Eastern Finnmark typically show two growth zones: Garnet 1 forms the cores of the grains and grew along a P-T path with a ~20 bar/°C slope. Its growth started at ~515 °C and ~3250-5500 bar and finished at ~570 °C. The maximum pressure experienced during garnet 1 growth increases down the nappe pile. Garnet 2, which forms the rims of the garnet grains, grew during a near-isothermal pressure increase of ~500-1500 bar. Microtextural evidence indicates pre- to syn-kinematic growth of garnet 1 and post-kinematic growth of garnet 2. Lu-Hf garnet/whole-rock age dating points to growth of garnet 1 at 463±17 Ma and a maximum age of ~429 Ma for garnet 2. The hiatus between garnet 1 and garnet 2 growth was of short duration, and garnet growth might have been continuous in the lowest structural levels.