Diachronous burial and exhumation of a single tectonic unit during collisional orogenesis (Sulitjelma, Arctic Scandinavian Caledonides)

The Sulitjelma fold nappe represents part of a Caledonian marginal basin obducted during the closure of the Iapetus Ocean and collision between Laurentia and Baltica. Metamorphic pressure-temperature (P-T) paths indicate that various parts of the Sulitjelma fold nappe followed characteristic clockwise P-T paths involving prograde burial followed by prograde exhumation and then near-isothermal exhumation prior to cooling. Geochronological results indicate that foreland rocks followed this general P-T path before more hinterlandward rocks, such that foreland rocks underwent exhumation while hinterlandward rocks were still being buried. This is consistent with the fold nappe passing through a collisional orogen; burial and ultimately prograde metamorphism were terminated sequentially by exhumation as a given part of the fold nappe came into contact with the lower plate, basement ramp (Baltica) and was driven upward. Burial, heating, exhumation, and cooling were thus diachronous within a single tectonic unit.