DIACHRONOUS BURIAL EXHUMATION OF A SINGLE TECTONIC UNIT DURING COLLISION OROGENESIS (SULITJELMA, CENTRAL SCANDINAVIAN CALEDONIDES)

The Sulitjelman fold nappe represents part of a Caledonian marginal ba sin abducted during the closure of the Iapetus Ocean and collision bet ween Laurentia and Baltica. Metamorphic pressure-temperature (P-T) pat hs indicate that various parts of the Sulitjelma fold nappe followed c haracteristic clockwise P-T paths involving prograde burial followed b y prograde exhumation and then near-isothermal exhumation prior to coo ling. Geochronological results indicate that foreland rocks followed t his general P-T path before more hinterlandward rocks, such that forel and rocks underwent exhumation while hinterlandward rocks were still b eing buried. This is consistent with the fold nappe passing through a collisional orogen; burial and ultimately prograde metamorphism were t erminated sequentially by exhumation as a given part of the fold nappe came into contact with the lower plate, basement ramp (Baltica) and w as driven upward. Burial, heating, exhumation, and cooling were thus d iachronous within a single tectonic unit.