Exhuming Norwegian ultrahigh-pressure rocks: Overprinting extensional structures and the role of the Nordfjord-Sogn Detachment Zone

摘要: [1] The Nordfjord-Sogn Detachment Zone (NSDZ) is widely cited as one of the primary structures responsible for exhumation Norwegian (ultra)high-pressure (UHP) rocks. Here we review data from considerable volume research describing this shear zone, and compile a strikeparallel cross section along NSDZ Solund Basin in south to Soroyane UHP domain north. This highlights several previously unrecognized patterns, revealing zone with top-to-the-west asymmetric fabrics that (1) initiated at amphibolite facies, (2) overprints metamorphic breaks tectonostratigraphic contacts, (3) has gradational continuum muscovite cooling ages. These patterns constrain kinematic evolution suggest new three-step model (U)HP initial stages were characterized by rise crustal rocks depths base crust buoyancydriven mechanisms not specified paper. Mantle was followed top-to-thewest, normal-sense displacement within broad noncoaxial ductile near overprinted contacts formed during mantle exhumation. In final exhumation, top-W brittleductile detachments soled into partially excised dropping Devonian basins contact varying levels. interpretation significant it accounts extreme excision observed western Norway using three sequentially overprinting active different rock Citation: Johnston, S. M., B. R. Hacker, T. Andersen (2007), Exhuming ultrahigh-pressure rocks: Overprinting extensional role Zone, Tectonics, 26, TC5001,