TY - DATA T1 - Structure and 40Ar/39Ar thermochronology of an ultrahigh-pressure transition in western Norway PY - 2016/06/21 AU - D.J. Young AU - B.R. Hacker AU - T.B. Andersen AU - P.B. Gans UR - https://geolsoc.figshare.com/articles/dataset/Structure_and_sup_40_sup_Ar_sup_39_sup_Ar_thermochronology_of_an_ultrahigh-pressure_transition_in_western_Norway/3452837 DO - 10.6084/m9.figshare.3452837 L4 - https://ndownloader.figshare.com/files/5420768 L4 - https://ndownloader.figshare.com/files/5420771 KW - Sandane Shear Zone KW - archetypal subducted crustal section KW - shear KW - Norway KW - Ma KW - Nordfjord KW - UHP KW - exhumation KW - allochthonous units KW - Detachment KW - extensional KW - depth KW - Ar KW - Geology N2 - The Nordfjord region of western Norway hosts an archetypal subducted crustal section, underpinned by ultrahigh-pressure (UHP) eclogite, overlain by Devonian sediments, and cored by a crustal-scale extensional shear zone. Structural mapping reveals two distinct displacement zones that played different roles during the formation and exhumation of this section: (1) the Sandane Shear Zone is a NW-dipping, amphibolite-facies, high-strain zone near the base of the eclogite-bearing crust that separates allochthonous units from underlying crystalline basement; it may have originated during early thrusting, but was overprinted by top-to-the-west extensional fabrics at lower crustal depths; (2) structurally above this, the Nordfjord–Sogn Detachment Zone is a top-to-the-west, amphibolite- to greenschist-facies detachment shear zone within allochthonous units that defines the upper boundary of the eclogitized crust and was responsible for exhumation through at least mid-crustal depths. Muscovite 40Ar/39Ar ages suggest that amphibolite-facies deformation below the Nordfjord–Sogn Detachment was mostly finished by c. 397 Ma, whereas muscovite ages from the deeper parts of the UHP domain indicate that it cooled after 390 Ma. During exhumation through the middle crust, west-directed stretching was accompanied by north–south folding. Late sinistral transpressional faulting in the middle to upper crust truncated the earlier folds and shear zones. ER -