EXHUMATION OF UHP ROCKS IN WESTERN NORWAY - THE ROLE OF THE NORDFJORD-SOGN DETACHMENT ZONE
This new understanding of the geometry of the NSDZ has important implications for the exhumation mechanics of the UHP province. If the topW extensional displacement along the NSDZ is removed, the UHP rocks are restored to a structurally higher position ~100 km farther inland, overlying the Baltica basement. However, this juxtaposes the UHP rocks (2.53.0 GPa), against basement eclogites showing similar peak pressures (2.22.5 GPa). Therefore, movement on the NSDZ was intra-crustal only, post-dating the return of the highpressure rocks to the base of the orogenic crust; the processes and structures that exhumed the UHP rocks through the mantle remain enigmatic. 40Ar/39Ar muscovite ages of ~393390 Ma throughout the NSDZ, indicate that this structure became inactive once it reached the mid-crust, and denudation was then transferred to the structurally higher normal faults.