Segmentation of the Caledonian orogenic infrastructure and exhumation of the Western Gneiss Region during transtensional collapse

The (ultra)high-pressure Western Gneiss Region of the Norwegian Caledonides represents an archetypical orogenic infrastructure a continent–continent collision zone. To test established exhumation models, we synthesize geochronology and structures major basement windows provide new ages from poorly dated areas. Migmatite U–Pb zircon samples date melt crystallization at c. 405 Ma in Øygarden Complex, expanding spatial extent Devonian migmatization. Micas shear zones Gulen domes yield 40 Ar/ 39 Ar mostly between 398 Ma, recording metamorphic core complexes. On larger scale, youngest various geochronometers different segments show abrupt breaks (10–30 myr) across low-angle detachments sinistral transfer zones, which also correspond to structural discontinuities. We explain segmentation by partitioned post-orogenic transtension due lateral vertical rheological contrasts edifice (strong cratonic foreland wedge v. soft infrastructure). Differential crustal stretching dragged out deep levels crust below became progressively dominated zones. Collapse obliterated syn-collisional structure root resulted diachronous distinct segments. Supplementary material: Complete analytical results are available https://doi.org/10.6084/m9.figshare.c.5241710