Slow subduction of a thick ultrahigh‐pressure terrane

High‐precision Lu‐Hf and Sm‐Nd ages reported here cover a large portion of the Western Gneiss Region (WGR) ultrahigh‐pressure (UHP) terrane, Norway, and range from 413.9 ± 3.7 to 397.1 ± 4.8 Ma. Collectively, new and existing geochronologic data for eclogites demonstrate that eclogite facies metamorphism occurred over a large area (60,000 km 2 ) for an unexpectedly long period of >20 Ma. A thermal model using slow subduction (2–4 mm a −1 ) of a relatively warm and thick slab can reproduce the observed P ‐ T ‐ t history of the WGR UHP terrane, indicating that large UHP terranes with protracted peak or near‐peak histories probably reflect slow subduction of relatively thick crustal sections.