The Paleoproterozoic Prøven Igneous Complex (PIC) in West Greenland extends from ca. 72°15′ to 73°10′N, approximately 500 km north of the subduction-related intrusive complex in the core of the +1100 km wide, asymmetric collisional Nagssugtoqidian-Rinkian Orogen. A new U-Pb SHRIMP age for the PIC of 1869±9 Ma indicates that it intruded synchronously with the main collisional phase of the orogen into the passive margin side of the collision. Sm-Nd and Lu-Hf isotopic and A-type geochemical signatures are compatible with its derivation from melted Archean lower crustal material contaminated to varying degrees by pelitic sedimentary rocks of the Karrat Group. The timing, petrogenesis and position of the PIC within the orogen support a model of collisionally induced delamination of the mantle lithosphere following initial collision. Upwelling asthenospheric mantle replacing the partially or completely detached mantle lithosphere caused widespread partial melting of lower crust that resulted in the areally extensive (∼250,000 km2) Cumberland-Prøven intrusive complexes of Baffin Island and West Greenland. Emplacement of the PIC at 1.87 Ga caused a high-temperature low- to medium-pressure metamorphic aureole that contrasts the regional, overprinting higher-pressure amphibolite facies metamorphism. The consequent high-temperature garnet-orthopyroxene-biotite-bearing assemblages occurring within the margin of the intrusion in the aureole are attributed to the intrusion event. Garnet-controlled Sm-Nd and Lu-Hf ages of 1.82-1.80 Ga require efficient diffusion of these elements during orogenic reheating at this time. This age range overlaps the post-collisional, north-south shortening in the Nagssugtoqidian Orogen to the south and serves to confirm the recently proposed genetic link between these two orogens. These new data infer that garnet-controlled isochrons based on the Lu-Hf and Sm-Nd systems cannot date high-grade events in slowly cooled or significantly reheated terrains in rocks possessing other phases that close at low temperatures.
- Programområde 4: Mineralske råstoffer