Protracted magmatism during the formation of the Rogaland anorthosite Province, Norway: Implications for the tectonic setting and the formation of Fe-Ti-P deposits

• Zircon U-Pb ages from the RAP (950–910 Ma) support protracted magmatic activity. • Zircon grains from anorthosites come from light-coloured rims around the HAOMs. • Hf isotopes (εHf i = -4.1 to + 5.5) support mixed mantle and crustal contributions. • Progressively more juvenile Hf isotopic signatures are found in younger intrusions. • The RAP formed in an extensional setting with sustained mafic underplating. The Rogaland Anorthosite Province (RAP) in Norway is an important locality for better understanding Proterozoic massif-type anorthosite magmatism and associated Fe–Ti–P mineralisation as significant resources are found in the province. We integrate field observations with new zircon U–Pb geochronology and Hf isotope data from anorthosites, jotunites, and Fe–Ti–P deposits and occurrences to reassess the duration and geodynamic context of RAP magmatism. Zircon U-Pb ages range from ca. 950 to 910 Ma, which give direct evidence for protracted magmatic activity. The older investigated rocks of the RAP (944 Ma; Homsevatnet norite) display an intrusive relationship with undeformed anorthosites from the Egersund-Ogna massif. This is compatible with literature a Sm–Nd isochron age of ca. 1040 Ma for high-Al orthopyroxene megacrysts (HAOMs) from the anorthosites and provide insights about the meaning of the 930 Ma ages previously reported for zircon from these anorthosites. We report here that zircon grains extracted from massif-type anorthosites come from light-coloured rims around the HAOMs, and not from the HAOMs themselves. We interpret the 930 Ma age obtained for these zircons to represent portions of fractionated melt from anorthosite mushes and that this age represents only the final emplacement stage of anorthosites. The Fe-Ti-P deposits and occurrences from the RAP formed between ca. 950 and 910 Ma, but most of the occurrences crystallised around ca. 920 Ma, coeval with the Tellnes Fe-Ti deposit. Although Fe-Ti-P deposits in the RAP formed over a significant span of time, the most primitive occurrences (Fe-Ti) crystallised at 910 Ma. Hf isotopic compositions (εHf i = -4.1 to + 5.5) reveal mixed mantle and crustal contributions, with progressively more juvenile signatures in younger intrusions. This is consistent with repeated mantle input during crustal reworking and supports the continuous input of juvenile mantle-derived material following the peak of the Sveconorwegian Orogeny. Results support that the RAP developed in a protracted (>40My) extensional setting associated with sustained mafic underplating and partial melting of lower crustal sources. This model reconciles the extended magmatic and metamorphic history of the province with the generation of massif-type anorthosites and their Fe–Ti–P mineralisation, providing broader insights into the formation of Proterozoic massif-type anorthosites.