Petrogenesis of the Paleoproterozoic Näränkävaara layered intrusion, northern Finland, Part II: U-Pb ID-TIMS age and Sm-Nd isotope systematics

Several mafic-ultramafic layered intrusions were emplaced in the NE Fennoscandian Shield during a magmatic episode at 2.44 Ga. The Paleoproterozoic Näränkävaara intrusion, northern Finland, is one of largest ultramafic bodies Shield, with surface area 25 km x 5 and stratigraphic thickness ~3 km. intrusion comprises 1.3 km-thick peridotitic–dioritic series (2436 ± Ma) two peridotitic reversals, 1.5–2 thick basal dunite mainly composed olivine adcumulates (dated here). has been studied since 1960’s, but several questions regarding its structure petrogenesis remain. shows lithological features typical komatiitic rather than intrusive cumulates; namely, >1 “extreme” adcumulates, some showing textures bimodal grain sizes, oscillating variations Mg# height, poikilitic chromite. With Archean greenstone belts nearby, it was previously hypothesized that could represent an wall rock to series. However, our new U-Pb ID-TIMS baddeleyite age 2441.7 0.9 Ma for are co-genetic. New whole-rock Sm-Nd isotope data from key units (initial εNd 2440 -3.5 -1.7) indicate constructed repeated emplacement LREE-enriched high-MgO basaltic magmas mantle-derived contaminated by crust, similarly other Ga intrusions. parental show similar compositions regardless position, suggesting most contamination homogenization had occurred before emplacement, situ being relatively minor process. open-system suggest may have formed (at least partly) as feeder channel cumulate, possibly related ~100 long Koillismaa-Näränkävaara Layered Igneous Complex. variably depleted metal ratios potential orthomagmatic mineral deposits, given availability S-rich rocks.