Geodynamic and Isotopic Constraints on the Genesis of Kimberlites, Lamproites and Related Magmas From the Finnish Segment of the Karelian Craton.

Despite the scientific and economic significance of kimberlites and related magmas, their origin is unclear. Here, we address this issue using whole‐rock and perovskite‐derived Sr‐Nd‐Hf isotopes for the three occurrences of kimberlite, lamproites and ultramafic lamprophyres (UMLs) in Finland. Mesoproterozoic olivine lamproites at Lentiira‐Kuhmo and UMLs at Kuusamo have different isotopic signatures yet were emplaced contemporaneously at 1,200 Ma in response to an extensional regime linked to the Baltica‐Laurentia breakup. The low εNd(i) and εHf(i) values of the olivine lamproites are consistent with an enriched subcontinental lithospheric mantle (SCLM) source while UML compositions are intermediate between those of typical kimberlites and lamproites and are interpreted to reflect mixing of asthenospheric melts and ∼10%–15% of melts sourced from metasomatized SCLM. The ∼750 Ma Kuusamo kimberlites, are probably linked to the mantle plume activity that initiated Rodinia's break‐up, exhibiting homogenous isotopic compositions which mirror the prominent Geodynamic and Source Constraints for ∼1,200 Ma Olivine Lamproite and Ultramafic Lamprophyre Magmatism in Eastern Finland (PREMA)‐like signature of kimberlites globally. By contrast, ∼620–585 Ma Kaavi‐Kuopio kimberlites show limited range in εNd(i) and 87Sr/86Sr(i) but have remarkably heterogeneous εHf(i) (+6.5 to −6.3) with a temporal trend toward lower εHf(i) values. While the Kuusamo kimberlites erupted during the early stage of continental break‐up, the Kaavi‐Kuopio kimberlites were emplaced when Rodinia break‐up was completed, coeval with formation of the Central Iapetus large igneous province. Magmas forming the Kaavi‐Kupio kimberlites may have formed from an upwelling mantle source similar to PREMA modified by increasing incorporation (up to 10%) of recycled crustal material through time accounting for the trend toward lower εHf(i) in these kimberlites. Plain Language Summary: Kimberlites and related rocks are of great economic and scientific importance as they are some of the deepest derived mantle melts (> 150–200 km) and carry a diverse cargo of mantle material, including diamonds. In this study, we utilize new radiogenic isotope data combined with geochemical modeling and existing geodynamic reconstructions to propose genetic models for the emplacement of kimberlites, ultramafic lamprophyres (UMLs) and olivine lamproites in Finland. The UMLs and olivine lamproites may be genetically related given their close temporal overlap and their compositions testify to progressively increasing contributions by geochemically enriched lithospheric mantle sources. We propose that kimberlite activity in Finland is fueled by melting of deep mantle sources that bookends both the onset and completion the break‐up of an ancient supercontinent, Rodinia. This supercontinent disintegration and, potentially, kimberlite activity, was likely driven by the deep mantle upwellings, or plumes, beneath the region. In addition, our modeling suggests the unique, isotopic evolution of the mantle source for the youngest Finnish kimberlites occurrence reflects progressive incorporation of ancient, recycled material into their mantle plume source. Key Points: New radiogenic isotope data reveals distinct sources and petrogenesis for three occurrences of kimberlite and related magmatism in FinlandKimberlite magmatism in Finland is synchronous with initiation and completion of Rodinia's break‐up with potential links to mantle plumesThe primitive source region of the Kaavi‐Kuopio kimberlites was significantly modified by increasing incorporation of recycled material [ABSTRACT FROM AUTHOR]