Geochemical and Isotopic Constraints on Long‐Lived Source Enrichment and Mantle Evolution in Paleoproterozoic Cratonic Lamprophyres

The cratonic lithospheric mantle records complex metasomatic processes and is frequently tapped by alkaline magmatism, offering a unique opportunity to trace the progressive evolution of the mantle. In the present contribution, we investigate a newly identified calc‐alkaline lamprophyre field from the Neoarchean Jonnagiri Schist Belt, Eastern Dharwar Craton, southern India. Petrographic and mineralogical observations reveal reversely zoned amphibole phenocrysts, indicating magma mixing and recharge within a multi‐level magma plumbing system. Amphibole cores, interpreted as antecrysts, crystallized in a deep‐seated magma reservoir (∼20 km) and were later overgrown by rims equilibrated with a more mafic melt at shallower crustal levels (∼7 km), recording a dynamic history of magmatic evolution. 40 Ar/ 39 Ar age (2,200–2,400 Ma) of the lamprophyres cast a significantly distinct Paleoproterozoic calc‐alkaline event that predates the widespread Mesoproterozoic (∼1,100 Ma) alkaline magmatism elsewhere in the craton. Whole‐rock geochemistry characterized by negative Nb‐Ta, Zr‐Hf, and Ti anomalies in the spidergram, suggests derivation from a sub‐continental lithospheric mantle source modified by slab‐derived fluids during the Neoarchean subduction. The Th/Yb (5.3–2.5) and Nb/U (9.4–2.1) trace‐element ratios, and the fractionated LREE/HREE pattern (La N /Yb N : 29–18) of the investigated lamprophyres are indistinguishable from those of lamprophyres from the Superior‐ and Yilgarn‐ Cratons. Near Chondritic εNd i signatures and enriched Archean mantle‐like Sr isotopic signatures imply a short residence time of the generated magma after metasomatic modification. The geodynamic setup of the Jonnagiri schist belt reflects post‐collisional reworking of the subduction‐modified lithosphere, possibly triggered by the slab break‐off and asthenospheric upwelling during the waning period of Neoarchean accretion. Partial melting of this enriched mantle during the Paleoproterozoic (∼2.3 Ga), likely related to Superia supercontinent break‐up, contributed to the polychronous magmatic activity in this domain. The Jonnagiri lamprophyres record the prolonged influence of a subduction‐enriched lithospheric domain tapped episodically during the Neoarchean to Mesoproterozoic.