Geochemistry and Sr-Nd isotopic studies of Palaeoproterozoic (ca. 2.3 Ga) meta-lamprophyre from Rapuru area, Nellore Schist Belt, Southern India: Implication for back-arc basin magmatism and its relevance to the Columbia Supercontinent assembly

Present study reports two lamprophyre dykes from the Rapuru area along the margin of Eastern Dharwar Craton (EDC) and Nellore Schist Belt (NSB). The Rapuru lamprophyre (RL) dykes are situated along southern extension of the Prakassam Alkaline Province (PAP). The Rapuru lamprophyre (RL) dykes are deformed yet preserves the porphyritic-panidiomorphic texture with mica phenocrysts and amphibole and feldspars in the groundmass. The geochemically RL have low Mg# (0.28-0.37), Ni (30 ppm - 60 ppm) and Cr (119 ppm - 228 ppm) concentration indicates their evolved nature like other reported lamprophyre from PAP and EDC. Which is a further supported Sr-Nd isotopic ratios shows affinity towards MORB-OIB like signature and juvenile magmatic nature. The RL seems to have inherited by two major influences, namely, primary source region: which is geochemically juvenile similar to the compositional field of enriched-MORB, and the continental lithosphere. Such magmas are known to have formed in the back-arc-basin environment. The initial 87 Sr/ 86 Sr ratio (∼0.7012-0.7045) and initial εNd (3.13 to 7.93) ratios are in line with the Back-Arc Basin Basalts (BABB) recorded in other parts of the world. The field observation and bulk-rock Sr-Nd radiogenic isotope in the present study support Palaeoproterozoic nature of RL. This concurrence of juvenile radiogenic isotopes and fluid-related trace element compositions apparently suggest dehydration of a subducted slab triggered metasomatism of the overlying mantle wedge in subduction related geodynamic setting. Such intrusive lamprophyre rocks of the older ages are limited in India as well as other part of the world. The rocks of 2.1 and 1.8 Ga, are widely considered to be the ages of initial accretion and final breakup of an erstwhile Columbia Supercontinent assembly. We argue that the RLs were formed in Palaeoproterozoic period during the waxing stages of the Columbia Supercontinent Assembly in BAB environment; most probably due to low degree of partial melting of asthenosphere and lithospheric interaction by the introduction of influx of subduction component into arc-back arc basin system.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5598266