Petrogenetic evolution of post-collisional paleoproterozoic mafic dykes from the contact of Bastar Craton and Eastern Ghat Mobile Belt, India: Insights from petrology, geochemistry and Sr-Nd-Hf-Pb-Os isotopes.

We reported post-collisional paleoproterozoic mafic dykes (NNW and EW trends) from the diamondiferous Mesoproterozoic (1.1 Ga.) Nuapada Lamproite Field (NLF) at the tectonic contact of Bastar Craton and the Eastern Ghat Mobile Belt, India. The study of these mafic dykes provides significant information about the crust-mantle interaction or the recycling of oceanic crust in the mantle. We presented here the detailed petrological evolution and significance of these mafic dykes. The studied mafic dykes are unmetamorphosed, ophitic to subophitic in nature, and the presence of hydrous phases (amphibole and mica-5 to 10 modal%) is a characteristic feature of these mafic dykes. Geochemically, dykes are basaltic to basaltic-andesitic in nature and show calc-alkaline affinity. The chondrite normalised REE diagrams depict slightly enriched LREE in comparison to HREE, with (La/Yb)N ranging between 1.5 and 6.2 indicating moderate degrees of partial melting of the mantle source. The flat and elevated pattern of HREE indicates lack of prominent garnet control in the source, especially in NNW trending dykes. Furthermore, the Sm vs Sm/Yb diagram shows that the E-W dykes have been derived from ~10% partial melting of spinel-garnet lherzolite whereas NNW trending mafic dykes were also derived from the similar source but with varying degrees of melting with ~15% partial melting. In primitive mantle normalised multielement distribution diagram, all dykes shows enrichment of LILEs and the negative anomalies of HFSEs like Nb, Ta, Ti. The dykes have high Ba/Yb ratio and moderately enriched εNdt, εHft (2 to -5.01 and - 3.2 to -11.2), along with the positive γOs(t) [192 to 727; high Re/Os ratio (3.3 to 34.1) are consistent with their enriched nature which is brought up by the subduction metasomatised source. The 206Pb/204Pb vs 207Pb/204Pb and 206Pb/204Pb vs 208Pb/204Pb plots reveal the NLF mafic dykes plot very close to upper continental crust and follows a global orogenic trend, supporting recycling of the crust which is trap by the dykes. The studied NLF mafic dykes are inferred to have been derived from a , long-lived enriched source and also tapped EM-1 type reservoir which was subsequently modified and hydrated through slab dehydration process. The NLF mafic dykes have very close geochemical and isotopic similarity with 1.88 Ga. Narayanpur-Kondagaon mafic dykes from the Bastar Craton (Panda et al., 2023) and treated as same magmatic event. The origin and the emplacement of these dykes are related to the assembly of the Columbia supercontinent.Reference:  Aurovinda Panda et al. (2023).Precambrian Research, 393, 107090. https://doi.org/10.1016/j.precamres.2023.107090