Paleoproterozoic Boninite-like Rocks in an Intracratonic Setting from Northern Bastar Craton, Central India

摘要

Boninite-like rocks represented by high-Ca boninitic dykes, melanogabbro dykes, recrystallized plagioclase bearing high MgO dykes and high-Mg norite suites occur at few places in the vicinity of Meso to Neoproterozoic Chhattisgarh sedimentary basin in the northern Bastar craton in Central India. These rocks are formed in an intracratonic setting, not at convergent margin, similar to Archaean boninitic rocks reported from intracratonic settings such as Mallina Basin, Northwest Australia and Abitibi, Optica regions of Canada. These high-MgO mafic dykes show a strong boninitic affinity with high SiO2 (> 52%), high MgO (9-15%), low TiO2 (0.30-0.54 wt%) and strong LILE enrichment. These unusual dykes show distinct mineralogical, petrological and geochemical characteristics and are totally different to that of the normally occurring abundant metadoleritic and metagabbroic dykes in Chhattisgarh region. The generation of boninite magmatism requires unique thermal conditions such as shallow melting, elevated geothermal gradient and subducted slab flux. On the basis of field, geological, petrological and geochemical inferences on these Chhattisgarh boninitic and noritic dykes, a two-stage melting model and derivation from a strongly depleted mantle source, enriched later by metasomatic events is suggested.