Petrogenesis of calc-alkaline lamprophyre from Jonnagiri green schist belt, Dharwar craton, southern India: Insights from major and trace element chemistry of amphiboles.

Lamprophyres are a group of igneous rock that are volumetrically minor and inherently restricted to continental setting. These volatile- rich, mantle derived alkaline rock, carry hydrous mineral such as amphibole and biotite within feldspathic groundmass and sometimes xenolith and xenocrysts, provide direct sample of the sub-continental lithospheric mantle. As such the porphyritic nature of the lamprophyres are known to preserve evolutionary processes of magma through open and closed system magma chamber processes (i.e., magma mixing, mingling, recharge, remobilization, assimilation and crystallization) reflecting cognate (phenocryst) as well as disequilibrium (antecryst) relationship in a complex magmatic plumbing systems whereas the latter are interpreted as xenocrystic fragments from amphibole-rich metasomatic veins in the upper mantle. Major and trace element mineral chemistry data are presented for amphibole phenocrysts from lamprophyric calc-alkaline magmatism from Jonnagiri schist belt, Eastern Dharwar Craton, southern India. Variability in major oxide geochemical signatures (e.g., Mg#, temperature, pressure, fO₂) of amphibole phenocrysts indicate phenocrysts cores to be representative of early-crystallised phenocrysts, whereas rims crystallised in equilibrium with amphibole microphenocrysts during final emplacement of host melts.  Amphibole trace element concentrations offset together with trace element modelling signatures in host rock – amphibole phenocryst pairs suggest a non-cognate relationship that likely represent the amphibole phenocryst cores as remnants of fractionated phase belonging to evolved lamprophyric melts. Our study reflect interaction between heterogeneous lamprophyric melt and/or cumulate amphiboles in the crustral levels that experienced localised varying degree of mantle melting in a moderately heterogeneous SCLM source.