Petrology of the Proterozoic Alkaline Carbonatite Complex of Samalpatti, District Dharmapuri, Tamil Nadu

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Abstract The gneissic rocks of Samalpatti area are intruded by the Proterozoic carbonatites, alkaline rocks, pyroxenites and minor dunites. Mineralogically carbonatites show wide variations in their composition but chemically most of them are silico-carbonatites. Presence of hornfelsic textures and metamorphic minerals like chlorite, scapolite, diopside and grossularite, suggest metamorphism of the present carbonatites. Alkaline rocks are either syenites or lamprophyres. Both carbonatites and alkaline rocks are generally enriched in large-ion lithophile elements (LILE) and high-field strength elements (HFSE) relative to the primordial mantle. Although carbonatite samples have lower concentration of LILE and HFSE than the average values of known carbonatites, they fall within the range of magmatic carbonatite concentrations. Lower concentrations of these elements are a result of hydrothermal metamorphism by hot fluids. Carbonatites are also enriched in d13C and d18O-values. The Rayleigh

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