Lamprophyres from the Chhota Udaipur Alkaline – Carbonatite Sub-Province, Deccan Large Igneous Province, India: Implication for Petrogenesis and Crustal Structure

Abstract This paper discusses the petrogenesis of lamprophyre dykes occurring in the Chhota Udaipur Alkaline-Carbonatite Sub-province (CUACS). Both calc-alkaline as well as alkaline varieties occur in the area. The major and trace elements geochemistry of the CUACS lamprophyres display good correlation with each other and other Deccan-related lamprophyres. Trace-elements ratios reveal a minor role of crustal contamination and support their derivation from partial melting of a lithospheric mantle source that is significantly modified by interaction with asthenosphere-derived melts emanating from an impinging mantle plume. The restricted initial 87 Sr/ 86 Sr (0.70599-0.70658) and 143 Nd/ 144 Nd (0.512501-0.512513) ratios of the CUACS lamprophyres further attest to their derivation from an OIB-type parental melt. Their negative εNdi values (−1 to −6) are comparable with other lamprophyres of the Deccan LIP. The lamprophyres from the present study share similar geochemical characteristics to Mt. Girnar lamprophyres, which are derived from the spinel-garnet transition zone at a depth of ∼85 km, distinct from the previously considered depth (∼100 km) of the post-Deccan lithosphere-asthenosphere boundary (LAB) beneath the NW India. Such geochemical characteristics of the Chhota Udaipur lamprophyres, indicate a vital role of plume-lithosphere interaction at the thermal boundary layer at about ∼66 Ma. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7244764