Lamprophyres from the Chhota Udaipur alkaline–carbonatite sub-province, Deccan Large Igneous Province, India: implication for petrogenesis and crustal structure

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 element 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 ocean island basalts (OIB)-type parental melt. Their negative εNdi values (−1 to −6) are comparable with other lamprophyres of the Deccan Large Igneous Province (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 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.