Petrogenesis of Olivine-phyric Basalts from the Aphanasey Nikitin Rise: Evidence for Contamination by Cratonic Lower Continental Crust

In this work we investigate the olivine-phyric basalt suiteof the Aphanasey Nikitin Rise, an intraplate volcanic structureformed during the Late Cretaceous in the Indian Ocean. The parentalmelt of the basalt suite has a hypersthene-normative tholeiiticcomposition with low H₂O content (0·3–0·5wt %) and high SiO₂/Al₂O₃ (3·5). The basalt suite ischaracterized by Nb, Ta, Th and U depletion, and uniquely low²⁰⁶Pb/²⁰⁴Pb and ¹⁴³Nd/¹⁴⁴Nd among the Cretaceous tholeiiticbasalts of the Indian Ocean. Our modelling demonstrates thatfractional crystallization of depleted mantle-derived melt andlower continental crust assimilation is a suitable model forthe genesis of the parental magma of this suite. The continentalcrustal material involved is characterized by long-term Rb,U and Th depletion and probably remained isolated for >10⁹years in cratonic Gondwanan lithosphere. On a broader scale,two geochemical groups can be distinguished among tholeiitesformed in the Indian Ocean basin during the period 115–75Ma, from the Aphanasey Nikitin Rise, the southern Kerguelenand Naturaliste plateaux and the Broken Ridge. Both groups havea compositional range from hypersthene-normative basalt to basalticandesite and are characterized by Nb–Ta depletion, extremelylow