Low-pressure fractional crystallization origin of the tholeiitic basalts of the Deccan plateau, India.

Petrographic descriptions and mineralogical data have been presented together with analyti cal results of major and trace elements for tholeiitic picritic basalt-ferrobasalt suite from the Deccan plateau, India.The compositional relation between coexisting augite and pigeonite was elucidated.Wide variations of incompatible element abundances were recognized among the samples but their patterns of relative enrichments parallel one another.The rock suite was probably produced by partial melting of mantle peridotite with abundances of incompatible elements rather close to primordial abundances.However, the Sr isotopic abundances were highly variable in the source, as also were alkali and alkali earth elements to a lesser extent.Fractional crystallization under low-pressure conditions was a major process in the evolution of this rock sequence.Olivine (FO85-80) was predominant in the differentiation and plagioclase was probably also involved together with augite.