Mineralogy and geochemistry of nephelinite–phonolite occurrences from Barmer region, Rajasthan, India

In Barmer alkaline complex, Rajasthan, melanephelinites are closely associated with two types of phonolites. Details of petrography, mineralogy and geochemistry are presented. Based on the trends defined by the major and trace element data, it seems highly unlikely that the origin of the phonolites from the Sarnu–Dandali region may be attributed to differentiation of a closed magma system. The contamination by crustal components is evident from the number of xenoliths in all alkaline rocks of this area. Without the data on radiogenic isotope, it is very difficult to test models involving phonolite magma derivation exclusively either by low-pressure crystal fractionation of a parental, mantle-derived melanephelinitic magma, or crustal contamination of a melanephelinitic melt undergoing crystal fractionation.