Petrology and Sr–Nd isotope geochemistry of Mosonik: a polygenetic phonolitic nephelinite–phonolite volcano located in the North Tanzanian Divergence of the East African Rift

Abstract Mosonik, a 3.25 Ma extensively dissected stratovolcano located in the North Tanzanian Divergence of East African Rift, consists predominantly phonolite and three types phonolitic nephelinite distinguished by presence or absence amphibole garnet antecrysts differing populations complexly zoned antecrystal phenocrystal pyroxenes. The antecryst–phenocryst assemblage is typical hybrid lavas derived magma mixing. Compositional data are given for all major minerals. Owing to high modal proportions (30–60 vol. %) phenocrysts pyroxene nepheline plus character lavas, bulk-rock compositions do not represent those parental liquids. Thus, assimilation–fractional crystallization modelling major- trace-element abundances inappropriate an unevolved cannot as yet be defined. Sr–Nd isotopic Mosonik other Older Extrusive Series rocks suggest derivation partial melting ancient metasomatized lithospheric mantle with mixing Sr Nd from two sources coupled minor lower crustal contamination, being induced plume currently impinging on craton, representing initial interaction cratonic lithosphere. In contrast, Younger Extrusives, exemplified Oldoinyo Lengai nephelinite–carbonatite volcanism, could this recent plume-derived asthenospheric component no contamination material. isotopically genetically distinct Natron–Engaruka melilitites considered direct adiabatic without contributions. Carbonatites melilite-bearing nephelinites also occur at but study they only very volumetric volcano.