Abstract An interbedded sequence of basic-silicic pyroclastics and lava flows associated with bedded volcanoclastic sediments (tuffites) is the main feature of the Igla Eliswid-Um Khariga metavolcanics. It contains both subaerial and subaqueous eruptions. The metamorphosed sequence comprises bimodal mafic and felsic assemblages, including basalts, dacites rhyodacites and their pyroclastic equivalents. The tuffites include metamorphosed tuffitic greywackes, tuffaceous siltstones, tuffaceous and tuffitic mudstones. Major and trace elements, rare earth elements and mineral chemistry indicate that the volcanic rocks are clearly tholeiitic in character and share a large number of geochemical features of island-arc tholeiites. The similar incompatible-element ratios La/Y, La/Zr and Ce/Nd, as well as the normalised ratios of La/Sm and La/Yb suggest a common source for all main volcanic rocks and thus derivation of felsic rocks from the basaltic rocks by fractional crystallization. The presence of large exposures of gabbros and diorites in the western part of the area makes it possible to apply the model of Thompson (1972) to explain the bimodality of the metavolcanics.