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Journal of the Geological Society

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The trace element and isotope geochemistry of the Sabaloka Igneous Complex, Sudan

The Sabaloka Igneous Complex comprises 2 igneous centres of 'within-plate' magmatism, intruded into Precambrian gneisses in northern Sudan. The Cauldron Complex is the larger centre and was emplaced at 383 ± 14 Ma. The earliest felsic magmas are highly fractionated, peraluminous rhyolites with isotope and trace element characteristics indicative of either a biotite tonalite–granodiorite source or of amphibole fractionation from a metalumi-nous melt. The rhyolites are overlain by ignimbrites, which have similar trace element characteristics to the rhyolites but are less aluminous. A mica granite boss intrudes both rhyolites and ignimbrites and has an unuaual trace element geochemistry, which is ascribed to volatile loss during emplacement. The Cauldron Complex is circumscribed by a microgranite ring dyke, which has isotopic and trace element characteristics which allow the microgranite magma to be the source from which the rhyolites fractionated; the microgranite itself requires a monzonite or syenite source. The subsidiary Tuleih Complex was emplaced at 465 ± 14 Ma and is largely composed of a silica saturated–marginally undersaturated syenite. Trace elements and isotopes from the syenite indicate a garnet eclogite source of mantle origin. The Sabaloka intrusions provide an example of several periods of magmatism contributing to the same igneous complex, although not necessarily to the same igneous centre.

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