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Continental large igneous provinces are among the largest magmatic events on Earth, characteristically manifesting at the surface as stacks of monotonous flood basalt lavas that form through a dynamic pattern of eruptive pulses separated by hiatuses. Such dynamic patterns may be difficult to detect from the composition of the lavas. Instead, lava crystal cargoes can be used to study how the eruption cycles inherent to continental large igneous provinces are moderated by episodic recharge and evacuation at multiple crustal levels. Here, we present a stratigraphically well-constrained series of 56 flood basalt flows from the Eocene Initial Phase of magmatic activity in East Africa. These flows and their crystal cargo permit temporal insight into the development of one of the youngest and best-preserved continental large igneous provinces. The stratiform mafic lavas exposed in northern Kenya consist of alternating aphyric and plagioclase-phyric lava packages consistent with periods of eruption punctuated by volcanic hiatus, where magmas stall and crystallize plagioclase at medium to shallow crustal levels. Plagioclase compositions (n  = 541) exhibit little intra-crystal or intra-sample compositional diversity. Intra-crystal equilibrium calculations for Sr and Ti indicate internal chemical equilibrium, requiring storage at high temperatures over a prolonged time interval (10 000–100 000 years). Using a series of seven interlinked partial crystal fractionation models under equilibrium conditions, we replicate the observed stratigraphic patterns in plagioclase composition. We find that the balance between recharge, evacuation, and diffusive equilibration within a shallow magmatic system controls the composition of plagioclase in these flood basalts. We conclude that the shallow fractionation system modulates eruptive cycles and thus constitutes a critical component in studies of continental large igneous provinces. [ABSTRACT FROM AUTHOR]

Within continental rift settings, extensional strain is initially accommodated along the nascent rift margins, subsequently localizing to zones of focused magmatic intrusion. The migration of strain from rift-border faults to diking places an emphasis on constraining the magmatic plumbing system of zones of focused intrusion to resolve how extension is accommodated in the rift lithosphere. While existing rifting models concentrate on the relationship between extension and focused magmatism within the rift, there is increasing evidence of rift-related magmatic activity outside the rift valley. We examine the Galema range, an area of focused magmatic activity along the eastern margin of the Central Main Ethiopian Rift, which is morphologically similar to areas of focused magmatism within the rift. We find that whole-rock thermodynamic modeling and thermobarometric calculations on mineral-liquid pairs suggest that fractionation (and hence magma stalling depths) within the Galema range is polybaric (~7 and ~3 kbar). These results, when compared to zones of focused intrusion within the rift, indicate an incipient magmatic plumbing system. We contend that diking associated with the Galema range, which predates magmatic belts within the rift, thermomechanically modified the lithosphere along this margin. While the cessation of magmatism within the Galema range may have been precipitated by a change in magma flux, the now thermomechanically modified lithospheric mantle along this margin facilitated the subsequent development of within-rift magmatic chains. The implications of this are that off-rift magmatic activity may play an integral role in facilitating the development of rift architecture. [ABSTRACT FROM AUTHOR]