129-20 Using Paleomagnetism and Rock Magnetism of Ethiopian Igneous Rocks from the East African Rift System to Understand Subsurface Mantle Evolution

Abstract:

The Ethiopian flood basalt province and volcanism of the East African Rift System preserve three distinct lava types: low-Ti (LT), high-Ti1 (HT1), and ultra-high-Ti1 (HT2) basalts. The geochemical variations of these lava types reflect mantle source heterogeneity and magma differentiation. To identify lava types and characterize their rock magnetic properties, we integrated whole-rock major-element geochemistry with rock magnetic analyses of Oligocene Maychew flood basalts and younger Selisa rift volcanics. Geochemical data show that the Maychew lavas comprise ultra-high-Ti transitional basalt–picrite compositions (TiO₂ >4 wt%), whereas the Selisa rift volcanics are low-Ti tholeiitic basalts (TiO₂ = <3 wt%), indicating derivation from compositionally distinct mantle sources. The ultra-high-Ti Maychew basalts exhibit substantially higher bulk magnetic susceptibility than the younger rift lavas, reflecting differences in magnetic mineral abundance. Hysteresis and first-order reversal curve (FORC) analyses indicate that both volcanic suites are dominated by pseudo-single-domain magnetic grains with subordinate single-domain contributions, demonstrating favorable magnetic mineral assemblages capable of preserving stable primary remanent magnetization. These preliminary results characterize the geochemical composition of the regional volcanic products and the grain-size distribution of their magnetic minerals. This framework provides a basis for future micro-textural and mineralogical investigations of Fe–Ti oxides using scanning electron microscopy and energy-dispersive X-ray spectroscopy to further resolve the links between magmatic evolution, magnetic mineralogy, and paleomagnetic behavior.

© Copyright 2026 The Geological Society of America (GSA), all rights reserved.