The making of an underplate: Pyroxenites from the Ethiopian lithosphere

摘要: Abstract Magmatic underplates, which are characterized by high seismic velocity and anomalously density in comparison to normal lower crust, among the most significant compositional heterogeneities identified rift lithosphere. The interaction of a magma with lithospheric mantle form pyroxenites is considered viable mechanism for creation an underplate, though details such difficult constrain geophysical techniques alone. Here we present petrographic geochemical study pyroxenite xenoliths erupted on western Ethiopian plateau from along Yerer Tullul Wellel Volcano-Tectonic lineament (YTVL). equilibration pressures recorded (0.88–1.49 GPa) consistent origin within seismically gravitationally defined underplate that exists beneath plateau. Three groups have been identified: Group I – relative enrichment orthopyroxene, clinopyroxene unfractionated heavy rare elements (HREE; TbN/YbN = 1.2–1.6); II clinopyroxene, fractionated HREE (TbN/YbN = 1.6–2.0); III transitional contain pyroxene characteristic but also II. responsible formation was likely sub-alkaline composition derived spinel peridotite basis relatively REE profiles. This may Oligocene Low Titanium (LT)-type flood basalts associated Afar plume, or subduction-related magmatism island arc activity during construction regional lithosphere Neoproterozoic Pan African Orogeny. alkaline source some garnet HREE. High (HT)-type plume Miocene-recent magmas reactivation YTVL development. Our results show impacted at least two metasomatic events exhibits characteristics more similar xenolith suites valley than elsewhere We propose magmatic formed multiple episodes magma-lithosphere interaction, developing over time rather single event.