Petrogenesis of Volcanic Plugs and Volcanic Rocks of the Infranz Area, Northwestern Ethiopia
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2018-06-01
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By: Gedefaw Tadele Vi Aau, Cncs,School Of Earth Sciences
The Bi-Modal Basalt-Rhyolite Ethiopian Continental Flood Basalt, Formed By The Impinge-Ment Of The Afar Mantle Plume Beneath The Ethiopian Lithosphere, Contains A Number Of Vertically Sided, Thought To Be Feeders Of Volcanic Rocks At The Time Of Their Formation, Volcanic Plugs. Whole-Rock Major- And Trace-Element Data Including Rees Are Presented For Volcanic Plugs Of The Infranz Area, Northwestern Ethiopia In Order To Investigate The Petrogenesis Of Volcanic Plugs And To Understand Petrogenetic Inter-Plug Relationships. The Geochemically Phonolite-Trachyte-Rhyolite Alkaline Volcanic Plugs Of The Infranz Area, Are Mostly Characterized By Nepheline, Alkali Feldspar And Quartz Phenocrysts Respective-Ly, Set In Dominantly Alkali Feldspar Microlites Of Parallely Aligned Groundmass That Form Typical Trachytic Texture. The Infranz Volcanic Plugs Have Almost Similar Major- And Trace-Element Concentrations On The Major-Element Oxide And Trace-Element Versus Silica Varia-Tion Diagrams Hence, Formed By The Little Role Of Fractional Crystallization Between Them. These Volcanic Plugs On Chondrite-Normalized Ree Patterns Show Highly Fractionated [La/Y]N ( 8.97-21.66) Rees With Negative Eu (Eu/Eu*= 0.43-0.83) Anomalies; On The Primitive Mantle-Normalized Multi-Element Plots They Illustrate Negative Anomalies In: Ba, Sr, P, And Ti. They Are Formed From The Same, Explained By The Well- Defined Trends In-Compatible Elements Form, By The Almost Similar Zr/Nb, Zr/Th Ratios They Have, Garnet Free, Shown By The Greater Than 10 X Chondrites Of Sample/Chondrite Ratios, Source Formed By The Same, Illustrated By Parallel To Subparallel Chondrite-Normalized Ree Patterns, Petrogenetic Processes.
The Variations In Concentration Of Major Elements (Tio2, Fe2o3, Al2o3, Na2o), Trace Elements (Nb, Th, Y) And Incompatible Trace Element Ratios (Zr/Th, Zr/Nb) Between The Infranz Volcanic Plugs And Lima Limo Rhyolites Demonstrates The Heterogeneity of Their Source. This Implies That The Lima Limo Rhyolites Are Not The Fed Products of The Infranz Volcanic Plugs.
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Infranz Volcanic Plugs, Alkali Feldspar, Geochemistry