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<p>Understanding how silicic volcanoes in continental rifts generate and store magma remains a central question in volcanology, particularly where volcanic centers appear strongly bimodal. Gedemsa Caldera in the central Main Ethiopian Rift&#xa0;(MER) offers a useful test case because its eruptive products span a wider range of compositions than previously recognized. In this study, we combine whole‑rock major and trace element data with mineral chemistry and thermobarometry to examine the full range of Gedemsa magmas and the processes that shaped them. The volcanic suite extends from basalt to rhyolite and includes a substantial group of intermediate trachyandesites, challenging the view that MER volcanoes are strictly bimodal. Major and trace element trends, together with continuous feldspar and pyroxene compositions, point to fractional crystallization as the main driver of differentiation across the suite. Several geochemical indicators—including negative Eu anomalies, peraluminous signatures, and elevated La/Nb, Ce/Pb, and Eu/Eu* ratios—also suggest a possible interaction with the crust during magma evolution. Thermobarometric calculations reveal a vertically layered magma storage system extending from roughly 6 to 28&#xa0;km depth, with pre‑ and post‑caldera magmas recording different pressure–temperature conditions. These results show that Gedemsa hosts a long‑lived, transcrustal plumbing system in which repeated recharge and extended residence generate a continuous spectrum of magma compositions. The findings refine current models of magmatism in the Main Ethiopian Rift and highlight the diversity of differentiation pathways beneath continental rift volcanoes.</p> Graphical abstract <p></p>

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A continuous magmatic spectrum at Gedemsa Caldera, central Main Ethiopian Rift: implications for magma evolution in continental rifts

  • 期刊论文

  • 发表日期：

    2026年5月29日

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  • Gemechu Bedassa,
  • Dereje Ayalew,
  • Worash Getaneh,
  • Karen Fontijn,
  • Muriel Laubier,
  • Jon Blundy,
  • Luelseged Emishaw,
  • Amdemichael Z. Tadesse,
  • Abate A. Melaku

摘要

Understanding how silicic volcanoes in continental rifts generate and store magma remains a central question in volcanology, particularly where volcanic centers appear strongly bimodal. Gedemsa Caldera in the central Main Ethiopian Rift (MER) offers a useful test case because its eruptive products span a wider range of compositions than previously recognized. In this study, we combine whole‑rock major and trace element data with mineral chemistry and thermobarometry to examine the full range of Gedemsa magmas and the processes that shaped them. The volcanic suite extends from basalt to rhyolite and includes a substantial group of intermediate trachyandesites, challenging the view that MER volcanoes are strictly bimodal. Major and trace element trends, together with continuous feldspar and pyroxene compositions, point to fractional crystallization as the main driver of differentiation across the suite. Several geochemical indicators—including negative Eu anomalies, peraluminous signatures, and elevated La/Nb, Ce/Pb, and Eu/Eu* ratios—also suggest a possible interaction with the crust during magma evolution. Thermobarometric calculations reveal a vertically layered magma storage system extending from roughly 6 to 28 km depth, with pre‑ and post‑caldera magmas recording different pressure–temperature conditions. These results show that Gedemsa hosts a long‑lived, transcrustal plumbing system in which repeated recharge and extended residence generate a continuous spectrum of magma compositions. The findings refine current models of magmatism in the Main Ethiopian Rift and highlight the diversity of differentiation pathways beneath continental rift volcanoes.

Graphical abstract