Journal Article

Magma Evolution During Main‐Phase Continental Flood Basalt Volcanism: A Case for Recharge‐Evacuation‐Assimilation‐Fractional Crystallization in the Ethiopian Low‐Ti Province

Krans, S. R., Rooney, T. O., Kappelman, J. W., Yirgu, G., Ayalew, D.

2024

Overview

Lavas erupted in Continental Flood Basalt (CFB) provinces are not primary magmas; they are differentiated products that result from large volumes of melt migrating and stalling in the lithosphere prior to eruption, resulting in complex liquid lines of descent. Geochemical models can be used to constrain the various influencers of magma differentiation (recharge, assimilation, fractional crystallization (FC), eruption, and mixing). Temporal constraints for changes in plumbing system dynamics are recorded in the petrography and stratigraphy of the erupted lava flows. This study focuses on the flow‐stratigraphy preserved within the Oligocene Ethiopian low‐Ti flood basalt province, located on the NW Ethiopian Plateau. We present new bulk rock geochemistry from 107 lavas and interpret these data within a petrostratigraphic framework. Our model results suggest that both a deep (∼0.6 GPa) and shallow (<0.2 GPa) magmatic system are active throughout the main phase of volcanism. Our recharge evacuation assimilation and fractional crystallization models (REAFC) show that during the main phase of magmatism evacuation from both the deep (65%) and shallow (55%) systems reached an apex. During the terminal phases, magma evacuation from the deeper system ceases while evacuation from the shallow system is much reduced (25%). The degree of crustal contamination predicted by REAFC (4%–10%) is lower than previous estimates determined for this region using assimilation with FC only models (12%–25%). Our study highlights the importance of evaluating petrography while interpreting geochemical models in CFB. Plain Language Summary Large eruptions of lava known as “flood basalts” have occurred several times in Earth's history. These eruptions have been linked to changes in Earth's climate, mass extinctions, the dawn of human civilization, and the splitting of large continents. Despite the impact these eruptions have, there is little understood about the journey of magma to the surface. As magma travels through Earth's crust, it changes physically and chemically. Consequently, each lava flow erupted is a record of these changes. There are multiple paths that magma can take to the surface, each leaves a unique signature on the lava. If we think of each lava flow as pages in a book, and groups of lava flows as chapters in a novel, then we can begin to tell the story of how some of the largest eruptions on Earth changed the world. In this paper, we explore one of the youngest and most complete sequences on flood basalt lavas on Earth, the Ethiopian Flood Basalt Province. We use physical and chemical signatures to identify and model key changes in eruption behavior. The results show how magma becomes shallower, and the volume of magma increasing and then decreasing over time. Key Points Combining petrographic and geochemical datasets yields a more complete picture of changes in magmatic flux in a continental flood basalt province Recharge‐evacuation models indicate lower crustal contribution for the Ethiopian Flood Basalt province than previously suggested Several geochemical trends in the Ethiopian low‐Ti province can be explained using recharge‐evacuation‐assimilation‐fractional crystallization models

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: assimilation / Basalt / continental flood basalt / Crystallization / Earth / Earth crust / East Africa / Evacuation / Floods / fractional crystallization / Geochemistry / Lava / Lava flows / Lithosphere / low‐Ti basalt / Magma / magma recharge / Mass extinctions / Oligocene / Petrography / Petrology / Recharge / Stratigraphy / Volcanic eruptions / Volcanism