Magma cracking through the lithosphere

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• Adina Pusok, University of Oxford
• Wednesday 06 November 2024, 14:00-15:00
• Wolfson Lecture Theatre.

If you have a question about this talk, please contact Tom Merry.

Magmatism plays a key role in the operation of plate tectonics, yet the details of magma generation in the mantle and transport to the surface remain unclear. In this talk, I will focus on the problem of magma transport across the ductile–brittle lithosphere with an application to the Turkana Depression, East African Rift. Magma transport changes from porous flow in the hot, ductile mantle to fluid-filled fractures, known as dikes and sills, in the cold, brittle crust. Accurate representation of these processes in geodynamics models is crucial for understanding lithospheric deformation, as magma transports heat and impacts lithospheric stresses.

The Turkana Depression, located between the Ethiopian and East African plateaus, represents a curious case of the interaction between magmatism and tectonics. It is missing the narrow, magma-rich morphology observed in the Main Ethiopian Rift that cuts through the Ethiopian Plateau; instead, diffuse faulting and isolated volcanic centres are widespread over several hundred kilometers. Even more enigmatic, Turkana has experienced less magmatism than adjacent plateaus, despite having the thinnest crust along the East African Rift south of Afar and overlying a mantle inferred to be hot and partially molten. Here, I hypothesise that lithospheric weakening relative to the Ethiopian Plateau has been the key control on magma transport across the lithosphere in the Turkana Depression and subsequent rift development. Using newly-developed models that incorporate the two-phase flow theory with a brittle–ductile (viscoelastic–viscoplastic) rheology of rocks, I show that magma extraction across a thin, weakened lithosphere is slower than across a thick, elastic lithosphere. The results suggest that the pre-rift thermal and/or mechanical weakening of the lithosphere can explain the magma-poor character of the Turkana region for most of its tectonic history.

This talk is part of the Bullard Laboratories Wednesday Seminars series.

This talk is included in these lists:

• Bullard Laboratories Wednesday Seminars
• Department of Earth Sciences seminars
• Wolfson Lecture Theatre

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