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Jones Seminar: Earth Orbital Cycles Inscribed on the Ocean Floor by Faulting
3:30pm - 4:30pm ET
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Meeting ID: 988 7372 7000
The dominant topographic features of the ocean floor are the fault-bounded abyssal hills that run parallel to the global system of mid-ocean ridges. At fast-spreading mid-ocean ridges, power spectra across this topography show concentrations of power at orbital frequencies. In particular, a significant excess is found at the 1/(41 ka) Milankovitch frequency, which corresponds to variations in Earth's obliquity. How do subtle variations in obliquity pace faulting on the ocean floor? I provide a tentative answer in terms of a pair of hypotheses in which ice ages, sea level, midocean ridge magmatism, oceanic plate bending, and faulting are coupled by mechanics and thermodynamics.
The obliquity frequency is prominent in many climate records, including sea-level variations of the past two million years. Variations in sea level, in turn, modulate the decompression-melting rate of magma production beneath mid-ocean ridges. For sea-level forcing at the obliquity frequency, such modulations are expressed as variations of the melt supply to mid-ocean ridges. At fast-spreading midocean ridges, melt supply controls the height of the ridge axis above the average depth of the oceans. It therefore also controls the curvature of oceanic plates as they move away from the ridge axis and are un-bent by gravity. Variations in melt supply and elastic plate thickness may hence affect bending stresses of the plate, and extensional faulting. This could leave a signature of obliquity variations on the sea floor.
The talk includes analysis of continuum mechanical models including poro-viscous Stokes flow of the mantle, Darcian flow of magma, and Euler-Bernoulli plate bending. Sea level variations are represented as formally small perturbations and their effects are modelled in terms of the analytical solutions of linearised equations. Numerical solutions are used to validate and extend the analytical results.
Hosted by Professor Colin Meyer.
About the Speaker(s)
Professor of Geodynamics, University of Oxford
Richard Katz is recognised for his research on partially molten rock and ice. He develops and analyses mathematical models of liquid-solid interaction in poro-viscous materials at their melting temperature. He has applied this theory to Earth and Io (a moon of Jupiter), to plate-tectonic boundaries, to ice sheets, and to laboratory rock-mechanics experiments. Katz recently authored the book, The Dynamics of Partially Molten Rock. He is professor of geodynamics at the University of Oxford and lectures on fluid dynamics at the African Institute for Mathematical Sciences in Cape Town.
For more information, contact Amos Johnson at email@example.com.