Segments of the Earth’s mid-ocean ridge (MOR) system are offset by laterally moving transform faults. Over time, once lateral motion ceases, and for 1000s of kilometres from MOR to continental margin, fracture zones (FZs) trace the scars left in the lithosphere that mark their past locations.
Besides these ubiquitous features recording the historic opening of the Earth’s oceans and the readjustment of plate motions over thousands of millennia; they act as migration pathways for benthic fauna, channel deep ocean water movements, circulate fluid deep to within the Earth, couple stress and heat between juxtaposed plates, and host economically and technologically important mineral assemblages. FZs can also mark surface boundaries between deep Earth mantle domains. As such they lie at the heart of many of the Earth’s processes that impact on: resilience to earthquake hazard; economic development for a technology-driven society; heat transfer between the inner Earth, ocean and atmosphere that drives the climate; and sequestration of CO2 that mitigates climate change.
Although found throughout the ocean basins, FZs have rarely been studied in preference to the MORs that lie between them where new oceanic lithosphere is made. Consequently, our understanding of the role they play in the evolution of the Earth is quite limited.
This studentship aims to provide a better understanding of the processes that drive transform-to-FZ evolution by investigating, using sub-seabed remote imaging techniques to couple surface observations to deep Earth processes, examples from current zero-age MOR settings (e.g. Mid-Atlantic and Costa Rica Ridges), continental margins (e.g. Mid-Cayman Spreading Centre-Honduras transform margin) and across major plate boundaries (e.g. Drake passage, South Atlantic- Antarctic plates).
Example questions to be addressed:
• Why do earthquakes occur along fracture zones when plate tectonic theory founds on the assumption that they should be a locked and inert location with the internal part of a plate?
• How do transforms and FZs initiate to accommodate lateral relative plate motion – e.g. are they a single crustal-cutting fault or a network of active faults between which rotational and translational deformation occurs, exhuming deep crustal and upper mantle rocks and extending to develop incipient spreading centres?
• How do transforms interact with MORs – e.g. do they affect the heating-cooling of along-ridge crust and focus upper mantle melting?
• Across a FZ, lithosphere has a different age, hence thermal maturity and strength – e.g. are the effects of cooling, which create subsidence and serpentinisation and elastic rebound that drives uplift, localised?
• How is stress coupled – e.g. is it released seismically or aseismically through perpetual creep or instantaneous release and does it pose a seismic hazard?
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13N transform-fracture zone system – coupling plate movement across the Mid-Atlantic Ridge. Sediments within the relic fracture (L) reveal progressive lateral movement before locking while the active transform (R) is steeply-faulted which may channel fluid flow serpentinizing the lower crust.