Transforming fractures – coupling deformation, heat and fluid flow within the Earth’s evolving oceanic lithosphere

Overview

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 to deep 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?

Click on an image to expand

Image Captions

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 serpentinising the lower crust.

Methodology

The purpose of this studentship is to determine the structure of type transform and fracture zone examples, and develop a model for their evolution from MOR to continental margin, and across a primary plate boundary. Research will be underpinned by the analysis of multi-disciplinary geophysical datasets and involve the processing and modelling of multichannel and wide-angle seismic, gravity, magnetic and bathymetry data using state-of-the-art and forefront developing techniques and software.

Project Timeline

Year 1

Training in data analysis, modelling and interpretation methods
Analysis of a transform fault-fracture zone MOR example – geophysical data processing, analysis and interpretation
Training courses embedded with the IAPETUS DTP
Author a publication
Attend a national conference and present a poster

Year 2

Analysis of a transform fault-fracture zone primary plate boundary example – geophysical data processing, analysis and interpretation
Training courses embedded with the IAPETUS DTP
Author a publication
Attend a national conference and orally present

Year 3

Analysis of a transform fault-fracture zone continental margin example – geophysical data processing, analysis and interpretation
Training courses embedded with the IAPETUS DTP
Synoptic overview of results and conclusions drawn from the three type sites.
Author a publication
Attend a national or international conference and make a presentation

Year 3.5

This 6-month period will concentrate on PhD write-up.
Author the synoptic publication.

Training
& Skills

The student will be trained in an inter-disciplinary geoscience research team, with expertise in start-of-the-art geophysical data interpretation, providing a solid basis for a future career in academia or industry. This studentship offers potential opportunities to experience geophysical data acquisition at sea first-hand aboard a research vessel.

References & further reading

Henson, C. et al., 2019. Marine transform faults and fracture zones: a joint perspective integrating seismicity, fluid flow and life. Frontiers in Earth Science. doi:10.3389/feart.2019.00039.
Peirce, C. et al., 2019. Constraints on crustal structure of adjacent OCCs and segment boundaries on the Mid-Atlantic Ridge. doi:10.1093/gji/ggz074.
Peirce, C. et al., 2019. Seismic investigations of an active ocean-continent transform margin: the interaction between the Swan Islands Fault Zone and the ultraslow-spreading Mid-Cayman Spreading Centre. doi:10.1093/gji/ggz283.
Kolandaivelu, K., et al., 2017. Analysis of a conductive heatflow profile in the Equator fracture zone. doi:10.1016/j.epsl.2017.03.024.
Livermore, R., et al., 1996. Unusual sea-floor fabric near the Bullard fracture zone imaged by GLORIA sidescan sonar. doi:10.1038/353158a0.
Kruse, S., et al., 1996. Evolution and strength of Pacific fracture zones. doi:10.1029/96JB00645.

Further Information

For further information contact: Professor Christine Peirce: email – christine.peirce@durham.ac.uk; tel – 0191 334 2300

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