Passive Imaging of the Lithosphere Asthensphere Boundary (PiLAB)

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

Plate tectonics has been a fundamental tenet of Earth Science for nearly 50 years, but fundamental questions remain, such as where is the base of the plate and what makes a plate, "plate-like?" A better understanding of the transition from the rigid lithospheric plate to the weaker mantle beneath has important implications for the driving forces of plate tectonics, natural hazards, and climate change.
There are many proxies used to estimate the depth and nature of the base of tectonic plates, but to date no consensus has been reached. For example, temperature is known to have a strong effect on the mechanical behaviour of rocks, and if this were the sole process governing the definition of the plate, then we would expect to see a thin plate near a mid ocean ridge and a very thick plate beneath old seafloor. However numerous geophysical studies observe what are interpreted as nearly constant thickness plate at all seafloor ages. This has led scientists to propose other mechanisms, such as dehydration of the mantle to strengthen the mantle to form a rigid plate. Similarly, observations of very strong anomalies have led others to suggest that melt might exist to weaken the mantle beneath the plates. However many of these observations come from only one ocean, the Pacific, from indirect, remote observations, at different areas and scales, and with different sensitivities to earth properties. Although results have been promising, comparisons among studies are challenging, hindering a complete understanding of the tectonic plate.
We will systematically image the entire length of an oceanic plate, from its birth at the Mid Atlantic Ridge to its oldest formation on the African margin. This is a large-scale focused effort with multiple scales of resolution and sensitivity, from a metre to kilometre scale using seismic and electromagnetic methods. This scale, focus, and interdisciplinary approach will finally determine the processes and properties that make a plate strong and define it. The project will be accomplished through a large, focused international collaboration that involves EU partners (3.5 M euro) and industry (6.4M euro), both already funded.

Planned Impact

We have three main end users of the knowledge acquired during this grant:
1) Energy and Minerals Exploration
2) Public
3) UK companies

We will engage with the end users through the following activities:
1) 2 Workshops at IPGP to liaise with our academic partners and industry partners about the progress and developments achieved through the proposed work.
2) Outreach the public through our Discover Oceanography Program, TEATime lectures for post-16 Students, Bringing Research to Life Roadshow and Learn through US program.
3) Data Sharing, Analyses Code Sharing and Web presence.

Our milestones for success will be uptake by industry and other academics of our methods and data products, levels of access of our websites and feedback and response to our outreach efforts.

Publications

10 25 50

publication icon
Chichester B (2018) Seismic Imaging of the North American Midcontinent Rift Using -to- Receiver Functions. in Journal of geophysical research. Solid earth

publication icon
Lavayssière A (2018) Imaging Lithospheric Discontinuities Beneath the Northern East African Rift Using -to- Receiver Functions. in Geochemistry, geophysics, geosystems : G(3)

publication icon
Rychert CA (2018) Scattered wave imaging of the oceanic plate in Cascadia. in Science advances

 
Description In 2018 we have learned the following:

The sedimentation rate varies with time in the equatorial mid Atlantic, showing a change around 8-10 M.a. possibly due to onset of the African monsoon.

We also mapped the Chain Fracture Zone and found that in contrast to other fracture zones on the Mid Atlantic Ridge crustal thickness within the fault zone is not uniformly thinner than the surrounding crust.
Exploitation Route Currently we are continuing forward with the research. Data will be archived and made publicly available.
Sectors Energy,Other

 
Description GEOMAR PILAB 
Organisation Helmholtz Association of German Research Centres
Department Helmholtz Centre for Ocean Research Kiel
Country Germany 
Sector Public 
PI Contribution As part of the imaging the lithosphere asthenosphere boundary project we performed passive source imaging of the atlantic ocean crust and mantle.
Collaborator Contribution GEOMAR has provided active source seismic experiments to image the crust and upper most mantle.
Impact No ouputs yet-the experiments have just come back from sea.
Start Year 2017
 
Description UCSD PILAB 
Organisation University of California, San Diego (UCSD)
Department Scripps Institution of Oceanography
Country United States 
Sector Academic/University 
PI Contribution As part of the imaging the lithosphere asthenosphere boundary experiment we performed passive seismic imaging of the crust and mantle.
Collaborator Contribution UCSD performed magnetelluric imaging of the crust and upper most mantle in the same region.
Impact No outputs yet research is ongoing.
Start Year 2016
 
Description University of Paris PILAB 
Organisation University of Paris
Country France 
Sector Academic/University 
PI Contribution As part of the larger imaging of the lithosphere asthenosphere boundary project, we have performed passive seismic imaging of the oceanic lithosphere. Research is ongoing.
Collaborator Contribution IPGP has performed active source seismic experiments to image the crust and upper mantle structure in the region of our experiment.
Impact No ouputs yet, as the active experiments have just come back from sea.
Start Year 2017