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 – the rheological lithosphere-asthenosphere boundary (LAB) - has important
implications for the driving forces of plate tectonics, natural hazard mitigation, mantle dynamics,
the evolution of the planet, 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.
However, it has also been suggested that the chemical composition of the plate provides additional
strength or that melt weakens the mantle beneath the plate.
This project is designed to systematically image an oceanic plate beneath the Atlantic
from birth at ridge to 40 My old seafloor. We will deploy ocean bottom seismometers (OBS) and
magnetotelluric (MT) instruments to image the plate at a range of resolution scales
(laterally and in depth) and sensitivities to physical and chemical properties. This large, focused,
interdisciplinary effort will finally determine the processes and properties that make a plate strong
and define it. The results will be put in context through seismic imaging in other locations and also through global seismic imaging.
We imaged the lithosphere-asthenosphere system beneath the Atlantic Ocean and globally with a range of resolutions and sensitivites. We found that the thickness of ocean plates increases with age monotonically in some locations, but is more variable in others. Therefore, the thickness of the plate is determined by temperature to first order. However, the base of the plate is also sharp in many locations. Other factors also define the plate, likely melt beneath the plate, which decreases the viscosity of the asthenosphere. Therefore, the lithosphere-asthenospere system is dynamic and dictated by melt generation and migration.
