EPSL: The influence of plate tectonic style on melt production and CO2 outgassing flux at mid-ocean ridges

The influence of plate tectonic style on melt production and CO2 outgassing flux at mid-ocean ridges

Jocelyn J. Fuentes, John W. Crowly, Rajdeep Dasgupta, and Jerry X. Mitrovica

Ocean ridges are one of the primary connections between Earth’s mantle and surface. Therefore, understanding the evolution of ocean ridge processes through Earth history is important for understanding how Earth’s surface and mantle have evolved. We combine an analytic model of mantle convection with a petrologic model of mantle melting in the presence of CO2 to compute the mantle temperature, plate speed, melt production, and CO2 outgassing flux at ocean ridges for the past 4 billion years. We explore a large suite of realistic mantle and lithospheric parameters to map out a full range of possible thermal histories. Our results show that in order to satisfy thermal constraints, the Earth must have started in a sluggish-lid mode of plate tectonics and transitioned to an active-lid mode. Furthermore, we show that plate speed and CO2 outgassing flux do not necessarily scale with mantle temperature, and that it is possible to reach present-day mantle temperatures and plate speeds with a simple force balance that does not invoke any feedbacks (e.g. grain size evolution, dehydration stiffening) or a fully stagnant-lid mode of convection in the Precambrian. The solutions show a range of evolutionary behaviors depending on the parameters chosen. The transition from sluggish- to active-lid can be smooth, abrupt, or somewhere in between. A smooth transition is difficult to distinguish from a purely active-lid evolutionary path based on temperature, plate speed, melt production, and CO2 outgassing flux. In contrast, an abrupt transition leads to a large increase in the average plate speed with a corresponding increase in melt production and CO2 outgassing flux. As an abrupt transition would have a much larger effect on CO2 outgassing and melt production than a change in ridge length, we investigate the impact of rapidly changing plate speeds and do not consider changes in ridge length. Finally, we show that carbon recycling is required for a large part of Earth history in order to explain present-day CO2 outgassing. Our model highlights the importance of understanding the style of mantle convection when calculating melt production and volatile fluxes through Earth’s history.
Fuentes, J., Crowley, J., Dasgupta, R. & Mitrovica, J. (2019). The influence of plate tectonic style on melt production and CO2 outgassing flux at mid-ocean ridges. Earth and Planetary Science Letters 511, 154-163. doi:10.1016/j.epsl.2019.01.020
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