Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport

Details Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport

Feb 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009e%26psl.278..233b&link_type=abstract

Earth and Planetary Science Letters, Volume 278, Issue 3-4, p. 233-242.

Mathematics

Logic

5

Scientific paper

Variations in Earth's rates of seafloor generation and recycling have far-reaching consequences for sea level, ocean chemistry, and climate. However, there is little agreement on the correct parameterization for the time-dependent evolution of plate motions. A strong constraint is given by seafloor age distributions, which are affected by variations in average spreading rate, ridge length, and the age distribution of seafloor being removed by subduction. Using a simplified evolution model, we explore which physical parameterizations of these quantities are compatible with broad trends in the area per seafloor age statistics for the present-day and back to 140 Ma from paleo-age reconstructions. We show that a probability of subduction based on plate buoyancy (slab-pull, or “sqrt(age)”) and a time-varying spreading rate fits the observed age distributions as well as, or better than, a subduction probability consistent with an unvarying “triangular” age distribution and age-independent destruction of ocean floor. Instead, we interpret the present near-triangular distribution of ages as a snapshot of a transient state of the evolving oceanic plate system. Current seafloor ages still contain hints of a ˜ 60 Myr periodicity in seafloor production, and using paleoages, we find that a ˜ 250 Myr period variation is consistent with geologically-based reconstructions of production rate variations. These long-period variations also imply a decrease of oceanic heat flow by ˜ - 0.25%/Ma during the last 140 Ma, caused by a 25 50% decrease in the rate of seafloor production. Our study offers an improved understanding of the non-uniformitarian evolution of plate tectonics and the interplay between continental cycles and the self-organization of the oceanic plates.

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