Constraining Initiation and Onset Time of Plate Tectonics on Earth

Abstract:

The onset time for modern-style plate tectonics is still heavily debated among geoscientists. Proposed timings range from the Phanerozoic to the Hadean. Here I present a new theoretical approach to tackle this question. I combine ideas of nuclear astrophysics and geochronology and apply the concept of sudden nucleosynthesis to calculate so-called nucleogeochronometric Rhenium-Osmium model ages. Sudden nucleosynthesis has been suggested by nuclear theory [1-2] as a possible mechanism for the creation of the heavy isotopes. Hence, this concept may generally be used to identify rapid (r-) neutron-capture process events. For Earth, nucleogeochronometric model age calculations based upon published pyroxenite and komatiite data [3-5] point to an r-process event around 3 Ga. Since the r-process requires high neutron densities and temperatures within seconds, a gravitational core collapse forming at least a part of the inner core is discussed as a possible cause, thus initiating modern-style plate tectonics at that time. This age is in line with an earlier proposed value of 2.7 Ga for an inner core forming event [6], pronounced changes in the magnitude of the geomagnetic field and geological evidence like the onset of extensive plutonism and crust formation starting around the Archean-Proterozoic transition. Besides, results from nucleogeochronometric age calculations for published peridotitic pentlandites [7] lead to corrections as to their previously inconsistent model ages: These are now in good agreement with their Proterozoic 1.43 Ga isochronous regression line, supporting the model.

[1] Burbidge et al. (1957) Revs. Mod. Phys. 29, 547 – 650.
[2] Hoyle et al. (1960) ApJ 132, 565 – 590.
[3] Reisberg et al. (1991) Earth Planet. Sci. Lett. 105, 196 – 213.
[4] Roy-Barman et al. (1996) Chem. Geol. 130, 55 – 64.
[5] Luck et al. (1984) Earth Planet Sci. Lett. 68, 205 – 208.
[6] Hale (1987) Nature 329, 233 -237.
[7] Smit et al. (2010) Geochim. Cosmochim. Acta 74, 3292 - 3306.