Did Plate Tectonics Shutdown During the Siderian/Rhyacian PaleoProterozoic?

Did plate tectonics shutdown in the Paleoproterozoic? A view from the Siderian geologic record

Authors:

Pehrsson et al

Abstract:

The early Proterozoic Era between 2.45-2.2 Ga is well known for a distinct minima in juvenile magmatism and detrital zircon abundance, an intriguing observation given its coincidence with many fundamental changes in Earth processes. A recent hypothesis seeks to explain this Siderian ‘quiet interval’ as the result of a plate tectonic shutdown in which extended tectonic quiescence is due to widespread lithospheric stagnation in an episodic mantle overturn regime. The model suggests this period characterizes a ‘pre-modern’ geodynamic style and has profound implications for many geodynamic processes.

We use spatially-linked chronostratigraphic and paleomagnetic databases to assess the major predictions of the model and find six of its key predictions are not supported by current data. The quiet interval includes a greater extent of contractional orogenesis and a broader range of paleopressures than previously known and is not characterized by LP-HT metamorphism proposed to have been related to higher upper mantle temperatures from decreased upper mantle cooling. Glacial conditions do not appear to have been triggered by the coincidence of the onset of magmatic shutdown with the end of mass-independent sulphur isotope fractionation and oxygenation of the atmosphere, as the initial glacial episodes predate this time. The glacial record, moreover, requires four episodes of climatic amelioration during the proposed shutdown, for which a mechanism appears lacking. A purported gap in Large-Igneous-Province formation, related to decreased mantle vigour, is not apparent. Quiet interval magmatism includes juvenile, arc-type and TTG magmatism, supporting significant crustal additions on a number of cratons. The prediction of negligible plate velocities during shutdown is not borne out by the well-constrained Superior Province paleomagnetic record. We suggest plate tectonics did not shut down but that the Siderian quiet interval represents overall diminished tectonic activity during peripheral orogenesis, as is known for other relatively quiet periods following supercontinent or supercraton amalgamation.