PLATE TECTONICS AND MANTLE PLUMES AS A BASIS OF DEEP-SEATED EARTH’S TECTONIC ACTIVITY FOR THE LAST 2 Ga
M.I. Kuzmin1, V.V. Yarmolyuk2
1A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 109017, Russia
Keywords: Plate tectonics, subduction, plumes, depleted mantle
Abstract
The onset of the modern tectonic style that combines plate-related and plume-related mechanisms has been discussed. Such a tectonic style could have started on the Earth when all layers of our planet had formed. Analysis of available geological data shows that the solid inner core crystallized by 2.7 Ga. Typical geologic complexes appeared on the continents as a result of plate tectonics processes at that time. The layer D ″ that accumulates lithospheric slabs, which do not remain at the upper-lower mantle interface but can go down to the core-mantle boundary, was finally produced by 2 Ga. At pressures and temperatures of the D ″ layer perovskite, a principal mineral of the lower mantle transforms into postperovskite phase. The isotope data suggest the existence of mantle (EM-I and EM-II) domains, being the sources for oceanic island basalts (OIB) and the depleted upper mantle (asthenosphere), the source for mid-ocean ridge basalts (MORB), from at least 2 Ga. It is accepted that the recent tectonic style started on the Earth at that period. Deep-seated processes suggest the involvement of all Earth’s layers. The asthenosphere-lithosphere interaction is responsible for different types of large surface structures that develop as fold mountains, oceanic spaces, and subduction zones. The descending lithospheric slabs (cold mantle material) and ascending mantle material in hot mantle provinces or the so-called low shear velocity provinces are responsible for the lower mantle convection. The plume is produced in the layer D ″, which accumulates the descending lithosphere slabs as well as light elements released from the outer liquid core, which are oxidized in this layer, thus resulting in thermochemical plume formation. At the same time the molten ferric iron penetrates the core. So, we see the interaction of all Earth’s layers. The article also considers the evolutionary history of the Siberian continent over 700 Myr as early as the breakdown of Rodinia and the formation of mountain folds and rifting structures and the associated metallogeny.
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