Abstract
Plate tectonics describes the horizontal motion of rigid lithospheric plates away from midoceanic ridges and parallel to transforms, towards deep-sea trenches, where the oceanic lithosphere is subducted into the mantle. This process is the surface expression of modern-day heat loss from Earth. One of the biggest questions in Geosciences today is “when did plate tectonics begin on Earth” with a wide range of theories based on an equally diverse set of constraints from geology, geochemistry, numerical modeling, or pure speculation. In this contribution, we turn the coin over and ask “when was the last appearance in the geological record for which there is proof that plate tectonics did not operate on the planet as it does today”. We apply the laws of uniformitarianism to the rock record to ask how far back in time is the geologic record consistent with presently-operating kinematics of plate motion, before which some other mechanisms of planetary heat loss may have been in operation. Some have suggested that evidence shows that there was no plate tectonics before 800 Ma ago, others sometime before 1.8–2.7 Ga, or before 2.7 Ga. Still others recognize evidence for plate tectonics as early as 3.0 Ga, 3.3–3.5 Ga, the age of the oldest rocks, or in the Hadean before 4.3 Ga. A key undiscussed question is: why is there such a diversity of opinion about the age at which plate tectonics can be shown to not have operated, and what criteria are the different research groups using to define plate tectonics, and to recognize evidence of plate tectonics in very old rocks? Here, we present and evaluate data from the rock record, constrained by relevant geochemical-isotopic data, and conclude that the evidence shows indubitably that plate tectonics has been operating at least since the formation of the oldest rocks, albeit with some differences in processes, compositions, and products in earlier times of higher heat generation and mantle temperature, weaker oceanic lithosphere, hotter subduction zones caused by more slab-melt generation, and under different biological and atmospheric conditions.
Highlights
Documenting the operation of plate tectonics in old terrains (Dewey and Bird, 1970)
In the modern tectonic regime, small fragments of oceanic lithosphere are occasionally scraped off subducting oceanic plates, along with their overlying sediments, to be accreted above the trenches at convergent margins, forming remnants of oceanic lithosphere known as ophiolites (Coleman, 2012)
Lateral motion of plates brings island arcs and continents into collision, where arc terranes may be added to active continental margins, or continents collide to form orogenic belts characterized by internal high-grade metamorphism, succeeded outwards by accreted terranes, belts of far-travelled nappes, fold-thrust belts, low-grade foreland basins (Fig. 1b)
Summary
Documenting the operation of plate tectonics in old terrains (Dewey and Bird, 1970). In the modern tectonic regime, small fragments of oceanic lithosphere are occasionally scraped off subducting oceanic plates, along with their overlying sediments (oceanic plate stratigraphy or OPS; Kusky et al, 2013b), to be accreted above the trenches at convergent margins, forming remnants of oceanic lithosphere known as ophiolites (Coleman, 2012). Since no ocean basins older than 200 Ma old are preserved today on Earth, we must seek records of what ancient ocean crust looked like from remnants of oceans that closed, where slices of these oceans were offscraped at paleo-convergent plate boundaries, becoming emplaced as ophiolites on top of continental margins, or within accretionary prisms
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