A seismic shift in continental tectonic plates

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Science  11 Aug 2017:
Vol. 357, Issue 6351, pp. 549-550
DOI: 10.1126/science.aao1285

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Continents have tolerated billions of years of tectonic stresses and disfigurement, yet they continue to survive. Compared with their oceanic counterpart, where a sinking demise is an almost certainty, continents and their internal cores, or cratons, are much thicker (>175 km), older (>2 billion years), colder, and more buoyant. However, their basic attributes, such as size and shape, are a still a matter of debate because of large uncertainties in deceivingly straightforward, but entirely complicated, measurements. Continental cratons are rigid bodies composed of both crust and mantle, and their thickness was thought to be related to temperature and extend to depths of 250 to 350 km. On page 580 of this issue, Tharimena et al. (1) use reflections of seismic waves within the cratons to constrain their thickness globally. The strength of the reflections suggests that the base of the cratonic plate is defined by a partial melt of carbon-laced silicate mantle, not temperature.