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Mid-mantle plume
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Title: Diamonds sampled by plumes from the core-mantle boundary
Authors: Trond H. Torsvik, Kevin Burke, Bernhard Steinberger, Susan J. Webb & Lewis D. Ashwal

Diamonds are formed under high pressure more than 150 kilometres deep in the Earth's mantle and are brought to the surface mainly by volcanic rocks called kimberlites. Several thousand kimberlites have been mapped on various scales, but it is the distribution of kimberlites in the very old cratons (stable areas of the continental lithosphere that are more than 2.5 billion years old and 300 kilometres thick or more) that have generated the most interest, because kimberlites from those areas are the major carriers of economically viable diamond resources. Kimberlites, which are themselves derived from depths of more than 150 kilometres, provide invaluable information on the composition of the deep subcontinental mantle lithosphere, and on melting and metasomatic processes at or near the interface with the underlying flowing mantle. Here we use plate reconstructions and tomographic images to show that the edges of the largest heterogeneities in the deepest mantle, stable for at least 200 million years and possibly for 540 million years, seem to have controlled the eruption of most Phanerozoic kimberlites. We infer that future exploration for kimberlites and their included diamonds should therefore be concentrated in continents with old cratons that once overlay these plume-generation zones at the core-mantle boundary.

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A blob of the Earth's gooey insides linked to volcanic eruptions has been detected below southern Africa.
The newly discovered blob is known to geologists as a mid-mantle plume. Mantle plumes are columns of hot, gushy gunk that flow toward the Earth's surface and are a known contributor to volcanic activity. Until now, the mid-section of a mantle plume has never been imaged.
Mid-mantle plumes are hotter and move faster - roughly 10 centimetres per year - than the scorching, molten rock deeper inside the Earth, which is called the Earth's mantle.

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