Journal Article

Diamonds sampled by plumes from the core–mantle boundary

Torsvik, Trond H., Burke, Kevin, Ashwal, Lewis D., Webb, Susan J., Steinberger, Bernhard

2010

Overview

Diamond distribution Diamond formation occurs in high-pressure conditions more than 150 kilometres deep in the Earth's mantle. The diamonds make it to the surface in vertical pipe-like structures made up of volcanic rocks called kimberlites. Several thousand such kimberlite pipes have been mapped so far, but research has focused on very old cratons, the areas of oldest continental crust, as this is where most economically viable diamonds are found. Trond Torsvik and colleagues use a plate-tectonic reconstruction for the past 540 million years to locate the positions of these cratons relative to the deep mantle at times when kimberlites were erupted. The kimberlites are shown to have been associated with the edges of large-scale heterogeneities in the deepest mantle, which the authors infer were zones at the core–mantle boundary where magma upwelling generated the mantle plumes that led to the formation of the kimberlites. These plumes may have controlled the distribution of almost all kimberlites that have erupted in the past 540 million years. 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. Here, plate reconstructions and tomographic images have been used 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. This has implications for future exploration for kimberlites. 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 1 , 2 , 3 , 4 , 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 5 ) 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.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/2151/210 / 704/2151/213 / 704/2151/598 / Core / Core-mantle boundary / Cratons / Crystalline rocks / Diamond crystals / Diamonds / Earth / Earth mantle / Earth sciences / Earth, ocean, space / Exact sciences and technology / Geology / Heterogeneity / High pressure / Humanities and Social Sciences / Igneous and metamorphic rocks petrology, volcanic processes, magmas / Internal geophysics / letter / Lithosphere / Mantle / Mineralogy / multidisciplinary / Natural history / Non silicates / Plate tectonics / Plumes (Fluid dynamics) / Science / Science (multidisciplinary) / Solid-earth geophysics, tectonophysics, gravimetry / Volcanic rocks