The Relationship Between Kimberlitic Magmatism and Electrical Conductivity Anomalies in the Mantle

• Published in: Geophysical research letters 2022-09, Vol.49 (18), p.n/a
• Main Authors: Özaydın, Sinan, Selway, Kate
• Format: Article
• Language: English
• Subjects: Anomalies; Biotite; Composition; cratons; Depth; diamond; Diamonds; Distribution; Earth; Earth mantle; Electrical conductivity; Electrical resistivity; Exploration; Fluids; Igneous rocks; Kimberlites; Lithosphere; Magma; magnetotellurics; Mathematical analysis; metasomatism; Mineral exploration; Minerals; Moisture content; Precambrian; Spatial distribution; Temporal distribution; Volcanoes; Water content
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099661

Kimberlites are igneous rocks whose formation remains enigmatic due to their severely altered nature, highly variable compositions and rapid ascent through the lithosphere. The spatiotemporal distribution of kimberlites suggests that mantle metasomatism may play an essential role in their emplacement. Since the magnetotelluric (MT) method is sensitive to metasomatic mantle modification in the forms of interconnected minerals and water, we compiled MT models from Australia, Brazil, Botswana, Canada, Namibia, South Africa and the USA, calculated water content variations and compared them to the distribution of kimberlites. Results indicate that kimberlites mostly ascend through hydrated/metasomatized lithosphere and avoid both dry and heavily metasomatized lithosphere. Diamondiferous kimberlites preferentially occur on moderately metasomatized lithosphere, with the diamondiferous rate increasing with the degree of metasomatism in Archean terranes and decreasing in Proterozoic terranes. These results link geophysical observations of mantle metasomatism to kimberlite magmatism and will improve mineral systems models for diamond exploration. Plain Language Summary We have identified deep signatures of kimberlites that may help explain how these unusual rocks form and help diamond exploration. Kimberlite magmas create the Earth's deepest volcanoes and ascend rapidly from where they form at >150 km depth to the surface. While ascending, they carry with them a lot of material (including diamonds) from depths that would be impossible to reach physically. It is possible that kimberlites can rise this fast because they form and ascend through regions with unusual compositions. To test this, we compiled electrical conductivity models of the Earth down to 200 km depth. We found that most kimberlites occur in places where minerals in the deep Earth formed through interactions with fluids and are unusually rich in water, making them more electrically conductive. Our findings help explain kimberlite formation because these minerals melt more easily and the magmas will ascend fast. For diamond exploration, they show that diamonds are more likely to be found in places where the deep Earth is electrically conductive. Key Points The relationship between mantle metasomatism and kimberlite emplacement is investigated using magnetotelluric models of the lithosphere Kimberlites ascend through moderately metasomatized mantle but avoid mantle that is depleted or strongly metasomati