Syn-eruptive agglutination of kimberlite volcanic ash

Haddock, David and Manya, Shukrani and Brown, Richard J. and Jones, Thomas and Wadsworth, Fabian B. and Dobson, Katherine J. and M. Gernon, Thomas (2020) Syn-eruptive agglutination of kimberlite volcanic ash. Volcanica, 3 (1). pp. 169-182. ISSN 2610-3540

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Pyroclastic deposits of the Holocene Igwisi Hills kimberlite volcanoes, Tanzania, preserve unequivocal evidence for rapid, syn-eruptive agglutination. The unusual pyroclasts are composed of ash-sized particles agglutinated to each other by thin necks. The textures suggest the magma was disrupted into droplets during ascent. Collisions between particles occurred within a volcanic plume and on deposition within the conduit to form a weakly agglutinated, porous pyroclastic deposit. Theoretical considerations indicate that agglutination occurred over short timescales. Agglutinated clasts were entrained into weak volcanic plumes and deposited around the craters. Our results support the notion that agglutination can occur during kimberlite eruptions, and that some coherent, dense rocks in ancient kimberlite pipes interpreted as intrusive rocks could instead represent agglutinated pyroclastic rocks. Differentiating between agglutinated pyroclastic rocks and effusive or intrusive rocks in kimberlite pipes is important because of the potential effects that pyroclastic processes might have on diamond concentrations in deposits.

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06 Oct 2022 14:10
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22 Nov 2022 11:50