HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information
Skip to Main content Skip to Navigation
Journal articles

H2O–CO2 solubility in low SiO2-melts and the unique mode of kimberlite degassing and emplacement

Abstract : Kimberlites are the most deep-seated magmas in the mantle and ascend to the surface at an impressive speed, travelling hundreds of kilometres in just hours while carrying a substantial load of xenolithic material, including diamonds. The ascent dynamics of these melts are buoyancy-controlled and certainly driven by outgassing of volatile species, presumably H2O and CO2, summing to concentration level of ca 15–30 wt.% in kimberlite melts. We provide H2O–CO2 solubility data obtained on quenched glasses that are synthetic analogues of kimberlite melts (SiO2 content ranging from 18 to 28 wt.%). The experiments were conducted in the pressure range 100 to 350 MPa. While the CO2 solubility can reach 20 wt.%, we show that the H2O solubility in these low silica melts is indistinguishable from that found for basalts. Moreover, whereas in typical basalts most of the water exsolves at shallower pressure than the CO2, the opposite relationship is true for the low-SiO2 composition investigated. These data show that kimberlites can rise to depths of the upper crust without suffering significant degassing and must release large quantities of volatiles (>15 wt.%) within the very last few kilometres of ascent. This unconventional degassing path may explain the characteristic pipe, widening-upward from a ≤2.5 km deep root zone, where kimberlites are mined for diamonds. Furthermore, we show that small changes in melt chemistry and original volatile composition (H2O vs. CO2) provide a single mechanism to explain the variety of morphologies of kimberlite pipes found over the world. The cooling associated to such massive degassing must freeze a large quantity of melt explaining the occurrence of hypabyssal kimberlite. Finally, we provide strong constraints on the primary volatile content of kimberlite, showing that the water content reported for kimberlite magma is mostly reflective of secondary alteration.
Document type :
Journal articles
Complete list of metadata

Cited literature [57 references]  Display  Hide  Download

Contributor : Nathalie Pothier Connect in order to contact the contributor
Submitted on : Tuesday, May 31, 2016 - 9:43:52 AM
Last modification on : Tuesday, May 10, 2022 - 3:25:01 PM
Long-term archiving on: : Thursday, September 1, 2016 - 11:14:26 AM


Kimberlite H2O-CO2_EPSL_revise...
Files produced by the author(s)




Yves Moussallam, Yann Morizet, Fabrice Gaillard. H2O–CO2 solubility in low SiO2-melts and the unique mode of kimberlite degassing and emplacement. Earth and Planetary Science Letters, Elsevier, 2016, 447, pp.151-160. ⟨10.1016/j.epsl.2016.04.037⟩. ⟨insu-01323216⟩



Record views


Files downloads