Deep mantle origin of large igneous provinces and komatiites

Abstract

Large igneous provinces (LIPs) resulted from intraplate magmatic events mobilizing volumes of magma up to several million cubic kilometers. LIPs and lavas with deep mantle sources have compositions ranging from komatiites found in Archean greenstone belts to basalts and picrites in Phanerozoic flood basalt and recent oceanic islands. In this study, we identify the mantle conditions appropriate to each type of lava based on an experimental study of the melting of pyrolite. The depth of the mantle source decreases from 600 to 700 km for the oldest komatiites to 100 to 300 km for picrites and basalts, and the extent of mantle melting ranges from 10 to 50%. We develop a geodynamical model that explains the origin of the hot mantle plumes capable of generating these melting P - T conditions. Within a superadiabatic temperature gradient persisting in the deep mantle, the ascent of hot mantle plumes creates excess temperatures up to 250 to 300 K by adiabatic decompression.

Solidus melting of pyrolite and bridgmanite: Implication for the thermochemical state of the Earth's interior

“…In the low pressure range, our solidus plots in very good agreement with our recent determination of the solidus at pressures up to 27 GPa, using the multi-anvil apparatus (Pierru et al, 2022). We note that higher melting temperatures were proposed for the melting of mantle-relevant materials in the upper mantle and transition zone (e.g.…”

“…The discrepancy may arise from several factors, including a rather high melt fraction reported in previous work. This matter is discussed at length elsewhere (Andrault et al, 2018;Pierru et al, 2022). To provide a convenient model for the pyrolite solidus at all mantle pressures, we coupled the two data sets on the same pyrolitic sample and fitted two Simon and Glatzel equations (Fig.…”

Komatiites: their geochemistry and origins

“…The Tp calculated from a given pressure of melting depends on the nature of the solidus. Recent 'low temperature' solidus parameterisations (Andrault et al, 2018) imply relatively low Tp of ~1530 °C for Archaean komatiites, with melting beginning at up to 25 GPa (Pierru et al, 2022). It is presently unclear how such low Tp mantle can produce melts that arrive near the surface with the high liquidus temperatures observed for komatiites, and this merits further investigation.…”

“…These features are also not observed in most komatiites. In a related model, Pierru et al (2022) invoked preferential melting of Ca-perovskite in the lower mantle with residual bridgmanite to explain the high CaO/Al2O3 of Al-depleted komatiites, though at higher degrees of melting. Again, this does not appear to be compatible with the lack of HFSE/REE fractionation observed in most komatiites, and we note that CaO/Al2O3 comparable to typical Al-depleted komatiites (Robin-Popieul et al, 2012) have been experimentally produced at much lower pressures (Walter, 1998).…”

Viscosity Measurements at High Pressures: A Critical Appraisal of Corrections to Stokes' Law

“…However, horizontal cylinders have been used in diamond-anvil-cells (DAC) to study fluids that are challenging to solidify at ambient pressures/ temperatures, that is, volatile-rich vaporous or supercritical fluids (Abramson, 2007(Abramson, , 2009Abramson & West-Foyle, 2008;Audétat & Keppler, 2004;King et al, 1992). The horizontal technique has also been applied in a multi-anvil press to identify changes in rheology during melting (Pierru et al, 2022). In a horizontal cylinder, the sphere falls perpendicular to the longitudinal axis and between two parallel walls, that is, the ends of the cylinder.…”