Olivine melilitites, mantle xenoliths, and xenocrysts of the Takarindiona district: Petrogenesis, magmatic evolution, and the sub-continental lithospheric mantle of east-central Madagascar

Pliocene-to-Holocene volcano-tectonic activity on Mohéli Island (Comoros archipelago) constrained by new K Ar ages

“…Building on partial melting experiments that position the origin of melilititic primary melts in the domain of garnet stability, in the presence of CO2, at pressures ranging from 3 to 4 GPa (Dasgupta et al, 2007;Gudfinnsson and Presnall, 2005;Hirose, 1997), Pelleter et al (2014) have interpreted melilitebearing magmas as coming from very low partial melting of apatite-dolomite-rich zones in the CO2-metasomatized lithospheric mantle. A similar conclusion was reached for the origin of Cenozoic melilitites from northern, central, and eastern Madagascar (Melluso et al, 2011;Cucciniello et al, 2016;Mazzeo et al, 2021). Though undated, olivine melilitites are thought to be related to rifting on Mayotte during the postshield stage (<4 Ma, Pelleter et al, 2014).…”

“…8a), strong enrichments in incompatible elements such as F, Ba, Sr, Nb, and relative enrichments in MREE with respect to the other mafic rocks (Figs 4, 8b). Mohéli's and Mayotte's olivine melilitites also share minor and trace element similarities with those of central and eastern Madagascar (Melluso et al, 2011;Mazzeo et al, 2021, and references therein), like K and Pb throughs (Fig. 8b).…”

“…8b). Following Pelleter et al (2014) for Mayotte, and Mazzeo et al (2021) for eastern Madagascar, we thus interpret Mohéli's undersaturated magmas as generated by very low partial melting of a peridotitic source located in the lithospheric mantle, enriched in highly incompatible elements by CO2 metasomatism. As for Mayotte's melilitites and for one melilitite in northern Madagascar (Cucciniello et al, 2016), Mohéli's olivine melilitite is among the most enriched in P (1.15 wt.%) of worldwide melilitites (max 1.35 wt.% in Mayotte and 1.27 wt.% in Nyiragongo, Fig.…”

Evolution of the East African Rift System from trap-scale to plate-scale rifting

“…The second endmember is characterized by a dominant role of the plate deformation in the location and timing of the volcanism. Following Presnall and Gudfinnsson (2005) and Rooney et al (2012) who suggested that the slow seismic velocities could evidence the occurrence of carbonatite melts in the upper mantle, we propose that the ascent of carbonatite melts from the lower mantle to the upper mantle beneath Africa has produced widespread carbonated silicate melts at shallow depth having compositions similar to the alkaline magmas emitted in the volcanic provinces of the EARS (Kampunzu and Mohr, 1991;Rudnick et al, 1993;Coltorti et al, 1999;Dasgupta et al, 2007;Furman, 2007;Mazzeo et al, 2021). Moreover, the widespread distribution of easily fusible lithospheric metasomes within the continental lithosphere mantle might have facilitated magma generation without the need for substantial lithospheric thinning or elevated mantle potential temperatures (Rooney et al, 2014).…”

“…6; Courgeon et al, 2017;O'Connor et al, 2019;Berthod et al, 2022). Magmas emitted in the West, Indian Ocean and South-East branches not only show a similar timing, but also share identical chemical affinities of the silica-saturated, silica-undersaturated alkaline, and melilitic-carbonatitic suites (e.g., Kampunzu and Mohr, 1991;Späth et al, 1996;Rudnick et al, 1993;Furman, 2007;Pelleter et al, 2014;Mazzeo et al, 2021;Berthod et al, 2022).…”