0000000000323355
AUTHOR
Anja Rosenthal
The composition of near-solidus melts of peridotite in the presence of CO2 and H2O between 40 and 60 kbar
Abstract Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5–0.63 wt.% H2O and 2.0–3.2 wt.% CO2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K2O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress gradually from carbonate-rich to carbonated silicate in composition: near-solidus melts have Ca/(Ca + Mg) of 0.46–0.53, which fall to 30 wt.%) and Al2O3 ( 9 wt.%) and concomitant decrease in CaO (> 20 to Partial melts of peridotite with CO2 and H2O are too low in MgO to resemble kimberlites, but will act as ef…
Petrogenesis of strongly alkaline primitive volcanic rocks at the propagating tip of the western branch of the East African Rift
Abstract Strongly silica-undersaturated potassic lavas (kamafugites) and carbonatitic tuffs are characteristic of the Toro-Ankole volcanic field in southwestern Uganda, forming the youngest and most northward volcanics of the western branch of the East African Rift. Lavas contain exceptionally low SiO2 (31.8–42.8 wt.%), high CaO (up to 16.6 wt.%) and K2O (up to 7 wt.%). They exhibit moderately enriched correlated Nd (eNd − 0.1 to − 4.7) and Hf (eHf − 0.1 to − 8.8) isotope signatures, indicating time-integrated enrichment in incompatible elements in the source, attributed to mixing between two metasomatic assemblages, a phlogopite-rich MARID-type and a later carbonate-rich assemblage. The re…