Experimental melting of phlogopite-bearing mantle at 1 GPa: Implications for potassic magmatism

Magmatism, mantle evolution and geodynamics at the converging plate margins of Italy

“…spanning the shoshonitic to lamproitic fields; Fig. 3) were obtained by Condamine & Médard (2014) by fluid-absent melting of phlogopite-bearing lherzolite and harzburgite at 1 GPa. Multiple-saturation studies exploring the liquidus phase relationships of ultrapotassic undersaturated rocks at high pressures with the presence of H 2 O + CO 2 found that undersaturated magmas such as kamafugites or olivine lamproites can be formed by partial melting of phlogopite-bearing lherzolite or wehrlite at pressures around 2.5-3.5 GPa and temperature around 1000-1300°C (e.g.…”

“…Zanetti et al 1999;Rampone & Morten 2001) that have phlogopite as the main K-bearing metasomatic phase, often coexisting with amphibole and carbonates (Sapienza et al 2009), can be envisaged for the source of Roman magmas. Experimental evidence discussed above suggests that melting of phlogopitebearing lherzolite or wehrlite at high pressure generates undersaturated ultrapotassic magmas, whereas melting at lower pressure produces potassic melts (Wendlandt & Eggler 1980a,b;Conceçao & Green 2004;Condamine & Médard 2014). The large volumes of erupted magmas and the strong explosivity index of volcanism require wide sections of mantle melting and occurrence of high quantities of volatiles in the source, probably H 2 O and CO 2 .…”

“…Doglioni et al 1998Doglioni et al , 1999. The petrological characteristics of mafic magmas support various degrees of melting at low pressure of a phlogopite-bearing harzburgite (Condamine & Médard 2014), representing remnants of old contaminated and dismembered lithosphere (e.g. Peccerillo et al 1988).…”

Study of silica-undersaturated magmas through the Kalsilite- Nepheline-Diopside-Silica system at 4.0 GPa and dry conditions

“…With higher pressures, in relation to previous work, we could better understand the genesis of some silicaundersaturated melts, like nepheline-bearing phonolites, and determinate the crystalline phases produced in such conditions and their petrologic implications. Although mica-and/ or amphibole-bearing mantle rocks are commonly accepted as the source of alkaline magmas (Conceição and Green, 2004;Condamine and Ménard, 2014;Laporte et al, 2014), we performed water-free experiments in order to better focus on the role of K 2 O, Na 2 O, and CaO (water would represent another variable, reducing the melting point of the compositions, which would deviate from the objective of this work). Up to now, there are no studies neither for the Lct-Ne-Di nor for the Kls-Ne-Di joins at 4.0 GPa or higher pressures.…”

“…Current geochemical and isotopic studies show that alkaline rocks can be originated through partial melting of primitive assemblages (from mantle sources) enriched in alkalis via several metasomatic processes, like interaction with volatilerich fluids or silicate liquids originated from partial melting of subducting slabs Conceição and Green, 2004;Bea et al, 2013;Condamine and Ménard, 2014;Laporte et al, 2014). Moreover, the presence of carbonates, mica (phlogopite) and/or amphiboles (pargasite, richterite) in peridotite xenoliths carried by alkaline magmas (like alkali basalts, kimberlites or lamproites) denotes the role of H 2 O and CO 2 (C-H-O system) generically lowering temperatures needed to magma generation Green, 2000, 2004).…”