The Massif d'Ambre is the largest stratovolcano (~2500 km 2 ) in the Cenozoic igneous province of northern Madagascar. It is broadly elongated in a N-S direction and is formed by hundreds of lava flows, plugs, spatter cones, tuff rings, pyroclastic flows, and pyroclastic fall deposits. New 40 Ar- 39 Ar age determinations for lavas of Massif d'Ambre and Bobaomby Peninsula (the northernmost tip of Madagascar) yield ages of 12.1 ± 0.2 Ma and 10.56 ± 0.09 Ma. These ages indicate that at least part of the volcanic activity of the Bobaomby Peninsula occurred later than the beginning of the activity of the Massif d'Ambre. The volcanic products of Massif d'Ambre are mildly to strongly alkaline (with sodic affinity) to tholeiitic with very limited amounts of evolved magmas. The mafic rocks have compositions similar to those of primitive mantle–derived magmas (MgO >10 wt%, Cr and Ni >400 and >200 ppm, respectively). The strongly alkaline suite shows a liquid line of descent from basanite to phonolite, dominated by fractional crystallization of clinopyroxene and olivine. The mafic rocks (basanites, alkali basalts, transitional and tholeiitic basalts) have Zr/Nb (2.4–5.8), Ba/Nb (7–24) and La/Nb (0.7–1.1) ratios typical of incompatible element–rich within-plate basalts. The primitive mantle–normalized incompatible element patterns of the Massif d'Ambre mafic rocks are characterized by peaks at Nb and troughs at K, and are identical in shape and absolute abundances to those of the Nosy Be and Bobaomby (Cap d'Ambre) basanites. The range of (La/Yb) n ratios (9–24) indicates that the Massif d'Ambre primitive compositions are the product of variable degrees of partial melting (4%–12%) of a broadly similar and slightly incompatible element–enriched mantle source. Initial 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ratios of alkali basalts and basanites vary from 0.70326 to 0.70359 and 0.51279 to 0.51286, respectively. Alkali basalts and basanites have little variation in 206 Pb/ 204 Pb (19.073–19.369), 207 Pb/ 204 Pb (15.613–15.616), and 208 Pb/ 204 Pb (39.046–39.257). This range is well within that of Sr-Nd-Pb isotope values of the basanites of the Nosy Be Archipelago, thus again confirming substantially similar source compositions throughout northern Madagascar.

Abstract The Colli Albani volcano belongs to the Roman Magmatic Province and is characterized by strongly silica undersaturated leucite-bearing ultrapotassic rocks. Melilite-bearing leucititic lavas, beside tephritic to tephritic phonolitic ignimbrites, were erupted during the pre-caldera (Vulcano Laziale) period. The post-caldera phase opened with magmas erupted from different feeding systems, with melilite-bearing leucitites in the early phases followed by tephritic and phonolitic tephritic lavas. The late-stage activity (i.e. the Via dei Laghi period) is characterized by hydromagmatic tuffs with small juvenile fragments that prevent a clear compositional definition of the magma triggering the eruptions. Despite their mineralogical and compositional similarities, the Vulcano Laziale period (pre-caldera) has significantly higher levels of incompatible trace elements and 87 Sr/ 86 Sr isotopes than found in magmatic rocks erupted after the caldera formation. Pre- and post-caldera parental magmas are considered to be significantly different from each other and generated within a metasomatized upper mantle under different degrees of partial melting. Crustal-derived carbonate-rich metasomatism is thought to have affected the mantle wedge of the Italian peninsula. Melting of pelitic sediments with different amounts of CaCO 3 is considered the source of the metasomatic agents, which are able to re-fertilize the lithospheric upper mantle. Partial melting of this modally metasomatized lithospheric mantle under high X CO 2 produced the strongly silica undersaturated ultrapotassic magmas observed at the Colli Albani volcano. A second-order differentiation process occurs at shallow levels, with fractional crystallization and crustal assimilation of wall rock (AFC), locally changing the compositions of magmas and producing several differentiation pathways that have given rise to the geochemical and petrological complexity of the Colli Albani volcano. Assimilation of carbonate sediments and silicoclastic sedimentary lithologies also occurred coevally, suggesting the existence of several separate magmatic reservoirs at shallow levels, possibly at different depths and surrounded by different sedimentary formations.